2007 publications citing ADF

First author: Decker, Andrea, Spectroscopic and quantum chemical studies on low-spin Fe-IV=O complexes: Fe-O bonding and its contributions to reactivity, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 129, 15983, (2007)
Abstract: High-valent Fe-IV=O species are key intermediates in the catalytic cycles of many mononuclear non-heme iron enzymes and have been structurally defined in model systems. Variable-temperature magnetic circular dichroism (VT-MCD) spectroscopy has been used to evaluate the electronic structures and in particular the Fe-O bonds of three Fe-IV=O (S = 1) model complexes, [Fe-IV(O)(TMC)(NCMe)](2+), [Fe-IV(O)(TMC)(OC(O)CF3)](+), and [Fe-IV(O)(N4py)](2+). These complexes are characterized by their strong and covalent Fe-O pi-bonds. The MCD spectra show a vibronic progression in the nonbonding -> pi(*) excited state, providing the Fe-O stretching frequency and the Fe-O bond length in this excited state and quantifying the pi-contribution to the total Fe-O bond. Correlation of these experimental data to reactivity shows that the [Fe-IV(O)(N4py)](2+) complex, with the highest reactivity toward hydrogen-atom abstraction among the three, has the strongest Fe-O pi-bond. Density functional calculations were correlated to the data and support the experimental analysis. The strength and covalency of the Fe-O pi-bond result in high oxygen character in the important frontier molecular orbitals (FMOs) for this reaction, the unoccupied beta-spin d(xz/yz) orbitals, that activates these for electrophilic attack. An extension to biologically relevant Fe-IV=O (S = 2) enzyme intermediates shows that these can perform electrophilic attack reactions along the same mechanistic pathway (pi-FMO pathway) with similar reactivity but also have an additional reaction channel involving the unoccupied alpha-spin d(z(2)) orbital (sigma-FMO pathway). These studies experimentally probe the FMOs involved in the reactivity of Fe-IV=O (S = 1) model complexes resulting in a detailed understanding of the Fe-O bond and its contributions to reactivity.

First author: Wolf, Robert, Substituent effects in formally quintuple-bonded ArCrCrAr compounds (Ar = terphenyl) and related species, INORGANIC CHEMISTRY, 46, 11277, (2007)
Abstract: The effects of different terphenyl ligand substituents on the quintuple Cr-Cr bonding in arylchromium(1) dimers stabilized by bulky terphenyl ligands (Ar) were investigated. A series of complexes, ArCrCrAr (1-4; Ar = C6H2-2,6-(C6H3-2,6-Pr-i(2))2-4-X, where X = H, SiMe3, OMe, and F), was synthesized and structurally characterized. Their X-ray crystal structures display similar trans-bent C(ipso)CrCrC(ipso) cores with short Cr-Cr distances that range from 1.8077(7) to 1.8351(4) angstrom. There also weaker Cr-C interactions [2.294(1)-2.322(2) angstrom] involving an C(ipso) of one of the flanking aryl rings. The data show that the changes induced in the Cr-Cr bond length by the different substituents X in the para positions of the central aryl ring of the terphenyl ligand are probably a result of packing rather than electronic effects. This is in agreement with density functional theory (DFT) calculations, which predict that the model compounds (4-XC6H4)CrCr(C6H4-4-X) (X = H, SiMe3, OMe, and F) have similar geometries in the gas phase. Magnetic measurements in the temperature range of 2-300 K revealed temperature-independent paramagnetism in 1-4. UV-visible and NMR spectroscopic data indicated that the metal-metal-bonded solid-state structures of 1-4 are retained in solution. Reduction of (4-F3CAr’)CrCl (4-F3CAr’ = C6H2-2,6-(C6H3-2,6-Pr-i(2))2-4-, CF3) with KC8 gave non-Cr-Cr-bonded fluorine-bridged dimer {(4-F3CAr’)Cr(mu-F)(THF)}(2) (5) as a result of activation of the CF3 moiety. The monomeric, two-coordinate complexes [(3,5-(Pr2Ar)-Pr-i*)Cr(L)] (6, L = THF; 7, L = PMe3; 3,5-(Pr2Ar)-Pr-i* = C6H1-2,6-(C6H-2,4,6-Pr-i(3))(2)-3,5-Pr-i(2)) were obtained with use of the larger 3,5-Pr-2(i)-Ar* ligand, which prevents Cr-Cr bond formation. Their structures contain almost linearly coordinated Cr-I atoms, with high-spin 3d(5) configurations. The addition of toluene to a mixture of (3,5-iPr2Ar*)CrCl and KC8 gave the unusual dinuclear benzyl complex [(3,5-(Pr2Ar)-Pr-i*)Cr(eta(3):eta(6)-CH2Ph)Cr(Ar*-1-H-3,5-Pr-i(2))] (8), in which a C-H bond from a toluene methyl group was activated. The electronic structures of 5-8 have been analyzed with the aid of DFT calculations.

First author: Lukoyanov, Dmitriy, Testing if the interstitial atom, X, of the nitrogenase molybdenum-iron cofactor is N or C: ENDOR, ESEEM, and DFT studies of the S=3/2 resting state in multiple environments, INORGANIC CHEMISTRY, 46, 11437, (2007)
Abstract: A high-resolution (1.16 A) X-ray structure of the nitrogenase molybdenum-iron (MoFe) protein revealed electron density from a single N, O, or C atom (denoted X) inside the central iron prismane ([6Fe]) of the [MoFe7S9: homocitrate] FeMo-cofactor (FeMo-co). We here extend earlier efforts to determine the identity of X through detailed tests of whether X = N or C by interlocking and mutually supportive 9 GHz electron spin echo envelope modulation (ESEEM) and 85 GHz electron-nuclear double resonance (ENDOR) measurements on N-14/15 and C-12/13 isotopomers of FeMo-co in three environments: (i) incorporated into the native MoFe protein environment; (ii) extracted into N-methyl formamide solution; and (iii) incorporated into the NifX protein, which acts as a chaperone during FeMo-co biosynthesis. These measurements provide powerful evidence that X; N/C, unless X in effect is magnetically decoupled from the S = 3/2 electron spin system of resting FeMo-co. They reveal no signals from FeMo-co in any of the three environments that can be assigned to X from either N-14/15 or C-13: If X were either element, its maximum observed hyperfine coupling at all fields of measurement is estimated to be A((14/15)Nx) < 0.07/0.1 MHz, A((13)Cx) < 0.1 MHz, corresponding to intrinsic couplings of about half these values. In parallel, we have explicitly calculated the hyperfine tensors for X = N-14/15/C-13/O-17, nuclear quadrupole coupling constant e(2)qQ for X = N-14, and hyperfine constants for the Fe sites of S = 3/2 FeMo-co using density functional theory (DFT) in conjuction with the broken-symmetry (BS) approach for spin coupling. If X = C/N, then the decoupling required by experiment strongly supports the “BS7′ spin coupling of the FeMo-co iron sites, in which a small X hyperfine coupling is the result of a precise balance of spin density contributions from three spin-up and three spin-down (3 up arrow:3 down arrow) iron atoms of the [6Fe] prismane “waist” of FeMo-co; this would rule out the “BS6” assignment (4 up arrow:2 down arrow for [6Fe]) suggested in earlier calculations. However, even with the BS7 scheme, the hyperfine couplings that would be observed for X near g(2) are sufficiently large that they should have been detected: we suggest that the experimental results are compatible with X = N only if a(iso)(N-14/15(x)) < 0.03-0.07/0.05-0.1 MHz and ai(so)(C-13(X)) < 0.05-0.1 MHz, compared with calculated values of aiso(N-14/15(x)) = 0.3/0.4 MHz and a(iso)(C-13(X)) = 1 MHz. However, the DFT uncertainties are large enough that the very small hyperfine couplings required by experiment do not necessarily rule out X = N/C.

First author: Georgieva, I., Bonding analyses, formation energies, and vibrational properties of M-R(2)dtc complexes (M = Ag(I), Ni(II), Cu(III), or Zn(II)), JOURNAL OF PHYSICAL CHEMISTRY A, 111, 13075, (2007)
Abstract: Detailed theoretical studies based on density functional theory (DFT)/B3LYP calculations of dimethyl- and diethyldithiocarbamate complexes of Ni(II), Cu(II), Zn(II), and Ag(I) are performed to characterize the metal ligand bonding type as well as the metal-ligand bonding strength depending on the metal and the dialkyl substituent. The metal-ligand interactions in the Studied complexes are investigated by means of charge decomposition analysis, energy partitioning analysis (EPA), and natural bond orbital analysis. According to the EPA calculations, the electrostatic attraction is the dominant contribution to the M-S-2(R(2)dtc) (dtc = dithiocarbamate) bonding. The electrostatic and the orbital energies follow the order of the total binding energy, and hence both contributions are responsible for the binding energy order of M(R(2)dtc)(2) complexes. The stability of the M(R(2)dtc)(2) complexes is estimated by means of calculated formation reaction energies in the gas phase and solution, and it decreases in the order Ni(R(2)dtc)(2) > Cu(R(2)dtc)(2) > Zn(R(2)dtc)(2). Larger formation reaction energies are found for M(Et(2)dtc)(2) than for M(Me(2)dtc)(2) complexes. The calculations predict stabilization of M(II)(R(2)dtc)(2) complexes going from the gas phase to a polar solvent and destabilization of the bidentate AgR(2)dtc complex in a polar solvent. Gas-phase frequency calculations of all possible bonding types, symmetrical, asymmetrical, and uni- and bidentate, predict one band due to the v(CS) IR absorption, and therefore the number of the bands in the 1060-920 cm(-1) region could not be used to discern the metal-ligand bonding type. Periodic DFT frequency calculations for Cu(Et(2)dtc)(2) reveal that the splitting observed in the solid-state spectra of the complexes arises from the nonplanar MS4 fragment and intermolecular contacts but not from asymmetrical bonding. The calculations suggest that the important vibrational characteristic that can be used to discern uni- and bidentate bonding is the Raman activity of the v(CS) band: It is very high for the unidentate dtc bonding (v(C=S)) and low for the bidentate bonding (v(as)(CS)).

First author: Mitoraj, Mariusz, Donor-acceptor properties of ligands from the natural orbitals for chemical valence,ORGANOMETALLICS, 26, 6576, (2007)
Abstract: Natural orbitals for chemical valence (NOCV) have been used to characterize donor-acceptor properties of ligands in model nickel(II) complexes. NOCV allows for separation of ligand -> metal and metal -> ligand electron transfer processes (Dewar-Chatt-Duncanson model). Bonding between the ligand X = CN-, PH3, NH3, C2H4, CO, CS, N-2, NO+ and the metal-containing fragment in the [Ni L-3](2+) complexes (L = NH3, CO) have been discussed. For both sigma-donation and pi-back-bonding, the resulting orders of ligands are in a qualitative agreement with those commonly accepted. However, it was also demonstrated that the influence of the metal-containing fragment can be substantial, changing the relative donor-acceptor characteristics of different ligands.

First author: Collins, Scott, Theoretical modeling of ethylene insertion by nickel iminophosphonamide and amidinate complexes, ORGANOMETALLICS, 26, 6612, (2007)
Abstract: Modeling of ethylene polymerization using density functional theory was undertaken for both generic and substituted nickel iminophosphonamide (PN(2)) and amidinate (CN(2)) complexes. The more highly substituted complexes were studied using quantum mechanics/molecular mechanics (QM/MM) techniques so as to probe the role of steric effects on insertion and chain-transfer processes. For the generic systems H(2)P(NSiH(3))(2)NiR(L) and HC(NSiH(3))(2)NiR(L) (R = alkyl; L = C(2)H(4)), insertion had a higher barrier in the PN2 versus CN2 complex. The energy of ethylene binding was strongly affected by the nature of the R group. This was shown to be a function of agostic stabilization of the alkyl group in the absence of monomer. Insertion barriers are also strongly dependent on the nature of the alkyl group, particularly in the case, of the sterically hindered Keim catalyst, which was modeled by (Me(3)Si)(2)NP(Me)(NSiMe(3))(2)NiR(L) and QM/MM techniques. Degenerate chain transfer was systematically studied in the case of the generic CN(2) complex HC(NSiH(3))(2)NiEt(C(2)H(4)) and proceeds through five-coordinate intermediates with distorted trigonal-bipyramidal geometries. The highest-energy intermediate corresponds to a bis(ethylene)-NiH complex, where loss of ethylene would constitute (degenerate) chain transfer. Intermediates in the analogous PN(2) complexes lie higher in energy, and thus these complexes should provide higher molecular weight material, as observed experimentally. beta-H elimination/chain walking was also investigated using both generic and substituted complexes. The ground states in these reactions are agostic alkyls, while the ethylene-NiH complex, in which ethylene is perpendicular to the square plane, is a weakly bound intermediate. These intermediates are related to those formed during chain transfer by binding of the monomer.

First author: Penka, Emmanuel F., Theoretical investigation of the bonding properties of N-heterocyclic carbenes coordinated to electron-rich d(8) metal centers, JOURNAL OF ORGANOMETALLIC CHEMISTRY, 692, 5709, (2007)
Abstract: Density functional theory (DFT) at the generalized gradient approximation (GGA) level has been applied for the analysis of the bond between group 10 metals and N-heterocyclic carbene (NHC) in complexes [MX3(NHC)](-) (M = Ni, Pd, Pt, X = H, Cl, I). For comparative purposes, similar calculations have been performed for analogous pyridine complexes [MX3(py)](-) (py = pyridine). Full geometry optimizations have been performed for all complexes. The role of the M-L pi interaction was investigated by the aid of respectively, energy decomposition analysis, Hirshfeld atomic charge variation, molecular orbital considerations and bond order decomposition analysis. The pi-bonding contribution increases in the order I < Cl < II, and Pt < Pd < Ni. Most significantly, the absolute p- acceptor ability of the NHC in these complexes is larger than that of pyridine. However, due to the dominant sigma donor interactions, the relative contribution, that is the pi/sigma ratio, is predicted to be smaller.

First author: Cranswick, Matthew A., Photoelectron spectroscopy and electronic structure calculations of d(1) vanadocene compounds with chelated dithiolate ligands: Implications for pyranopterin Mo/W enzymes, INORGANIC CHEMISTRY, 46, 10639, (2007)
Abstract: Gas-phase photoelectron spectroscopy and density functional theory have been used to investigate the electronic structures of open-shell bent vanadocene compounds with chelating dithiolate ligands, which are minimum molecular models of the active sites of pyranopterin Mo/W enzymes. The compounds Cp2V(dithiolate) [Where dithiolate is 1,2-ethenedithiolate (S2C2H2) or 1,2-benzenedithiolate (bdt), and Cp is cyclopentadienyl] provide access to a 17-electron, d(1) electron configuration at the metal center. Comparison with previously studied Cp2M(dithiolate) complexes, where M is Ti and Mo (respectively d(0) and d(2) electron configurations), allows evaluation of d(0), d(1), and d(2) electronic configurations of the metal center that are analogues for the metal oxidation states present throughout the catalytic cycle of these enzymes. A “dithiolate-folding effect” that involves an interaction between the vanadium d orbitals and sulfur p orbitals is shown to stabilize the d(1) metal center, allowing the d(1) electron configuration and geometry to act as a low-energy electron pathway intermediate between the d(0) and d(2) electron configurations of the enzyme.

First author: Frantz, Richard, C-3-symmetric trinuclear molybdenum cluster sulfides: Configurational stability, supramolecular stereocontrol, and absolute configuration assignment, INORGANIC CHEMISTRY, 46, 10717, (2007)
Abstract: The chiral C-3-symmetric [Mo3S4Cl3(dppe)(3)](+) cluster [dppe = 1,2-bis(diphenylphosphinoethane), P or M enantiomers] with incomplete cuboidal structure is shown to be configurationally-stable at room temperature and configurationally labile at elevated temperature using enantiopure Delta- or Lambda-TRISPHAT [(tris(tetrachlorobenzenediolato) phosphate-(V)] anions both as chiral NMR solvating and asymmetry-inducing reagents. It is evidenced that the enantiomers of this trinuclear cluster cation can equilibrate at higher temperature (typically 72 degrees C), and in the presence of the hexacoordinated phosphate anion, a moderate level of stereocontrol (1.2:1) can be achieved. It results in a diastereomeric enrichment of the solution in favor of the heterochiral ion pairs, e.g., M+ Delta(-) or P+ Lambda(-). At higher temperature, a partial racemization of the TRISPHAT anion is also observed, and precipitation at room temperature of [rac-Mo3S4Cl3(dppe)(3)][rac-TRISPHAT] salts from the diastereomeric enriched solution improves the diastereomeric purity of the mother liquor to a 4:1 ratio. A low-energy pathway for the inverconversion between the [P-Mo3S4Cl3(dppe)(3)](+) and [M-Mo3S4Cl3(dppe)(3)](+) enantiomers has been found using combined quantum mechanics and molecular mechanics methodologies. This pathway involves two intermediates with three transition state regions, which result from the partial decoordination of the diphosphane coordinated at each metal center. Such decoordination creates a vacant,position on the metal, producing a Lewis acidic site that presumably catalyzes the TRISPHAT epimerization.

First author: Georgieva, Ivelina, Theoretical study of metal-ligand interaction in Sm(III), Eu(III), and. Tb(III) complexes of coumarin-3-carboxylic acid in the gas phase and solution, INORGANIC CHEMISTRY, 46, 10926, (2007)
Abstract: The interaction of lanthanide(III) cations (Ln(III) = Sm(III), Eu(III), and Tb(III)) with the deprotonated form of the coumarin-3-carboxylic acid (cca(-)) has been investigated by density functional theory (DFT/B3LYP) and confirmed by reference MP2 and CCSD(T) computations. Solvent effects on the geometries and stabilities of the Ln(III) complexes were computed using a combination of water clusters and a continuum solvation model. The following two series of systems were considered: (i) Ln(cca)(2+), Ln(cca)(2)(+), Ln(cca)(3) and (ii) Ln(cca)(H(2)O)(2)Cl(2), Ln(cca)(2)(H(2)O)(2)Cl, Ln(cca)(3). The strength and character of the Ln(III)-cca(-) bidentate bonding were characterized by calculated Ln-O bond lengths, binding energies, ligand deformation energies, energy partitioning analysis, sigma-donation contributions, and natural population analyses. The energy decomposition calculations predicted predominant electrostatic interaction terms to the Ln-cca bonding (ionic character) and showed variations of the orbital interaction term (covalent contributions) for the Ln-cca complexes studied. Electron distribution analysis suggested that the covalent contribution comes mainly from the interaction with the carboxylate moiety of cca(-).

First author: Real, Florent, Theoretical investigation of the energies and geometries of photoexcited uranyl(VI) ion: A comparison between wave-function theory and density functional theory, JOURNAL OF CHEMICAL PHYSICS, 127, 10926, (2007)
Abstract: In order to assess the accuracy of wave-function and density functional theory (DFT) based methods for excited states of the uranyl(VI) UO(2)(2+) molecule excitation energies and geometries of states originating from excitation from the sigma(u), sigma(g), pi(u), and pi(g) orbitals to the nonbonding 5f(delta) and 5f(phi) have been calculated with different methods. The investigation included linear-response CCSD (LR-CCSD), multiconfigurational perturbation theory (CASSCF/CASPT2), size-extensivity corrected multireference configuration interaction (MRCI) and AQCC, and the DFT based methods time-dependent density functional theory (TD-DFT) with different functionals and the hybrid DFT/MRCI method. Excellent agreement between all nonperturbative wave-function based methods was obtained. CASPT2 does not give energies in agreement with the nonperturbative wave-function based methods, and neither does TD-DFT, in particular, for the higher excitations. The CAM-B3LYP functional, which has a corrected asymptotic behavior, improves the accuracy especially in the higher region of the electronic spectrum. The hybrid DFT/MRCI method performs better than TD-DFT, again compared to the nonperturbative wave-function based results. However, TD-DFT, with common functionals such as B3LYP, yields acceptable geometries and relaxation energies for all excited states compared to LR-CCSD. The structure of excited states corresponding to excitation out of the highest occupied sigma(u) orbital are symmetric while that arising from excitations out of the pi(u) orbitals have asymmetric structures. The distant oxygen atom acquires a radical character and likely becomes a strong proton acceptor. These electronic states may play an important role in photoinduced proton exchange with a water molecule of the aqueous environment.

First author: van Bochove, Marc A., Nucleophilic substitution at phosphorus centers (S(N)2@P), CHEMPHYSCHEM, 8, 2452, (2007)
Abstract: We have studied the characteristics of archetypal model systems for bimolecular nucleophilic substitution at phosphorus (S(N)2@P) and, for comparison, at carbon (S(N)2@C and silicon (S(N)2@Si) centers. In our studies, we applied the generalized gradient approximation (GGA) of density functional theory DFT) at the OLYP/ TZ2P level. Our model systems cover nucleophilic substitution at carbon in X- + CH3Y (S(N)2@C), at silicon in X- + SiH3Y (S(N)2@Si), at tricoordinate phosphorus in X- + PH2Y (S(N)2@P3), and at tetracoordinate phosphorus in X- + POH2Y (S(N)2@P4). The main feature of going from S(N)2@C to S(N)2@P is the loss of the characteristic double-well potential energy surface (PES) involving a transition state [X-CH3-Y](-) and the occurrence of a single-well PES with a stable transition complex, namely, [X-PH2-Y](-) or [X-POH2-Y](-). The differences between S(N)2@P3 and S(N)2@P4 are relatively small. We explored both the symmetric and asymmetric (i.e. X, Y = Cl, OH) S(N)2 reactions in our model systems, the competition between backside and frontside pathways, and the dependence of the reactions on the conformation of the reactants. Furthermore, we studied the effect, on the symmetric and asymmetric S(N)2@P3 and S(N)2@P4 reactions, of replacing hydrogen substituents at the phosphorus centers by chlorine and fluorine in the model systems X- + PR2Y and X- + POR2Y, with R=Cl, F. An interesting phenomenon is the occurrence of a triple-well PES not only in the symmetric, but also in the asymmetric S(N)2@P4 reactions of X-+ POCl2-Y.

First author: Xia, Fei, Reaction mechanisms for C-O bond coupling from Pt4CH2+ and O-2: A relativistic density functional study, ORGANOMETALLICS, 26, 6076, (2007)
Abstract: Computational investigations on the reaction of Pt4CH2+ with O-2 have been carried out by the relativistic density functional approach. Calculations indicate that the reactivity Of Pt4CH2+ toward O-2 is different from the metallic carbene PtCH2+. The dehydrogenation route in the reaction of Pt4CH2+ with O-2 is quite unfavorable, both dynamically and thermodynamically. The reaction channels to products H2O/CO and HCOOH with involvement of O-O bond activation and C-O bond coupling are strikingly exothermic, where the C-O bond coupling and the release of CO are the crucial steps for the entire reaction channels. Predicted overall Gibbs free energies of reaction Delta G are -66.2 kcal mol(-1) for H2O/CO and -73.5 kcal mol(-1) for HCOOH, respectively. Both energy-favored routes have thus relatively high reaction efficiencies toward O-2 in comparison with dehydrogenation. On the basis of theoretical results, plausible mechanisms for the reaction of Pt4CH2+ with O-2 and candidates for the experimental neutral products [C, H-2, O-2] in reaction have been proposed.

First author: Kilah, Nathan L., Triphenylphosphine-stabilized diphenyl-arsenium, -stibenium, and -bismuthenium salts,ORGANOMETALLICS, 26, 6106, (2007)
Abstract: Two series of triphenylphosphine-stabilized diphenyl-arsenium, -stibenium, and -bismuthenium salts of the types [(Ph3P)EPh2]PF6 (where E = As, Sb, Bi) and [(Ph3P)(2)EPh2]PF6 (where E = Sb, Bi) have been synthesized and their structures and bonding investigated by X-ray crystallography and density functional theory at the PBE/TZP level. The coordination geometries around the central group 15 elements are distorted trigonal pyramidal in the mono(triphenylphosphine) complexes and distorted trigonal bipyramidal in the bis(triphenylphosphine) complexes, where in each case the stereochemically active lone pair of the six-electron, angular diphenyl-arsenium, -stibenium, or -bismuthenium ion occupies an equatorial position in the trigonal plane containing the C-E-C bonds. For the complexes [(Ph3P)EPh2]PF6 (E = As, Sb, Bi), the theoretical results for the cations are consistent with the dative covalent fonnulation [Ph3P -> EPh2](+), especially for E = As and Sb, but for [(Ph3P)(2)EPh2]PF6 (E = Sb, Bi) the bonding between the phosphines and the stibenium or bisthmuthenium ion is best described as an induced dipole-ion interaction.

First author: Manzur, Jorge, Coordination alternatives in dinuclear bis(pyridin-2-ylalkyl)benzylaminecopper(II) complexes with OH-, RO-, F-, or Cl- bridges: Experimental structures and DFT preferences, EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 26, 5500, (2007)
Abstract: The compounds [(LCu)-Cu-1(mu-OH)2CuL1](ClO4)(2) (1), [(LCu)-Cu-2(mu-OH)(2)CuL2 (ClO4)(2) (2), [(LCu)-Cu-3(mu-OH)(2)CuL3] (ClO4)(2) (3), [(LCu)-Cu-3- (mu-OMe)(2)CuL3] (ClO4)(2) (4), [(LCu)-Cu-3(mu-F)(2)CuL3] (BF4)(2) (5), [(LCu)-Cu-4- (mu-Cl-2)CuL4] (CIO4)(2) (6), and [Cu(mu-L-5)(2)Cu](ClO4)(2) (7), where L-1 = bis(pyridin-2-ylmethyl)benzylamine, L 2 = (6-methylpyridin-2-ylmethyl)(pyridin-2-ylmethyl)benzylamine, L-3 = bis(6-methylpyridin-2-ylmethyl)benzylamine, L-4 = (pyridin2-ylethyl)(pyiidin-2-ylmethyl)benzylamine, and L-5 = (6 -oxidomethylpyridin -2-ylmethyl) (6 -methylpyridin- 2 -ylmethyl)benzylamine, were structurally characterized and studied by low-temperature EPR spectroscopy. The formation of compound 5 involved fluoride abstraction from BF4- and that of 7 involved O-2-assisted C-H (methyl) activation/monooxygenation of L-3. Whereas the dications of 1-4 and 7 possess a square-pyramidal configuration at the copper(II) centers with hydroxide or alkoxide bridges in equatorial positions, the dications of 5 and 6 exhibit equatorial/axial arrangements for the bridging halide ions. In the dication of 5, the tridentate ligand binds in a meridional fashion and includes two adjacent five-membered chelate rings. Such a situation has been observed previously only with chloride, alkoxide, or aqua bridges. In contrast to the syn configuration of the dication of 2, the dications of complexes 1, 3, 4, and 7 adopt an anti configuration with respect to the binding of L-n. The dications of 1, 2, and 7 have the pyridinyl or 6-methylpyridinyl groups in the axial position, whereas those of 3 and 4 feature the tertiary amine N atom at that site. DFT calculations of various configurations of the dications of 1-6 reproduce the experimentally observed structural alternatives in complexes 1-4, but they do not predict the axial/equatorial structure of 5 as the lowest-energy configuration. The systematic overestimation of repulsive forces and thus of distances by DFT may result in an underestimation of the pi-pi interaction between the largely coplanar mer-L-3 ligands separated by about 3.6 angstrom in 5, which probably affects its structure. By incorporating these and previous results, the syn versus anti, equatorial/equatorial versus equatorial/axial, and axial pyridine versus axial amine structural alternatives are discussed.

First author: Valiente, Rafael, Red-to-yellow pressure-induced phase transition in Pt(bpy)Cl-2: Spectroscopic study supported by DFT calculations, EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 26, 5735, (2007)
Abstract: The combination of spectroscopic and computational methods has been employed to explore the origin of the luminescence in the red and yellow forms of Pt(bpy)Cl-2. The luminescence of the red (linear-chain) form of Pt(bpy)Cl-2 (bpy 2,2′-bipyridine) has been measured as a function of hydrostatic pressure up to 65 kbar. The luminescence band maximum is redshifted (-147 cm(-1) kbar(-1)), and the intrachain Pt-Pt distance decreases from 3.46 to 3.25 angstrom between ambient pressure and 17.7 kbar. Strong discontinuities in the optical properties at 17.7 kbar were interpreted in terms of a crystallographic phase transition from the red to a denser yellow form of Pt(bpy)Cl-2. First-principles calculations based on density functional theory were used to study the red to yellow phase transformation.

First author: Swart, Marcel, pi-pi stacking tackled with density functional theory, JOURNAL OF MOLECULAR MODELING,13, 1245, (2007)
Abstract: Through comparison with ab initio reference data, we have evaluated the performance of various density functionals for describing pi-pi interactions as a function of the geometry between two stacked benzenes or benzene analogs, between two stacked DNA bases, and between two stacked Watson-Crick pairs. Our main purpose is to find a robust and computationally efficient density functional to be used specifically and only for describing pi-pi stacking interactions in DNA and other biological molecules in the framework of our recently developed QM/QM approach “QUILD”. In line with previous studies, most standard density functionals recover, at best, only part of the favorable stacking interactions. An exception is the new KT1 functional, which correctly yields bound pi-stacked structures. Surprisingly, a similarly good performance is achieved with the computationally very robust and efficient local density approximation (LDA). Furthermore, we show that classical electrostatic interactions determine the shape and depth of the pi-pi stacking potential energy surface.

First author: Dunlap, Brett I., Alternative perspective on density-functional perturbation theory, PHYSICAL REVIEW A, 76, 1245, (2007)
Abstract: Perturbation theory is examined in analytic density-functional theory (ADFT), for which V representability means slightly more than in conventional density-functional theory because the potential is fitted. There is synergism between variationality and V representability. Together they redirect the object of perturbation theory from the set of occupied virtual orbital rotations to the change in the fit to the Kohn-Sham potential, which is called the Sambe-Felton potential. This reduces the dimensionality of perturbation theory from order N(2) to order N, where N is the number of basis functions. With variational fitting, no fractional or negative powers of the density appear when using the Slater exchange kernel, which is proportional to the cube root of the spin density. Requiring the Fock matrix and density matrix to commute through each order of perturbation theory determines the role of fractional occupation numbers in density-functional perturbation theory, which are treated via the corresponding nonintegral differences between the occupation numbers of orbitals. This theory is tested by removing a tenth or twentieth of an electron from the highest occupied molecular orbital for a standard set of small molecules, in which case the first- and second-order perturbed energies are accurate to 70%, when compared to the energy difference of the two corresponding self-consistent-field (SCF) calculations. For an all-electron ADFT calculation on a C(4v)-symmetric Zr(6)O(12) cluster, the timing for all SCF coupled perturbed iterations is not significant compared to the single required N(4) sum over occupied and virtual orbitals.

First author: Pierrefixe, Simon C. A. H., Hypervalence and the delocalizing versus localizing propensities of H-3(-), Li-3(-), CH5- and SiH5-, STRUCTURAL CHEMISTRY, 18, 813, (2007)
Abstract: Lithium and silicon have the capability to form hypervalent structures, such as Li-3(-) and SiH5-, which is contrasted by the absence of this capability in hydrogen and carbon, as exemplified by H-3(-) and CH5- which, although isoelectronic to the former two species, have a distortive, bond-localizing propensity. This well-known fact is nicely confirmed in our DFT study at BP86/TZ2P. We furthermore show that the hypervalence of Li and Si neither originates from the availability of low-energy 2p and 3d AOs, respectively, nor from differences in the bonding pattern of the valence molecular orbitals; there is, in all cases, a 3-center-4-electron bond in the axial X-A-X unit. Instead, we find that the discriminating factor is the smaller effective size of C compared to the larger Si atom, and the resulting lack of space around the former. Interestingly, a similar steric mechanism is responsible for the difference in bonding capabilities between H and the effectively larger Li atom. This is so, despite the fact that the substituents in the corresponding symmetric and linear dicoordinate H-3(-) and Li-3(-) are on opposite sides of the central atom.

First author: Sahel, K., Photocatalytic decolorization of Remazol Black 5 (RB5) and Procion Red MX-5B – Isotherm of adsorption, kinetic of decolorization and mineralization, APPLIED CATALYSIS B-ENVIRONMENTAL, 77, 100, (2007)
Abstract: The isotherm of adsorption and the kinetic of photocatalytic degradation of two azo dyes, Remazol Black 5 (RB5) and Procion Red MX-5B are reported and compared using different concentrations of dyes. The photocatalytic degradation is performed in aqueous solutions in the presence of TiO(2) Degussa P25 under artificial UV light radiation (lambda > 290 nm).The isotherms of adsorption of the both dyes are very different. These differences are discussed considering the pH of the solution and the structure of the dye. In opposition to the isotherm of adsorption, the kinetic of both dyes are very similar, and fit well with the Langmuir-Hinshelwood model in the concentration range 5-60 mu mol/L. However, at higher dyes concentration, the initial rate of decolorization decreases. The important absorption of light by the dyes was suggested to be at the origin of this decrease of the decolorization. The absence of correlation between isotherm of adsorption in the dark and the decolorization kinetics is discussed.The attribution of main UV-vis bands of each dye has been performed by molecular modelisation using Density Functional Theory (DFTT). Their evolution as a function of time, the evolution of pH during the photocatalytic process and the determination of the decrease of Total Organic Carbon (TOC) and of the evolution of inorganic ions are used to better understand the decolorization mechanism occurring for these both dyes.

First author: Neupane, Kosh P., Probing variable axial ligation in nickel superoxide dismutase utilizing metal lopeptide-based models: Insight into the superoxide disproportionation mechanism, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 129, 14605, (2007)
Abstract: Nickel superoxide dismutase (NiSOD) is a bacterial metalloenzyme that possesses a mononuclear Ni-center and catalyzes the disproportionation Of O2(center dot-) by cycling between Ni-II and Ni-III oxidation states. Herein we present evidence from several SOD active metallopeptide maquettes ([Ni((SODH)-H-M2(1)X)]; (SODH)-H-M2(1)X = H2N-XCDLPCG-COOH; X = H, D, or A) that the Ni-center of NiSOD most likely remains five-coordinate during SOD catalysis using thin-film voltammetry. N-3- and CN- titration studies suggest that O-2(center dot-) disproportionation by [Ni(SODM2 H(1)X)] proceeds via an outersphere mechanism. Computationally derived values for the nuclear reorganization energy of the [Ni-II(SODM2)]/[Ni-III(SODM2)] self-exchange reaction combined with the experimentally determined value for k(o) (similar to 450 s(-1)) suggest that axial ligation enhances the O-2(center dot-) disproportionation reaction in [Ni(SODM2)] (and NiSOD by analogy) by optimizing the Ni-II/Ni-III redox couple such that it is close to the midpoint of the O-2(center dot-) reduction and oxidation couples.

First author: Lyon, Jonathan T., Formation of unprecedented actinide carbon triple bonds in uranium methylidyne molecules, PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA,104, 18919, (2007)
Abstract: Chemistry of the actinide elements represents a challenging yet vital scientific frontier. Development of actinide chemistry requires fundamental understanding of the relative roles of actinide valence-region orbitals and the nature of their chemical bonding. We report here an experimental and theoretical investigation of the uranium methylidyne molecules X3U CH (X = F, Cl, Br), F2ClU CH, and F3U CF formed through reactions of laser-ablated uranium atoms and trihalomethanes or carbon tetrafluoride in excess argon. By using matrix infrared spectroscopy and relativistic quantum chemistry calculations, we have shown that these actinide complexes possess relatively strong U C triple bonds between the U 6d-5f hybrid orbitals and carbon 2s-2p orbitals. Electron-withdrawing ligands are critical in stabilizing the U(VI) oxidation state and sustaining the formation of uranium multiple bonds. These unique U C-bearing molecules are examples of the long-sought actinide-alkylidynes. This discovery opens the door to the rational synthesis of triple-bonded actinide-carbon compounds.

First author: Zhang, Guozhen, Decomposition of CH2O by lanthanum: A theoretical study, JOURNAL OF PHYSICAL CHEMISTRY A, 111, 11894, (2007)
Abstract: This work aims to investigate the reaction mechanism of lanthanum atom with formaldehyde in the gas phase using density functional theory and coupled cluster calculations. The results indicate that the minimum energy pathway, similar to the reactions of its neighboring yttrium with formaldehyde, is the formation of the eta(2)-formaldehyde-metal complex followed by two C-H insertions which leads to metal dihydrides and carbon monoxide. The competing pathway producing a metal-carbonyl compound and hydrogen molecule favors a high-spin state and thus involves a spin conversion from doublet state to quartet state. The crossing region of the doublet and quartet potential energy surfaces (PES) has been estimated by a simple approach as proposed by Yoshizawa et al. Less favorable pathways leading to metal monoxide and carbene radical by C-O insertion as well as formyllanthanum by single C-H insertion are also studied. Compared with the CCSD(T) method, the BP86 method tends to overestimate the binding energies of the d-rich compounds, though the two methods qualitatively agree well on the reaction mechanism. Finally, the (n – 1)d(1)ns(2) to (n – 1)d(2)ns(1) promotion effect is proposed to account for the difference in the formation mechanism of the metal-carbonyl compounds LaCO and YCO, which may also extend to the reactions of formaldehyde with other “general” group III rare earth elements including Sc, Ce, Gd, and Lu.

First author: Caramori, Giovanni F., The nature of the Ru-NO bond in ruthenium tetraammine nitrosyl complexes,ORGANOMETALLICS, 26, 5815, (2007)
Abstract: Quantum chemical calculations at the DFT level have been carried out for trans- [Ru-II(NH3)(4)(L)NO](q) and trans- [RuII(NH3)(4)(L)NO](q-1) complexes, where L = NH3, Cl-, and H2O. The equilibrium geometries and the vibrational frequencies are reported not only for the ground state (GS) but also for light-induced metastable states MS I and MS2. The nature of the Ru-NO+ and Ru-NOo bonds has been investigated by means of the energy decomposition analysis (EDA). The nature of the Ru-NOo bond has been analyzed for the three states GS, MS1, and MS2, considering two different situations: before and after one-electron reduction. The results suggest that not only the orbital term but also the Delta E-Pauli term is responsible for weakening of the Ru-II-NOo bond, the Delta E-Pauli term increasing in comparison with the Ru-NO+ bonds, thus making the NOo ligand more susceptible to dissociation in comparison with NO+. Calculations of the Ru-III-NOo species show that in this case the bonds are mainly covalent, but the electrostatic stabilization also plays an important role. Among the orbital interactions, the T-back-donation is the most important term.

First author: Santi, Saverio, Charge transfer through isomeric unsaturated hydrocarbons. Redox switchable optical properties and-electronic structure of substituted Indenes with a pendant ferrocenyl, ORGANOMETALLICS, 26, 5867, (2007)
Abstract: A family of (ferrocenyl)indenes, (2-ferrocenyl)indene, (2-ferrocenyl)tetramethylindene, (2-ferrocenyl)hexamethylindene, (3-ferrocenyl)indene, and (3-ferrocenyl)hexamethylindene, and the corresponding monooxidized cations have been prepared. The results of a structural and spectroelectrochemical study are discussed. The availability of pairs of isomers with known geometries and differently methylated indenes allowed the detailed investigation of how slight geometric and electronic modifications affect their physical properties. The molecular structures have been determined by X-ray diffraction and compared with the fully optimized structures calculated with state-of-the-art DFT methods. Calculated and crystallographic structures agree in establishing the dependence of the orientation of the indene moiety and the ferrocenyl cyclopentadienyl rings on the degree of methylation. The UV-vis spectra and in particular the appearance upon oxidation of a new near-IR absorption, whose energy and intensity increase with the degree of methylation and cyclopentadienyl-indene planarity, are rationalized in the framework of the Hush theory and at quantum chemistry level by DFT and TD-DFT calculations.

First author: Fantasia, Serena, Electronic properties of n-heterocyclic carbene (NHC) ligands: Synthetic, structural, and spectroscopic studies of (NHC)Platinum(II) complexes, ORGANOMETALLICS, 26, 5880, (2007)
Abstract: N-Heterocyclic carbene complexes of platinum(II) have been synthesized, notably monocarbene complexes cis-[(IPr)Pt(dmso)(Cl)(2)], 6, cis-[(IMes)Pt(dmso)(Cl)(2)], 7, cis- [(SIPr)Pt(dmso)(Cl)(2)], 8, cis[(SIMes)Pt(dmso)(Cl)(2)], 9, and cis- [(TTP)Pt(dmso)(Cl)(2)], 10. All complexes have been fully characterized by multinuclear NMR spectroscopy. Complex 7, 9, and 10 have been characterized by X-ray crystallography. The data obtained have allowed for the differentiation between electronic contributions (a and T) present in the Pt-NHC bond. Supported by computational analyses, the percentage of pi back-donation from the metal to the NHC is found to be on the order of 10%. More interestingly, we find that saturated NHC (SIPr and SIMes) are more efficient pi back-acceptors than their unsaturated NHC congeners (IPr and lMes). The synergistic effect between pi back-donation and sigma donation present in the saturated NHC systems results in increased electron density at the platinum center compared to the bonding situation in the unsaturated NHC examples.

First author: Ekanayake, Kaushalya S., Model transition states for methane diazonium ion methylation of guanine runs in oligomeric DNA, JOURNAL OF COMPUTATIONAL CHEMISTRY, 28, 2352, (2007)
Abstract: The DNA reaction pattern of the methane diazonium ion, which is the reactive intermediate formed from several carcinogenic methylating agents, was examined at N7 and O-6 sites in guanine runs occurring in oligo-nucleotides and model oligonucleotides. Density functional B3LYP/6-31G*, and SCF 3-21G and STO-3G energies of model transition states were calculated in the gas phase and in the CPCM reaction field. For nucleotides containing two, three, and four stacked guanines with counterions in the gas phase, 06 reactivity is greater than N7 reactivity. In the reaction field, N7 reactivity is 9.0 to 9.8 times greater than O-6 reactivity. For a double-stranded oligonucleotide containing two stacked guanines with counterions in the reaction field, the N7 and O-6 reactivities of the 3 ‘-guanine are 3.9 times greater than the corresponding sites in the 5 ‘-guanine. For double-stranded oligonucleotides with three or four stacked guanines and counterions, the reactivities of the interior guanines are higher than corresponding reactivities of guanines at the ends. These reaction patterns agree with most of the available experimental data. Activation energy decomposition analysis for gas-phase reactions in a double-stranded dinucleotide containing two stacked guanines with counterions indicates that selectivity at O-6 is almost entirely due to electrostatic forces. Selectivity at N7 also has a large electrostatic interaction. However, the orbital interaction also contributes significantly to the gas-phase selectivity, accounting for 32% of the total interaction energy difference between the 3 ‘- and 5 ‘-guanine reactions. In aqueous solution, the relative orbital contribution to N7 selectivity is likely to be larger.

First author: Shi, Li-Li, Theoretical studies on the electronic structure and spectral properties of versatile diarylethene-containing 1,10-phenanthroline ligands and their rhenium(I) complexes, JOURNAL OF ORGANOMETALLIC CHEMISTRY,692, 5368, (2007)
Abstract: The structures of versatile diarylethene-containing 1,10-phenanthroline ligands (L-1 and L-2) and their rhenium( I) complexes [ Re( CO) 3( L) Cl] ( 1 and 2) in the ground and low-lying excited states have been optimized at the B3LYP functional and the ab initio configuration interaction singlets (CIS) level, respectively. The spectral properties are predicted with use of time-dependent density functional theory (TDDFT). As shown, the transition character of the strongest absorption band and luminescent spectrum for closed-ring complex 1 is different from that of 2, the former has pi pi* character and the latter has MLCT and LLCT character. We presume the second triplet excited state contributes to the phosphorescence of 1, while the lowest triplet excited state accounts for the phosphorescence of 2. Spin-orbit coupling influences the excitation energies for d(Re)-joined transitions whereas it has negligible effect on the transition character for complexes 1 and 2.

First author: Tuma, Jennifer, Structure and electronic spectra of DNA mini-hairpins with G(n): C-n stems, JOURNAL OF PHYSICAL CHEMISTRY B, 111, 13101, (2007)
Abstract: The solution structure of a synthetic DNA mini-hairpin possessing a stilbenediether linker and three G:C base pairs has been obtained using H-1 NMR spectral data and constrained torsion angle molecular dynamics. Notable features of this structure include a compact hairpin loop having a short stilbene-guanine plane-to-plane distance and approximate B-DNA geometry for the three base pairs. Comparison of the electronic spectra of mini-hairpins having one-to-four G:C base pairs and stilbenediether or hexamethyleneglycol linkers reveals the presence of features in the UV and CD spectra of the stilbene-linked hairpins that are not observed for the ethyleneglycol-linked hairpins. Investigation of the electronic structure of a stilbene-linked hairpin having a single G:C base pair by means of time-dependent density functional theory shows that the highest occupied molecular orbital, but not the lowest unoccupied molecular orbital, is delocalized over the stilbene and adjacent guanine. The calculated UV and CD spectra are highly dependent upon hairpin conformation, but reproduce the major features of the experimental spectra. These results illustrate the utility of an integrated experimental and theoretical approach to understanding the complex electronic spectra of T-stacked chromophores.

First author: Ducere, Jean-Marie, Parametrization of an empirical correction term to density functional theory for an accurate description of pi-stacking interactions in nucleic acids, JOURNAL OF PHYSICAL CHEMISTRY B, 111, 13124, (2007)
Abstract: We present an accurate parametrization of density functional theory augmented with an empirical correction term to describe properly a-stacking interactions in nucleic acids. The approach is based on the popular Perdew-Burke-Ernzerhof (PBE), Becke-Perdew (BP), and hybrid Becke-Lee-Yang-Parr (B3LYP) density functionals augmented by a classical London C6R-6 dispersion term. The novelty of our implementation lies in the accurate tuning of the empirical parameters, included in the f(a)(R) damping function, to reproduce high-level post Hartree-Fock calculations. In particular, we present sets of parameters and the needed code to correct the PBE, BP, and B3LYP results from the Turbomole and ADF packages in connection with basis sets of double and triple quality. The developed approach is validated by comparison with the JSCH-2005 benchmark and with best quality stacking energies reported in the literature for the stacking of H-bonded nucleic acids base pairs.

First author: Conradie, Jeanet, DFT calculations on the spin-crossover complex Fe(salen)(NO): a quest for the best functional, JOURNAL OF PHYSICAL CHEMISTRY B, 111, 12621, (2007)
Abstract: DFT calculations on the spin-crossover complex Fe(salen)(NO) provide a striking illustration of the comparative performance of different exchange-correlation functionals vis-a-vis the issue of transition metal spin state energetics. Thus, although the “classic” pure functionals PW91 and BLYP favor the S = 1/2 state by about 10 kcal/mol, relative to the S = 3/2 state, the hybrid functional B3LYP favors the latter state by nearly the same margin. In contrast, the newer pure functionals OLYP and OPBE, based on the OPTX exchange functional, as well as the B3LYP* hybrid functional (which has 15% Hartree-Fock exchange, compared with 20% for B3LYP) predict nearly isoenergetic S = 1/2 and 3/2 states, as required for a spin-crossover complex. Intriguingly, the OLYP and B3LYP* spin density profiles for the S = 1/2 state of Fe(salen)(NO) are substantially dissimilar.

First author: Romaniello, P., Relativistic two-component formulation of time-dependent current-density functional theory: Application to the linear response of solids, JOURNAL OF CHEMICAL PHYSICS, 127, 12621, (2007)
Abstract: In this paper we derive the relativistic two-component formulation of time-dependent current-density-functional theory. To arrive at a two-component current-density formulation we apply a Foldy-Wouthuysen-type transformation to the time-dependent four-component Dirac-Kohn-Sham equations of relativistic density-functional theory. The two-component Hamiltonian is obtained as a regular expansion which is gauge invariant at each order of approximation, and to zeroth order it represents the time-dependent version of the relativistic zeroth order regular Hamiltonian obtained by van Lenthe , for the ground state [J. Chem. Phys.99, 4597 (1993)]. The corresponding zeroth order regular expression for the density is unchanged, whereas the current-density operator now comprises a paramagnetic, a diamagnetic, and a spin contribution, similar to the Gordon decomposition of the Dirac four current. The zeroth order current density is directly related to the mean velocity corresponding to the zeroth order Hamiltonian. These density and current density operators satisfy the continuity equation. This zeroth order approximation is therefore consistent and physically realistic. By combining this formalism with the formulation of the linear response of solids within time-dependent current-density functional theory [Romaniello and de Boeij, Phys. Rev. B71, 155108 (2005)], we derive a method that can treat orbital and spin contributions to the response in a unified way. The effect of spin-orbit coupling can now be taken into account. As first test we apply the method to calculate the relativistic effects in the linear response of several metals and nonmetals to a macroscopic electric field. Treatment of spin-orbit coupling yields visible changes in the spectra: a smooth onset of the interband transitions in the absorption spectrum of Au, a sharp onset with peak at about 0.46 eV in the absorption spectrum of W, and a low-frequency doublet structure in the absorption spectra of ZnTe, CdTe, and HgTe in agreement with experimental results.

First author: Choualeb, Aldjia, Olefin complexes of low-valent rhenium, EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 127, 5246, (2007)
Abstract: Replacement of the MeCN group in the acetonitrile-cis-dibromo(nitrosyl)-trans-bis(phosphane)rhenium compounds 1a, b (R = iPr a, R = Cy b) with ethylene afforded the olefin derivatives {Re(eta(2)-H2C=CH2)(NO)(PR3)(2)Br-2] (2a,b) (R = iPr a, R = Cy b). Compound la could be converted into the dimethyl species [Re(MeCN)(NO)(PiPr(3))(2)Me-2] (3a) applying MeLi in toluene; the related methylation of 1b, however, failed. Abstraction of a Br- ion from 1a, b with [Na][BAr4′] in acetontrile yields the air-stable salts [Re(MeCN)(2)(NO)(PR3)(2)-Br}(+)[BAr4′](-) (4a,b) (R = iPr a, R = Cy b) and under 1 bar of H-2 complexes la,b were converted into the known dihydrogen species [Re(eta(2)-H-2)(NO)(PR3)(2)(Br)(2)] (5a,b) (R = iPr a, R = Cy b). Reduction of [Re(MeCN)(NO)(PR3)(2)Br-2] (1a,b) with Na/Hg under 1 bar of C2H4 afforded the butadiene complex [Re(eta(4)-C4H6)(eta(2)- H2C=CH2)(NO)(PR3)(2)] (6a,b) (R = iPr a, R = Cy b) via oxidative coupling of two coordinated ethylene groups followed by double 0-H shift and subsequent reductive H2 elimination from the formed dihydride complex. Reduction of the complexes [Re(CO)(NO)(PR3)(2)Cl-2] (7a,b) (R = iPr a, R = Cy b) with Na/Hg yields the pentacoordinate species [Re(CO)(NO)(PR3)(2)(eta(2) -H2C=CH2)] (8a,b) (R = iPr a, R = Cy b) under the same conditions as for 6a,b. Reaction of 8a with 1 equiv. of B(C6F5)(3) leads to the [Re(CO)(2){NOB(C6F5)(3)}-(PiPr(3))(2)] compound (9a) and to the carbonyl nitrosyl complexes [Re(CO)(2)(NO)(PiPr(3))(2)] (10a) with evolution of ethylene. The same reaction of 8a and 8b, but applying 1 bar of CO, leads to exclusive formation of 9a,b. Complexes 4a, 4b, 6b, 8a, 9a, and 9b were characterized by X-ray diffraction studies.

First author: Jacobsen, Heiko, Decomposition cascades of dicoordinate copper(I) chalcogenides, EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 127, 5294, (2007)
Abstract: Cu-E, Si-E, and Cu-P bond energies of R3PCuESiR3 and CuESiR3 complexes (E = O, S, Se) have been investigated using PBE density-functional calculations, and including empirical corrections for dispersive interactions (DFT-D). The bond energies have been used to investigate likely pathways of molecular decomposition. The energy profile for thermal decomposition is to a large degree independent of the nature of the phosphane ligands and silyl groups. Oxides, sulfides, and selenides have qualitatively the same thermal decomposition profile. Thermal decomposition is not likely to produce copper chalcogenide units CuE, but elemental copper Cu instead. Consideration of intermolecular van der Waals attraction suggests that the linear geometry of system tBU(3)PCuOSiPh(3) as found in the crystal is most likely due to crystal packing and intermolecular forces.

First author: Frenking, Gernot, Double group transfer reactions as indicators of aromatic stabilization, EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, 127, 5410, (2007)
Abstract: The main features of double hydrogen atom transfer reactions in syn-sesquinorbornanes, which involve the concomitant formation of an aromatic ring, have been studied computationally within the framework of Density Functional Theory. The very good linear correlations, which exhibit high correlation coefficients between the recently available Aromatic Stabilization Energies (ASE) from the Energy Decomposition Analysis (EDA) method and the activation and reaction energies, as well as geometric features (C-C bond lengths) of the corresponding transition states of the transformations, suggest that the calculated values are useful in estimating the aromatic character of a molecule. The studied process may be used for benchmarking of energetic aromatic indices.

First author: Urbano-Cuadrado, Manuel, New quantum mechanics-based three-dimensional molecular Descriptors for use in QSSR approaches: Application to asymmetric catalysis, JOURNAL OF CHEMICAL INFORMATION AND MODELING,47, 2228, (2007)
Abstract: This paper presents a new protocol based on 3D molecular descriptors using QM calculations for use in CoMFA-like 3D-QSSR. The new method was developed and then applied to predict catalytic selectivity in the asymmetric alkylation of aldehydes catalyzed by Zn-aminoalcohols. The molecular descriptors are obtained straightforwardly from the electronic charge density function, p(r), and the molecular electrostatic potential (MEP) distributions. The chemically meaningful Molecular Shape Field (MSF) descriptor that accounts for the shape properties of the catalyst is defined from p(r). Alignment independence was achieved by computing the product of the MSF and MEP values of pairs of points over a given distance range on a molecular isosurface and then selecting the product with the highest value. The new QSSR method demonstrated good predictive ability (q(2) = 0.79) when full cross-validation procedures were carried out. Accurate predictions were made for a larger data set, although some deviations occurred in the predictions for catalytic systems with low enantiodiscrimination. Analysis of this QSSR model allows for the following: (1) evaluation of the contribution of each functional group to enantioselectivity and (2) the molecular descriptors to be related to previously proposed stereochemical models for the reaction under study.

First author: Eickerling, Georg, Relativistic effects on the topology of the electron density, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 3, 2182, (2007)
Abstract: The topological analysis of electron densities obtained either from X-ray diffraction experiments or from quantum chemical calculations provides detailed insight into the electronic structure of atoms and molecules. Of particular interest is the study of compounds containing (heavy) transition-metal elements, which is still a challenge for experiment as well as from a quantum-chemical point of view. Accurate calculations need to take relativistic effects into account explicitly. Regarding the valence electron density distribution, these effects are often only included indirectly through relativistic effective core potentials. But as different variants of relativistic Hamiltonians have been developed all-electron calculations of heavy elements in combination with various electronic structure methods are feasible. Yet, there exists no systematic study of the topology of the total electron density distribution calculated in different relativistic approximations. In this work we therefore compare relativistic Hamiltonians with respect to their effect on the electron density in terms of a topological analysis. The Hamiltonians chosen are the four-component Dirac-Coulomb, the quasi-relativistic two-component zeroth-order regular approximation, and the scalar-relativistic Douglas-Kroll-Hess operators.

First author: Tenderholt, Adam L., Sulfur K-edge XAS of W-V=O vs. Mo-V=O bis(dithiolene) complexes: Contributions of relativistic effects to electronic structure and reactivity of tungsten enzymes, JOURNAL OF INORGANIC BIOCHEMISTRY,101, 1594, (2007)
Abstract: Molybdenum- or tungsten-containing enzymes catalyze oxygen atom transfer reactions involved in carbon, sulfur, or nitrogen metabolism. It has been observed that reduction potentials and oxygen atom transfer rates are different for W relative to Mo enzymes and the isostructural Mo/W complexes. Sulfur K-edge X-ray absorption spectroscopy (XAS) and density functional theory (DFT) calculations on [(MoO)-O-V(bdt)(2)](-) and [(WO)-O-V(bdt)(2)](-), where bdt = benzene-1,2-dithiolate(2-), have been used to determine that the energies of the half-filled redox-active orbital, and thus the reduction potentials and M=O bond strengths, are different for these complexes due to relativistic effects in the W sites.

First author: Tang, Joel A., Solid-state Cu-63 and Cu-65 NMR spectroscopy of inorganic and organometallic copper(I) complexes, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 129, 13049, (2007)
Abstract: Solid-state Cu-63 and Cu-65 NMR experiments have been conducted on a series of inorganic and organometallic copper(l) complexes possessing a variety of spherically asymmetric two-, three-, and fourcoordinate Cu coordination environments. Variations in structure and symmetry, and corresponding changes in the electric field gradient (EFG) tensors, yield Cu-63/65 quadrupolar coupling constants (C-Q) ranging from 22.0 to 71.0 MHz for spherically asymmetric Cu sites. These large quadrupolar interactions result in spectra featuring quadrupolar-dominated central transition patterns with breadths ranging from 760 kHz to 6.7 MHz. Accordingly, Hahn-echo and/or QCPMG pulse sequences were applied in a frequency-stepped manner to rapidly acquire high SIN powder patterns. Significant copper chemical shielding anisotropies (CSAs) are also observed in some cases, ranging from 1000 to 1500 ppm. (31)p CP/MAS NMR spectra for complexes featuring (CU)-C-63/65-P-31 spin pairs exhibit residual dipolar coupling and are simulated to determine both the sign of C-Q and the EFG tensor orientations relative to the Cu-P bond axes. X-ray crystallographic data and theoretical (Hartree-Fock and density functional theory) calculations of Cu-63/65 EFG and CS tensors are utilized to examine the relationships between NMR interaction tensor parameters, the magnitudes and orientations of the principal components, and molecular structure and symmetry.

First author: Singh, Priti, Spectroelectrochemistry and DFT analysis of a new {RuNO}(n) redox system with multifrequency EPR suggesting conformational isomerism in the {RuNO}(7) state, INORGANIC CHEMISTRY, 46, 9254, (2007)
Abstract: The compound [Ru(NO)(bpym)(terpy)](PF6)(3), bpym = 2,2′-bipyrimidine and terpy = 2,2′:6′,2″-terpyridine, with a {RuNO}(6) configuration (angle Ru-N-O 175.2(4)degrees) was obtained from the structurally characterized precursor [Ru(NO2)(bpym)(terpy)](PF6), which shows bpym-centered reduction and metal-centered oxidation, as evident from EPR spectroscopy. The relatively labile [Ru(NO)(bpym)(terpy)](3+), which forms a structurally characterized acetonitrile substitution product [Ru(CH3CN)(bpym)(terpy)](PF6)(2) upon treatment with CH3OH/CH3CN, is electrochemically reduced in three one-electron steps of which the third, leading to neutral [Ru(NO)(bpym)(terpy)], involves electrode adsorption. The first-two reduction processes cause shifts of v(NO) from 1957 via 1665 to 1388 cm(-1), implying a predominantly NO-centered electron addition. UV-vis-NIR Spectroscopy shows long-wavelength ligand-to-ligand charge transfer absorptions for [Ru-II(NO-1)(bpym)(terpy)](+) in the visible region, whereas the paramagnetic intermediate [Ru(NO)(bpym)(terpy)]21 exhibits no distinct absorption maximum above 309 nm. EPR spectroscopy of the latter at 9.5, 95, and 190 GHz shows the typical invariant pattern of the {RuNO}(7) configuration; however, the high-frequency measurements at 4 and 10 K reveal a splitting of the g(1) and g(2) components, which is tentatively attributed to conformers resulting from the bending of RuNO. DFT calculations support the assignments of oxidation states and the general interpretation of the electronic structure.

First author: Ayuela, A., Silicate chain formation in the nanostructure of cement-based materials, JOURNAL OF CHEMICAL PHYSICS, 127, 9254, (2007)
Abstract: Cement-based materials are ubiquitous in almost all built environment. In spite of this, little is known about the formation and the role played by the silicate chains always present in the cement nanostructure. By means of first principles simulations we provide compelling evidence on the pivotal role played by certain ionic species in the formation of the silicate chains inside the cementitious matrix. Moreover, we corroborate the experimental evidence which shows that the length of the most stable chains with m Si atoms follows a magic-number sequence: m=3n-1 with n=1,2,… Our results have been applied in the development of new higher performance cement-based materials by adding nanosilica.

First author: Berard, Joel J., A density functional study of the various forms of UN4O12 containing uranyl nitrate,JOURNAL OF PHYSICAL CHEMISTRY A, 111, 10789, (2007)
Abstract: In this paper we report the computational results of a density functional study of 73 UN4O12 isomers containing uranyl nitrate, UO2(NO3)2, as a component. The isomers are grouped into three categories and 19 types. Forty-four isomers of 14 types are dinitrogen tetroxide adducts of uranyl nitrate, UO2(NO3)(2)center dot N2O4, 22 are nitrosonium salt adducts of uranyl nitrate, NO+UO2(NO3)(3-), NO+UO2(NO3)(2)O(NO2)(-), NO+UO2(NO3)(2)(ONOO)(-), or (NO+)(2)UO2(NO3)(2)O-2(2-), and 7 are bis(nitrogen dioxide) adducts of uranyl nitrate, UO2(NO3)(2)center dot 2NO(2). The 22 most stable isomers in solution, representing the 20 most stable gas-phase isomers, were selected for analysis. Of these selected structures only two categories and six types were represented. Structures, frequencies, gas-phase and solution energetics, atomic charges, dipole moments, and the bonding within the N2O4 unit and between NO+ and UO2(NO3)(3) components have been analyzed in detail. On the basis of relative Gibbs free energy calculations five isomers (the N2O4 adducts a1, a2, and a3 and the nitrosonium salts b1 and b2) were identified as strong candidates to exist and possibly predominate in the gas phase, with a1 and a2 being the strongest candidates. Similarly, four isomers (a6, a5, a8, and a1, all of them N2O4 adducts) were identified as strong candidates to exist and possibly predominate in a nonaqueous solution of nitromethane/dinitrogen tetroxide. Of these, a6 was determined to be the most likely candidate to predominate in solution. The possibility of dissociation in solution has been addressed briefly. In addition, computational evidence for the existence of four new N2O4 isomers 20, 22, 27, and 28 in both the gas and the solution phases is presented for the first time.

First author: Bose, Shubhankar Kumar, Linked and fused tungstaborane clusters: Synthesis, characterization, and electronic structures of bis-{(eta(5)-C(5)Me(5)W)(2)B(5)H(8)}(2) and (eta 5-C(5)Me(5)W)(2P){Fe(CO)(3)}(n)B(6-n)H(10-n), n=0,1, ORGANOMETALLICS, 26, 5377, (2007)
Abstract: in addition to (eta(5)-C(5)Me(5)W)(2)B(5)H(9), (eta(5)-C(5)Me(5)W)(3)(mu-H)B(8)H(8), and (eta(5)-C(5)Me(5)W)(2)B(7)H(9) reported earlier, thermolysis of {eta(5)-C(5)Me(5)W}H(3)B(4)H(8) (1) with BH(3)center dot THF leads to the formation of bicapped closo-{eta(5)-C(5)Me(5)W}B(5)H(9) (2) in parallel with a B-B linked dimer of {eta(5)-C(5)Me(5)W}(2)B(5)H(9) (4) and bis-{eta(5)-C(5)Me(5)W}(2)B(5)H(8)}(2) (3). Reaction of 4 with a 3-fold excess of Fe(2)(CO)(9) in hexane generates an iron analogue of 2, (eta(5)-C(5)Me(5)W)(2)B(5)H(9)Fe(CO)(3) (5) in 46% yield. All the metallaboranes, 2, 3, and 5, have been characterized by (1)H, (11)B NMR spectra and crystal structure determinations. The structures of 2 and 5 appear to follow the regular electron counting rules as they possess seven skeletal electron pairs (sep) appropriate for bicapped octahedral structures. However, their electronic structures revealed by a molecular orbital analysis is more closely related to that of [{eta(5)-C(5)Me(5)Re}(2)B(7)H(7)], a cluster that does not obey the classical electron counting rules. Clusters 2 and 5 are notable examples of closo clusters containing four bridging hydrogens. 3 is a coupled-cage structure in which two bicapped trigonal bipyramidal frameworks, W(2)B(5), are joined by an exopolyhedral boron-boron bond.

First author: Felton, Greg A. N., Hydrogen generation from weak acids: Electrochemical and computational studies of a diiron hydrogenase mimic, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 129, 12521, (2007)
Abstract: Extended investigation of electrocatalytic generation of dihydrogen using [(mu-1,2-benzenedithiolato)][Fe(CO)(3)](2) has revealed that weak acids, such as acetic acid, can be used. The catalytic reduction producing dihydrogen occurs at approximately -2 V for several carboxylic acids and phenols resulting in overpotentials of only -0.44 to -0.71 V depending on the weak acid used. This unusual catalytic reduction occurs at a potential at which the starting material, in the absence of a proton source, does not show a reduction peak. The mechanism for this process and Structures for the intermediates have been discerned by electrochemical and computational analysis. These studies reveal that the catalyst is the monoanion of the starting material and an ECEC mechanism occurs.

First author: Dragonetti, Claudia, The role of substituents on functionalized 1,10-phenanthroline in controlling the emission properties of cationic iridium(III) complexes of interest for electroluminescent devices, INORGANIC CHEMISTRY, 46, 8533, (2007)
Abstract: The photophysical and electrochemical properties of the novel complexes [Ir(ppy)(2)(5-X-1,10-phen)][PF6] (ppy = 2-phenylpyridine, phen = phenanthroline, X = NMe2, NO2), [Ir(pq)(2)(5-X-1,10-phen)][PF6] (pq = 2-phenylquinoline, X, = H, Me, NMe2, NO2), [Ir(ppy)(2)(4-Me,7-Me-1,10-phen)][PF6], [Ir(ppy)(2)(5-Me,6-Me-1,10-phen)][PF6], [Ir(ppy)(2)(2-Me,9-Me-1,10-phen)][PF6], and [Ir(pq)(2)(4-Ph,7-Ph-1,10-phen)][PF6] have been investigated and compared with those of the known reference complexes [Ir(ppy)(2)(4-Me or 5-H or 5-Me-1,10-phen)][PF6] and [Ir(ppy)(2)(4-Ph,7-Ph-1,10-phen)][PF6], showing how the nature and number of the phenanthroline substituents tune the color of the emission, its quantum yield, and the emission lifetime. It turns out that the quantum yield is strongly dependent on the nonradiative decay. The geometry, ground state, electronic structure, and excited electronic states of the investigated complexes have been calculated on the basis of density functional theory (DFT) and time-dependent DFT approaches, thus substantiating the electrochemical measurements and providing insight into the electronic origin of the absorption spectra and of the lowest excited states involved in the light emission process. These results provide useful guidelines for further tailoring of the photophysical properties of ionic Ir(III) complexes.

First author: Sanyal, Anasuya, Singlet diradical complexes of chromium, molybdenum, and tungsten with azo anion radical ligands from M(CO)(6) precursors, INORGANIC CHEMISTRY, 46, 8584, (2007)
Abstract: The homoleptic diamagnetic complexes M(mer-L)(2), M = Cr, Mo,W (1a,b, 2a,b, and 4a,b), were obtained by reacting the hexacarbonyls M(CO)(6) with the tridentate liglands 2-[(2-N-arylamino)phenylazo]pyridine (HL = NH4C5N=NC6H4N- (H)C6H4(H) (HLa) or NH4C5N=NC6H4N(H)C6H4(CH3) (HLb)) in refluxing n-octane, In the case of M = Mo, the dinuclear compounds [Mo(L)(pap)]2(mu-O) (3a,b) (pap = 2-(phenylazo)pyridine), were obtained as second products in moist solvent. X-ray diffraction analysis for Cr(L)2 (1b), Mo(La)2 (2a), and W(La)2 (4a) reveals considerably distorted-octahedral structures with trans-positioned azo-N atoms and cis-positioned 2-pyridyi-N and anilido nitrogen atoms. Whereas the N-azo-M-N-azo angle is larger than 170 degrees, the other two trans angles are smaller, at about 155 degrees (M = Cr, 1b) or 146 degrees (M = Mo, W; 2a, 4a), due to the overarching bite of the mer-tridentate ligands. The bonds from M to the neutral 2-pyridyl-N atoms are distinctly longer by more than 0.08 angstrom than those to the anilido or azo nitrogen atoms, reflecting negative charge on the latter. The N-N bond distances vary between 1.339(2) angstrom for 1b and 1.373(3) angstrom for 4a, clearly indicating the azo radical anion oxidation state. Considering the additional negative charge on anilido-N, the mononuclear complexes are thus formulated as M-IV(L.(2-))(2). The diamagnetism of the complexes as shown by magnetic susceptibility and H-1 NMR experiments is believed to result from spin-spin coupling between the trans-positioned azo radical functions, resulting in a singlet diradical situation. The experimental structures are well reproduced by density functional theory calculations, which also support the overall electronic structure indicated. The dinuclear 3a with N-N distances of 1.348(10) angstrom for L-a and 1.340(9) angstrom for pap is also formulated as an azo anion radical-containing molybdenum(IV) species, i.e., [Mo-IV(L.(2-))(pap.(-))](2)(mu-O). All compounds can be reversibly reduced; the Cr complexes la,b are also reversibly oxidized in two steps. Electron paramagnetic resonance spectroscopy indicates metal-centered spin for 1a(+) and 1a(-) and g approximate to 2 signals for 2a(-), 3a(+), 3a(-), and 4a(-). Spectroelectrochemistry in the UV-vis-NIR region showed small changes for the reduction of 2a, 3a, and 4a but extensive spectral changes for the reduction and oxidation of la.

First author: Briand, Glen G., Probing lead(II) bonding environments in 4-substituted pyridine adducts of (2,6-Me2C6H3S)(2)Pb: An X-ray structural and solid-state Pb-207 NMR study, INORGANIC CHEMISTRY, 46, 8625, (2007)
Abstract: The effect of subtle changes in the or-electron donor ability of 4-substituted pyridine ligands on the lead(l I) coordination environment of (2,6-Me2C6H3S)(2)Pb (1) adducts has been examined. The reaction of 1 with a series of 4-substituted pyridines in toluene or dichloromethane results in the formation of 1:1 complexes [(2,6-Me2C6H3S)(2)Pb(pyCOH)](2) (3), [(2,6-Me2C6H3S)(2)Pb(pyOMe)](2) (4), and (2,6-Me2C6H3S)(2)Pb(pyNMe(2)) (5) (pyCOH = 4-pyridinecarboxaldehyde; pyOMe = 4-methoxypyridine; pyNMe(2) = 4-dimethylaminopyridine), all of which have been structurally characterized by X-ray crystallography. The structures of 3 and 4 are dimeric and have psi-trigonal bipyramidal S3N bonding environments, with the 4-substituted pyridine nitrogen and bridging sulfur atoms in axial positions and two thiolate sulfur atoms in equatorial sites. Conversely, compound 5 is monomeric and exhibits a psi-trigonal pyramidal S2N bonding environment at lead(II). The observed structures may be rationalized in terms of a simple valence bond model and the sigma-electron donor ability of the 4-pyridine ligands as derived from the analysis of proton affinity values. Solid-state Pb-207 NMR experiments are applied in combination with density functional theory (DFT) calculations to provide further insight into the nature of bonding in 4, 5, and (2,6-Me2C6H3S)(2)Pb(py)(2) (2). The lead chemical shielding (CS) tensor parameters of 2, 4, and 5 reveal some of the largest chemical shielding anisotropies (CSA) observed in lead coordination complexes to date. DFT calculations using the Amsterdam Density Functional (ADF) program, which take into account relativistic effects using the zeroth-order regular approximation (ZORA), yield lead CS tensor components and orientations. Paramagnetic contributions to the lead CS tensor from individual pairs of occupied and virtual molecular orbitals (MOs) are examined to gain insight into the origin of the large CSA. The CS tensor is primarily influenced by mixing of the occupied MOs localized on the sulfur and lead atoms with virtual MOs largely comprised of lead 6p orbitals.

First author: Rosenthal, Joel, Structurally homologous beta- and meso-alkynyl amidinium porphyrins, INORGANIC CHEMISTRY, 46, 8668, (2007)
Abstract: Alkynylamidinium groups have been introduced at the beta and meso positions of a nickel(II) porphyrin (PNi(II)) framework. The modification permits the distance between the amidinium-amidine acid-base group and porphyrin to be increased while effectively maintaining pi conjugation between the porphyrin macrocycle and the acid-base functionality. Use of an ethynyl spacer as a linker (i) extends the amidinium functionality away from the sterically bulky mesityl groups of the porphyrin, allowing it to be nearly planar with respect to the porphyrin ring, and (ii) draws the pi-orbital character of the porphyrin out toward the amidinium functionality, thereby engendering sensitivity of the electronic properties of the porphyrin macrocycle to the protonation state of the amidinium. The barrier for rotation of the amidinium group, as calculated by time-dependent density functional theory (TDDFT), is similar to 8.5kT (5 kcal/mol) for both porphyrins. Analysis of UV-visible absorption profiles for the beta- and meso-alkynylamidinium PNi(II) upon deprotonation enables accurate determination of the amidinium acidity constants for the ground state (pK(a)(beta) = 7.03 +/- 0.1, pK(a)(meso) = 7.74 +/- 0.1 in CH3CN) and excited state (pK(a)(*)(beta) = 6.89 +/- 0.1, pK(a)(*)(meso) = 8.37 +/- 0.1 in CH3CN) porphyrins. Whereas pK(a)(*) < pK(a) for the beta-alkynylamidinium porphyrin, pK(a)(*) > pK(a) for the meso-alkynylamidinium porphyrin, indicating that beta-alkynylamidinium PNi(II) is a photoacid and meso-alkynylamidinium PNi(II) is a photobase. These divergent behaviors are supported by analysis of the frontier molecular orbitals of the homologous pair with TDDFT.

First author: Lyon, Jonathan T., Infrared and DFT investigations of the XC ReX3 and HC ReX3 complexes: Jahn-Teller distortion and the methylidyne C-X(H) stretching absorptions, INORGANIC CHEMISTRY, 46, 8728, (2007)
Abstract: The XC ReX3 complexes (X = F, Cl) are produced by CX4 reaction with laser-ablated Re atoms, following oxidative C-X insertion and alpha-halogen migration in favor of the carbon-metal triple bond and are identified through the observation of characteristic absorptions in the argon matrix infrared spectra and comparison with vibrational frequencies calculated by density functional theory. The methylidyne C-F and C-Cl stretching absorptions are observed near 1584 and 1328 cm(-1), and the C-H stretching modes for HC ReX3 at 3104 and 3097 cm(-1), respectively, which are substantially higher than the precursor stretching modes and in agreement with the general trend that higher s-orbital character in carbon hybridization leads to a higher stretching frequency. The Jahn-Teller effect in the doublet-state XC ReX3 and HC ReX3 complexes gives rise to distorted structures with C-S symmetry and two equivalent longer Re-X bonds and one slightly shorter Re-X bond.

First author: Cuthbert, Heather L., Synthesis, structure, and unexpected magnetic properties of La3Re2O10, INORGANIC CHEMISTRY, 46, 8739, (2007)
Abstract: The compound La3Re2O10 has been synthesized by solid-state reaction and characterized by powder neutron diffraction, SQUID magnetometry, and heat capacity measurements. Its structure consists of isolated [Re2O10](9-) dimer units of two edge-shared ReO6 octahedra, separated by La3+ within the lattice. The Re-Re distance within the dimer units is 2.488 angstrom, which is indicative of metal-metal bonding with a bond order of 1.5. The average oxidation state of the Re atom is +5.5, leaving one unpaired electron per dimer unit (S = 1/2). Although the closest interdimer distance is 5.561 angstrom, the magnetic susceptibility data and heat capacity measurements indicate this compound exhibits both short- and long-range magnetic order at surprisingly high temperatures. The zero field cooled (ZFC) magnetic susceptibility data show two broad features at 55 and 105 K, indicating short-range order, and a sharper cusp at 18 K, which signifies long-range antiferromagnetic order. The heat capacity of La3Re2O10 shows a A-type anomaly at 18 K, which is characteristic of long-range magnetic order. DFT calculations determined that the unpaired electron resides in a pi-bonding orbital and that the unpaired electron density is widely delocalized over the atoms within the dimer, with high values at the bridging oxygens. Extended Huckel spin dimer calculations suggest possible interaction pathways between these dimer units within the crystal lattice. Results from the calculations and fits to the susceptibility data indicate that the short-range magnetic ordering may consist of 1-D antiferromagnetic linear chains of coupled S = 1/2 dimers. The magnetic structure of the antiferromagnetic ground state could not be determined by unpolarized neutron powder diffraction.

First author: Kapicka, Libor, Bonding and aromaticity of cyclic phosphazenes viewed as interaction of D-nh fragments,JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM, 820, 148, (2007)
Abstract: The qualitative molecular orbital approach based on orbital interactions was used to explore the nature of bonding in cyclic fluorophosphazenes (F2PN)(n), where n is 2-6. Besides the classical skeleton of sigma-bonds, only two, one radial and one axial, 2n-center two-electron pi-bonds significantly participate in the extra stabilization of the (PN)(n) ring. The pi-radial interaction is more effective and comparable by size with the sigma ones. Additional slight stabilization of a (PN)(n) ring is achieved by nonbonding pi-radial and pi-axial molecular orbitals (MOs) which are mainly localized on nitrogen atoms. The orbital interactions have a hyperconjugation character. The bonding energy decomposition analysis showed that the cyclic interactions are about half covalent and half electrostatic. The covalent bonding is dominated by radial interactions. The aromaticity concept is not appropriate for description of bonding in cyclophosphazenes. The contribution of phosphorus d atomic orbitals to the concept of chemical bonding in phosphazenes is negligible, but the inclusion of d phosphorus functions in a basis set is appropriate for a correct quantitative description of electronic and geometric structure. Extended Huckel (EHT), ab initio and density functional (DFT) calculations provide the same qualitative picture of the bonding. The very flat B3LYP/6-311+G(3df)//B3LYP/6-31G(3df) potential energy surface (PES) with the low energy barrier (similar to 1.6 kJ mol(-1)) indicates the very fast and easy conformational motion of (F2PN)(4). The global minimum on this PES is the S-4 conformation.

First author: Ingram, Kieran I. M., Covalency in the f-element-chalcogen bond computational studies of [M(N(EPH2)(2))(3)] (M = La, U, Pu; E = O, S, Se, Te), JOURNAL OF ALLOYS AND COMPOUNDS, 444, 369, (2007)
Abstract: The geometric and electronic structures of the title complexes have been studied using gradient corrected density functional theory. Excellent agreement is observed between computed r(M-E) and experimental values in analogous Pr-i complexes. Natural charge analysis indicates that the M-E bond becomes less ionic in the order O > S > S > Te, and that this decrease is largest for U and smallest for La. Natural and Mulliken overlap populations suggest increasing M-E covalency as group 16 is descended, and also in the order La < Pu < U for a given chalcogen. Increased covalency down group 16 arises from increased metal d (and s) participation in the bonding, while that from La to Pu and U stems from larger 5f orbital involvement compared with 4f.

First author: Ayuela, A., Optimized geometry of the cluster Gd2O3 and proposed antiferromagnetic alignment of f-electron magnetic moment, JOURNAL OF PHYSICAL CHEMISTRY A, 111, 10162, (2007)
Abstract: There is currently experimental interest in assemblies of Gd2O3 clusters. This has motivated the present study in which a single such cluster in free space is examined quantitatively by spin-density functional theory, with appropriate relativistic corrections incorporated for Gd. First, the nuclear geometry of the cluster is optimized, and it is found to be such that the two Gd atoms lie in a symmetry axis perpendicular to the isosceles triangle formed by the 0 atoms. Then, a careful study is made of the magnetic arrangement of the localized f-electron moments on the two Gd atoms. The prediction of the present treatment is that the localized spins are aligned antiferromagnetically. An alternative picture using superexchange ideas leads to the same conclusion.

First author: Jensen, L., Resonance vibrational Raman optical activity: A time-dependent density functional theory approach, JOURNAL OF CHEMICAL PHYSICS, 127, 10162, (2007)
Abstract: We present a method to calculate both on- and off-resonance vibrational Raman optical activities (VROAs) of molecules using time-dependent density functional theory. This is an extension of a method to calculate the normal VROA by including a finite lifetime of the electronic excited states in all calculated properties. The method is based on a short-time approximation to Raman scattering and is, in the off-resonance case, identical to the standard theory of Placzek. The normal and resonance VROA spectra are calculated from geometric derivatives of the different generalized polarizabilites obtained using linear response theory which includes a damping term to account for the finite lifetime. Gauge-origin independent results for normal VROA have been ensured using either the modified-velocity gauge or gauge-included atomic orbitals. For the resonance VROA only the modified-velocity gauge has been implemented. We present some initial results for H2O2 and (S)-methyloxirane and compare with predictions from a simple two-state approximation.

First author: Noguera, M., On the bonding of first-row transition metal cations to guanine and adenine nucleobases,JOURNAL OF PHYSICAL CHEMISTRY A, 111, 9823, (2007)
Abstract: The binding of first-row transition metal monocations (Sc(+)-Cu(+)) to N7 of guanine and N7 or N3 of adenine nucleobases has been analyzed using the hybrid B3LYP density functional theory (DFT) method. The nature of the bonding is mainly electrostatic, the electronic ground state being mainly determined by metal-ligand repulsion. M(+)-guanine binding energies are 18-27 kcal/mol larger than those of M(+)-adenine, the difference decreasing along the row. Decomposition analysis shows that differences between guanine and adenine mainly arise from Pauli repulsion and the deformation terms, which are larger for adenine. Metal cation affinity values at this level of calculation are in very good agreement with experimental data obtained by Rodgers et al. (J. Am. Chem. Soc. 2002, 124, 2678) for adenine nucleobases.

First author: Abe, Taichi, [2,6-Bis(5-methyl-2-pyridyl)phenyl-kappa N-3,C-1,N ‘]chloridoplatinum(II), ACTA CRYSTALLOGRAPHICA SECTION C-CRYSTAL STRUCTURE COMMUNICATIONS, 63, M456, (2007)
Abstract: In the title compound, [ Pt( C18H15N2) Cl], the Pt-II centre adopts a distorted square- planar coordination geometry due to the pincer- type monoanionic N – C – N tridentate ligand. The planar complexes stack via pi – pi interactions to form twodimensional accumulated sheets. This packing pattern is in contrast to that in related pincer- type N – C – N complexes, which exhibit a one- dimensional columnar stacking.

First author: Struzhkin, Viktor V., Hydrogen storage in molecular clathrates, CHEMICAL REVIEWS, 107, 4133, (2007)
Abstract: In the title compound, [ Pt( C18H15N2) Cl], the Pt-II centre adopts a distorted square- planar coordination geometry due to the pincer- type monoanionic N – C – N tridentate ligand. The planar complexes stack via pi – pi interactions to form twodimensional accumulated sheets. This packing pattern is in contrast to that in related pincer- type N – C – N complexes, which exhibit a one- dimensional columnar stacking.

First author: Maldivi, Pascale, Theoretical description of metal-ligand bonding within f-element complexes: A successful and necessary interplay between theory and experiment, COMPTES RENDUS CHIMIE, 10, 888, (2007)
Abstract: The quantum chemical study presented here shows various aspects of the bonding of lanthanide (La3+, Gd (3+)) and actinide (U3+, AM(3+), CM3+) ions with N-heterocyclic ligands (polyazines, BTP: bis(1,2,4-triazinyl)-2,6-pyridine). Several families of complexes, differing by their coordination sphere, have been examined. Clearly, the lanthanide complexes always show a purely ionic bonding. The behaviour of U(III) is also well defined with a more or less strong backbonding interaction whatever the complex is. In contrast, the heavy actinides (Am3+ and Cm3+) are changeable, with a weak covalent character, going from donation to backdonation, depending on the coordination sphere of the complex.

First author: Vallet, Valrie, On the structure and relative stability of uranyl(VI) sulfate complexes in solution, COMPTES RENDUS CHIMIE, 10, 905, (2007)
Abstract: The mode of coordination, mono-, bidentate, sulfate in UO2(SO4) and UO2(SO4)(2) (2-), and the relative energy of the various isomers have been studied at the DFT and MP2 levels using DFT-optimized geometry in a CPCM solvent model. The U-S distances in the mono- and bidentate coordination, 3.63 and 3.08 angstrom, respectively, agree very well with experimental observations from solutions. The U-O-sulfate distance is significantly different in complexes with mono- and bidentate coordination, 2.23, vs. 2.37 angstrom, an observation difficult to deduce from the experimental studies. The experimental distance between uranium and the equatorial oxygen atoms, U-O-eq, is very close to the calculated average distance in a five-coordination model, but significantly longer in a six-coordination model, indicating a preference for the former; this finding is supported by energy calculations, where the five coordinated isomers for the UO2(SO4) have the lowest Gibbs energy. For UO2(SO4)(2)(-2) the calculated Gibbs energy of reaction indicates that the six-coordinated isomer is slightly more stable than the five-coordinated one; however, the difference is small and less than the expected uncertainty in calculations of this type. Bidentate coordination of the sulfate group is always preferred over monodentate coordination. However, all differences in Gibbs energy between the different isomers is small, indicating that the mode of coordination may change with the composition of test solutions used, as observed experimentally. The U-O-S-mono angle is close to 143 degrees in complexes with a monodentate sulfate group; this is traced to steric effects, which overcome the electronic preference for a linear U-O-S bond. This study demonstrates the significant increase in chemical information that may be obtained by combining experimental data on structures and thermodynamics with quantum chemical methods.

First author: Budzelaar, Peter H. M., Geometry optimization using generalized, chemically meaningful constraints,JOURNAL OF COMPUTATIONAL CHEMISTRY, 28, 2226, (2007)
Abstract: An external geometry optimizer (BOptimize) is described that can be used together with a number of existing quantum-chemical codes (Gaussian, Gamess-UK, Turbomole, ADF, Orca, Priroda, Spartan-PM3, Mopac) and allows flexible and general constrained optimizations. Some details of the implementation are discussed, and examples are provided of constrained optimizations that would be difficult or impossible to perform with existing optimizers.

First author: Pittalis, S., Orbital currents in the Colle-Salvetti correlation energy functional and the degeneracy problem,JOURNAL OF CHEMICAL PHYSICS, 127, 2226, (2007)
Abstract: Popular density functionals for the exchange-correlation energy typically fail to reproduce the degeneracy of different ground states of open-shell atoms. As a remedy, functionals which explicitly depend on the current density have been suggested. We present an analysis of this problem by investigating functionals that explicitly depend on the Kohn-Sham orbitals. Going beyond the exact-exchange approximation by adding correlation in the form of the Colle-Salvetti functional, we show how current-dependent terms enter the Colle-Salvetti expression and their relevance is evaluated. A very good description of the degeneracy of ground states for atoms of the first and second rows of the Periodic Table is obtained.

First author: Bagno, Alessandro, Metal-mediated J coupling in DNA base pairs: Relativistic DFT predictions, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 129, 11360, (2007)
Abstract: Relativistic DFF calculations of NMR properties (metal-mediated J (NN) couplings) support the proposed coordination motif of Hg(II) to DNA bases and allow for predictions of other useful NMR parameters.

First author: Wasbotten, Ingar H., Spin-state energetics and spin-crossover behavior of pseudotetrahedral Cobalt(III)-imido complexes. The role of the tripodal supporting ligand, INORGANIC CHEMISTRY, 46, 7890, (2007)
Abstract: DFT calculations have underscored the importance of the tripodal supporting ligand in tuning the spin-state energetics of pseudotetrahedral transition metal imido complexes. In particular, we have focused on Co(III)-imido complexes, where our best estimate (OLYP) of the singlet-triplet splitting varies from 0.75 eV for a trisphosphine complex (1) and 0.3 eV for a tris(N-heteroyclic-carbene) complex (2) to essentially 0.0 eV for a hydrotris(pyrazolyl) borate (3) complex. The experimentally studied analogues of 1, 2, and 3 all exhibit S = 0 ground states; however, the experimental analogue of 3 exhibits spin-crossover behavior due to a low-lying S = 1 state. Interestingly, whereas all the pure functionals examined successfully predict nearly equienergetic singlet end triplet states for 3, the hybrid functionals B3LYP and O3LYP exhibit a clear (and incorrect) preference for the S = 2 state. In addition, we have also carried out an exploratory survey of Cr(III), Mn(III), and Fe(III) imido complexes with trisphosphine and hydrotris(pyrazolyl) borate (Tp) supporting ligands. Among the more interesting predictions of this study is that an Fe-III(Tp)(imido) species should exhibit a high-spin S = 5/2 ground state, which would be unique for an iron-imido complex.

First author: Fernandez, Israel, EDA study of pi-conjugation in tunable bis(gem-diethynylethene) fluorophores, JOURNAL OF ORGANIC CHEMISTRY, 72, 7367, (2007)
Abstract: [GRAPHICS]The strength of pi-conjugation in a family of bis(gem-diethynylethene) fluorophores is estimated within Z the density functional theory framework using the energy decomposition analysis (EDA) method. The observed very good linear correlations between the calculated pi-conjugation and the experimental values for the UV absorption and fluorescence emission for this series of compounds suggest that the values given by the EDA are useful for the interpretation and prediction of photochemical properties of the molecules. The calculated data predict that adequate modifications in the core moiety of the molecule such as pi-donor substituents in the aromatic ring or in the periphery of the bis-enedyine unit like.pi-acceptor Groups placed in the para position of the aryl substituent increase the total pi-conjugation in the systems and thus provoke significant changes in both the absorption and emission spectra leading to large Stokes shifts. The effect of such substituents is quantitatively predicted by the EDA data.

First author: Bagno, Alessandro, Prediction of the H-1 and C-13 NMR spectra of alpha-D-glucose in water by DFT methods and MD Simulations, JOURNAL OF ORGANIC CHEMISTRY, 72, 7373, (2007)
Abstract: [GRAPHICS]We have applied computational protocols based on DFT and molecular dynamics simulations to the prediction of the alkyl H-1 and C-13 chemical shifts Of alpha-D-glucose in water. Computed data have been compared with accurate experimental chemical shifts obtained in our laboratory. C-13 chemical shifts do not show a marked solvent effect. In contrast, the results for H-1 chemical shifts provided by structures optimized in the gas phase are only fair and point out that it is necessary to take into account both the flexibility of the glucose structure and the strong effect exerted by solvent water thereupon. Thus, molecular dynamics simulations were carried out to model both the internal geometry as well as the influence of solvent molecules on the conformational distribution of the solute. Snapshots from the simulation were used as input to DFT NMR calculations with varying degrees of sophistication. The most important factor that affects the accuracy of computed H-1 chemical shifts is the solute geometry; the effect of the solvent on the shielding constants can be reasonably accounted for by self-consistent reaction field models without the need of explicitly including solvent molecules in the NMR property calculation.

First author: Velazquez, Alejandro, Multimetallocenes. A theoretical study, ORGANOMETALLICS, 26, 4731, (2007)
Abstract: Quantum chemical calculations using gradient-corrected density functional theory at the BP86 level in conjunction with TZ2P basis sets have been carried out for the multimetallocenes CpMnCp, where M = Be. Mg, Ca, and Zn with it = 2-5. The equilibrium geometries and energetics with respect to loss of one metal atom are theoretically predicted. The nature of the metal-ligand interactions between the M-n(2+) and (CP-)(2) moieties was investigated with energy decomposition analysis (EDA). The calculations predict that the CpMnCp species with n > 2 are thermodynamically unstable with respect to loss of one metal atom except for the beryllium compounds. The beryllocenes exhibit unusual stabilities in the gas phase for the whole series CpBenCp up to n = 5. The calculations suggest that the energy for loss Of One metal atom from CpBe2Cp is significantly higher than from CpZn2CP. The energy for the metal extrusion reaction of CpBe3CP is much less endothermic than for CpBe2Cp but it is still more endothermic than the reaction of CpZn2Cp. The thermodynamic stability of the higher members CpBe4Cp and CpBe5CP toward loss of one metal atom is only slightly less than for CpBe3CP, while the other multimetallocenes, CPM3CP CpM4Cp, and CpM5Cp (M = Mg, Ca, Zn), possess little extra stabilization with respect to the dimetallocenes. The calculated reaction energies which include the heats of sublimation of the metals indicate that CpBe2Cp might become isolated in the condensed phase, while the prospect for CpCa2Cp and CpMg2Cp and for the higher members CPM3CP, CPM4Cp, and CpM5Cp is less likely. The analysis of the metal-ligand bonding in CpMnCp using the EDA method suggests that the interactions between M-n(2+). and (CP-)(2) have a larger electrostatic than covalent character. The beryllocenes are more covalently bonded than the other multimetallocenes. The orbital interactions in the lower members of CpMnCp come mainly from pi orbitals, but the sigma contribution continuously increases when n becomes larger and eventually may become stronger than the pi contributions, which become weaker in the higher members of the series.

First author: Doslic, Nada, Signature of the conformational preferences of small peptides: a theoretical investigation,JOURNAL OF PHYSICAL CHEMISTRY A, 111, 8650, (2007)
Abstract: An extensive computational study of the conformational preferences of N-acetylphenylalaninylamide (NAPA) is reported, including conformational and anharmonic frequency analyses, as well as calculations of excitation energies of the four NAPA conformers lowest in energy. Particular attention is paid to the influence of hydrogen-bonding interactions on the relative stability of the conformers, which was found to be very sensitive to both the level of quantum chemical computations and the anharmonic treatment of molecular vibrations. The assignments of the UV spectral peaks are well supported by the muldreference CASSCF/MS-CASPT2 calculations. Upon consideration of the second-order Moller-Plesset (MP2) and density functional theory (DFT) structures, overall energetics, and harmonic and anharmonic corrections, we found no conclusive theoretical evidence for the assumed conformational propensity of small model peptides toward extended beta-strand structures.

First author: Maity, Amarendra N., Tetranuclear complexes of [Fe(CO)(2)(C5H5)](+) with TCNX ligands (TCNX = TCNE, TCNQ, TCNB): Intramolecular electron transfer alternatives in compounds (mu(4)-TCNX)[MLn](4), INORGANIC CHEMISTRY, 46, 7312, (2007)
Abstract: The complexes {(mu(4)-TCNX)[Fe(CO)(2)(C5H5)](4)}(BF4)(4) were prepared as light-sensitive materials from [Fe(CO)(2)(C5H5) (THF)](BF4) and the corresponding TCNX ligands (TCNE = tetracyanoethene, TCNQ = 7,7,8,8-tetracyano-p-quinodimethane, TCNB = 1,2,4,5-tetracyanobenzene). Whereas the TCNE and TCNQ complexes are extremely easily reduced species with reduction potentials >+0.3 V vs ferrocenium/ferrocene, the tetranuclear complex of TCNB exhibits a significantly more negative reduction potential at about -1.0 V. Even for the complexes with strongly pi-accepting TCNE and TCNQ, the very positive reduction potentials, the unusually high nitrile stretching frequencies > 2235 cm(-1), and the high-energy charge-transfer transitions indicate negligible metal-to-ligand electron transfer in the ground state, corresponding to a largely unperturbed (TCNX degrees)(Fe-II)(4) formulation of oxidation states as caused by orthogonality between the metal-centered HOMO and the pi* LUMO of TCNX. Mossbauer spectroscopy confirms the low-spin iron(II) state, and DFT calculations suggest coplanar TCNE and TCNQ bridging ligands in the complex tetracations. One-electron reduction to the 3+ forms of the TCNE and TCNQ complexes produces EPR spectra which confirm the predominant ligand character of the then singly occupied MO through isotropic g values slightly below 2, in addition to a negligible g anisotropy of frozen solutions at frequencies up to 285 GHz and also through an unusually well-resolved solution X band EPR spectrum of {(mu(4)-TCNE)[Fe(CO)(2)(C5H5)](4)}(3+) which shows the presence of four equivalent [Fe(CO)(2)(C5H5)](+) moieties through Fe-57 and C-13(CO) hyperfine coupling in nonenriched material. DFT calculations reproduce the experimental EPR data. A survey of discrete TCNE and TCNQ complexes [(mu(4)-TCNX)(MLn)(4)] exhibits a dichotomy between the systems {(mu(4)-TCNX)[Fe(CO)(2)(C5H5)](4)}(4+) and {(mu(4)-TCNQ)[Re(CO)(3)(bpy)](4)}(4+) with their negligible metal-to-ligand electron transfer and several other compounds of TCNE or TCNQ with Mn, Ru, Os, or Cu complex fragments which display evidence for a strong such interaction, i.e., an appreciable value delta in the formulation {(mu(4)-TCNX delta-)[Mx+delta/4Ln](4)}. Irreversibility of the first reduction of {(mu(4)-TCNB)[Fe(CO)(2)(C5H5)](4)}(BF4)(4) precluded spectroelectrochemical studies; however, the high-energy CN stretching frequencies and charge transfer absorptions of that TCNB analogue also confirm the exceptional position of the complexes {(mu(4)-TCNX)[Fe(CO)(2)(C5H5)](4)}(BF4)(4).

First author: Piro, Nicholas A., Ethylenebis(triphenylphosphine)platinum as a probe for niobium-mediated diphosphorus chemistry, INORGANIC CHEMISTRY, 46, 7387, (2007)
Abstract: Ethylenebis(triphenylphosphine)platinum is used as a trap for the P-2-containing molecule W(CO)(5)(P-2), which is eliminated at room temperature from a niobium-complexed diphosphaazide ligand. The rate of W(CO)(5)(P-2) elimination is unaffected by the presence of the platinum species. Attempts to generate and trap free P-2 with the platinum ethylene complex were hindered by the direct reaction between the platinum starting material and the P-2 generator, (Mes*NPP)Nb(N[Np]Ar)(3). In this case, reductive cleavage of the P-P bond in the diphosphaazide ligand is induced by platinum coordination, resulting in the formation of a trimetallic system with two bridging, three-coordinate phosphorus atoms.

First author: Zouchoune, Bachir, On the electronic structure of distorted cubic rhodium cluster complexes containing bridging germanium or phosphorus ligands, JOURNAL OF CLUSTER SCIENCE, 18, 720, (2007)
Abstract: DFT calculations show that the optimal metal valence electron (MVE) count of omnicapped cubic rhodium clusters containing more than eight terminal ligands, is 114. For such a count, a closed-shell configuration is computed with a substantial HOMO-LUMO gap. The presence of more than eight terminal ligands in the clusters favors highly distorted cubic architectures with capping ligands asymmetrically bound to the distorted metallic square faces. Removal of terminal ligands leads to the replacement of bonding M-L electron pairs by nonbonding electron pairs localized on the metal atoms, giving rise to unchanged MVE count.

First author: Trodi, Fatima Zohra, Hypothetical Hypercloso octahedral M4N2 clusters: A new mode of dinitrogen coordination?, JOURNAL OF CLUSTER SCIENCE, 18, 729, (2007)
Abstract: Density functional theory (DFT) calculations carried out on a series of [M-4(CO)(12)N-2](2+) and M-4(CO)(12)N-2 (M=Fe, Ru, Os) predict that the M4N2 square bipyramidal (octahedral) architecture should be stable for the particular electron count of 6 skeletal electron pairs (or 60 metal valence electrons). This octahedral architecture is electron-deficient with respect to the Wade-Mingos rules and exhibits a through-cage N-N bond of order one. Thus, these hypothetical clusters present a new coordination mode of dinitrogen.

First author: Gallardo, Cristina, Organometallic 1,5-benzodiazepine and 1,5-benzodiaze pinium compounds: Synthesis, characterization, X-ray diffraction structures and theoretical investigation, JOURNAL OF THE CHILEAN CHEMICAL SOCIETY, 52, 1266, (2007)
Abstract: The organometallic tridentate ketoamine or enaminone compound, (eta(5)-Cp)Fe(eta(5)-C5H4)-C(=O)-CH=C(Me)-NH-C-6 H-4-o-NH2, undergoes an intramolecular cyclocondensation promoted by Cu(ClO4)(2) 6H(2)O (2:1 molar ratio) affording the neutral 2-ferrocenyl-4-methyl-1,5-benzodiazepine, 1. However, when the molar ratio used is 1:1, the ketoamine or enaminone compound transforms into the 2-ferrocenyl-4-methyl-1,5-benzodiazepinium cation, [2](+). The X-ray molecular structure of 1 exhibits a seven-membered ring with a boat conformation, and two folding dihedral angles along the N(1)-N(2) and C(1 I)-C(13) axes. In the case of [2](+), the structure shows only one folding dihedral angle along the N(1)-N(2) axis. A rationalization of the properties of 1 and [2](+) is provided through DFT calculations.

First author: Matovic, Zoran D., Synthesis and DFT defined trans(O5O6) molecular structure of Cs[Fe(1,3-pddadp)] center dot 2H(2)O. Strain analysis and spectral assignment of the complex, MONATSHEFTE FUR CHEMIE, 138, 823, (2007)
Abstract: An iron(III) complex with the hexadentate ligand 1,3-propanediamine-N,N’-diacetate-N,N’-di-3-propionate (1,3-pddadp) was prepared, chromatographically isolated as its isomer trans(O5O6)-Cs[Fe(1,3-pddadp)] center dot 2H(2)O, and characterized. The trans(O5O6) configuration of the iron(III) compound was found to dominate and this geometry was established by means of IR spectroscopy and Density Functional Theory (DFT). Structural data correlating the octahedral geometry of the [Fe(1,3-pddadp)](-) unit and an extensive strain analysis are discussed in relation to the information obtained for similar complexes. Antibacterial activities of the free ligand and its corresponding iron(III) complex towards common Gram-negative and Gram-positive bacteria are reported as well.

First author: Moreno, M., Transition metal impurities in wide gap materials: are the electronic properties well described through the ligand field theory?, THEORETICAL CHEMISTRY ACCOUNTS, 118, 665, (2007)
Abstract: In the traditional ligand field theory the electronic properties due to a transition metal (TM) impurity, M, in an insulator are explained only in terms of the MXN complex formed with the N nearest anions. This work is aimed at emphasizing the role played by the electrostatic potential, V-R(r), exerted by the rest of lattice ions upon the localized electrons of the TM complex. This potential, neglected in the traditional ligand field theory, is shown to play a key role when comparing the electronic properties of the same TM complex but embedded in two lattices which are not isomorphous even if both are cubic. As a relevant example it is shown that the different 10Dq values exhibited by CrF63- in the normal perovskite KMgF3(10 Dq = 14, 100 cm(-1)) and in the inverted perovskite BaLiF3( 10 Dq = 16, 720 cm(-1)) can hardly be understood only through a distinct Cr3+ – F- distance. In contrast such a difference is shown to come mainly from the different shape of VR( r) in these two cubic lattices. The importance of this internal electric field is pointed out to grow when comparing two host lattices with the same ligand and coordination number but very different symmetry. This situation is found in the case of ruby ( Al2O3 : Cr3+) and emerald ( Be3Si6Al2O18 : Cr3+) where VR(r) is behind the different colours exhibited by such gemstones. For the sake of clarity a brief discussion on the foundations of the ligand field theory is reported in the present work as well.

First author: Lukoyanova, Olena, “Open rather than closed” malonate methano-fullerene derivatives. The formation of methanofulleroid adducts of Y3N@C-80, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 129, 10423, (2007)
Abstract: Cycloaddition of bromomalonates to Y3N@C-80 unexpectedly gave rise to fulleroid derivatives with unusually high stability. Complete characterization of these derivatives is described including X-ray crystallography, H-1 NMR, C-13 NMR, HMQC, UV-visible, HPLC, MALDI-MS, and electrochemistry. Density functional theory calculations are also presented, which provide a rationale for the formation of the fulleroid and reveal the underlying thermodynamic basis for their stability.

First author: Conradie, Jeanet, Electronic structure and FeNO conformation of nonheme Iron-Thiolate-NO complexes: An experimental and DFT study, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 129, 10446, (2007)
Abstract: Reactions of NO and CO with Fe(II) complexes of the tripodal trithiolate ligands NS3 and PS3* yield trigonal-bipyramidal (TBP) complexes with varying redox states and reactivity patterns with respect to dissociation of the diatomic ligand. The previously reported four-coordinate [Fe-II(NS3)](-) complex reacts irreversibly with NO gas to yield the S = (3)/(2) {FeNO}(7) [Fe(NS3)(NO)](-) anion, isolated as the Me4N+ salt. In contrast, the reaction of NO with the species generated by the reaction of FeCl2 with Li(3)PS3* gives a high yield of the neutral, TBP, S = 1 complex, [Fe(PS3*)(NO)], the first example of a paramagnetic {FeNO}(6) complex. X-ray crystallographic analyses show that both [Fe(NS3)(NO)](-) and [Fe(PS3*)(NO)] feature short Fe-N(NO) distances, 1.756(6) and 1.676(3) A, respectively. However, whereas [Fe(NS3)(NO)](-) exhibits a distinctly bent FeNO angle and a chiral pinwheel conformation of the NS3 ligand, [Fe(PS3*)(NO)] has nearly C-3v local symmetry and a linear FeNO unit. The S = 1 [Fe-II(PS3)L] complexes, where L = 1-MeIm, CN-, CO, and NO+, exhibit a pronounced lengthening of the Fe-P distances along the series, the values being 2.101(2), 2.142(1), 2.165(7), and 2.240(1) A, respectively. This order correlates with the pi-backbonding ability of the fifth ligand L. The cyclic voltammogram of the [Fe(NS3)(NO)](-) anion shows an irreversible oxidation at +0.394 V (vs SCE), apparently with loss of NO, when scanned anodically in DMF. In contrast, [Fe(PS3*)(NO)] exhibits a reversible {FeNO}(6)/{FeNO}(7) couple at a low potential of -0.127 V. Qualitatively consistent with these electrochemical findings, DFT (PW91/STO-TZP) calculations predict a substantially lower gas-phase adiabatic ionization potential for the [Fe(PS3)(NO)](-) anion (2.06 eV) than for [Fe(NS3)(NO)](-) (2.55 eV). The greater instability of the {FeNO}(7) state with the PS3* ligand results from a stronger antibonding interaction involving the metal d(z)(2) orbital and the phosphine lone pair than the analogous orbital interaction in the NS3 case. The antibonding interaction involving the NS3 amine lone pair affords a relatively “stereochemically active” d(z)(2) electron, the z direction being roughly along the Fe-N(NO) vector. As a result, the {FeNO}(7) unit is substantially bent. By contrast, the lack of a trans ligand in [Fe((SBu)-Bu-t)(3)(NO)](-), a rare example of a tetrahedral {FeNO}(7) complex, results in a “stereochemically inactive” d(z)(2) orbital and an essentially linear FeNO unit.

First author: Nafady, Ayman, Hyperelectronic metal-carborane analogues of cymantrene (MnCp(CO)(3)) anions: Electronic and structural noninnocence of the tricarbadecaboranyl ligand, ORGANOMETALLICS, 26, 4471, (2007)
Abstract: The reduction of 1,1,1-(CO)(3)-2-Ph-closo-1,2,3,4-MnC3B7H9, 1, to the hyperelectronic dianion 1(2-) has been studied by electrochemistry, spectroscopy, X-ray crystallography, and DFT calculations. Depending on the medium, this cymantrene derivative displays either a single two-electron wave or two separate one-electron waves in cyclic voltammetry scans, always at potentials (e.g., E-1/2 = -1.14 V vs ferrocene for 1/1(-) in THF) that are very far positive of that reported for MnCp(CO)(3) (-2.86 V). Reduction of the corresponding Re compound 2 occurs in a single two-electron process. Both 1(-) and 1(2-) were isolated as their decamethylcobaltocenium salts and characterized by X-ray crystallography. The hapticity of the tricarbadecaboranyl ligand is reduced from hexahapto (eta(6)) in 1 to tetrahapto (eta(4)) in 1(2-), mimicking an eta(5)/eta(3) haptotropic rearrangement of a cyclopentadienyl ligand. The dianion 1(2-) retains coordination to the C7-B3-B4-C9 face of the tricarbadecaboranyl ligand, much like that found previously for the neutral isocyanide adduct (CNBut)(CO)(3)MnC3B7H9, 3, showing that the metal-ligand bonding reacts similarly to gain of either two electrons or an electron pair donor. The monoanion 1(-) also shows ligand slippage to an eta(4) coordination in which relevant distances and angles are roughly intermediate of 1 and 1(2-). The SOMO of 1(-) is highly delocalized over the Mn-C3B7 framework. Although the tricarbadecaboranyl anion has a strongly electron-accepting ligand effect, the majority of the stabilization energy it imparts to nominally hyperelectronic metals originates from its flexibility in hapticity changes. By analogy to well-documented metal-chelate chemistry, the tricarbadecaboranyl group behaves as a “noninnocent” ligand in these electron-rich systems.

First author: Li, Qiaohong, Solvent and intermolecular effects on first hyperpolarizabilities of organometallic tungsten-carbonyl complexes, a TDDFT study, JOURNAL OF PHYSICAL CHEMISTRY A, 111, 7925, (2007)
Abstract: The first hyperpolarizability of two tungsten-carbonyl complexes, tungsten pentacarbonyl pyridine and tungsten pentacarbonyl trans-1,2-bis(4-pyridyl)-ethylene, has been studied by the high-level TDDFT method. The consideration of the solvent effect and intermolecular pi-pi weak interaction in the calculations quantitatively improve the final result of both the electronic excitations and the first hyperpolarizabilities. By using the orbital decomposition scheme (J. Phys. Chem. A 2006, 110, 1014-1021), the NLO mechanisms of these two complexes have been ascribed to the dominant contribution from the metal-to-ligand charge transfer, with HOMO -> LUMO character, and the indispensable contribution from the intraligand charge transfer as well. A supplementary formula has been proposed to implement the orbital-pair transition analysis. This study reports the significant influences of solvation and intermolecular interactions on the first hyperpolarizabilities of organometallic NLO chromophores.

First author: Fernandez, Israel, Hyperconjugative stabilization in alkyl carbocations: Direct estimate of the beta-effect of group-14 elements, JOURNAL OF PHYSICAL CHEMISTRY A, 111, 8028, (2007)
Abstract: DFT calculations at the BP86/TZ2P level have been carried out for the primary, secondary, and tertiary carbenium ions [H2C-CH(EH3)(2)](+) (1a-e), [HC{CH(EH3)(2)}(2)](+), (2a-e), and [C{CH(EH3)(2)}(3)](+) (3a-e) for E = C, Si, Ge, Sn, Pb. The nature of the interaction between the carbenium center H2-nC+ and the substituents {CH(EH3)(2)}(m) has been investigated with an energy decomposition analysis (EDA) aiming at estimating the strength of the pi hyperconjugation which electronically stabilizes the carbenium ions. The results of the EDA show that the calculated Delta E-pi values can be used as a measure for the strength of hyperconjugation in carbenium ions arising from the interactions of saturated groups possessing pi orbitals. The theoretical data suggest that the ability of sigma C-E bonds to stabilize positive charges by hyperconjugation follow the order C << Si < Ge < Sn < Pb. Hyperconjugation of C-Si bonds is much stronger than hyperconjugation of C-C bonds while the further rising from silicon to lead is smaller and has about the same step size for each element. The strength of the hyperconjugation in primary, secondary, and tertiary alkyl carbenium ions does not increase linearly with the number of hyperconjugating groups; the incremental stabilization becomes smaller from primary to secondary to tertiary cations. The effect of hyperconjugation is reflected in the shortening of the C-C bond distances and in the lengthening of the C-E bonds, which exhibits a highly linear relationship between the calculated C-C and C-E distances in carbocations 1-3 and the hyperconjugation estimated by the Delta E-pi values.

First author: Guan, Jingang, Ligand field photofragmentation spectroscopy of [Ag(L)(N)](2+) complexes in the gas phase: Experiment and theory, JOURNAL OF CHEMICAL PHYSICS, 127, 8028, (2007)
Abstract: Experiments have been undertaken to record photofragmentation spectra from a series of [Ag(L)(N)](2+) complexes in the gas phase. Spectra have been obtained for silver(II) complexed with the ligands (L): acetone, 2-pentanone, methyl-vinyl ketone, pyridine, and 4-methyl pyridine (4-picoline) with N in the range of 4-7. A second series of experiments using 1,1,1,3-fluoroacetone, acetonitrile, and CO2 as ligands failed to show any evidence of photofragmentation. Interpretation of the experimental data has come from time-dependent density functional theory (TDDFT), which very successfully accounts for trends in the spectra in terms of subtle differences in the properties of the ligands. Taking a sample of three ligands, acetone, pyridine, and acetonitrile, the calculations show all the spectral transitions to involve ligand-to-metal charge transfer, and that wavelength differences (or lack of spectra) arise from small changes in the energies of the molecular orbitals concerned. The calculations account for an absence in the spectra of any effects due to Jahn-Teller distortion, and they also reveal structural differences between complexes where the coordinating atom is either oxygen or nitrogen that have implications for the stability of silver(II) compounds. Where possible, comparisons have also been made with the physical properties of condensed phase silver(II) complexes.

First author: Koepke, Juergen, pH modulates the quinone position in the photosynthetic reaction center from Rhodobacter sphaeroides in the neutral and charge separated states, JOURNAL OF MOLECULAR BIOLOGY, 371, 396, (2007)
Abstract: The structure of the photosynthetic reaction-center from Rhodobacter sphaeroides has been determined at four different pH values (6.5, 8.0, 9.0, 10.0) in the neutral and in charge separated states. At pH 8.0, in the neutral state, we obtain a resolution of 1.87 A, which is the best ever reported for the bacterial reaction center protein. Our crystallographic data confirm the existence of two different binding positions of the secondary quinone (Q(B)). We observe a new orientation of Q(B) in its distal position, which shows no ring-flip compared to the orientation in the proximal position. Datasets collected for the different pH values show a pH-dependence of the population of the proximal position. The new orientation of Q(B) in the distal position and the pH-dependence could be confirmed by continuum electrostatics calculations. Our calculations are in agreement with the experimentally observed proton uptake upon charge separation. The high resolution of our crystallographic data allows us to identify new water molecules and external residues being involved in two previously described hydrogen bond proton channels. These extended proton-transfer pathways, ending at either of the two oxo-groups of Q(B) in its proximal position, provide additional evidence that ring-flipping is not required for complete protonation of Q(B) upon reduction.

First author: Cavigliasso, German, Periodic trends in metal-metal bonding in edge-shared [M2Cl10](4-) systems,POLYHEDRON, 26, 2942, (2007)
Abstract: Periodic trends in metal-metal interactions in edge-shared [M2Cl10r](4-) systems, involving the transition metals from groups 4 through 8 and electronic configurations ranging from d(1)d(1) through d(5) 5 d5, have been investigated by calculating metal-metal bonding and spinpolarization (exchange) effects using density functional theory. The trends found in this study are compared with those for the analogous face-shared W209](3-) systems reported in earlier work. Strong linear correlations between the metal-metal bonding and spin-polarization terms have been obtained for all groups considered. In general, spin polarization and electron localization are predominant in 3d-3d species whereas electron delocalization and metal-metal bonding are favoured in 5d-5d species, with more variable results observed for 4d-4d systems. As previously found for face-shared [M-2 Cl-9]3- systems, the strong correlations between the metal-metal bonding and spin polarization energy terms can be related to the fact that both properties appear to be similarly affected by the changes in the metal orbital properties and electron density occurring within the d(n)d(n) groups. A significant difference between the face-shared and edge-shared systems is that while the 4d metals in the former show a strong tendency for delocalized metal-metal bonded structures, the edge-shared counterparts display much greater variation with both metal metal bonded and weakly coupled complexes observed. The tendency for weaker metal-metal interactions can be traced to the inability of the edge-shared bridging structure to accommodate the smaller metal-metal distances required for strong metal-metal bonding.

First author: Chierotti, Michele R., An unusual carbonyl chemical shift in a carbonylhexairidium cluster: A combined solid-state NMR and DFT approach, EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 26, 3477, (2007)
Abstract: The C-13 NMR spectrum of TMBA(2)[Ir-6(CO)151 [TMBA = (CH3)(3)N(CH2C6H5)] shows, at low temperatures, an unprecedented mu(2)-bridging carbonyl low-frequency shift, with the resonances of the terminal mu(1)-carbonyl ligands placed at higher frequencies. The chemical shift tensors and the shielding anisotropies of the carbonyl ligands, obtained from solid-state NMR analysis, allow us to determine the nature of the M-CO interaction. The results have been compared with the C-13 MAS data of lr6(CO)16 where mu(3)-CO ligands are present. Further evidence for the assignment and for the peculiar chernical shift value of bridging carbonyl ligands in TMBA(2)[Ir-6(CO)15] has been obtained by the DFT calculation of the NNIR parameters. The scalar and spin-orbit (SO) relativistic two-component zero-order regular approximation (ZORA) methods were employed in the geometry optimization and NMR chemical shift calculations, respectively. The large SO contribution (delta = 26.6 ppm) to the mu(2)-bridging CO ligand C-13 chemical shifts accounts for the position of the experimentally observed resonance.

First author: Swart, Marcel, Proton affinities in water of maingroup-element Hydrides – Effects of hydration and methyl substitution, EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 26, 3646, (2007)
Abstract: We have computed the proton affinities in water of archetypal anionic and neutral bases across the periodic table using the generalized gradient approximation (GGA) of density functional theory (DFT) at BP86/QZ4P//BP86/TZ2P. The main purpose of this work is to provide an intrinsically consistent set of values of the 298-K proton affinities in aqueous solution of all anionic (XHn-1-) and neutral bases (XHn) constituted by maingroup-element hydrides of groups 14-17 and the noble gases (i.e., group 18) along the periods 1-6. Hydration has little effect on the trends in PA values, especially in the case of the neutral bases. However, in the case of the anionic bases, hydration drastically reduces the magnitude of the PA values. Finally, we have studied how proton affinities in water are affected by methyl substitution at the protophilic center.

First author: Christian, Gernma, Cleavage of CO by Mo[N(R)Ar](3) complexes, EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 26, 3736, (2007)
Abstract: The reaction of MoL3 [L = NH2 and N(tBu)Arl with CO was explored using DFT in order to rationalize why CO cleavage is not observed experimentally for this system in contrast to the corresponding N-2 reaction which results in spontaneous cleavage of the N-N bond. The binding of CO to MoL3 was found to be both kinetically and thermodynamically favored over the binding of N2, with the formation of the encounter complex, L3Mo-CO, calculated to be without barrier and exothermic. While the overall reaction to form the C-MoL3 and O-MoL3 products was calculated to be energetically favorable, both the encounter complex and intermediate dimer, L3MO-CO-MoL3, were found to be lower in energy than the products, with the final C-O cleavage step calculated to be endothermic by 169 kJ mol(-1) and 163 kJ mol(-1) for L = NH2 and N(tBu)Ar, respectively. The unfavorable CO cleavage step can be attributed to the fact that Mo does not possess the optimum d-electron configuration to sufficiently stabilise the carbide and oxide products relative to the CO-bridged intermediate dimer.

First author: Jacobsen, Heiko, Dicoordinate copper(I) chalcogenides – Structure and bonding, INORGANICA CHIMICA ACTA, 360, 3511, (2007)
Abstract: Structure and bonding of H3PCuESiH3 and CuESiH3 complexes (E = O, S, Se) has been investigated using BP86 density functional (DF) calculations. Linear (angle(Cu-E-Si) = 180 degrees) and bent (angle(Cu-E-Si) < 180 degrees) coordination geometries have been considered. A detailed bond analysis reveals that Pauli repulsion represents the dominant interaction that characterizes the Cu-E bond. A reduction in Pauli repulsion is the major factor that favors a bent arrangement. An electron density analysis based on the localized orbital locator (LOL) further suggests that bending increases the covalency of the Cu-E bond.

First author: Lo, John M. H., Density functional theory and kinetic studies of methanation on iron surface, JOURNAL OF PHYSICAL CHEMISTRY C, 111, 11012, (2007)
Abstract: The production of methane from CO and H-2 on a clean Fe(100) surface was studied using periodic DFT calculations in conjunction with kinetic modeling. It was found that the adsorption and subsequent dissociation of CO and H-2 at a finite temperature are significantly influenced by the presence of coadsorbed CO and H. The surface coverage of CO is controlled by entropy, and a maximum of 50% coverage can be attained. The kinetic modeling adopting the computed activation barriers for the elementary steps involved in methanation revealed that CH is a major C-1 species on the surface. The production of CH4 was found to be more favored at a high reaction temperature and H-2 partial pressure but suppressed by a high pressure of CO.

First author: Prins, Paulette, Charge transport along coiled conjugated polymer chains, JOURNAL OF PHYSICAL CHEMISTRY C, 111, 11104, (2007)
Abstract: The motion of charges on coiled polymer chains was studied using a combination of experimental and theoretical methods. The conductive properties of dilute solutions of polyfluorene and fluorene-binaphthyl copolymers were studied by the pulse-radiolysis time-resolved microwave conductivity technique. This technique enables measurement of the (high frequency, 34 GHz) mobility of charges on isolated polymer chains. The motion of positive charges on the coiled polymer chains was studied theoretically by charge transport simulations with parameters from density functional theory calculations. This combined experimental and theoretical study shows that the mobility of charges decreases with increasing degree of chain coiling. The mobility along (infinitely long) stretched polyfluorene is calculated to be as high as tens of centimeters(2)/volt center dot second. Our results imply that the performance of conjugated polymers in optoelectronic devices can be significantly improved by optimization of the organization on a molecular scale.

First author: Fillaut, Jean-Luc, Alkynyl ruthenium colorimetric sensors: Optimizing the selectivity toward fluoride anion,INORGANIC CHEMISTRY, 46, 5922, (2007)
Abstract: We report on the synthesis of alkynyl ruthenium colorimetric sensors whose receptors are constituted by thiazolidinedione, rhodanine, or barbituric heads as recognition centers for anions. As modifications in the charge density at these recognition centers affect the whole molecule, through the alkynyl ligand acting as a communicating wire, the effects of hydrogen-bonding interactions with the anions were observed with the naked eye and monitored by UV-vis absorption spectrometry. The selectivity of the sensors was improved through electronic modifications of the alkynyl ruthenium subunit: the higher the electron density at the receptor head, the higher the selectivity is. TD-DFT calculations rationalize the long-range electronic communication as a main characteristic of the alkynyl ruthenium species and as a key to improve the selectivity of alkynyl ruthenium-based sensors toward anions.

First author: De Luca, Giovanna, Evidence for tetraphenylporphyrin monoacids, INORGANIC CHEMISTRY, 46, 5979, (2007)
Abstract: Upon dilution from a concentrated solution in dichloromethane, the diacid form of tetraphenylporphyrin {H4TPP(X)(2)} (X = Cl, PF6 and tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, TFPB) affords eventually the unprotonated free base species H2TPP. At a difference of chloride, in the case of PF6- and TFPB- anions the conversion occurs with the intermediacy of a species, which has been assigned to a monoacid derivative on the basis of UV/vis absorption, fluorescence emission (static and dynamic), and resonance light scattering. Ground-state gas-phase geometries have been calculated both for the diacid {H4TPP(PF6)(2)} and monoacid {H3TPP(PF6)} and {H3TPP(Cl)} species at the DFT/BP86 level of theory. TDDFT calculations using different functionals (BP86, SAOP, and B3LYP) have been exploited to provide electronic vertical excitation energies and oscillator strengths, yielding a remarkably good description of the optical spectra for these compounds and supporting the identification of the monoacid species. Gas-phase thermodynamic calculations on the chloride species provide an estimate of the Gibbs free energy changes associated with the two protonation steps, supporting the observed different behavior of this anion with respect to PF6- and TFPB-.

First author: De Angelis, Filippo, Controlling phosphorescence color and quantum yields in cationic iridium complexes: A combined experimental and theoretical study, INORGANIC CHEMISTRY, 46, 5989, (2007)
Abstract: We report a combined experimental and theoretical study on cationic Ir(III) complexes for OLED applications and describe a strategy to tune the phosphorescence wavelength and to enhance the emission quantum yields for this class of compounds. This is achieved by modulating the electronic structure and the excited states of the complexes by selective ligand functionalization. In particular, we report the synthesis, electrochemical characterization, and photophysical properties of a new cationic Ir(III) complex, [Ir(2,4-difluorophenylpyridine)(2)(4,4′-dimethylamino-2,2′-bipyridine)]( PF6) (N969), and compare the results with those reported for the analogous [Ir(2-phenylpyridine)(2)(4,4′-dimethylamino-2,2′-bipyridine)](PF6) (N926) and for the prototype [Ir(2-phenylpyridine)(2)(4,4′-tert-butyl-2,2′-bipyridine)](PF6) complex, hereafter labeled N925. The three complexes allow us to explore the ((CN)-N-and) and ((NN)-N-and) ligand functionalization: considering N925 as a reference, we investigate in N926 the effect of electron-releasing substituents on the bipyridine ligand, while in N969, we investigate the combined effect of electron-releasing substituents on the bipyridine ligand and the effect of electron-withdrawing substituents on the phenylpyridine ligands. For N969 we obtain blue-green emission at 463 nm with unprecedented high quantum yield of 85% in acetonitrile solution at room temperature. To gain insight into the factors responsible for the emission color change and the different quantum yields, we perform DFT and TDDFT calculations on the ground and excited states of the three complexes, characterizing the excited-state geometries and including solvation effects on the calculation of the excited states. This computational procedure allows us to provide a detailed assignment of the excited states involved in the absorption and emission processes and to rationalize the factors determining the efficiency of radiative and nonradiative deactivation pathways in the investigated complexes. This work represents an example of electronic structure-driven tuning of the excited-state properties, thus opening the way to a combined theoretical and experimental strategy for the design of new iridium(III) phosphors with specific target characteristics.

First author: Gerken, Michael, Solid-state NMR spectroscopic study of coordination compounds of XeF2 with metal cations and the crystal structure of [Ba(XeF2)(5)][AsF6](2), INORGANIC CHEMISTRY, 46, 6069, (2007)
Abstract: The coordination compounds [Mg(XeF2)(2)][AsF6](2), [Mg(XeF2)(4)][AsF6](2), [Ca(XeF2)(2.5)][AsF6](2), [Ba(XeF2)(3)][AsF6](2), and [Ba(XeF2)(5)][AsF6](2) were characterized by solid-state F-19 and Xe-129 magic-angle spinning NMR spectroscopy. The F-19 and Xe-129 NMR data of [Mg(XeF2)(2)][AsF6](2), [Mg(XeF2)(4)][AsF6](2), and [Ca(XeF2)(2.5)][AsF6](2) were correlated with the previously determined crystal structures. The isotropic F-19 chemical shifts and (1)J(Xe-129-F-19) coupling constants were used to distinguish the terminal and bridging coordination modes of XeF2. Chemical-shift and coupling-constant calculations for [Mg(XeF2)(4)][AsF6](2) confirmed the assignment of terminal and bridging chemical-shift and coupling-constant ranges. The NMR spectroscopic data of [Ba(XeF2)(3)][AsF6](2) and [Ba(XeF2)(5)][AsF6](2) indicate the absence of any terminal XeF2 ligands, which was verified for [Ba(XeF2)(5)][AsF6](2) by its X-ray crystal structure. The adduct [Ba(XeF2)(5)][AsF6](2) crystallizes in the space group Fmmm, with a = 11.6604(14) A, b = 13.658(2) A, c = 13.7802(17) A, V = 2194.5(5) A(3) at -73 degrees C, Z = 4, and R = 0.0350 and contains two crystallographically independent bridging XeF2 molecules and one nonligating XeF2 molecule. The AsF6- anions in [Mg(XeF2)(4)][AsF6](2), [Ca(XeF2)(2.5)][AsF6](2), [Ba(XeF2)(3)][AsF6](2), and [Ba(XeF2)(5)][AsF6](2) were shown to be fluxional with the fluorines-on-arsenic being equivalent on the NMR time scale, emulating perfectly octahedral anion symmetry.

First author: Rayon, Victor M., Cyanides and isocyanides of first-row transition metals: Molecular structure, bonding, and isomerization barriers, JOURNAL OF PHYSICAL CHEMISTRY A, 111, 6334, (2007)
Abstract: Cyanides and isocyanides of first-row transition metal M(CN) (M = Sc-Zn) are investigated with quantum chemistry techniques, providing predictions for their molecular properties. A careful analysis of the competition between cyanide and isocyanide isomers along the transition series has been carried out. In agreement with the experimental observations, late transition metals (Co-Zn) clearly prefer a cyanide arrangement. On the other hand, early transition metals (Sc-Fe), with the only exception of the Cr(CN) system, favor the isocyanide isomer. The theoretical calculations predict the following unknown isocyanides, ScNC((3)Delta), TiNC((4)Phi), VNC((5)Delta), and MnNC((7)Sigma(+)), and agree with the experimental observation of FeNC((6)Delta) and the CrCN((6)Sigma(+)) cyanide. First-row transition metal cyanides and isocyanides are predicted to have relatively large dissociation energies with values within the range 80-101 kcal mol(-1), except Zn(CN), which has a dissociation energy around 50-55 kcal mol(-1), and low isomerization barriers. A detailed analysis of the bonding has been carried out employing the topological analysis of the charge density and an energy decomposition analysis. The role of the covalent and electrostatic contributions to the metal-ligand bonding, as well as the importance of pi bonding, are discussed.

First author: Raab, Juraj, A combined experimental and theoretical study of uranium polyhydrides with new evidence for the large complex UH4(H-2)(6), JOURNAL OF PHYSICAL CHEMISTRY A, 111, 6383, (2007)
Abstract: Several monouranium and diuranium polyhydride molecules were investigated using quantum chemical methods. The infrared spectra of uranium and hydrogen reaction products in condensed neon and pure hydrogen were measured and compared with previous argon matrix frequencies. The calculated molecular structures and vibrational frequencies were used to identify the species present in the matrix. Major new absorptions were observed and compared with the previous argon matrix study. Spectroscopic evidence was obtained for the novel complex, UH4(H-2)(6), which has potential interest as a metal hydride with a large number of hydrogen atoms bound to uranium. Our calculations show that the series of complexes UH4(H-2)(1,2,4,6) are stable.

First author: Hodgkiss, Justin M., Ligand-field dependence of the excited state dynamics of hangman bisporphyrin dyad complexes, JOURNAL OF PHYSICAL CHEMISTRY B, 111, 8258, (2007)
Abstract: A new Hangman porphyrin architecture has been developed to interrogate the ligand-field dependence of photoinduced PCET versus excitation energy transfer and intersystem crossing in PZnII-PFeIII-OH dyads (P = porphyrin). In this design, a hanging carboxylic acid group establishes a hydrogen-bonding network to anchor the weak-field OH- ligand in the distal site of the PFeIII-OH acceptor, whereas the proximal site is left available to accept strong-field imidazole ligands. Thus, controlling the tertiary coordination environment gives access to the first synthetic example of a porphyrin dyad with a biologically relevant weak-field/strong-field configuration of axial ligands at the heme. Transient absorption spectroscopy has been employed to probe the fate of the initial PZnII-based S-1 excited state, revealing rapid S-1 quenching for all dyads in the presence and absence of strong-field imidazole ligands (tau = 6-50 ps). The absence of a (P center dot+)Zn-II signal that would complement photoinduced PCET at the PFeIII-OH subunit (i.e., PFeIII-OH -> PFeII-OH2) shows that excitation energy transfer and intersystem crossing channels dominate the quenching, regardless of whether proximal strong field ligands are present. Moreover, this photophysical assignment is independent of the solvent dielectric constant and whether a phenylene or biphenylene spacer is used to span the two porphyrin subunits. Electronic structure calculations suggest that the structural reorganization attendant to reductive PCET at the high-spin Fe-III-OH center imposes a severe kinetic cost that can only be alleviated by inducing a low-spin electronic configuration with two strong-field axial ligands.

First author: Atanasov, Mihail, On the ground state T-g circle times epsilon(g) (T-g = T-2(2g), T-3(1g)) Jahn-Teller-coupling in hexacyano complexes of 3d-transition metals, JOURNAL OF MOLECULAR STRUCTURE, 838, 157, (2007)
Abstract: The linear and quadratic T-g circle times epsilon(g) Jahn-Teller effect in the T-g (T-g – T-2(2g), T-3(1g)) ground states of low-spin octahedral cyano complexes of 3d-transition metals (M = Ti-III, V-III, Mn-III, Fe-III, Cr-II, Mn-II) has been studied. Vibronic coupling parameters have been derived using density functional theory to calculate energies of Slater determinants, which result from various electron distributions within the t(2g)(n) configuration due to the metal based t(2g)(3d) molecular orbitals (n = 1, 2, 3, 4). Tetragonal elongations are found in the case of Ti-III, Mn-III and Cr-II, and compressions for V-III, Fe-III and Mn-II, and these establish the metal-ligand pi-back donation as the dominant effect and driving force for the geometry distortions and energy stabilizations towards non-degenerate B-2(2g)(t(2g)(1), t(2g)(5)) and (3)A(2g)(t(2g)(2), t(2g)(4)) ground states. The strength of the Jahn-Teller coupling is very weak and found not to follow a monotonic trend across the transition metal series but is shown to be weakest for Ti-III, V-III and Fe-III, slightly larger for Mn-III, increases further to Mn-III and is found to be the strongest but is still weak for Cr-II.

First author: Bruce, Michael I., Redox-active complexes containing group 8 metal centers linked by C-2 bridges,ORGANOMETALLICS, 26, 3735, (2007)
Abstract: A series of complexes containing dicarbon ligands bridging redox-active group 8 metal-ligand fragments M(dppe)Cp’ (M = Fe, Ru, Os; Cp’ = Cp, Cp*) have been prepared. These complexes give up to four one-electron anodic processes at a platinum electrode, with separations of successive oxidation potentials of ca. 850 mV, giving rise to large comproportionation constants, K-C (ca. 10(12)). Examples of the 36-electron neutral, 35-electron monocationic, and 34-electron dicationic species, together with some related monoprotonated complexes, have been isolated. Structural studies of the 36-, 35-, and 34-electron species derived from the dicarbon complex featuring two Ru(dppe)Cp end-caps (7) show that shortening of the M-C and lengthening of the C-C bonds occur upon oxidation. A complementary spectroelectrochemical investigation has revealed an intense band near 14 300 cm(-1) associated with [7]PF6, which is tentatively attributed to a Ru(d)-[Ru(d)/C-2(pi)]* transition, rather than a genuine IVCT band. These observations have been rationalized using DFT calculations and collectively indicate that the frontier orbitals are delocalized over both group 8 metal centers and the carbon chain.

First author: Orian, Laura, Cyclotrimerization reactions catalyzed by rRhodium(I) half-sandwich complexes: A mechanistic density functional study, ORGANOMETALLICS, 26, 3816, (2007)
Abstract: We propose and examine a comprehensive mechanism of the [(eta(5)-C5H5)Rh]-catalyzed [2+2+2] cycloadditions of acetylene to benzene and of acetylene and acetonitrile to 2-methylpyridine, based on an extensive and detailed exploration of the potential energy surfaces using density functional theory. Both processes involve the formation of a coordinatively unsaturated 16-electron metallacycle, occurring after the replacement of the ancillary ligands L of the catalyst precursor of general formula [(eta(5)-C5H5)RhL2] (typically L = C2H4, CO, PH3 or L-2 = 1,5-cyclooctadiene) by two acetylene molecules. The facile coordination of a third acetylene molecule, and its subsequent addition to the pi electron system of the rhodacycle, leads to the formation of an intermediate, which is characterized by a six-membered arene ring coordinated to the metal in eta(4) fashion. The release of benzene occurs by stepwise addition of two acetylene molecules, which regenerates the catalyst. In the presence of acetonitrile, a nitrile molecule coordinates to the rhodacycle, and different stages are outlined for the process, leading to the eventual release of 2-methylpyridine. The steric and electronic effects of the pi ligand coordinated to the metal are also included in our exploration by addressing the whole mechanism of the [(eta(5)-C9H7)Rh]-catalyzed alkyne self-trimerization to benzene. The kinetic parameters, i.e., the energies in vacuum and in different solvents, and the geometries of the intermediates and of the transition states are analyzed in detail.

First author: Swart, Marcel, Energy landscapes of nucleophilic substitution reactions: A comparison of density functional theory and coupled cluster methods, JOURNAL OF COMPUTATIONAL CHEMISTRY, 28, 1551, (2007)
Abstract: We have carried out a detailed evaluation of the performance of all classes of density functional theory (DFT) for describing the potential energy surface (PES) of a wide range of nucleophilic substitution (S(N)2) reactions involving, amongst others, nucleophilic attack at carbon, nitrogen, silicon, and sulfur. In particular, we investigate the ability of the local density approximation (LDA), generalized gradient approximation (GGA), meta-GGA as well as hybrid DFI’ to reproduce high-level coupled cluster (CCSD(T)) benchmarks that are close to the basis set limit. The most accurate GGA, meta-GGA, and hybrid functionals yield mean absolute deviations of about 2 kcal/mol relative to the coupled cluster data, for reactant complexation, central barriers, overall barriers as well as reaction energies. For the three nonlocal DFT classes, the best functionals are found to be OPBE (GGA), OLAP3 (meta-GGA), and mPBE0KCIS (hybrid DFT). The popular B3LYP functional is not bad but performs significantly worse than the best GGA functionals. Furthermore, we have compared the geometries from several density functionals with the reference CCSD(T) data. The same GGA functionals that perform best for the energies (OPBE, OLYP), also perform best for the geometries with average absolute deviations in bond lengths of 0.06 angstrom and 0.6 degrees, even better than the best meta-GGA and hybrid functionals. In view of the reduced computational effort of GGAs with respect to meta-GGAs and hybrid functionals, let alone coupled cluster, we recommend the use of accurate GGAs such as OPBE or OLYP for the study of S(N)2 reactions.

First author: Pang Xiao-Hong, Theoretical study on the structure and conductivity of tungsten bronzes NaxLayWO3, ACTA CHIMICA SINICA, 65, 1197, (2007)
Abstract: The geometric structures and electronic structures of tungsten bronzes NaxWO3 and Na-x- LayWO3 (x>0.36, y<0.015) have been explored by density functional theory (DFT). The geometry was optimized using ADF (Amsterdam density functional) program package with TZ2P basis set. The energy bands and density of states were calculated using the VASP (Vienna ab-initio simulation package) program. The calculated structures are close to the experimental values. After the substitution of La3+ for Na+, the space symmetry is not changed but the lattice parameters and volumes of NaxLayWO3 increase. The energy bands are condensed and the appearance probabilities of the electrons are enhanced near the Fermi-surface. Therefore, the introduction of La3+ is important to improve the conductivity of the sodium tungsten bronze. Keywords tungsten bronze; NaxLayWO3; electron conductivity; geometry optimization; band structure; density of states.

First author: Liao, Meng-Sheng, Electronic structure of some substituted iron(II) porphyrins. Are they intermediate or high spin?, JOURNAL OF PHYSICAL CHEMISTRY A, 111, 5927, (2007)
Abstract: The electronic structure of some substituted, four-coordinate iron(II) porphyrins has been investigated with DFT methods. These systems include iron tetraphenylporphine (FeTPP), iron octamethyltetrabenzporphine (FeOTBP), iron tetra(alpha,alpha,alpha,alpha-orthopivalamide)phenylporphine (FeTpivPP, also called “picket fence” porphyrin), halogenated iron porphyrins (FeTPPXn, X = F, Cl; n = 20, 28), and iron octaethylporphine (FeOEP). A number of density functionals were used in the calculations. Different from the popular, intermediate-spin FeTPP, the ground states of FeOTBP, FeTPPCl28, and FeTPPF20 beta Cl-8 are predicted to be high spin. The calculated result for FeOTBP is in agreement with the early experimental measurement, thereby changing the previous conclusion drawn from the calculations with only the BP functional (J. Chem. Phys. 2002, 116, 3635). But FeTpivPP might have an intermediate-spin ground state, a conclusion that is different from the “experimental” one. With a notably expanded Fe-N bond length, FeOEP might exist as an admixed-spin (S = 1, 2) state. We also calculated the electron affinities (EAs) for the various iron porphyrins and compared them to experiment. On the basis of the calculated trends in the EAs and in the orbital energies, the experimental EAs for FeTpivPP, FeTPPF20, and FeTPPCl28 may be too small by 0.4-0.5 eV.

First author: Karle, Isabella L., Cooperative CH center dot center dot center dot pi interactions in the crystal structure of 2,5-di(3-biphenyl)-1,1-dimethyl-3,4-diphenyl-silole and its effect on its electronic properties, JOURNAL OF PHYSICAL CHEMISTRY C, 111, 9543, (2007)
Abstract: In order to develop a fundamental understanding for the effect of molecular packing on the carrier transport properties of organic semiconductors, single crystals of 2,5-di-(3-biphenyl)-1,1-dimethyl-3,4-diphenylsilacyclopentadiene (PPSPP) were prepared using the physical vapor transport technique and characterized by X-ray crystallography. There is no evidence of pi-pi stacking in the PPSPP single-crystal because of the nearly orthogonal arrangements of the phenyl rings in the biphenyl moieties. Although the PPSPP molecules do not have any -NH or -OH groups that would provide donors for normal hydrogen bonds, the crystal structure reveals the presence of several CH groups that act as donors for CH center dot center dot center dot pi interactions with nearby phenyl groups in an edge-to-face motif. It is proposed that the cooperativity between several weak CH center dot center dot center dot pi bonds enhances their effects and gives rise to a tighter molecular packing than what would be observed for a typical molecular crystal where van der Waals forces dominate. Theoretical electronic-structure calculations indicate that there is a decoupling between the CH…pi interactions that stabilize the crystal structure and the electronic interactions that give the largest electronic couplings defining the preferred electron hopping directions. However, the dense molecular packing between adjacent PPSPP molecules may influence its electron transport properties in the solid state.

First author: Illa, Ona, Cyclopropanation of cyclohexenone by diazomethane catalyzed by palladium diacetate: Evidence for the formation of palladium(0) nanoparticles, ORGANOMETALLICS, 26, 3306, (2007)
Abstract: The diazomethane-mediated cyclopropanation of cyclohexenone using Pd(OAc)(2) and different sources of Pd(0) species as precatalysts has been studied. In the presence of an excess of diazomethane, Pd(OAc)(2) rapidly evolves to the formation of palladium nanoparticles (less than 1 min), which are active as catalysts in the cyclopropanation process. The nature of these particles has been analyzed through transmission electron microscopy showing a size distribution between 6 and 40 nm. These nanoparticles generated in situ are more active than Pd(0) complexes, preformed nanoparticles, and commercial palladium powder. Cyclic voltammetry measurements of the reaction solution after completion show the presence of Pd(0) species. This is the first time that Pd(0) nanoparticles are evidenced in a cyclopropanation reaction. Moreover, the reduction of Pd(OAc)(2) to Pd(0) in the presence of diazomethane has been theoretically studied through density functional calculations. The formation of methyl and allyl acetates as organic byproducts has been predicted by the theoretical calculations, and these species, as well as oligomers derived from them, have been detected by spectrometric and spectroscopic techniques (MS, NMR, and IR).

First author: Bornand, Marc, Mechanistically designed dual-site catalysts for the alternating ROMP of norbornene and cyclooctene, ORGANOMETALLICS, 26, 3585, (2007)
Abstract: Mechanistic work on the olefin metathesis reaction by well-characterized ruthenium carbene complexes led to the rational design and synthesis of a modified, unsymmetrical “first-generation” catalyst, which, in contrast to either first- or second-generation systems with symmetrical ligands, converts a mixture of two cycloolefin monomers to a largely alternating copolymer. The mechanistic concept of a homogeneous catalyst that switches between more than one state at each turnover is general. The structures of the complexes, determined by mass spectrometry, NMR, and X-ray crystallography, reveal some unexpected features, which explain sequence errors in the copolymer.

First author: Brylinski, Michal, Localization of ligand binding site in proteins identified in silico, JOURNAL OF MOLECULAR MODELING, 13, 665, (2007)
Abstract: Knowledge-based models for protein folding assume that the early-stage structural form of a polypeptide is determined by the backbone conformation, followed by hydrophobic collapse. Side chain-side chain interactions, mostly of hydrophobic character, lead to the formation of the hydrophobic core, which seems to stabilize the structure of the protein in its natural environment. The fuzzy-oil-drop model is employed to represent the idealized hydrophobicity distribution in the protein molecule. Comparing it with the one empirically observed in the protein molecule reveals that they are not in agreement. It is shown in this study that the irregularity of hydrophobic distributions is aim-oriented. The character and strength of these irregularities in the organization of the hydrophobic core point to the specificity of a particular protein’s structure/function. When the location of these irregularities is determined versus the idealized fuzzy-oil-drop, function-related areas in the protein molecule can be identified. The presented model can also be used to identify ways in which protein-protein complexes can possibly be created. Active sites can be predicted for any protein structure according to the presented model with the free prediction server at http://www.bioinformatics.cm-uj.krakow.pl/activesite. The implication based on the model presented in this work suggests the necessity of active presence of ligand during the protein folding process simulation.

First author: Lombardi, John R., Time-dependent picture of the charge-transfer contributions to surface enhanced Raman spectroscopy, JOURNAL OF CHEMICAL PHYSICS, 126, 665, (2007)
Abstract: We reexamine the Herzberg-Teller theory of charge-transfer contributions to the theory of surface enhanced Raman scattering (SERS). In previous work, the Kramers-Heisenberg-Dirac framework was utilized to explain many of the observed features in SERS. However, recent experimental and theoretical developments suggest that we revise the theory to take advantage of the time-dependent picture of Raman scattering. Results are obtained for molecular adsorption on nanoparticles in both the strong confinement limit and the weak confinement limit. We show that the Herzberg-Teller contributions to the charge-transfer effect in SERS display a resonance at the molecule-to-metal or metal-to-molecule transition while retaining the selection rules associated with normal Raman spectroscopy (i.e., harmonic oscillator, as opposed to Franck-Condon overlaps). The charge-transfer contribution to the enhancement factor scales as Gamma(-4), where Gamma is the homogeneous linewidth of the charge-transfer transition, and thus is extremely sensitive to the magnitude of this parameter. We show that the Herzberg-Teller coupling term may be associated with the polaron-coupling constant of the surface phonon-electron interaction. A time-dependent expression for the Raman amplitude is developed, and we discuss the implications of these results for both metal and semiconductor nanoparticle surfaces.

First author: Zhu, Yulan, Theoretical investigation of electronic structures and excitation energies of doubly N-confused porphyrin and its group 11 transition metal (III) complexes, JOURNAL OF CHEMICAL PHYSICS, 126, 665, (2007)
Abstract: Density functional theory is carried out to study cis-doubly N-confused porphyrin and its metal (Cu3+, Ag3+, and Au3+) complexes. The electronic structures and bonding situations of these molecules have been investigated by using the natural bond orbital analysis and the topological analysis of the electron localization function. We have studied the electronic spectra of cis-doubly N-confused porphyrin and its metal complexes with time-dependent density functional theory. The introduction of group 11 transition metals leads to blueshifts of their electronic spectra with respect to that of cis-doubly N-confused porphyrin. In particular, the absorption spectra of the copper complex show some weak Q bands that mainly arise from a combination of ligand-to-metal charge transfer and ligand-to-ligand charge transfer transitions. The relativistic time-dependent density functional theory with spin-orbit coupling calculations indicates that the effects of spin-orbit coupling on the excitation energies of the copper and silver complexes are so small that it is safe enough to neglect spin-orbit interactions for these two complexes. However, it has a significant effect on the absorption spectra of the gold complex.

First author: Buhl, Michael, Coordination mode of nitrate in Uranyl(VI) complexes: A first-principles molecular dynamics study, INORGANIC CHEMISTRY, 46, 5196, (2007)
Abstract: According to Car-Parrinello molecular dynamics simulations for [UO2(NO3)(3)](-), [UO2(NO3)(4)](2-), and [UO2(OH2)(4)(NO3)](+) complexes in the gas phase and in aqueous solution, the nitrate coordination mode to uranyl depends on the interplay between ligand-metal attractions, interligand repulsions, and solvation. In the trinitrate, the eta(2)-coordination is clearly favored in water and in the gas phase, leading to a coordination number (CN) of 6. According to pointwise thermodynamic integration involving constrained molecular dynamics simulations, a change in free energy of +6 kcal/mol is predicted for eta(2)- to eta(1)-transition of one of the three nitrate ligands in the gas phase. In the gas phase, the mononitrate-hydrate complex also prefers a eta(2)-binding mode but with a CN of 5, one H2O molecule being in the second shell. This contrasts with the aqueous solution where the nitrate binds in a eta(1)-fashion and uranyl coordinates to four H2O ligands. A driving force of ca. -3 kcal/mol is predicted for the eta(2)- to eta(1)- transition in water. This structural preference is interpreted in terms of steric arguments and differential solvation of terminal vs uranyl-coordinated O atoms of the nitrate ligands. The [UO2(NO3)(4)](2-) complex with two eta(2)- and two eta(1)- coordinated nitrates, observed in the solid state, is stable for 1-2 ps in the gas phase and in solution. In the studied series, the modulation of uranyl-ligand distances upon immersion of the complex in water is found to depend on the nature of the ligand and the composition of the complex.

First author: Labeguerie, Pierre, DFT modeling of sandwich complexes involving cationic palladium chains and polyenic or polycyclic aromatic hydrocarbons, INORGANIC CHEMISTRY, 46, 5283, (2007)
Abstract: DFT calculations are reported on a series of one-dimensional palladium complexes with general formula [Pd-m(C2nH2n+2)(2)](2+) (m = 2-4, n = 2-8, n >= m), in order to model and analyze the bonding in the series of organometallic sandwich compounds recently reported by the group of T. Murahashi and H. Kurosawa. The bonding interactions are elucidated, and the frontier orbitals involved are described as a function of the haptotropic conformation of the metal atoms, either di-hapto or tri-hapto. In both cases, the driving force to the complex organization is a strong donation interaction from the pi system of the hydrocarbons to an orbital with appropriate phase and composition, delocalized over the metal chain, and depopulated by the double oxidation process. No net bonding interaction can be characterized along the metal string, and the metal-metal distances are mainly governed by the hapticities of adjacent atoms. The energy associated with the formation of a complex is calculated with respect to its fragments, assumed either isolated or solvated. The results emphasize the stabilizing role of a large delocalization of the positive charge transferred to the hydrocarbons. This delocalization extends to the hydrocarbon regions not directly in contact with palladium and highlights the importance of these “inactive” regions in complexes made from diphenyl polyenes or polycyclic aromatic hydrocarbons. Finally, the bonding pattern deduced from calculations has been utilized to consider the feasibility of novel sandwich architectures, whose computed energy balance eventually proves similar to that of already existing compounds.

First author: Bickelhaupt, F. Matthias, Table salt and other alkali metal chloride oligomers: Structure, stability, and bonding, INORGANIC CHEMISTRY, 46, 5411, (2007)
Abstract: We have investigated table salt and other alkali metal chloride monomers, ClM, and (distorted) cubic tetramers, (ClM)(4), with M = Li, Na, K, and Rb, using density functional theory (DFT) at the BP86/TZ2P level. Our objectives are to determine how the structure and thermochemistry (e.g., Cl-M bond lengths and strengths, oligomerization energies, etc.) of alkali metal chlorides depend on the metal atom and to understand the emerging trends in terms of quantitative Kohn-Sham molecular orbital (KS-MO) theory. The analyses confirm the high polarity of the Cl-M bond (dipole moment, VDD, and Hirshfeld atomic charges). They also reveal that bond overlap derived stabilization (approximately -26, -20, and -8 kcal/mol), although clearly larger than in the corresponding F-M bonds, contributes relatively little to the (trend in) bond strengths (-105, -90, and -94 kcal/mol) along M = Li, Na, and K. Thus, the Cl-M bonding mechanism resembles more closely that of the even more ionic F-M bond than that of the more covalent C-M or H-M bonds. Tetramerization causes the Cl-M bond to expand, and it reduces its polarity.

First author: Jacob, Christoph R., Exact functional derivative of the nonadditive kinetic-energy bifunctional in the long-distance limit, JOURNAL OF CHEMICAL PHYSICS, 126, 5411, (2007)
Abstract: We have investigated the functional derivative of the nonadditive kinetic-energy bifunctional, which appears in the embedding potential that is used in the frozen-density embedding formalism, in the limit that the separation of the subsystems is large. We have derived an exact expression for this kinetic-energy component of the embedding potential and have applied this expression to deduce its exact form in this limit. Comparing to the approximations currently in use, we find that while these approximations are correct at the nonfrozen subsystem, they fail completely at the frozen subsystem. Using test calculations on two model systems, a H2O center dot Li+ complex and a cluster of aminocoumarin C151 surrounded by 30 water molecules, we show that this failure leads to a wrong description of unoccupied orbitals, which can lead to convergence problems caused by too low-lying unoccupied orbitals and which can further have serious consequences for the calculation of response properties. Based on our results, a simple correction is proposed, and we show that this correction is able to fix the observed problems for the model systems studied.

First author: Casarin, Maurizio, Spin-orbit relativistic time-dependent density functional calculations of the metal and ligand pre-edge XAS intensities of organotitanium complexes: TiCl4, Ti(eta(5)-C5H5)Cl-3, and Ti(eta(5)-C5H5)(2)Cl-2,JOURNAL OF PHYSICAL CHEMISTRY A, 111, 5270, (2007)
Abstract: Time-dependent density functional theory (TDDFT) coupled to the relativistic two-component zeroth-order regular approximation, both available in the last version of the ADF package, have been successfully used to simulate X-ray absorption spectra of TiCl4, Ti(eta(5)-C5H5)Cl-3, and Ti(eta(5)-C5H5)(2)Cl-2 in terms of their oscillator strength distributions. Besides allowing a first principle assignment of Ti 1s, Cl 1s, and Ti 2p (L-2,L-3 edges) core excitation spectra, theoretical outcomes provide a rationale for deviations from the expected L-3/L-2 branching ratio.

First author: Wang, Jun-Jieh, Synthesis of structural analogues of the oxidized sites in the xanthine oxidoreductase enzyme family, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 129, 7512, (2007)
Abstract: The oxidized active site of members of the xanthine oxidoreductase enzyme family consists of a pyranopterindithiolene ligand chelated to square pyramidal (SP) Mo(VI) with an apical oxo ligand and basal sulfido and oxo or hydroxo ligands. The first structural analogues of this sites have been synthesized and structurally characterized as [(WO2S)-O-VI (bdt)](2-) for the unprotonated site and [(WOS)-O-VI(OSiPr3i)(bdt)](1-) for the protonated site in which the silyloxide simulates protonation. Complexes were isolated as Et4N+ salts. The bdt and sulfido ligands occupy basal positions. In addition, (Et4N)(2)[(WOS2)-O-VI(S2C2Me2)] was prepared. Density functional theory calculations predict small structural preferences (< 1 kcal/mol) for SP structures with basal versus apical sulfido ligands and for SP versus trigonal bipyramidal (TBP) structures (< 2 kcal/mol). In the crystalline state, [(WOS2)-O-VI(S2C2Me2)](2-) occurs in both (distorted) SP and TBP configurations, presumably stabilized by weak lattice forces (bdt = benzene-1,2-dithiolate(2-)).

First author: Atesin, Tulay A., Experimental and theoretical examination of C-CN and C-H bond activations of acetonitrile using zerovalent nickel, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 129, 7562, (2007)
Abstract: Experimental and density functional theory show that the reaction of acetonitrile with a zerovalent nickel bis(dialkylphosphino)ethane fragment (alkyl = methyl, isopropyl) proceeds via initial exothermic formation of an eta(2)-nitrile complex. Three well-defined transition states have been found on the potential energy surface between the eta(2)-nitrile complex and the activation products. The lowest energy transition state is an eta(3)-acetonitrile complex, which connects the eta(2)-nitrile to a higher energy eta(3)-acetonitrile intermediate with an agostic C-H bond, while the other two lead to cleavage of either the C-H or the C-CN bonds. Gas-phase calculations show C-CN bond activation to be endothermic, which contradicts the observation of thermal C-CN activation in THF. Therefore, the effect of solvent was taken into consideration by using the polarizable continuum model (PCM), whereupon the activation of the C-CN bond was found to be exothermic. Furthermore the C-CN bond activation was found to be favored exclusively over C-H bond activation due to the strong thermodynamic driving force and slightly lower kinetic barrier.

First author: Krapp, Andreas, Transition metal-carbon complexes. A theoretical study, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 129, 7596, (2007)
Abstract: The equilibrium geometries and bond dissociation energies of 16VE and 18VE complexes of ruthenium and iron with a naked carbon ligand are reported using density functional theory at the BP86/TZ2P level. Bond energies were also calculated at CCSD(T) using TZ2P quality basis sets. The calculations of [Cl-2(PMe3)(2)Ru(C)] (1Ru), [Cl-2(PMe3)(2)Fe(C)] (1Fe), [(CO)(2)(PMe3)(2)Ru(C)] (2Ru), [(CO)(2)(PMe3)(2)Fe(C)] (2Fe), [(CO)(4)Ru(C)] (3Ru), and [(CO)(4)Fe(C)] (3Fe) show that 1Ru has a very strong Ru-C bond which is stronger than the Fe-C bond in 1Fe. The metal-carbon bonds in the 18VE complexes 2Ru-3Fe are weaker than those in the 16VE species. Calculations of the related carbonyl complexes [(PMe3)(2)Cl2Ru(CO)] (4Ru), [(PMe3)(2)Cl2Fe(CO)] (4Fe), [(PMe3)(2)Ru(CO)(3)] (5Ru), [(PMe3)(2)Fe(CO)(3)] (5Fe), [Ru(CO)(5)] (6Ru), and [Fe(CO)(5)] (6Fe) show that the metal-CO bonds are much weaker than the metal-C bonds. The 18VE iron complexes have a larger BDE than the 18VE ruthenium complexes, while the opposite trend is calculated for the 16VE compounds. Charge and energy decomposition analyses (EDA) have been carried out for the calculated compounds. The Ru-C and Fe-C bonds in 1Ru and 1Fe are best described in terms of two electron-sharing bonds with sigma and pi symmetry and one donor-acceptor pi bond. The bonding situation in the 18 VE complexes 2Ru-3Fe is better described in terms of closed shell donor-acceptor interactions in accordance with the Dewar-Chatt-Duncanson model. The bonding analysis clearly shows that the 16VE carbon complexes 1Ru and 1Fe are much more strongly stabilized by metal-C sigma interactions than the 18VE complexes which is probably the reason why the substituted homologue of 1Ru could become isolated. The EDA calculations show that the nature of the TM-C and TM-CO binding interactions resembles each other. The absolute values for the energy terms which contribute to Delta E-int are much larger for the carbon complexes than for the carbonyl complexes, but the relative strengths of the energy terms are not very different from each other. The pi bonding contribution to the orbital interactions in the carbon complexes is always stronger than sigma bonding. There is no particular bonding component which is responsible for the reversal of the relative bond dissociation energies of the Ru and Fe complexes when one goes from the 16VE complexes to the 18VE species. That the 18 VE compounds have longer and weaker TM-C and TM-CO bonds than the respective 16 VE compounds holds for all complexes. This is because the LUMO in the 16 VE species is a sigma-antibonding orbital which becomes occupied in the 18 VE species.

First author: Zhao, Jing, Interaction of plasmon and molecular resonances for rhodamine 6G adsorbed on silver nanoparticles, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 129, 7647, (2007)
Abstract: Localized surface plasmon resonance (LSPR) is a key optical property of metallic nanoparticles. The peak position of the LSPR for noble-metal nanoparticles is highly dependent upon the refractive index of the surrounding media and has therefore been used for chemical and biological sensing. In this work, we explore the influence of resonant adsorbates on the LSPR of bare Ag nanoparticles (lambda(max,bare)). Specifically, we study the effect of rhodamine 6G (R6G) adsorption on the nanoparticle plasmon resonance because of its importance in single-molecule surface-enhanced Raman spectroscopy (SMSERS). Understanding the coupling between the R6G molecular resonances and the nanoparticle plasmon resonances will provide further insights into the role of LSPR and molecular resonance in SMSERS. By tuning lambda(max,bare) through the visible wavelength region, the wavelength-dependent LSPR response of the Ag nanoparticles to R6G binding was monitored. Furthermore, the electronic transitions of R6G on Ag surface were studied by measuring the surface absorption spectrum of R6G on an Ag film. Surprisingly, three LSPR shift maxima are found, whereas the R6G absorption spectrum shows only two absorption features. Deconvolution of the R6G surface absorption spectra at different R6G concentrations indicates that R6G forms dimers on the metal surface. An electromagnetic model based on quasi-static (Gans) theory reveals that the LSPR shift features are associated with the absorption of R6G monomer and dimers. Electronic structure calculations of R6G under various conditions were performed to study the origin of the LSPR shift features. These calculations support the view that the R6G dimer formation is the most plausible cause for the complicated LSPR response. These findings show the extreme sensitivity of LSPR in elucidating the detailed electronic structure of a resonant adsorbate.

First author: Balazs, Gabor, Cerium(III) and cerium(IV) bis(eta(8)-pentalene) sandwich complexes: Synthetic, structural, spectroscopic, and theoretical studies, ORGANOMETALLICS, 26, 3111, (2007)
Abstract: The Ce(III) anionic bis(pentalene) sandwich complex K[Ce{C8H4((SiPr3)-Pr-i-1,4)(2)}(2)] (1) has been prepared by treatment of CeCl3 with K-2[C8H4((SiPr3)-Pr-i-1,4)(2)] and crystallographically characterized as its 18-crown-6 complex. Oxidation of 1 with Ag[BPh4] affords the neutral, formally Ce(IV) sandwich complex [Ce{C8H4((SiPr3)-Pr-i-1,4)(2)}(2)] (2), whose molecular structure has also been determined. The electronic structure of 2 has been investigated in detail by a combination of magnetic studies, K-edge XANES measurements, gas-phase photoelectron spectroscopy, and density functional calculations.

First author: Marashdeh, Ali, NaAlH4 clusters with two titanium atoms added, JOURNAL OF PHYSICAL CHEMISTRY C,111, 8206, (2007)
Abstract: We present density functional theory calculations on a NaAlH4 cluster with two titanium atoms added. The two titanium atoms were adsorbed on the (001) surface of NaAlH4 as a Ti dimer or as two separate atoms. Various absorption sites inside the cluster were investigated, either by placing the Ti atoms in interstitial sites or by exchanging them with Na and Al atoms. The results imply that Ti is more stable in the subsurface region of the cluster than on the surface and that exchange with Na is preferred. Almost equally stable is the exchange with one Na and one Al, as long as the resulting structure contains a direct Ti-Ti bond. The calculations also show that when considering adsorption on the surface only, Ti prefers to adsorb as atomic Ti rather than as a Ti-2. In this case, the Ti atoms adsorb above Na sites, with the Na atoms being displaced toward the subsurface region. A zipper model is proposed for explaining the enhanced kinetics due to Ti.

First author: Gu, Xiao, Au-34(-): A fluxional core-shell cluster, JOURNAL OF PHYSICAL CHEMISTRY C, 111, 8228, (2007)
Abstract: Among the large Au-n(-) clusters for n > 20, the photoelectron spectra of Au-34(-) exhibit the largest energy gap (0.94 eV) with well-resolved spectral features, making it a good candidate for structural consideration in conjunction with theoretical studies. Extensive structural searches at several levels of density functional and ab initio theory revealed that the low-lying isomers of Au-34(-) can be characterized as fluxional core-shell type structures with 4 or 3 inner atoms and 30 or 31 outer atoms, i.e., Au-4@Au-30(-) and Au-3@Au-31(-), respectively. Detailed comparisons between theoretical and photoelectron results suggest that the most probable ground state structures of Au-34(-) are of the Au-4@Au-30(-) type. The 30 outer atoms seem to be disordered or fluxional, giving rise to a number of low-lying isomers with very close energies and simulated photoelectron spectra. The fluxional nature of the outer layer in large gold clusters or nanoparticles may have important implications for their remarkable catalytic activities.

First author: Brown, Christina D., VTVH-MCD and DFT studies of thiolate bonding to {FeNO}(7)/{FeO2}(8) complexes of isopenicillin N synthase: Substrate determination of oxidase versus oxygenase activity in nonheme Fe enzymes,JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 129, 7427, (2007)
Abstract: Isopenicillin N synthase (IPNS) is a unique mononuclear nonheme Fe enzyme that catalyzes the four-electron oxidative double ring closure of its substrate ACV. A combination of spectroscopic techniques including EPR, absorbance, circular dichroism (CD), magnetic CD, and variable-temperature, variable-field MCD (VTVH-MCD) were used to evaluate the geometric and electronic structure of the {FeNO}(7) complex of IPNS coordinated with the ACV thiolate ligand. Density Function Theory (DFT) calculations correlated to the spectroscopic data were used to generate an experimentally calibrated bonding description of the Fe-IPNS-ACV-NO complex. New spectroscopic features introduced by the binding of the ACV thiolate at 13 100 and 19 800 cm(-1) are assigned as the NO pi*(ip) -> Fe d(x)2(-y)2 and S pi -> Fe d(x)2(-y)2 charge transfer (CT) transitions, respectively. Configuration interaction mixes S CT character into the NO pi*(ip) -> Fe d(x)2(-y)2 CT transition, which is observed experimentally from the VTVH-MCD data from this transition. Calculations on the hypothetical {FeO2}(8) complex of Fe-IPNS-ACV reveal that the configuration interaction present in the {FeNO}(7) complex results in an unoccupied frontier molecular orbital (FMO) with correct orientation and distal O character for H-atom abstraction from the ACV substrate. The energetics of NO/O-2 binding to Fe-IPNS-ACV were evaluated and demonstrate that charge donation from the ACV thiolate ligand renders the formation of the Fe-III-superoxide complex energetically favorable, driving the reaction at the Fe center. This single center reaction allows IPNS to avoid the O-2 bridged binding generally invoked in other nonheme Fe enzymes that leads to oxygen insertion (i.e., oxygenase function) and determines the oxidase activity of IPNS.

First author: Dey, Abhishek, Sulfur K-edge XAS and DFT studies on Ni-II complexes with oxidized thiolate ligands: Implications for the roles of oxidized thiolates in the active sites of Fe and Co nitrile hydratase, INORGANIC CHEMISTRY,46, 4989, (2007)
Abstract: S K-edge X-ray absorption spectroscopy data on a series of Ni-II complexes with thiolate (RS-) and oxidized thiolate (RSO2-) ligands are used to quantify Ni-S bond covalency and its change upon ligand oxidation. Analyses of these results using geometry-optimized density functional theory (DFT) calculations suggest that the Ni-S sigma bonds do not weaken on ligand oxidation. Molecular orbital analysis indicates that these oxidized thiolate ligands use filled high-lying S-O pi* orbitals for strong sigma donation. However, the RSO2- ligands are poor pi donors, as the orbital required for pi interaction is used in the S-O sigma-bond formation. The oxidation of the thiolate reduces the repulsion between electrons in the filled Ni t(2) orbital and the thiolate out-of-plane pi-donor orbital leading to shorter Ni-S bond length relative to that of the thiolate donor. The insights obtained from these results are relevant to the active sites of Fe- and Co-type nitrile hydratases (Nhase) that also have oxidized thiolate ligands. DFT calculations on models of the active site indicate that whereas the oxidation of these thiolates has a major effect in the axial ligand-binding affinity of the Fe-type Nhase (where there is both sigma and pi donation from the S ligands), it has only a limited effect on the sixth-ligand-binding affinity of the Co-type Nhases (where there is only sigma donation). These oxidized residues may also play a role in substrate binding and proton shuttling at the active site.

First author: Santhanamoorthi, N., Theoretical investigation on intramolecular electron transfer in polypeptides,CHEMICAL PHYSICS LETTERS, 440, 302, (2007)
Abstract: Theoretical investigations on the intramolecular electron transfer between the intermediate residues of different secondary structures of an oligopeptide have been carried out. Density functional theory calculations have been performed to calculate the charge transfer integral, spatial overlap integral and site-energies for the optimized secondary structures of the glycine oligopeptide by varying the dihedral angles (phi and psi) along the alpha-carbon atom of amino acid subgroups. The reorganization energy has been calculated in the presence of an excess negative charge. The electron transfer rates for the model peptide have been estimated and the dependence of the rate on secondary structures is discussed.

First author: Zhang, Junfeng, Which configuration is more stable for La-2@C-80, D-3d or D-2h? Recomputation with ZORA methods within ADF, JOURNAL OF PHYSICAL CHEMISTRY C, 111, 7862, (2007)
Abstract: Geometry optimization and frequency analysis were performed for a La-2@C-80 molecule using the Amsterdam density functional (ADF) package. The relativistic effects are taken into account by the zero-order regular approximation (ZORA) basis sets. Interestingly, we found that the D-2h configuration is the global minimum in total energy, being about 1 kcal/mol lower than the D-3d configuration, which has been recently considered to be the most stable by Shimotani et al. On the basis of calculations, a new La-2 pair motion scenario is proposed, in which the two La ions passing through saddle-point C-2h, travel between equivalent D-2h configurations. The motion of these La ions forms a pentagonal-dodecahedral path just like the pattern of La-2 MEM charge density in the I-h C-80 cage. In addition, the calculated Raman spectrum on low-frequency metal-cage vibrations is also in good agreement with the experimental results.

First author: de Jong, G. Theodoor, Transition-state energy and position along the reaction coordinate in an extended activation strain model, CHEMPHYSCHEM, 8, 1170, (2007)
Abstract: We investigate polladium-induced activation of the C-H, C-C, C-F, and C-Cl bonds in methane, ethane, cyclopropone, fluoromethane, and chloromethane, using relativistic density functional theory (DFT) at ZORA-BLYP/TZ2P Our purpose is to arrive at a qualitative understanding, based on accurate calculations, of the trends in activation barriers and transition state (TS) geometries (e.g. early or late along the reaction coordinate) in terms of the reactants’ properties. To this end, we extend the activation strain model (in which the activation energy Delta E-not equal is decomposed into the activation strain Delta E-strain(not equal) of the reactants and the stabilizing TS interaction Delta E-int(not equal) between the reactants) from a single-point analysis of the TS to an analysis along the reaction coordinate xi, that is, Delta E(xi)=Delta E-strain(xi)+Delta E-int(xi). This extension enables us to understand qualitatively, trends in the position of the TS along xi and, therefore, the values of the activation strain Delta E-strain(not equal)=Delta Estrain(xi(TS)) and TS interaction Delta E-int(not equal) = Delta E-int(xi(TS)) and trends there-in. An interesting insight that emerges is that the much higher barrier of metal-mediated C-C versus C-H activation originates from steric shielding of the C-C bond in ethane by C-H bonds. Thus, before a favorable stabilizing interaction with the C-C bond can occur, the C-H bonds must be bent away, which causes the metal-substrate interaction Delta E-int(xi) in C-C activation to lag behind. Such steric shielding is not present in the metal-mediated activation of the C-H bond, which is always accessible from the hydrogen side. Other phenomena that are addressed are anion assistance, competition between direct oxidative insertion (Oxln) versus the alternative S(N)2 pathway, and the effect of ring strain.

First author: Balazs, Gabor, Electronic structure of linearly coordinated EQ complexes of the type [(N3N)W(EQ)] [N3N=N(CH2CH2NSiMe3)(3); E=P, As, Sb, Bi; Q = O, S, Se, Te]: A DFT study, EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 8, 2443, (2007)
Abstract: Density functional theory (DFT) calculations were carried out on the terminal EQ complexes [(N3N)W(EQ)] {N3N = N(CH2CH2NSiMe3)(3); E = P, As, Sb, Bi; Q = O, S, Se Tel} to clarify the bonding situation within the linear N-ax-W-E-Q core. This unusual structural motif gives rise to a bonding arrangement in which the pi-electron density is delocalised over the three atoms of the W-E-Q unit. Fragment calculations and natural bond order (NBO) data indicated that the a-bonding component of the N-ax-W-E-Q unit comprises two occupied a orbitals, while the pi component of bonding comprises two sets of degenerate pi orbitals. In general, the pi orbitals of the N-ax-W-E-Q core are higher in energy compared to the a orbitals. The phosphorus monoxide (EQ = PO) complexes provide an exception to this rule, with the lit orbitals of the W-P-O core lower in energy than the a orbitals. Generally, as the atomic number of either the pnicogen (E) or chalcogen (Q) atom increases the extent of a-orbital delocalisation decreases, whereas the pi-orbital delocalisation increases. Fractional bond orders and Wiberg bond indices were used to establish whether localisation of the pi-electron density gives rise to a W-E or an E-Q double or triple bond. Both methods indicate a W-E as well as an E-Q double bond. The ionic nature of the complexes were analysed by inspection of the Hirschfeld charge distribution which shows only a moderate ionic character. Exceptions are the pnicogen monoxide complexes, which are more ionic.

First author: Bonifacio, Alois, Altered spin state equilibrium in the T309V mutant of cytochrome P450 2D6: a spectroscopic and computational study, JOURNAL OF BIOLOGICAL INORGANIC CHEMISTRY, 12, 645, (2007)
Abstract: Cytochrome P450 2D6 (CYP2D6) is one of the most important cytochromes P450 in humans. Resonance Raman data from the T309V mutant of CYP2D6 show that the substitution of the conserved I-helix threonine situated in the enzyme’s active site perturbs the heme spin equilibrium in favor of the six-coordinated low-spin species. A mechanistic hypothesis is introduced to explain the experimental observations, and its compatibility with the available structural and spectroscopic data is tested using quantum-mechanical density functional theory calculations on active-site models for both the CYP2D6 wild type and the T309V mutant.

First author: Orian, Laura, A DFT investigation of the structural and electronic properties of Co(I) and Rh(I) half-sandwich complexes with heteroaromatic pi ligands, REVUE ROUMAINE DE CHIMIE, 52, 551, (2007)
Abstract: Co(I) and Rh(I) half-sandwich complexes of the heteroaromatic 1,2-azaborolyl and 3a,7a-azaborindenyl anions with the ancillary ligand COD (1,5-cycloctadiene) are designed by using accurate state-of-the-art Density Functional Theory (DFT) calculations. Their structural and electronic properties are compared to those of the analogous compounds containing the classic hydrocarbon isoelectronic ligands, i.e. cyclopentadienyl and indenyl anions. A comparison is made between the catalytic ability of (eta(5)-C5H5)-Co and (1,2-azaborolyl)-Co fragments toward alkyne [2+2+2] cyclizations, a class of reactions of paramount importance in industrial and pharmaceutical research for the synthesis of substituted benzenes, polycyclic and heterocyclic compounds, by theoretically addressing the fundamental mechanistic steps.

First author: Jalilehvand, Farideh, Structural characterization of Molybdenum(V) species in aqueous HCl solutions,INORGANIC CHEMISTRY, 46, 4430, (2007)
Abstract: Mo(V) aqua-chloro complexes in hydrochloric acid solutions have been studied by means of Mo K- and L-2,L-3-edge X-ray absorption and Raman spectroscopic methods. The solid compounds (HPPh3)(2)[MoOCl5] (1), 6[MoOCl4(H2O)](-)center dot 10(pyH)(+)center dot 4Cl(-) (2), and (pyH)(2)[Mo2O4Cl4(trans-OH2)(2)] (3) were used for structural comparisons. The compound 2 crystallizes in the orthorhombic space group Pmma (no. 51) with a = 21.398(3), b = 8.057(4), c = 13.330(4) A, and Z = 4. In 0.2 M solutions of MoCl5 in 7.4-9.4 M HCl the mononuclear [MoOCl4(OH2)](-) complex dominates with the bond distances MoO 1.66(2) A, Mo-Cl 2.38(2) A, and Mo-OH2 2.30(2) A. Its Raman band at 994 cm(-1) for the MoO symmetric stretching vibration is closer to that of 2 (988 cm(-1)) than of 1 (969 cm(-1)). The Mo K-edge EXAFS spectrum for 0.2 M MoCl5 in 1.7 M HCl solution reveals a dinuclear [Mo2O4Cl6-n(OH2)(n)](n-4) (n = 2, 3) complex with a double oxygen bridge and the average distances MoO 1.67(2) A, Mo-(mu-O) 1.93(2) A, Mo-Cl 2.47(3) A, Mo-Mo 2.56(2) A, and a short Mo-OH2 distance of 2.15(2) A, which implies that at least one of the aqua ligands is in equatorial position relative to the two axial MoO bonds. This position differs from the Mo-OH2 configuration exclusively trans to the MO groups of the isomeric (with n = 2) dinuclear complex in 3. The difference in the ligand field is also reflected in their L-2,L-3-edge XANES spectra. For 0.2 M MoCl5 solutions in intermediate HCl concentrations (3.7-6.3 M) the Raman bands at 802 cm(-1) (Mo-O-Mo) and 738 cm(-1) (Mo-(mu-O)(2)-Mo) verify three coexisting classes of Mo(V) complexes: mononuclear complexes together with dinuclear mono-oxo (e.g., [Mo2O3Cl6(H2O)(2)](2-)) and dioxo bridged species, even though principal component analysis (PCA) of the corresponding series of EXAFS spectra only could distinguish two major components. By fitting linear combinations of the appropriate EXAFS oscillation components, dioxo-bridged dinuclear complexes were found to dominate at HCl concentrations <= 4.5 M, a conclusion supported by the Mo L-2,L-3-edge XANES spectra.

First author: Maliarik, Mikhail, Metal-metal bonding in tetracyanometalates (M = Pt-II, Pd-II, Ni-II) of monovalent thallium. Crystallographic and spectroscopic characterization of the new compounds Tl2Ni(CN)(4) and Tl2Pd(CN)(4), INORGANIC CHEMISTRY, 46, 4642, (2007)
Abstract: The new crystalline compounds Tl2Ni(CN)(4) and Tl2Pd(CN)(4) were synthesized by several procedures. The structures of the compounds were determined by single-crystal X-ray diffraction. The compounds are isostructural with the previously reported platinum analogue, Tl2Pt(CN)(4). A new synthetic route to the latter compound is also suggested. In contrast to the usual infinite columnar stacking of [M(CN)(4)](2-) ions with short intrachain M-M separations, characteristic of salts of tetracyanometalates of Ni-II, Pd-II, and Pt-II, the structure of the thallium compounds is noncolumnar with the two Tl-I ions occupying axial vertices of a distorted pseudo-octahedron of the transition metal, [MTl2C4]. The Tl-M distances in the compounds are 3.0560(6), 3.1733(7), and 3.140(1) A for Ni-II, Pd-II, and Pt-II, respectively. The short Tl-Ni distance in Tl2Ni(CN)(4) is the first example of metal-metal bonding between these two metals. The strength of the metal-metal bonds in this series of compounds was assessed by means of vibrational spectroscopy. Rigorous calculations, performed on the molecules in D-4h point group symmetry, provide force constants for the Tl-M stretching vibration constants of 146.2, 139.6, and 156.2 N/m for the Ni-II, Pd-II, and Pt-II compounds, respectively, showing the strongest metal-metal bonding in the case of the Tl-Pt compound. Amsterdam density-functional calculations for isolated Tl2M(CN)(4) molecules give Tl-M geometry-optimized distances of 2.67, 2.80, and 2.84 A for M = Ni-II, Pd-II, and Pt-II, respectively. These distances are all substantially shorter than the experimental values, most likely because of intermolecular Tl-N interactions in the solid compounds. Time-dependent density-functional theory calculations reveal a low-energy, allowed transition in all three compounds that involves excitation from an a(1g) orbital of mixed Tl 6p(z)-M nd(z)(2) character to an a(2u) orbital of dominant Tl 6p(z) character.

First author: Pierloot, Kristine, Electronic spectrum of UO22+ and [UO2Cl4](2-) calculated with time-dependent density functional theory, JOURNAL OF CHEMICAL PHYSICS, 126, 4642, (2007)
Abstract: The electronic spectra of UO22+ and [UO2Cl4](2-) are calculated with a recently proposed relativistic time-dependent density functional theory method based on the two-component zeroth-order regular approximation for the inclusion of spin-orbit coupling and a noncollinear exchange-correlation functional. All excitations out of the bonding sigma(+)(u) orbital into the nonbonding delta(u) or phi(u) orbitals for UO22+ and the corresponding excitations for [UO2Cl4](2-) are considered. Scalar relativistic vertical excitation energies are compared to values from previous calculations with the CASPT2 method. Two-component adiabatic excitation energies, U-O equilibrium distances, and symmetric stretching frequencies are compared to CASPT2 and combined configuration-interaction and spin-orbit coupling results, as well as to experimental data. The composition of the excited states in terms of the spin-orbit free states is analyzed. The results point to a significant effect of the chlorine ligands on the electronic spectrum, thereby confirming the CASPT2 results: The excitation energies are shifted and a different luminescent state is found.

First author: Yalovega, Galina, Cd-metallothionein: Analysis of local atomic structure, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 575, 162, (2007)
Abstract: Cadmium-metallothioneins (Cd-MT) are small proteins containing seven cadmium atoms in a tetrahedral arrangement of sulfur atoms. Comparison of experimental X-ray absorption fine structure (XAFS) with theoretical full multiple-scattering XAFS spectra have been used as a tool for verification of the structural models generated using both available experimental NMR data and theoretical simulations on the basis of molecule mechanics/molecular dynamics (MM/MD) and density functional theory (DFT).

First author: Hulsman, Niels, Chemical insights in the concept of hybrid drugs: The antitumor effect of nitric oxide-donating aspirin involves a quinone methide but not nitric oxide nor aspirin, JOURNAL OF MEDICINAL CHEMISTRY, 50, 2424, (2007)
Abstract: Hybrid drug 1 (NO-ASA) continues to attract intense research from chemists and biologists alike. It consists of ASA and a -ONO2 group connected through a spacer and is in preclinical development as an antitumor drug. We report that, contrary to current beliefs, neither ASA nor NO contributes to this antitumor effect. Rather, an unsubstituted QM was identified as the sole cytotoxic agent. QM forms from 1 after carboxylic ester hydrolysis and, in accordance with the HSAB theory, selectively reacts with cellular GSH, which in turn triggers cell death. Remarkably, a derivative lacking ASA and the -ONO2 group is 10 times more effective than 1. Thus, our data provide a conclusive molecular mechanism for the antitumor activity of 1. Equally importantly, we show for the first time that a “presumed invisible” linker in a hybrid drug is not so invisible after all and is in fact solely responsible for the biological effect.

First author: Groenhof, Andre R., Proton assisted oxygen-oxygen bond splitting in cytochrome p450, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 129, 6204, (2007)
Abstract: Proton assisted O-O bond splitting of cytochromes’ P450 hydroperoxo Compound 0 has been investigated by density functional theory, showing a barrier for the slightly endothermic formation of the iron-oxo Compound 1. The barrier and the endothermicity increase with decreasing acidity of the distal proton source. Protonation of the proximal iron heme ligand favors the O-O bond scission and provides an important regulatory component in the catalytic cycle. The Compound 0 -> 1 conversion is slightly exothermic for the peroxidase and catalase models. Implications of the energetic relationship between the two reactive intermediates are discussed in terms of possible oxidative pathways.

First author: Donzello, Maria Pia, Tetrakis(thiadiazole)porphyrazines. 5. Electrochemical and DFT/TDDFT studies of the free-base macrocycle and its Mg-II, Zn-II, and Cu-II complexes, INORGANIC CHEMISTRY, 46, 4145, (2007)
Abstract: The redox properties of the phthalocyanine-like tetrakis(thiadiazole)porphyrazines, [TTDPzM] (M = Mg-II(H2O), Zn-II, Cu-II, 2H(I)), were investigated by cyclic voltammetry, and their ground- and excited-state electronic properties were studied in detail by density functional theory (DFT) and time-dependent DFT (TDDFT) methods. Bulk and specific (axial ligation) solvent effects on the molecular and electronic structure were also taken into account. The title compounds show stepwise reversible ligand-centered one-electron reductions in the range 0 to -2.0 V vs SCE, with E-1/2 values being systematically less negative than corresponding reduction potentials for the same processes of the phthalocyanine (Pc) analogues. No electroxidations were observed at positive potentials. The observed redox behavior is rationalized on the basis of the ground-state electronic structures which reveal that replacement of the benzo rings of the Pc macrocycle by electron-withdrawing thiadiazole rings induces a large stabilization of both the HOMO and LUMOs in the investigated macrocycles. An excellent correlation is found between the first one-electron reduction potentials and the gas-phase LUMO energies along the series. The same sequence in the first reduction potentials is theoretically reproduced in pyridine, even if the Zn-II and Mg-II complexes are assumed to be in the axially ligated form, [TTDPzM(py)]. TDDFT calculations of the lowest excited states of the Zn-II, Mg-II, and Cu-II complexes in pyridine provide an accurate description of their UV-visible spectra. The calculated optical spectra for the free-base macrocycle in chlorobenzene and pyridine confirm previous data in that the thiadiazoleporphyrazine [TTDPzH(2)] is mostly present in pyridine in its deprotonated form [TTDPz](2-). DFT results, in keeping with electrochemical data, indicate, however, that in pyridine it is the neutral species [TTDPzH(2)] being reduced instead of its deprotonated form [TTDPz](2-).

First author: Srinivas, Kola, Enhanced diradical nature in oxyallyl derivatives leads to near infra red absorption: A comparative study of the squaraine and croconate dyes using computational techniques, JOURNAL OF PHYSICAL CHEMISTRY A, 111, 3378, (2007)
Abstract: We apply many criteria to estimate the diradical character of the ground state singlets of several oxyallyl derivatives. This is carried out as the oxyallyl derivatives like squaraine and croconate dyes can be represented by both mesoionic and diradical formulas, the domination of which would characterize its lowest energy transition. One criterion applied is the singlet-triplet gap, which is known to be inversely proportional to the diradical character. Another criterion is the occupation number; this is determined for the symmetry broken state of the molecules in the unrestricted formalism, and the difference of occupation in the HOMO and LUMO is related to the diradical character. The diradical character of all of the croconates and few squaraines is estimated to be large. All of these have absorption above 750 nm and can be classified as near infrared (NIR) dyes, leading to the inference that NIR absorptions in these molecules are largely due to the dominance of the diradical character. To understand the reliability of the DFT methods for the absorption property predictions of these molecules, TD-DFT studies to calculate the vertical excitation energies have been carried out, using the B3LYP/ BLYP exchange correlation functionals and the LB94 asymptotic functional with and without the inclusion of solvent. The deviations, in both the squaraine series (average lower diradical character), are found to be systematic, and with the inclusion of the solvent in the calculation, the deviations decrease. The best least-squares fit with the experimentally observed values using B3LYP /6-311G(d, p) for the symmetric squaraines yields an R value of 0.92 and, for the unsymmetric squaraines, an R value of 0.936. With inclusion of the solvent, the R value is 0.96 for the symmetric squaraines and 0.961 for the unsymmetric squaraines, indicating that these DFT functionals with linear scaling may be used to study these systems. The croconate dyes, however, have larger deviation from the experimentally observed values in all of the functionals studied even after inclusion of the solvent effects. The deviations are also not systematic. The deviation with respect to the experiment in this case is attributed to the average larger diradical character in this series.

First author: Liao, Meng-Sheng, Interaction of metal porphyrins with fullerene C-60: A new insight, JOURNAL OF PHYSICAL CHEMISTRY B, 111, 4374, (2007)
Abstract: The electronic structure and bonding in the noncovalent, supramolecular complexes of fullerene C-60 with a series of first-row transition metal porphines MP (MFe, Co, Ni, Cu, Zn) have been re-examined with DFT methods. A dispersion correction was made for the C-60-MP binding energy through an empirical method (J. Comput. Chem. 2004, 25, 1463). Several density functionals and two types of basis sets were employed in the calculations. Our calculated results are rather different from those obtained in a recent paper (J. Phys. Chem. A 2005, 109, 3704). The ground state of C-60 center dot FeP is predicted to be high spin (S = 2); the low-spin (S = 0), closed-shell state is even higher in energy than the intermediate-spin (S = 1) state. With only one electron in the Co-d(z)2 orbital, the calculated Co-C-60 distance is in fact rather short, about 0.1 A longer than the Fe-C-60 distance in high-spin C-60 center dot FeP. Double occupation of an M-d(z)2 orbital in MP prevents close association of any axial ligand, and so the Ni-C-60, Cu-C-60, and Zn-C-60 distances are much longer than the Co-C-60 one. The evaluated MP-C-60 binding energies (E-bind) are 0.8 eV (18.5 kcal/mol) for MFe/Co and 0.5 eV (11.5 kcal/mol) for MNi/Cu/Zn (E-bind is about 0.2 eV larger in the case of C-60-MTPP). They are believed to be reliable and accurate based on our dispersion-corrected DFT calculations that included the counterpoise (CP) correction. The effects of the C-60 contact on the redox properties of MP were also examined.

First author: Matovic, Zoran D., Copper(II) complexes with unsymmetrical pentadentate ed3a-type diamino-tricarboxylate ligands. Crystal structures, configurational analysis and DFT study of complexes, INORGANICA CHIMICA ACTA, 360, 2420, (2007)
Abstract: The O-O-N-N-O-type pentadentate ligands H(3)ed3a, H(3)pd3a and H(3)pd3p (H(3)ed3a stands ethylenediamine-N,N,N’-triacetic acid; H3pd3a stands 1,3-propanediamine-N,N,N’-triacetic acid and H3pd3p stands 1,3-propanediamine-N,N,N’-tri-3-propionic acid) and the corresponding novel octahedral or square-planar/trigonal-bipyramidal copper(II) complexes have been prepared and characterized. H(3)ed3a, H(3)pd3a and H(3)pd3p ligands coordinate to copper(II) ion via five donor atoms (three deprotonated carboxylate atoms and two amine nitrogens) affording octahedral in case of ed3a(3-) and intermediate square-pyramidal/trigonal-bipyramidal structure in case of pd3a(3-) and pd3p(3-). A six coordinate, octahedral geometry has been established crystallographically for the [Mg(H2O)(6)][Cu(ed3a) (H2O)](2) center dot 2H(2)O complex and five coordinate square-pyramidal for the [Mg(H2O)(5)Cu(pd3a)][Cu(pd3a)] center dot 2H(2)O. Structural data correlating similar chelate Cu(II) complexes have been used for the better understanding the pathway: octahedral -> square-pyramidal <-> trigonal- bipyramid geometry. An extensive configuration analysis is discussed in relation to information obtained for similar complexes. The infra-red and electronic absorption spectra of the complexes are discussed in comparison with related complexes of known geometries. Molecular mechanics and density functional theory (DFT) programs have been used to model the most stable geometric isomer yielding, at the same time, significant structural data. The results from density functional studies have been compared with X-ray data.

First author: Nagaraja, C. M., Heterolytic activation of H-X (X = H, Si, B, and C) bonds: An experimental and theoretical investigation, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 129, 5587, (2007)
Abstract: The highly electrophilic, coordinatively unsaturated, 16-electron [Ru(P(OH)(3))(dppe)(2)][OTf](2) (dppe = Ph2PCH2CH2PPh2) complex 1 activates the H-H, the Si-H, and the B-H bonds, in H-2(g), EtMe2SiH and Et3SiH, and H3B center dot L (L = PMe3, PPh3), respectively, in a heterolytic fashion. The heterolysis of H-2 involves an eta(2)-H-2 complex (observable at low temperatures), whereas the computations indicate that those of the Si-H and the B-H bonds proceed through unobserved eta(1)-species. The common ruthenium-containing product in these reactions is trans-[Ru(H)(P(OH)(3))(dppe)(2)][OTf], 2. The [Ru(P(OH)(3))(dppe)(2)][OTf](2) complex is unique with regard to activating the H-H, the Si-H, and the B-H bonds in a heterolytic manner. These reactions and the heterolytic activation of the C-H bond in methane by the model complex [Ru(POH)(3))(H2PCH2CH2PH2)(2)][Cl][OTf], 4, have been investigated using computational methods as well, at the B3LYP/LANL2DZ level. While the model complex activates the H-H, the Si-H, and the B-H bonds in H-2, SiH4, and H3B center dot L (L = PMe3, PPh3), respectively, with a low barrier, activation of the C-H bond in CH4 involves a transition state of 57.5 kcal/mol high in energy. The inability of the ruthenium complex to activate CH4 is due to the undue stretching of the C-H bond needed at the transition state, in comparison to the other substrates.

First author: Zhou, Xin, Electronic structures and spectroscopic properties of [Pt(CNMe)(2)(CN)(2)](n) (n=1-4): A theoretical exploration of promising phosphorescent materials, EUROPEAN JOURNAL OF INORGANIC CHEMISTRY,129, 2181, (2007)
Abstract: The structures of [Pt(CNMe)(2)(CN)(2)](n) (n = 1-4) in the ground states (SO) and lowest-energy triplet excited states (T-1) were calculated by using the second-order Moller-Plesset perturbation (MP2) and density functional theory (DFT) methods, respectively. The MP2 results show that the formation of the dimer causes a significant red shift in emission energy, and the frequency calculations reveal that a weak metal-metal interaction exists in the So state, which is greatly enhanced in the 3[f(sigma)center dot p(sigma)] excited state. The aggregation of [Pt(CNMe)(2-)(CN)(2)], (n = 1-4) was explored by using the slate-type VWN functional in the DFT method. The B-3(u)-> Ag-1 transition in the dimer at 509 nm corresponds to the experimental higher-energy emission at 530 nm in CH3CN solution, while the 3A’->(1)A’ transitions in the trimer and tetramer at 557 and 650 rim, respectively, are responsible for the low-energy emission at 584 nm observed experimentally. The analyses of the Wiberg bond indices for the Pt-Pt bond indicate that the dimer may be the most stable form in solution and that the oligomer species (n = 3 and 4) can be treated as a special dimer in which the excess z electron ligand is bonded to the Pt atoms of the central dimer.

First author: Conradie, Jeanet, Electronic structure of trigonal-planar transition-metal-imido complexes: Spin-state energetics, spin-density profiles, and the remarkable performance of the OLYP functional, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 3, 689, (2007)
Abstract: We have carried out a detailed multifunctional density functional theory study of first-row transition-metal (Cr to Cu)beta-diketiminato (“nacnac”) imido and oxo complexes. All the complexes studied exhibit essentially the same d-orbital energy ordering, which is a(1) (d(x)(2)-(2)(z)) <= a(2) (d(xy)) <= a(1) (d(y2)) < b(2) (d(yz)) < b(1) (d(xz)), where the metal-imido vector is identified with the z axis and metal-N3 plane is identified with the xz plane. A curious aspect of this orbital ordering is that the metal dx(2)-z(2) orbital, one of whose lobes points directly at the imido nitrogen, is considerably lower in energy than the d pi orbitals. We have determined that the remarkable stability of the d(o)-type orbitals owes largely to the way these orbitals hybridize or “shape-shift” as a result of the absence of ligands trans or equatorial with respect to the imido (or oxo) group. Of the many functionals examined, OLYP and OPBE, based on the Handy-Cohen OPTX exchange functional, appear to provide the best overall description of the spin-state energetics of the various complexes. In particular, these two functionals predict an S = 3/2 ground state for Fe(III) nacnac imido complexes and an S = 0 ground state for Co( III) nacnac imido complexes, as observed experimentally. In contrast, classic pure functionals such as PW91 predict S = 1/2 ground states or at best equienergetic S = 1/2 and S = 3/2 states for the Fe(III) imido complexes, while hybrid functionals such as B3LYP and O3LYP predict S = 1 or 2 ground states for the Co(III) nacnac imido complexes.

First author: Piquemal, Jean-Philip, Toward a separate reproduction of the contributions to the Hartree-Fock and DFT intermolecular interaction energies by polarizable molecular mechanics with the SIBFA potential, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 3, 824, (2007)
Abstract: Following recent refinements of the SIBFA intermolecular potential to the multipolar electrostatic contribution by inclusion of an explicit ‘penetration’ component, the short-range repulsion term is augmented with a S-2/R-2 component. The SIBFA potential, and the behaviors of its individual contributions encompassing polarization and charge transfer, were evaluated in a diversity of hydrogen-bonded complexes as well as in a model stacked complex by comparisons with results from ab initio quantum-chemical (QC) computations with energy decomposition. Close agreements between SIBFA and QC results are found on both the interaction energies and their contributions. Extensions to computations at the DFT level are also presented.

First author: Stapleton, Russell A., Synthesis of low density poly(ethylene) using nickel iminophosphonamide complexes,MACROMOLECULES, 40, 2993, (2007)
Abstract: Ethylene polymerization using a catalyst derived from the reaction of the phosphorane (Me3Si)(2)NP(NSiMe3)(2) (1) with either Ni(COD)(2) or bis(pi-allyl)Ni complexes affords branched poly(ethylene) (PE) of variable MW (10(3)-10(6)) depending on conditions. The branched PE of high MW is semicrystalline with T-m < 100 degrees C. High field C-13 NMR spectra reveal the presence of methyl branches (ca. 10-15 per 1000 C atoms), branches longer than six C atoms (15-20 per 1000 C atoms) and trace levels of ethyl, propyl, n-butyl, and sec-butyl branches (total < 2 per 1000 C atoms). The branching distribution changes modestly in response to changes in ethylene pressure in a manner consistent with a chain-walking mechanism. Analysis of high MW polymers by GPC-light scattering reveals the presence of sparse long-chain branching (g(M) = 0.78-0.93 with < 1 long-chain branch per molecule); the branched PE formed is thus similar to low-density PE. Addition of alpha-olefin during polymerization leads to enhanced activity but is accompanied by chain transfer. The only evidence of alpha-olefin incorporation is at the chain-ends in the case of 4-methylpentene, and there is little change to the branching distribution in the presence of alpha-olefin. A sterically hindered nickel iminophosphonamide (PN2) complex (Me3Si)(2)NP(Me)(NSiMe3)(2)NiPh(PPh3) (2) was prepared and characterized by X-ray crystallography. This complex oligomerizes ethylene to branched material with a microstructure very similar to that observed using the catalysts derived from phosphorane 1 and Ni(COD)(2) or (pi-allyl)(2)Ni. DFT modeling of the active catalyst, coupled with stochastic simulation of chain growth, reveals that a chain-walking vs insertion mechanism can account for the short-chain branching distributions observed. Kinetic modeling of the observed branching distribution can account for relative intensity of the short branches (<= C-5) as well as those of the longer branches. However, in order to fit the intensity of the Hx(+) branches, one of the key parameters in the model, the probability of chain-walking for higher secondary Ni-R groups, converges to a value similar to 1. This finding is not anticipated by the DFT results and suggests that the longer branches present in these materials do not form by a chain-walking vs insertion mechanism.

First author: Bagno, Alessandro, Computational NMR spectroscopy: reversing the information flow, THEORETICAL CHEMISTRY ACCOUNTS, 117, 603, (2007)
Abstract: Work on computational NMR recently carried out at our Laboratory in Padova is reviewed. We summarize our results concerning the calculation of NMR properties (chemical shifts and spin-spin coupling constants) in a variety of contexts, from the structure elucidation of complex organic molecules or molecules containing heavy atoms to weakly interacting species, such as those involved in hydrogen bonding or van der Waals CH-pi interactions. We also present some original results, viz. the calculated H-1 and C-13 spectra of the putative natural substance nimbosodione, the first examples of calculated Ta-181 chemical shifts, spin-spin couplings in Hg-4(2+) and through-space coupling constants involving Tl-205.

First author: Cinquini, Fabrizio, Theory of oxides surfaces, interfaces and supported nano-clusters, THEORETICAL CHEMISTRY ACCOUNTS, 117, 827, (2007)
Abstract: Oxides surfaces and thin films are finding continuous new technological applications and represent an important class of systems in materials science. Today we assist to a considerable effort to characterize the surfaces and the interfaces of oxide materials at an atomistic level. The intense experimental activity in this field has stimulated a parallel computational activity based on high-quality first principle calculations. In this review we focus our attention on the properties of oxide surfaces, and we describe the main factors that contribute to determine their behaviour: (1) nature of the bonding and electronic structure of the oxide; (2) surface morphology and defectivity; (3) doping and functionalization; (4) redox properties; (5) nano-dimensionality (e.g. in ultra-thin films). We also show how each of these parameters can affect the properties of supported metal atoms and nano-particles.

First author: De Angelis, Filippo, An integrated computational tool for the study of the optical properties of nanoscale devices: application to solar cells and molecular wires, THEORETICAL CHEMISTRY ACCOUNTS, 117, 1093, (2007)
Abstract: We present a combined computational strategy for the study of the optical properties of nanoscale systems, using a combination of codes and techniques based on Density Functional Theory (DFT) and its Time Dependent extension (TDDFT). In particular, we describe the use of Car-Parrinello molecular dynamics simulations for the study of nanoscale devices and show the integration of the obtained results with available quantum chemistry codes for the calculation of TDDFT excitation energies, including solvation effects by continuum solvation models. We review some prototypical applications of this integrated computational strategy, ranging from the interaction of dye sensitizers with TiO2 nanoparticles, of interest in the field of dye-sensitized solar cells, to transition metal molecular wires exceeding 3 nm length.

First author: Cavigliasso, German, Energy decomposition analysis of metal-metal bonding in [M2X8](2-) (X = Cl, Br) complexes of 5f (U, Np, Pu), 5d (W, Re, Os), and 4d (Mo, Tc, Ru) elements, INORGANIC CHEMISTRY, 46, 3557, (2007)
Abstract: The electronic structures of a series of [M2X8](2-) (X = Cl, Br) complexes involving 5f (U, Np, Pu), 5d (W, Re, Os), and 4d (Mo, Tc, Ru) elements have been calculated using density functional theory, and an energy decomposition approach has been used to carry out a detailed analysis of the metal-metal interactions. The energy decomposition analysis involves contributions from orbital interactions (mixing of occupied and unoccupied orbitals), electrostatic effects (Coulombic attraction and repulsion), and Pauli repulsion (associated with four-electron two-orbital interactions). As previously observed for Mo, W, and U M2X6 species, the general results suggest that the overall metal-metal interaction is considerably weaker or unfavorable in the actinide systems relative to the d-block analogues, as a consequence of a significantly more destabilizing contribution from the combined Pauli and electrostatic (prerelaxation) effects. Although the orbital-mixing (postrelaxation) contribution to the total bonding energy is predicted to be larger in the actinide complexes, this is not sufficiently strong to compensate for the comparatively greater destabilization originating from the Pauli-plus-electrostatic effects. A generally weak electrostatic contribution accounts for the large prerelaxation destabilization in the f-block systems, and ultimately for the weak or unfavorable nature of metal-metal bonding between the actinide elements. There is a greater variation in the energy decomposition results across the [M2Cl8](2-) series for the actinide than for the d-block elements, both in the general behavior and in some particular properties.

First author: Li, Hong, First-principles theoretical investigation of the electronic couplings in single crystals of phenanthroline-based organic semiconductors, JOURNAL OF CHEMICAL PHYSICS, 126, 3557, (2007)
Abstract: The electronic couplings between adjacent molecules in the phenanthroline-based bathocuproine (BCP) and bathophenanthroline (Bphen) crystals have been studied using density functional theory on model dimers. Within the frame of the ” two-state model ” of charge-transfer theory, a generalized definition of the ” effective transfer integral ” is proposed. This definition addresses the issue arising when the lowest unoccupied molecular orbital (LUMO) [highest occupied molecular orbital (HOMO)] and LUMO+1 (HOMO-1) of the single molecules both have significant contributions to the dimer LUMO (HOMO) level. Charge-transfer integrals based on the new definition are compared with those from previous models; significant differences are found. The authors’ results indicate that, within a simple Marcus theory approach, the charge-transport parameters of the BCP and Bphen crystals are expected to be similar.

First author: Bach, Marc A., Bimetallic complexes of metallacyclopentynes: cis versus trans and planarity versus nonplanarity, ORGANOMETALLICS, 26, 2149, (2007)
Abstract: Density functional theory calculations show that the Cp2M in cis-dimetallabicycles of metallacyclopentynes, Cp2M[mu-(eta(4):eta(2)-H2C4H2)]M’L-2 (M = Ti, Zr and M’ = Ti, Zr), deviates from the C4 plane. Both the metal fragments deviate from the C4 plane in the nickel complexes of metallacyclopentynes (3Ti-Ni and 3Zr-Ni). The nonplanarity of Ni(PH3)(2) from the C4 plane reduces the antibonding interaction between nickel orbitals and the pi-MO at the C2-C3 bond, whereas that of the Cp2M acts mainly to reduce the antibonding interaction between C1 and C2. The energetics of the isodesmic equations show that the nickel complexes 3Ti-Ni and 3Zr-Ni are more stable than the homodimetallabicycles, 3Zr-Zr and 3Ti-Ti. The electron deficiency on the cis-homodimetallabicycles due to the vacant d-orbital on eta(2)-M’ can be decreased by accepting electrons from a Lewis base or by flipping into trans geometry. This is reflected in the experimental realization of cis-Cp2Zr[mu-(eta(4):eta(2)-H2C4H2)]ZrCp2(PMe3) and the trans geometry for Cp2Ti[mu-(eta(3):eta(3)-H2C4H2)]TiCp2 and Cp2Zr[mu-(eta(3):eta(3)-H2C4H2)]ZrCp2.

First author: Tomasi, Simone, Termination and transfer reactions in the group transfer polymerizations of acrylates catalyzed by mononuclear early d-block and f-block metallocenes: A DFT study, ORGANOMETALLICS, 26, 2157, (2007)
Abstract: The group transfer polymerization (GTP) of acrylates with early d-block and f-block metallocenium ester enolates suffers from side reactions, which cause the process not to be living, with a lack of control of the number-average molecular weight, molecular weight distribution, and tacticity, as well as an incomplete monomer conversion at low catalyst loadings. GTP of acrylates has so far met with limited success, due to the presence of a proton on the alpha-carbon, which provides low steric protection to the enolate in the unwanted backbiting reaction. Furthermore, the proton on the alpha-carbon is relatively acidic and therefore can be transferred. The computational study with the BP86 DFT functional of the backbiting and proton transfer reactions on realistic models for acrylate GTP provides detailed information on the mechanisms and hints on how to tailor the existing catalysts in order to minimize the unwanted side reactions.

First author: Zhu, Hongjuan, Influence of different ligands X- (X = F, Cl, Br, I, NO2, CN) on the rate and mechanism for methane activation by PtCl2X2 in aqueous solution. A density functional theory study, ORGANOMETALLICS, 26, 2277, (2007)
Abstract: A density functional study has been carried out on catalytic methane activation by a 1:2 molar mixture of PtCl2(H2O)(2) and X- with X = none, F, Cl, Br, I, NO2, CN. The objective of this study was to better understand the original Shilov experiments, for which a detailed characterization of the active species and the rate determining step has been difficult experimentally. We have found that the rate-determining step for all mixtures is methane uptake rather than C-H activation. Our calculations indicate further that the active species for the weakly coordinating ligands X- = Cl-, Br-, I- are trans-PtCl2X(H2O)(-) and cis-PtX2Cl(H2O)(-), whereas the most abundant complex PtCl2X22- and other species with only halogens have no noticeable activity. For the more strongly coordinating ligands X- = F-, NO2-, CN-, the most abundant species are PtCl2(H2O)(2), PtCl2X(H2O)(-), PtClX2(H2O)(-), PtX42-, and PtClX3-. Of these species only cis-PtCl2(H2O)(2) and cis-PtCl2X(H2O)(-) are active catalysts for H+/D+ exchange. For all the species formed, the free energy barriers of methane and C-H activation have been reported, along with their energy of formation relative to cis-PtCl2(H2O)(2) and X-.

First author: Calhorda, Maria Jose, A new look at the ylidic bond in phosphorus ylides and related compounds: Energy decomposition analysis combined with a domain-averaged fermi hole analysis, JOURNAL OF PHYSICAL CHEMISTRY A,111, 2859, (2007)
Abstract: Geometries and bond dissociation energies of the ylide compounds H2CPH3, H2CPMe3, H2CPF3, (BH2)(2)CPH3, H2CNH3, H2CAsH3, H2SiPH3, and (BH2)(2)SiPH3 have been calculated using ab initio (MP2, CBS-QB3) and DFT (B3LYP, BP86) methods. The nature of the ylidic bond R2E1-(EX3)-X-2 was investigated with an energy decomposition analysis and with the domain-averaged Fermi hole (DAFH) analysis. The results of the latter method indicate that the peculiar features of the ylidic bond can be understood in terms of donor-acceptor interactions between closed-shell R2E1 and (EX3)-X-2 fragments. The DAFH analysis clearly shows that there are two bonding contributions to the ylidic bond. The strength of the donor and acceptor contributions to the attractive orbital interactions can be estimated from the energy decomposition analysis (EDA) calculations, which give also the contributions of the electrostatic attraction and the Pauli repulsion of the chemical bonding. The EDA and DAFH results clearly show that the orbital interactions take place through the singlet ground state of the R2E1 fragment where the donor orbital of E-1 yields pi-type back-donation while the (EX3)-X-2 lone-pair orbital yields sigma-type bonding. Both bonds are polarized toward (EX3)-X-2 when E-2 = P, while the sigma-type bonding remains more polarized at (EX3)-X-2 when E-2 = N, As. This shows that the phosphorus ylides exhibit a particular bonding situation which is clearly different from that of the nitrogen and arsenic homologues. With ylides built around a P-C linkage, the pi-acceptor strength of phosphorus and the sigma-acceptor strength at carbon contribute to a double bond which is enhanced by electrostatic contributions. The strength of the sigma and pi components and the electrostatic attraction are then fine-tuned by the substituents at C and P, which yields a peculiar type of carbon-phosphorus bonding. The EDA data reveal that the relative strength of the ylidic bond may be determined not only by the R2E1 -> (EX3)-X-2 pi back-donation, but also by the electrostatic contribution to the bonding. The calculations of the R2E1-(EX3)-X-2 bond dissociation energy using ab initio methods predict that the order of the bond strength is H2C-PMe3 > H2C-PF3 > H2C-PH3 > (BH2)(2)C-PH3 > H2C-AsH3 > H2C-NH3 similar to H2Si-PH3 similar to (BH2)(2)Si-PH3. The DFT methods predict a similar trend, but they underestimate the bond strength of (BH2)(2)CPH3.

First author: Fratiloiu, Silvia, Opto-electronic properties of fluorene-based derivatives as precursors for light-emitting diodes, JOURNAL OF PHYSICAL CHEMISTRY C, 111, 5812, (2007)
Abstract: This paper reports optical absorption spectra of oxidized fluorene copolymers obtained by chemical oxidation with Ce(IV) and by pulse radiolysis experiments in chlorinated solvents. Comparison of the results observed by the two techniques is used to provide spectral data on the copolymer radical ions and information on stability of the oxidized species. In addition, a detailed quantum chemical characterization is presented, concerning the electronic and optical properties of three series of charged oligomers containing alternating fluorene and phenylene or thienylene or benzothiadiazole units, respectively. The introduction of the comonomer strongly influences the optical properties, leading to a red shift in the absorption spectra of the charged oligomers. This shift is more pronounced in the case of fluorene benzothiadiazole anions due to the strong electron-accepting character of the benzothiadiazole moieties. The charge distribution of the fluorene benzothiadiazole anion is different from that corresponding to fluorene phenylene and fluorene thienylene anions. The negative charge of the latter oligomers is evenly distributed over the fluorene units, while the former oligomer localizes the negative charge on the benzothiadiazole units. The charge distribution correlates with the optical absorption spectra. When the positive charge is localized on a different unit than the negative charge, the cation and anion spectra are different. Similar spectra are obtained if both the positive and negative charges are localized on the same unit.

First author: Vega, Andres, Stabilization of acepentalene by coordination to transition metals: A DFT investigation,INORGANIC CHEMISTRY, 46, 3295, (2007)
Abstract: The possibility of stabilizing the unstable acepentalene (acp) molecule through coordination to transition metals is investigated by means of DFT calculations. Comparison with related experimentally known pentalene complexes indicate that their acp homologues are just slightly less stable, suggesting that they could be synthesized and isolated. Other original mono- and trinuclear species, such as M(acp)(2) (M = Zr, Hf), Co-3(acp)(2)(-), and Nb-3(acp)(2)(+), are also predicted to be stable.

First author: Jones, Travis E., Molecular orbital model for pyridine/alpha-pyridyl adsorption on metal surfaces, JOURNAL OF PHYSICAL CHEMISTRY C, 111, 5493, (2007)
Abstract: Electronic density functional calculations were used to explain the proposed formation of alpha-pyridyl from pyridine on silver, copper, cadmium, and gold surfaces. Our results show that the formation of alpha-pyridyl is governed by the mixing of metal wavefunctions with pyridine’s near-HOMOs. When the organic orbitals mix with metal sp-character, a bonding interaction results and pyridine is the dominant surface species. If the metal orbitals mixing most strongly with the pyridine near-HOMOs are of d-character then an antibonding or nonbonding interaction results and alpha-pyridyl is the dominant surface species. A predicted correlation between the ratio of the concentration of the two surfaces species and the applied electrode potential is supported by analysis of surface-enhanced Raman data.

First author: del Carmen Michelini, Maria, Gas-phase chemistry of actinides ions: New insights into the reaction of UO+ and UO2+ with water, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 129, 4229, (2007)
Abstract: The ability of uranium monoxide cations, UO+ and UO2+, to activate the O-H bond of H2O was studied by using two different approaches of the density functional theory. First, relativistic small-core pseudopotentials were used together with B3LYP hybrid functional. In addition, frozen-core PW91-PW91 calculations were performed within the ZORA approximation. A close description of the reaction mechanisms leading to two different reaction products is presented, including all the involved minima and transition states. Different possible spin states were considered as well as the effect of spin-orbit interactions on the transition state barrier heights. The nature of the chemical bonding of the key minima and transition states was studied by using topological methodologies (ELF, AIM). The obtained results are compared with experimental data, as well as with previous studies on the reaction of the bare uranium cations with water, to analyze the influence of the oxo-ligand in reactivity.

First author: Tomasi, Simone, Density functional theory investigation into the stereocontrol of the syndiospecific polymerization of propylene catalyzed by C-s-symmetric zirconocenes, ORGANOMETALLICS, 26, 2024, (2007)
Abstract: The mechanisms of the two most likely routes for the generation of stereodefects in the syndiospecific polymerization of propylene, mediated by the C-s-symmetric ansa-zirconocenes Me(2)CCpFluZrR(+)X(-) (1), Me2CCp(3,6-di-Me-Flu)ZrR+X- (2a), Me2SiCp(3,6-di-Me-Flu)ZrR+X- (2b), and Me2CCp(3,6-di-tBu-Flu)ZrR+X- (3) (X- = MeB(C6F5)(3)(-), FAl(Bip(f))(3)(-), MAOMe(-)) are explored using density functional theory. Site epimerization events (also known as back-skip or missed insertion) generate defective single m dyads, while enantiomeric misinsertions are the main source of double mm triads. The most important factor affecting the frequency of enantiomeric misinsertion is the structure of the ligand, while the counterion and solvation have little effect. Site epimerization is also influenced by the nature of the ligand system, but the bulk and the charge distribution of the anion are more prominent factors. The inclusion of solvent effects in the modeling of the site epimerization is critical for explaining reactivity and to achieving at least qualitatively correct results. Application of the two-parameter probabilistic scheme developed by Farina and co-workers allows for the prediction of pentad distributions from the computed selectivities. The good agreement found between experiment and computations for the basic unsubstituted system invented by Ewen and Razavi validates the proposed model. Thus, the computed pentad distributions may be used for assessing the effectiveness of modifications to the ligands on syndioselectivity. Increasing the bulk of 3,6-substituents on the fluorenyl ligand leads to increased syndiotacticity, without significantly affecting the reactivity. By introducing a stereogenic center on the alkyl chain, it is possible to assess the influence of chain end control on stereoselectivity. The main effect of chain end control is to increase the stereoselectivity after a stereoerror.

First author: Neugebauer, Johannes, Couplings between electronic transitions in a subsystem formulation of time-dependent density functional theory, JOURNAL OF CHEMICAL PHYSICS, 126, 2024, (2007)
Abstract: A subsystem formulation of time-dependent density functional theory (TDDFT) within the frozen-density embedding (FDE) framework and its practical implementation are presented, based on the formal TDDFT generalization of the FDE approach by Casida and Wesolowski [Int. J. Quantum Chem. 96, 577 (2004)]. It is shown how couplings between electronic transitions on different subsystems can be seamlessly incorporated into the formalism to overcome some of the shortcomings of the approximate TDDFT-FDE approach in use so far, which was only applicable for local subsystem excitations. In contrast to that, the approach presented here allows to include couplings between excitations on different subsystems, which become very important in aggregates composed of several similar chromophores, e.g., in biological or biomimetic light-harvesting systems. A connection to Forster- and Dexter-type excitation energy coupling expressions is established. A hybrid approach is presented and tested, in which excitation energy couplings are selectively included between different chromophore fragments, but neglected for inactive parts of the environment. It is furthermore demonstrated that the coupled TDDFT-FDE approach can cure the inability of the uncoupled FDE approach to describe induced circular dichroism in dimeric chromophores, a feature known as a “couplet,” which is also related to couplings between (nearly) degenerate electronic transitions.

First author: Zuidema, Erik, Ester versus polyketone formation in the palladium-diphosphine catalyzed carbonylation of ethene, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 129, 3989, (2007)
Abstract: The origin of the chemoselectivity of palladium catalysts containing bidentate phosphine ligands toward either methoxycarbonylation of ethene or the copolymerization of ethene and carbon monoxide was investigated using density functional theory based calculations. For a palladium catalyst containing the electron-donating bis(dimethylphosphino)ethane (dmpe) ligand, the rate determining step for chain propagation is shown to be the insertion of ethene into the metal-acyl bond. The high barrier for chain propagation is attributed to the low stability of the ethene intermediate, (dmpe)Pd(ethene)(C(O)CH(3)). For the competing methanolysis process, the most likely pathway involves the formation of (dmpe)Pd(CH(3)OH)(C(O)CH(3)) via dissociative ligand exchange, followed by a solvent mediated proton-transfer/reductive- elimination process. The overall barrier for this process is higher than the barrier for ethene insertion into the palladium-acetyl bond, in line with the experimentally observed preference of this type of catalyst toward the formation of polyketone. Electronic bite angle effects on the rates of ethene insertion and ethanoyl methanolysis were evaluated using four electronically and sterically related ligands (Me)(2)P(CH(2))(n)P(Me)(2) (n = 1-4). Steric effects were studied for larger tert-butyl substituted ligands using a QM/MM methodology. The results show that ethene coordination to the metal center and subsequent insertion into the palladium-ethanoyl bond are disfavored by the addition of steric bulk around the metal center. Key intermediates in the methanolysis mechanism, on the other hand, are stabilized because of electronic effects caused by increasing the bite angle of the diphosphine ligand. The combined effects explain successfully which ligands give polymer and which ones give methyl propionate as the major products of the reaction.

First author: Zhang Zhong, Stabilizing effect of amine on small molecules in electrolyte of lithium batteries, ACTA PHYSICO-CHIMICA SINICA, 23, 526, (2007)
Abstract: intermolecular interactions between ethylamine or ethylenediamine and H2O or HF were studied theoretically using density functional theory (DFT) at the PBE0/6-31+G(d, p) level. Natural bond orbital (NBO) analyses were employed to elucidate the hydrogen bond characteristics in these complexes. Energy decomposition analysis (EDA) method was applied to complexes of II-1, II-2, III-1, and III-2 at the PBE/TZP level. From this study, four important conclusions were drawn as follows: (1) Both HF and H2O can be stabilized by amines through N center dot center dot center dot H-F(O), F(O)center dot center dot center dot H-N or F(O)center dot center dot H-C hydrogen bonds; (2) An-tines have the priority to stabilize HF, because the high electronegativies of florine atom results in the intense N-H center dot center dot center dot F hydrogen bonds; (3) Stability of the ethylenediamine-associated complexes is higher than that of ethylamine-associated complexes; (4) The most stable complexes, formed by an-tines with HF or H2O, include F(O)-H center dot center dot center dot N and F(O)center dot center dot center dot H-C hydrogen bonds.

First author: Armelao, L., Molecular photochromic systems: a theoretical and experimental investigation on zinc(II) dithizonate, APPLIED ORGANOMETALLIC CHEMISTRY, 21, 246, (2007)
Abstract: Zinc(II)-dithizone based molecular systems [Zn(HDz)(2)] are intriguing candidates for the development of optical devices thanks to their interesting photochromic and nonlinear optical properties. In the present work, the behavior of Zn(HDz)(2) in different solvents was investigated by a combined theoretical and experimental approach. In particular, solutions of both dithizone (H(2)Dz) and Zn(HDz)(2) were analyzed by optical absorption spectroscopy and nuclear magnetic resonance (NMR) techniques, with particular attention to structure-properties relationships. Density functional and time-dependent density functional calculations were performed on the stable and the activated forms of the complex, obtaining information on the energetics of their interconversion, as well as on the nature of their electronic excitations.

First author: Endou, Akira, Development of constraint algorithm for the number of electrons in molecular orbitals consisting mainly 4f atomic orbitals of rare-earth elements and its introduction to tight-binding quantum chemical molecular dynamics method, JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, 46, 2505, (2007)
Abstract: Our original tight-binding quantum chemical molecular dynamics code, “Colors”, has been successfully applied to the theoretical investigation of complex materials including rare-earth elements, e.g., metal catalysts supported on a CeO2 surface. To expand our code so as to obtain a good convergence for the electronic structure of a calculation system including a rare-earth element, we developed a novel algorithm to provide a constraint condition for the number of electrons occupying the selected molecular orbitals that mainly consist of 4f atomic orbitals of the rare-earth element. This novel algorithm was introduced in Colors. Using Colors, we succeeded in obtaining the classified electronic configurations of the 4f atomic orbitals of Ce4+ and reduced Ce ions in a CeO2 bulk model with one oxygen defect, which makes it difficult to obtain a good convergence using a conventional first-principles quantum chemical calculation code.

First author: Puyad, Avinash L., Structure and bonding differences in C3N4 and Si3N4 isomers – A comparative study of [Si-3,N-4] and [C-3,N-4] potential energy surfaces using DFT and MP2 methodologies, JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM, 807, 73, (2007)
Abstract: Potential energy surface (PES) of the singlet ground states of [Si-3,N-4] and [C-3,N-4] in the gas phase have been mapped using high level DFT and ab initio calculations. The energy surface, consisting of many stationary points with several atom connectivities like chain (linear and non linear), planar, rings, tetrahedral (T-d) and three-dimensional geometries, has been analyzed in search of the minima. Comparing only the most stable isomers in the two PES it is observed that there are no common structures. It has also been observed that on the Si-PES there is only one very low lying minimum, a T-d like structure and all other isomers are more than 30 kcal/mol higher in relative energy. Unlike this in the C-series there are around three low-lying minima with very little energy difference among them. These are the chain isomer (C-2) and the isomers showing higher symmetry like C-2v and D-3h. The T-d structure is of very high energy in this series. Natural bond orbital analysis (NBO) has been carried out for the most stable isomers in both series to understand the bonding nature. Here both the localization and delocalization energy has been estimated. The most stable structure in the Si-series is the one with the largest localization energy unlike in the case of carbon series where the stability of the most stable isomer compared to the T-d structure is due to the delocalization energy. This understanding of these two potential energy surfaces and the bonding in these isomers would be helpful in the synthesis Of C3N4 films

First author: Garcia-Lastra, J. M., Anomalous superhyperfine tensor observed in BaFCl doped with the 5d(1) ion La2+: Role of 5d-4f hybridization, PHYSICAL REVIEW B, 75, 73, (2007)
Abstract: The fluorine superhyperfine (shf) tensor measured in BaFCl:La2+ has been found to be practically isotropic, a result which is certainly anomalous when compared to that for d(9) centers with one unpaired electron in a x(2)-y(2) orbital. This puzzling fact has been explored by means of density functional calculations. Obtained results confirm that in the C-4v equilibrium geometry the unpaired electron lies in a b(1)(similar to x(2)-y(2)) orbital which overlaps with the 2s orbitals of four F- ligands. For explaining the origin of the near isotropy, which is well reproduced by the present calculations, the simple D-4h and C-4v LaF42-, YF42-, and AgF42- centers have also been investigated. Although the obtained results stress the high dependence of the isotropic shf constant A(s) on the metal-ligand distance R, a near isotropy of the shf tensor is only reached for LaF42- (but not for YF42-) under C-4v symmetry which corresponds to the actual symmetry of the La2+ center in the BaFCl lattice. The origin of this peculiar situation is shown to come from the mixing between 5d and 4f orbitals of La2+ allowed in C-4v symmetry thus stressing the role played by 4f orbitals in bonding properties. Writing A(s)=CRs-n it is shown that for the D-4h LaF42- and YF42- complexes the exponent n(s) is around 20, while it is only equal to 4 for AgF42-. This huge difference is shown to stem from the quite distinct slope of the radial d wave function at the equilibrium distance for the two d(1) centers and the d(9) AgF42- unit. Finally, the present calculations strongly support that the intense band peaked at 17 890 cm(-1) recorded in the optical absorption spectrum of BaFCl:La2+ is indeed a 5d -> 4f transition.

First author: Garcia-Lastra, J. M., 3d impurities in normal and inverted perovskites: Differences are not explained by ligand field theory, PHYSICAL REVIEW B, 75, 73, (2007)
Abstract: Although the lattice constants of KMgF3 (normal cubic perovskite structure) and BaLiF3 (inverted perovskite) materials differ only by 0.3%, there is a significant difference between the measured cubic field splitting parameters 10Dq for KMgF3:Ni2+ (7800 cm(-1)) and BaLiF3:Ni2+ (8400 cm(-1)). By means of density functional theory calculations, it is shown that such a difference (similar to that observed for Co2+ and Mn2+ impurities) can hardly be understood within the traditional ligand field theory, which ignores the influence of the electrostatic potential V-R(r) exerted by the rest of the lattice ions upon the localized electrons of the NiF64- complex. Although V-R(r) is known to be very flat for a normal perovskite structure, it is shown that this is no longer true for an inverted perovskite. The origin of this significant difference is accounted for by simply considering, for the two cubic lattices, the electrostatic interaction of the two first ion shells around the complex with the electrons in the NiF64- unit. The results of this work emphasize the importance of V-R(r) when comparing the electronic properties of the same transition metal complex but embedded in two lattices that are not isomorphous even if both are cubic.

First author: Smolentsev, G., Three-dimensional local structure refinement using a full-potential XANES analysis,PHYSICAL REVIEW B, 75, 73, (2007)
Abstract: A technique of three-dimensional (3D) local structure refinement is proposed and demonstrated by applying it to the metal complex Ni(acacR)(2). The method is based on the fitting of experimental x-ray absorption near-edge structure (XANES) using a multidimensional interpolation of spectra and full potential calculations of XANES. The low number of calculations required is the main advantage of the method, which allows a computationally time-expensive method using a non-muffin-tin potential to be applied. The possibility to determine bond angles in addition to bond lengths accessible to extended x-ray-absorption fine structure opens new perspectives of XANES as a 3D structure probe.

First author: Datta, Ayan, Computational design of high hydrogen adsorption efficiency in molecular “Sulflower”,JOURNAL OF PHYSICAL CHEMISTRY C, 111, 4487, (2007)
Abstract: Calculations of the structure of molecular sulflower (C16S8) shows that this molecule, because of its planar structure, can adsorb up to 10 hydrogen molecules. The favorable mode of interaction is along the centers of mass of the alternate thiophene ring and the H-2 molecule, oriented vertically above and below at a distance of 3.2 A. The nature of interactions between the molecule and the hydrogen molecules is physical adsorption, and the moderate binding energy for this material suggests that potential hydrogen-storage devices can be constructed using this molecule.

First author: Jensen, Lasse, Size-dependence of the enhanced Raman scattering of pyridine adsorbed on Ag-n (n=2-8, 20) clusters, JOURNAL OF PHYSICAL CHEMISTRY C, 111, 4756, (2007)
Abstract: We present a time-dependent density functional theory (TDDFT) study of the size-dependence of the absorption and Raman scattering properties of pyridine interacting with small silver nanoclusters Ag-n (n = 2-8, 20). By employing a recently developed short-time approximation for the Raman scattering cross section we simulate both the normal and the “surface”-enhanced Raman spectra. The absorption spectra of the small silver clusters are studied both in the gas phase and embedded in rare gas matrices. We find that both the absorption and Raman properties depend strongly on cluster size and adsorption site. The normal Raman spectra of Ag-n-pyridine complexes resemble that of isolated pyridine, with enhancements which increase as cluster size increases. In contrast to this, both the enhancement and the appearance of the “surface”-enhanced Raman spectrum show a very strong dependence on cluster size. The total enhancements for the complexes are between 10(3) and 10(4) and quite surprisingly the strongest enhancement is found for the Ag-2-Py complex. However, the enhancement trends can be correlated with the distance of the molecule to the center of the metal cluster and with the resonance polarizability in a way that is suggestive of electromagnetic enhancements, so the enhancement mechanism for these small clusters is similar to what is found for larger particles.

First author: Kan, Yuhe, The nature of metal-metal bond of the dimetallocene complexes [M-2(eta(5)-C5R5)(2)] (M = Zn, Cd, Hg; R = H, Me): An energy decomposition analysis, JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM, 805, 127, (2007)
Abstract: The nature of the metal-metal chemical bond in the dimetallocene sandwich complexes M-2(eta(5)-C5Me5)(2) (M = Zn, Cd, Hg) and their parent molecules M-2(eta(5)-C5H5)(2) have been investigated using an energy decomposition analysis (EDA) at BP86/TZ2P level. Quantitative bonding analysis results show that both the bond dissociation energy (BDE) and Delta E-int values follow the same trend for the metals Zn > Hg > Cd. The metal-metal bonds have slightly more attractive contributions from classical electrostatic interactions than the attractive orbital interactions. The covalent bonding in metal metal is mainly from a(1)(sigma) orbital interactions. Hg-Hg bond is slightly shorter than Cd-Cd bond, as a result of a remarkable difference of orbital interactions Delta E-orb. The results give a deep and unambiguous insight into the nature of the chemical interactions in transition metals nonpolar bonding dimetallocene complexes.

First author: Mitoraj, Mariusz, Relating the radical stabilization energy and steric bulk of a hydrocarbyl group to the strength of its bonds with metals and hydrogen. A theoretical study, ORGANOMETALLICS, 26, 1627, (2007)
Abstract: We have analyzed the strength of the XR bond for a number of hydrocarbyl groups (R) attached to X = hydrogen, X = (CNCH3)(H)(Tp)Rh [Tp = H-B(pyrazolyl)(3)], and X = (OSi(CH3)(3))(OSi(CH3)(3))(NH-Si(CH3)(3))Ti with the help of a density functional theory (DFT) based energy decomposition scheme (EDA). The hydrocarbyl groups included had a radical sp(3) carbon with unsaturated aromatic or olefinic bonds (R-1 = Ph-CH2, mesityl, Me-allyl, allyl) or saturated alkyl substituents (R-2 = Me, Et, Pe, i-Pr, t-Bu), a radical carbon as part of a saturated ring (R-3 = c-Pr, c-Bu, c-Pe, c-He), or a radical sp(2) carbon (R-4 = Ph, t-Bu-vinyl, Me-vinyl, vinyl). The EDA scheme was used to rationalize the relative order of the X-R-i bond energies between groups (i = 1,4), within groups (same i), and between metals X = Rh, Ti, and hydrogen (X = H). It was found that the average bond energy within each group increases as R-4 > R-3 similar to R-2 > R-1 for the two metals as well as H. This trend correlates with the radical stabilization energy of R-i that decreases in absolute terms as R-4 < R-3 similar to R-1 < R-2. This trend enables one to make rough correlations between M-C bonds and M-H links on going from one group to another. Within each of the XRi systems where i = 1, 3, 4 there is also a correlation between the trend in the X-R-i bond energies and the R-i distortion energy. However, for the R-2 group trends in the X-R-2 bond energies are not determined by the radical stabilization but directly (X = H) or indirectly (X = Rh, Ti) by increasing steric bulk on R-2. For X = H, steric bulk directly destabilizes the H-R-2 bond by increasing the steric interaction between H and R-2 without significantly changing the H-C bond distance. For X = Rh, Ti steric bulk indirectly destabilizes the M-R-2 bond by increasing the M-C bond distance in order to relieve the steric strain. This leads to a reduction in the M-C bonding overlap and the M-C bond strength. We note finally that the Rh-R-i and Ti-R-i bonds are some 60 kcal/mol weaker than the H-R-i link. The major contributing factor here is the poorer overlap and larger energy gap between the orbitals involved in forming the M-C bond compared to the H-C link. Additional factors are larger steric interactions and the need for some distortion of the Rh and Ti fragments.

First author: Martin-Diaconescu, Vlad, Sulfur K-edge XAS as a probe of sulfur-centered radical intermediates, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 129, 3034, (2007)
Abstract: Sulfur K-edge XAS is used in the identification and characterization of sulfur based radicals obtained from UV irradiated glutathione. Ground state and time-dependent DFT calculations are used to identify thiyl (RS center dot) and perthiyl (RSS center dot) radical species.

First author: de Montigny, Frederic, Metallaborane reactivity. A stoichiometric mechanism for the insertion of two alkynes into an iridaborane framework via a disposable molybdenum chaperone, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 129, 3392, (2007)
Abstract: Building on earlier work that showed the formation of [1-Cp*-2,2,2-(CO)(3)-2-THF-nido-1,2-IrMoB(4)H(8)], 2, from the reaction of [1-Cp*-arachno-1-IrB(4)H(10)], 1, with (arene)Mo(CO)(3), the stoichiometric mechanism for the generation of [1-Cp*-5,6,7,8-(R)(4)-nido-1,5,6,7,8-IrC(4)B(3)H(3)], 8, from the reaction of 2 with RCCR, R = Me, Ph, has been identified. For R = Me, the major product in solution is [1-Cp*-5,6,7,8-(CH(3))(4)-closo-1,5,6,7,8-IrC(4)B(3)H(3)Mo(CO)(3)], 7, which is in equilibrium with 8. The equilibrium 8 + Mo(THF)(3)(CO)(3) -><- 7 + 3THF is characterized by Delta H = 8 kcal/mol and Delta S = 34 cal/mol K. Density functional theory calculations carried out on 7 indicate that the Mo(CO)(3) moiety is weakly bound to the cluster mainly through Mo-C rather than Mo-B interactions. Under alkyne deficient conditions, the product [1-Cp*-2,2,2-(CO)(3)(mu-CO)-3,4-(CH(3))(2)-closo-1,2,3,4-IrMoC(2)B(3)H(3 )], 6, can be isolated. Solid-state structures of 1 and 2 have been reported previously, and those of 6, 7, and 8, R = Me, Ph, are reported here. The evolution of products with time was monitored by (1)H and (11)B NMR and showed the formation and decay of two additional species which have been identified as the structural isomers [1-Cp*-7,7,7-(CO)(3)-7-THF-2,3-(CH(3))(2)-nido-1,7,2,3-IrMoC(2)B(3)H(5)] , 4, and [5-Cp*-7,7,7-(CO)(3)-7-THF-2,3-(CH(3))(2)-nido-5,7,2,3-IrMoC(2)B(3)H(5)] , 5, with the metals nonadjacent in 4 and adjacent in 5. Circumstantial evidence suggests that 4 is the precursor to 5 and 5 is the precursor to both 6 and 7. Cluster 2 also is a catalyst or catalyst precursor for the isomerization of olefins, namely, hex-1-ene to cis-hex-2-ene and tetramethyl allene to 2,4-dimethylpenta-1,3-diene. These novel results also establish that [1-Cp*-2,2,2-(CO)(3)-2-(alkyne)-nido-1,2-IrMoB(4)H(8)], 3, forms from 2 and constitutes a logical precursor to 4. The entire process, 1 + 2alkyne = 8 + BH(3) + 2H(2), which is promoted by (arene)Mo(CO)(3), constitutes an explicit example of a transition-metal-facilitated process analogous to metal-facilitated organic transformations observed in organometallic chemistry.

First author: Soldatova, Alexandra V., Effects of benzoannulation and alpha-octabutoxy substitution on the photophysical behavior of nickel phthalocyanines: A combined experimental and DFT/TDDFT study, INORGANIC CHEMISTRY, 46, 2080, (2007)
Abstract: The photophysical properties of a group of Ni(II)-centered tetrapyrroles have been investigated by ultrafast transient absorption spectrometry and DFT/TDDFT methods in order to characterize the impacts of alpha-octabutoxy substitution and benzoannulation on the deactivation pathways of the S-1(pi,pi*) state. The compounds examined were NiPc, NiNc, NiPc(OBu)(8), and NiNc(OBu)(8), where Pc = phthalocyanine and Nc = naphthalocyanine. It was found that the S-1(pi,pi*) state of NiNc(OBu)(8) deactivated within the time resolution of the instrument (200 fs) to a vibrationally hot T-1(pi,pi*) state. The quasidegeneracy of the S-1(pi,pi*) and (3)(d(z2),d(x2-y2)) states allowed for fast intersystem crossing (ISC) to occur. After vibrational relaxation (ca. 2.5 ps), the T-1(pi,pi*) converted rapidly (ca. 19 ps lifetime) and reversibly into the (LMCT)-L-3(pi,d(x2-y2)) state. The equilibrium state, so generated, decayed to the ground state with a lifetime of ca. 500 ps. Peripheral substitution of the Pc ring significantly modified the photodeactivation mechanism of the S-1(pi,pi*) by inducing substantial changes in the relative energies of the S-1(pi,pi*), (3)(d(pi),d(x2-y2)), (3)(d(z2,),d(x2-y2)), T-1(pi,pi*), and (LMCT)-L-1,3(pi,d(x2-y2)) excited states. The location of the Gouterman LUMOs and the unoccupied metal level (d(x2-y2)) with respect to the HOMO is crucial for the actual position of these states. In NiPc, the S-1(pi,pi*) state underwent ultrafast (200 fs) ISC into a hot (d,d) state. Vibrational cooling (ca. 20 ps lifetime) resulted in a cold (d(z2),d(x2-y2)) state, which repopulated the ground state with a 300 ps lifetime. In NiPc(OBu)(8), the S-1(pi,pi*) state deactivated through the (3)(d(z2),d(x2)>(-y2)), which in turn converted to the (LMCT)-L-3(pi,d(x2-y2)) state, which finally repopulated the ground state with a lifetime of 640 ps. Insufficient solubility of NiNc in noncoordinating solvents prevented transient absorption data from being obtained for this compound. However, the TDDFT calculations were used to make speculations about the photoproperties.

First author: Bento, A. Patricia, Nucleophilic substitution at silicon (S(N)2@Si) via a central reaction barrier, JOURNAL OF ORGANIC CHEMISTRY, 72, 2201, (2007)
Abstract: It is textbook knowledge that nucleophilic substitution at carbon (S(N)2@C) proceeds via a central reaction barrier which disappears in the corresponding nucleophilic substitution reaction at silicon (S(N)2@ Si). Here, we address the question why the central barrier disappears from S(N)2@ C to S(N)2@ Si despite the fact that these processes are isostructural and isoelectronic. To this end, we have explored and analyzed the potential energy surfaces (PES) of various Cl- + CR3Cl (R = H, CH3) and Cl- + SiR3Cl model reactions (R = H, CH3, C2H5, and OCH3). Our results show that the nature of the S(N)2 reaction barrier is in essence steric, but that it can be modulated by electronic factors. Thus, simply by increasing the steric demand of the substituents R around the silicon atom, the S(N)2@ Si mechanism changes from its regular single-well PES (with a stable intermediate transition complex, TC), via a triple- well PES (with a pre- and a post-TS before and after the central TC), to a double-well PES (with a TS; R = OCH3), which is normally encountered for S(N)2@C reactions.

First author: Cardenas, Carlos, Nuclear fukui functions from nonintegral electron number calculations, INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 107, 807, (2007)
Abstract: Numerical results for the nuclear Fukui function (NFF) based on a nonintegral number of electrons methodology (NIEM) are reported for a series of simple diatomic molecules. A comparison with those obtained from other methodologies is focused on the estimation of the error associated with a finite difference approximation for the evaluation of the NFF. The dependence of NFFs on the type and size of the basis set is also discussed. The NIEM values are in close agreement with those obtained from a finite difference approximation using Delta N = +/- 1 with large basis sets.

First author: Axenov, Kirill V., Hafnium bis(phenoxyimino) dibenzyl complexes and their activation toward olefin polymerization, ORGANOMETALLICS, 26, 1444, (2007)
Abstract: Hf bis(phenoxyimino) dibenzyl complexes bearing benzylimino and perfluorophenylimino groups were prepared by a direct reaction between the desired ligand precursors and Hf(CH2Ph)(4). In the solid state, the Hf complexes adopt an octahedral configuration where imino nitrogens are in positions cis to each other and oxygens occupy apical vertices of the coordination polyhedron. According to H-1 NMR and 2D-NOESY studies, this cis-N,N configuration was also maintained in solution. In addition, the structures of Hf bis(phenoxyimino) dibenzyl complexes were studied with DFT calculations. Activation of the Hf dibenzyl complexes with B(C6F5)(3) led to the highly air-, moisture-, solvent-, and temperature-sensitive cationic bis(phenoxyimino) Hf monobenzyl species, which were further investigated by H-1 and F-19 NMR, H-1-C-13 heteronuclear correlation, 2D-NOESY, and ESI-MS methods. It was observed that the cationic, benzylimino-substituted Hf complexes have a propensity toward CH activation. The correlation between the stability of the cationic species toward CH activation and the catalytic behavior of the MAO-activated dibenzyl complexes was established. Accordingly, the MAO-activated Hf bis(phenoxyimino) dibenzyl complexes and their dichloro analogues, depending on the ligand substitution, have from low to very high catalytic activities (up to 14 000 kg of PE/((mol of cat.) h (bar of ethylene))) in ethylene polymerizations. In general, the produced polyethylene had a monomodal molar mass distribution with relatively narrow polydispersity. Polypropylene produced with perfluorophenyl-substituted Hf complexes had a large amount of 2,1-misinsertions in the polymer chains. To further shed light on the catalytic reaction, polymerizations of ethylene and propylene with the cationic species generated from Hf bis(phenoxyimino) dibenzyl complexes with B(C6F5)(3) were studied with H-1 NMR.

First author: Wang, Shaowu, Coordination and reactivity diversity of N-piperidineethyl-functionalized indenyl ligands: Synthesis, structure, theoretical calculation, and catalytic activity of organolanthanide complexes with the ligands,ORGANOMETALLICS, 26, 1512, (2007)
Abstract: The interactions of N-piperidineethyl-functionalized indene compounds 1-R-3-C5H10NCH2CH2C9H6 (R = H- (1), Me3Si- (2)) with lanthanide(III) amides [(Me3Si)(2)N](3)Ln(mu-Cl)Li(THF)(3) (Ln = Yb, Eu, Sm, Nd) were studied. The results indicated that the ligands and reductive potentials of Ln(3+)/Ln(2+) have an influence on the reaction patterns and the coordination mode of the indenyl ligands with the central metals. Reactions of [(Me3Si)(2)N](3)Ln(mu-Cl)Li(THF)(3) (Ln = Yb, Eu) with 2 equiv of corresponding indene compounds 1-R-3-C5H10NCH2CH2C9H6 (R = H- (1), Me3Si- (2)) produced organolanthanide(II) complexes [eta(5):eta(1)-C5H10NCH2CH2C9H6](2)Ln(II) (Ln = Yb (3), Eu (5)) and novel organolanthanide(II) complexes with general formula [eta(4):eta(2):eta(1)-(C5H10NCH2CH2C9H5SiMe3)Li(mu-Cl)]Ln(II)(eta(5):eta (1)-C5H10NCH2CH2C9H5SiMe3) (Ln = Yb (4), Eu (6)), and a new highly conjugated bis(N-piperidineethyl)dibenzofulvalene, (C5H10NCH2CH2C9H5)(2) (9), was unexpectedly isolated as a byproduct in the preparation of 6, indicating the ligands’ effects on the coordination and reactivity patterns. Theoretical calculations on ytterbium(II) complexes having indenyl ligands indicated that the indenyl hapticity depends on the strain, steric, and electronic effects. Treatment of lanthanide(III) amides [(Me3Si)(2)N](3)Ln(mu-Cl)Li(THF)(3) (Ln = Sm, Nd) with 2 equiv of C5H10NCH2CH2C9H7 (1) afforded indenyl lanthanide(III) complexes with general formula [eta(3)-C5H10NCH2CH2C9H6](2)Ln(III)[eta(3):eta(1)-C5H10NCH2CH2C9H6] (Ln = Sm (7), Nd (8)). The shortest distances involving the nonbridging atoms of the C-5 portions of the indenyl groups indicated an allyl-like nature of the ligand-to-metal coordination. The interaction of [(Me3Si)(2)N](3)Sm-III(mu-Cl)Li(THF)(3) with 2 equiv of 1-Me3Si-3-C5H10NCH2CH2C9H6 (2) produced an unexpected bis(N-piperidineethyl)dibenzofulvalene (C5H10NCH2CH2C9H5)(2) (9) and other unidentified solids, suggesting the ligands’ influence on the reactivity patterns. All the compounds were fully characterized by spectroscopic methods and elemental analyses. The structures of compounds 4, 7, 8, and 9 were additionally determined by X-ray diffraction study. The catalytic activity of the organolanthanide complexes 3-8 on MMA polymerization was examined.It was found that the pi-bonded tris(N-piperidineethylindenyl)lanthanide(III) complexes 7 and 8 exhibit unexpected good catalytic activity on MMA polymerizatin, and complex 7 also showed an unexpected high catalytic activity on epsilon-caprolactone polymerization. It was found that the catalytic activity of the complexes depended on the polymerization conditions. The solvents, temperatures, substituted groups, and lanthanide ionic radii effects on the catalytic activity of the complexes were examined.

First author: Remko, Milan, Conformational behavior of basic monomeric building units of glycosaminoglycans: Isolated systems and solvent effect, JOURNAL OF PHYSICAL CHEMISTRY B, 111, 2313, (2007)
Abstract: Our work reports in detail the results of systematic large-scale theoretical investigations of the glycosaminoglycan building units 1-OMe Delta IdoA-2SNa(2) (1; H-2(1) and H-1(2) forms), 1-OMe GlcN-S6SNa(2) (2), 1,4-DiOMe GlcNa (3), 1,4-DiOMe GlcN-S3S6SNa(3) (4), 1,4-DiOMe IdoA-2SNa(2) (5; C-4(1), C-1(4), and S-2(o) conformations), and 1,4-DiOMe GlcN-S6SNa(2) (6) at the BP86/TZ2P level of the density functional theory. The optimized geometries indicate that the most stable structure of these monomeric units in the neutral state is stabilized via “multifurcated” sodium bonds. The equilibrium structure of the biologically active anionic forms of the glycosaminoglycans studied changed considerably in a water solution. The computed interaction energies, Delta E, of sodium coordinated systems 1-6 are negative and span a rather broad energy interval (from -130 to -590 kcal mol(-1)). Computations that include the effect of solvation indicated that in water the relative stability of Na+…ligand ionic bonds is considerably diminished. The computed interaction energy in water is small (from -20 to -53 kcal mol(-1)) and negative, that is, stabilizing.

First author: Calle, Carlos, Continuous-wave and pulse EPR study of the copper(II) complex of N-confused tetraphenylporphyrin: Direct observation of a sigma metal-carbon bond, INORGANIC CHEMISTRY, 46, 1847, (2007)
Abstract: N-confused or inverted porphyrins, a family of porphyrin isomers that contain a confused pyrrole ring connected through its alpha and beta’ positions in the macrocycle, exhibit unique physical and chemical properties, like, for instance, the ability to stabilize unusual oxidation states of metals due to the reactivity of the inverted pyrrole. In this Article, a combined multifrequency continuous-wave and pulse electron paramagnetic resonance (EPR) study of the copper(II) complex of N-confused tetraphenylporphyrin (TPP) is presented. By use of pulse EPR methods like ENDOR and HYSCORE, the magnetic interactions between the unpaired electron of the compound and the surrounding nitrogen nuclei were revealed. Through C-13 labeling of the macrocycle, a detailed study of the carbon hyperfine interaction became possible and provided further insight into the character of the metal-carbon bond. The observed hyperfine couplings of the ligand atoms in the first coordination sphere showed the presence of a remarkably strong sigma Cu-C bond and allowed for a detailed analysis of the spin delocalization over the porphyrin macrocycle. Interestingly, it was found that the observed delocalization is approximately 11% larger than the corresponding one for CuTPP.

First author: Spackman, Mark A., Comment on On the calculation of the electrostatic potential, electric field and electric field gradient from the aspherical pseudoatom model by Volkov, King, Coppens & Farrugia (2006), ACTA CRYSTALLOGRAPHICA SECTION A, 63, 198, (2007)
Abstract: N-confused or inverted porphyrins, a family of porphyrin isomers that contain a confused pyrrole ring connected through its alpha and beta’ positions in the macrocycle, exhibit unique physical and chemical properties, like, for instance, the ability to stabilize unusual oxidation states of metals due to the reactivity of the inverted pyrrole. In this Article, a combined multifrequency continuous-wave and pulse electron paramagnetic resonance (EPR) study of the copper(II) complex of N-confused tetraphenylporphyrin (TPP) is presented. By use of pulse EPR methods like ENDOR and HYSCORE, the magnetic interactions between the unpaired electron of the compound and the surrounding nitrogen nuclei were revealed. Through C-13 labeling of the macrocycle, a detailed study of the carbon hyperfine interaction became possible and provided further insight into the character of the metal-carbon bond. The observed hyperfine couplings of the ligand atoms in the first coordination sphere showed the presence of a remarkably strong sigma Cu-C bond and allowed for a detailed analysis of the spin delocalization over the porphyrin macrocycle. Interestingly, it was found that the observed delocalization is approximately 11% larger than the corresponding one for CuTPP.

First author: Zhang, Yi-Quan, A theoretical study of the nearest Cu center dot center dot center dot Cu antiferromagnetic exchange coupling interactions in [LaCu6] and [YCu6], EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 63, 1261, (2007)
Abstract: A density functional study of the exchange coupling interactions between the two nearest Cu-II centers in [LaCU6] and [YCu6] is presented. Two approaches show that the (CuCu)-Cu-… antiferromagnetic interactions increase with a decrease of the ionic radius of the diamagnetic central La-III and Y-III ions. However, the influence of the central ions on the (CuCu)-Cu-… interactions is small compared to that of their structures according to our calculations. We therefore conclude that the stronger antiferromagnetic interactions between the two nearest Cu-II centers in [LaCu6] than in [YCu6] are not a result of the central La-III ion but the structure. The antiferromagnetic contributions of the direct overlap between the two nearest Cull magnetic orbitals also play a major role according to the calculations of the overlap integral S-ij based on Kahn’s theory.

First author: Seth, Michael, Calculation of the B term of magnetic circular dichroism. A time-dependent density functional theory approach, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 3, 434, (2007)
Abstract: A method for calculating the B term of magnetic circular dichroism utilizing time-dependent density functional theory is presented. The expression for the B term is formulated through the standard sum-over-states approach, and all necessary matrix elements and transition energies are provided by the time-dependent density functional theory calculation. Test calculations of the magnetic circular dichroism spectra of ethene, propene, furan and its heavier homologues, and pyrrole and two of its derivatives are presented. The discrepancy between theory and experiment previously observed for ethene is not resolved, but the experimental spectra of the aromatic compounds are very well reproduced by the theory.

First author: Tangen, Espen, Bonding in low-coordinate environments: Electronic structure of pseudotetrahedral iron – Imido complexes, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 3, 448, (2007)
Abstract: A detailed density functional theory study of pseudotetrahedral Fe-III/IV-imido-phosphine complexes has yielded a host of new insights. The calculations confirm d(xy)(2)d(x2-y2)(2)d(z2)(1) (or d(delta)(2)d(delta)'(2)d(sigma)(1)) electronic configurations for Fe-III-imido complexes of this type, as previously proposed, where the z direction may be identified with the Fe-N-imido vector. However, geometry optimization of a sterically unencumbered model complex indicated a bent (162 degrees) imido linkage, in sharp contrast to the linear imido groups present in the sterically hindered complexes that have been studied experimentally. Under C-3v symmetry, the Fe-III-imido molecular orbital (MO) energy-level diagram indicates the existence of near-degenerate (2)A(1) and E-2 states, and accordingly, the bending of the imido group appears to be ascribable to a pseudo-Jahn-Teller distortion. For Fe-IV-imido complexes, our calculations indicate a d(xy)(2)d(x2-y2)(1)d(z2)(1) (or d(delta)(2)d(delta)'(1)d(sigma)(1)) electronic configuration, which is somewhat different from the d(xy)(1)d(x2-y2)(1)d(z2)(2) (or d(delta)(1)d(delta)'(1)d(sigma)(2)) configuration proposed in the literature. Not surprisingly, for a sterically unencumbered Fe-IV-imido complex, the degenerate E-3 state (under C-3v symmetry) results in a mild Jahn-Teller distortion and a slightly bent (173 degrees) imido linkage (on relaxing the symmetry constraint). The calculations also shed light on the surprising stability of the d(z2)-based MO, which points directly at the imido nitrogen, relative to the d(pi)-based MOs. The low-coordinate nature of the complexes-the absence of equatorial ligands and of a ligand trans with respect to the imido ligand-plays a key role in stabilizing the d(z2) orbital as well as the complexes as a whole. The electronic configurations of Fe-IV-imido porphyrins are radically different from that of the pseudotetrahedral complexes studied here, and we have speculated that these differences may well account for the nonobservation so far of Fe-IV-imido porphyrins.

First author: Casanova, David, Evaluation of the SCF combination of KS-DFT and 3D-RISM-KH; Solvation effect on conformational equilibria, tautomerization energies, and activation barriers, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 3, 458, (2007)
Abstract: The effect of solvation on conformational equilibria, tautomerization energies, and activation barriers in simple S(N)2 reactions is reproduced by using the self-consistent field coupling of the Kohn-Sham density functional theory (KS-DFT) for electronic structure and the three-dimensional reference interaction site model with the closure approximation of Kovalenko and Hirata (3D-RISM-KH) for molecular solvation structure. These examples are used in order to validate the implementation of the 3D-RISM-KH method in the Amsterdam Density Functional package. The computations of the free energy difference in the trans/gauche conformational equilibrium for 1,2-dichloroethane in different solvents; the relative tautomerization free energy for cytosine, isocytosine, and guanine; and the free energy activation barrier for a CH3X-type (X = F, Cl, Br) S(N)2 reaction exhibit agreement with the experimental data. The method is also applied to the electronic and hydration structure of carbon single-wall nanotubes of different diameters, including the effect of water located in the inner space of the nanotubes. A comparison with continuum models of solvation (including COSMO) as well as with other more precise and computationally more expensive calculations is made to demonstrate the accuracy and predictive capability of the new KS-DFT/3D-RISM-KH method.

First author: de Jong, G. Theodoor, Catalytic carbon-halogen bond activation: Trends in reactivity, selectivity, and solvation, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 3, 514, (2007)
Abstract: We have theoretically studied the oxidative addition of all halomethanes CH3X (with X = F, Cl, Br, I, At) to Pd and PdCl-, using both nonrelativistic and zeroth-order-regular-approximation-relativistic density functional theory at BLYP/QZ4P. Our study covers the gas phase as well as the condensed phase (water), where solvent effects are described with the conductor-like screening model. The activation of the C-star-X bond may proceed via two stereochemically different pathways: (i) direct oxidative insertion (OxIn) which goes with retention of the configuration at C-star and (ii) an alternative S(N)2 pathway which goes with inversion of the configuration at C-star. In the gas phase, for Pd, the OxIn pathway has the lowest reaction barrier for all CH3X’s. Anion assistance, that is, going from Pd to PdCl-, changes the preference for all CH3X’s from OxIn to the S(N)2 pathway. Gas-phase reaction barriers for both pathways to C-X activation generally decrease as X descends in group 17. Two striking solvent effects are (i) the shift in reactivity of Pd + CH3X from OxIn to S(N)2 in the case of the smaller halogens, F and Cl, and (ii) the shift in reactivity of PdCl- + CH3X in the opposite direction, that is, from S(N)2 to OxIn, in the case of the heavier halogens, I and At. We use the activation strain model to arrive at a qualitative understanding of how the competition between OxIn and S(N)2 pathways is determined by the halogen atom in the activated C-X bond, by anion assistance, and by solvation.

First author: Calhorda, Maria Jose, Geometry optimization of a Ru(IV) allyl dicationic complex: A DFT failure?, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 3, 665, (2007)
Abstract: Five pure and four hybrid DFT functionals associated with VDZP, VTZP, and VQZP basis sets are tested (Gaussian 03) for their performance on the geometry optimization of [Ru(eta(5)-C5H5)(eta(3)-CH2CHCHC6H5)(CH3CN)(2)](2+). When the calculated geometries were compared with the X-ray structure determination for the analogous complex with permethylated cyclopentadienyl, it was found that in all cases the coordination mode of the eta(3)-allyl was very poorly described, despite the functional used. The Ru-C bond distance corresponding to the substituted allyl carbon was overestimated by 0.23-0.50 A, depending on the functional and the basis set used. These results were reproduced by further testing carried out with the ADF program and larger basis sets. MP2 leads to an acceptable value for the same Ru-C distance, with an underestimation of 0.07 A, suggesting that, at least in the case of the functionals tested, DFT does not provide an accurate description of a weak Ru-C interaction.

First author: Fang, Hua, Geometric structure of X(AuPH3)(4)(+) (X = N, P, As, Sb): T-d or C-4 nu?, JOURNAL OF PHYSICAL CHEMISTRY A, 111, 1562, (2007)
Abstract: The geometric structures of X(AuPH3)(4)(+) (X = N, P, As, Sb) compounds have been determined by DFT and ab-initio methods. In agreement with experiment, N(AuPH3)(4)(+) is T-d and As(AuPH3)(4)(+) is C-4v with an apical As atom. Calculated molecular and experimental crystal structure parameters are compared. The structures of X(AuPH3)(4)(+) (X = P, Sb) are predicted. P(AuPH3)(4)(+) favors T-d, as confirmed by CC2. The closed-shell interaction distances of Au center dot center dot center dot Au from X alpha are consistent with the experimental values. The electronic structures and chemical deformation densities are analyzed.

First author: Carvalho, A., Local-density-functional calculations of the vacancy-oxygen center in Ge, PHYSICAL REVIEW B, 75, 1562, (2007)
Abstract: We carry out a comprehensive density-functional study of the vacancy-oxygen (VO) center in germanium using large H-terminated Ge clusters. The importance of a nonlinear core correction to account for the involvement of the 3d electrons in Ge-O bonds is discussed. We calculate the electrical levels and the vibrational modes of VO(0), VO(-), and VO(=) finding close agreement with experiment. We also explore the reorientation, migration, and dissociation mechanisms of neutral and negatively charged VO and compare the calculated energy barriers with experimental data. We conclude that the defect is likely to anneal through both mechanisms.

First author: Takahata, Yuji, Core electron binding energy (CEBE) as descriptors in quantitative structure-activity relationship (QSAR) analysis of cytotoxicities of a series of simple phenols, QSAR & COMBINATORIAL SCIENCE, 26, 378, (2007)
Abstract: Core Electron Binding Energies (CEBEs) of ring carbon atoms in 4-X-phenols were calculated using density-functional theory with the scheme Delta E-KS (PW86-PW91)/TZP//HF/ 6-31G*. The phenols show toxicity to fast growing cells. Using CEBEs of four distinguished carbon atoms in the phenyl ring and oxygen atom in -OH of the phenols, the compounds were well separated and grouped by Principal Component Analysis (PCA). Using three out of the five CEBEs, together with sigma(+) and log P of the phenols as descriptor, we established a QSAR model with Partial Least Squares (PLS) regression which resulted in Q(2)=0.914. CEBE values when used together with traditionally used descriptors such as log P and sigma(+) turned out to be useful descriptors in modeling the activity (QSAR) of the compounds with PLS.

First author: Filatov, Michael, On convergence of the normalized elimination of the small component (NESC) method,THEORETICAL CHEMISTRY ACCOUNTS, 117, 333, (2007)
Abstract: The convergence behavior of the iterative solution of the normalized elimination of the small component (NESC) method is investigated. A simple and efficient computational protocol for obtaining the exact positive-energy eigenvalues of the relativistic Hamiltonian starting from the energies obtained within the regular approximation is suggested. The protocol is based on the analysis of the relationship between the eigenvalues of the quasi-relativistic Hamiltonian in the regular approximation and the positive-energy eigenvalues of the exact relativistic Hamiltonian which was derived in the course of this work.

First author: Pistonesi, C., Theoretical and experimental study of methane steam reforming reactions over nickel catalyst,APPLIED SURFACE SCIENCE, 253, 4427, (2007)
Abstract: In this work we perform DFT theoretical calculations of methane and steam interactions on Ni(111) surface. The calculations allow us to improve our understanding of the competition between these reactants by catalytic sites in methane steam reforming (MSR) process. For this purpose we compare theoretical results with kinetic measurements of MSR on a Ni(II)-Al(III) catalyst prepared from lamellar double hydroxides as precursor. This comparison shows that, for low H2O/CH4 ratios methane and water intermediate species adsorb on different catalytic sites. While CHO species adsorbs on top of Ni atom, OH one occupies preferentially a tri-coordinate surface site. On the other hand, for high H2O/CH4 ratios a competency between these species by Ni sites would establish, diminishing methane conversion. In addition competition between methane and steam for Ni sites would lead to a decrease in CO production. Nevertheless, intermediate species adsorbed on different active sites would produce CO2, whatever the steam/methane ratio. Thus, it would be optimum steam concentration in hydrocarbon feed and active sites distribution on catalyst surface, which could maximize H, production and minimize CO selectivity. The theoretical findings agree with kinetic measurements, which show that maximum methane conversion depends on steam partial pressure in the feed; whereas always, selectivity to CO2 increases and to CO diminishes.

First author: Soran, Albert P., Organobismuth(III) dihalides with T-shaped geometry stabilized by intramolecular N -> Bi interactions and related diorganobismuth(III) halides, ORGANOMETALLICS, 26, 1196, (2007)
Abstract: Organobismuth(III) compounds containing (N,C,N)-pincer ligands were prepared and characterized both in solution and in the solid state. Compound RBiCl2 1 [R = 2,6-(Me2NCH2)(2)C6H3] was obtained from RLi and BiCl3 (1:1 molar ratio). RBiBr2 2 and RBiI2 3 were obtained by halogen-exchange reactions from 1. Reaction of 1 with MeMgI afforded RBi(Me)I 4. Compound R2BiCl 5, obtained from RLi and BiCl3, is rearranged in solution to 1 and R3Bi. The molecular structures of compounds 1-5 were established by single-crystal X-ray diffraction. All dihalides RBiX2 show a T-shaped CBiX2 core. They are the first stable compounds corresponding to the edge inversion “transition state” at the bismuth center, stabilized by two strong intramolecular N -> Bi interactions in trans positions to each other, which contribute to an overall distorted square pyramidal (N,C,N)BiX2 coordination geometry. The electronic structure of [2,6-(Me2NCH2)(2)C6H3]BiCl2 (1) was analyzed by density functional theory (DFT) calculations, which provide evidence that the stabilization of the square pyramidal geometry of bismuth is electronic rather than steric in nature.

First author: Tarmyshov, Konstantin B., Interface between platinum(111) and liquid isopropanol (2-propanol): A model for molecular dynamics studies, JOURNAL OF CHEMICAL PHYSICS, 126, 1196, (2007)
Abstract: A molecular dynamics model and its parametrization procedure are devised and used to study adsorption of isopropanol on platinum(111) (Pt(111)) surface in unsaturated and oversaturated coverages regimes. Static and dynamic properties of the interface between Pt(111) and liquid isopropanol are also investigated. The magnitude of the adsorption energy at unsaturated level increases at higher coverages. At the oversaturated coverage (multilayer adsorption) the adsorption energy reduces, which coincides with findings by Panja in their temperature-programed desorption experiment [Surf. Sci. 395, 248 (1998)]. The density analysis showed a strong packing of molecules at the interface followed by a depletion layer and then by an oscillating density profile up to 3 nm. The distribution of individual atom types showed that the first adsorbed layer forms a hydrophobic methyl “brush.” This brush then determines the distributions further from the surface. In the second layer methyl and methine groups are closer to the surface and followed by the hydroxyl groups; the third layer has exactly the inverted distribution. The alternating pattern extends up to about 2 nm from the surface. The orientational structure of molecules as a function of distance of molecules is determined by the atom distribution and surprisingly does not depend on the electrostatic or chemical interactions of isopropanol with the metal surface. However, possible formation of hydrogen bonds in the first layer is notably influenced by these interactions. The surface-adsorbate interactions influence the mobility of isopropanol molecules only in the first layer. Mobility in the higher layers is independent of these interactions.

First author: Manzur, Carolina, Iron-molybdenum charge-transfer hybrids containing organometallic and inorganic fragments bridged by aryldiazenido ligands in a mu-eta(6):eta(1) coordination mode: Syntheses, characterization, X-ray structures, electrochemistry, and theoretical investigation, INORGANIC CHEMISTRY, 46, 1123, (2007)
Abstract: Representative members of a new family of covalently bonded charge-transfer molecular hybrids, of general formula [(eta(5)-C5H5)Fe(mu,eta(6):eta(1)-p-RC6H4NN)Mo(eta(2)-S2CNEt2)(3)] +PF6- (R: H, 5(+)PF(6)(-); Me, 6(+)PF(6)(-); MeO, 7(+)PF(6)(-)) and [(eta(5)-C5Me5)Fe(mu,eta(6):eta(1)-C6H5NN)Mo(eta(2)-S2CNEt2)(3)]+PF6-, 8(+)PF(6)(-), have been synthesized by reaction of the corresponding mixed-sandwich organometallic hydrazines [(eta(5)-C5H5)Fe(eta(6)-p-RC6H4NHNH2)]+PF6- (R: H, 1(+)PF(6)(-); Me, 2(+)PF(6)(-); MeO, 3(+)PF(6)(-)) and [(eta(5)-C5Me5)Fe(eta(6)-C6H5NHNH2)]+PF6-, 4(+)PF(6)(-), with cis-dioxomolybdenum(VI) bis(diethyldithiocarbamato) complex, [MoO2(S2CNEt2)(2)], in the presence of sodium diethyldithiocarbamato trihydrate, NaSC(S)NEt2 center dot 3H(2)O, in refluxing methanol. These iron-molybdenum complexes consist of organometallic and inorganic fragments linked each other through a pi-conjugated aryldiazenido bridge coordinated in eta(6) and eta(1) modes, respectively. These complexes were fully characterized by FT-IR, UV-visible, and H-1 NMR spectroscopies and, in the case of complex 7(+)PF(6)(-), by single-crystal X-ray diffraction analysis. Likewise, the electrochemical and solvatochromic properties were studied by cyclic voltammetry and UV-visible spectroscopy, respectively. The electronic spectra of these hybrids show an absorption band in the 462-489 and 447-470 nm regions in CH2Cl2 and DMSO, respectively, indicating the existence of a charge-transfer transition from the inorganic donor to the organometallic acceptor fragments through the aryldiazenido spacer. A rationalization of the properties of 5(+)PF(6)(-)-8(+)PF(6)(-) is provided through DFT calculations on a simplified model of 7(+)PF(6)(-). Besides the heterodinuclear complexes 5(+)PF(6)(-)-8(+)PF(6)(-), the mononuclear molybdenum diazenido derivatives, [(eta(1)-p-RC6H4NN)Mo(eta(2)-S2CNEt2)(3)] (R: H, 9; Me, 10; MeO, 11), resulting from the decoordination of the [(eta(5)-C5H5)Fe](+) moiety of complexes 5(+)PF(6)(-)-7(+)PF(6)(-), were also isolated. For comparative studies, the crystalline and molecular structure of complex 10 center dot Et2O was also determined by X-ray diffraction analysis and its electronic structure computed.

First author: Poater, Jordi, Polycyclic benzenoids: Why kinked is more stable than straight, JOURNAL OF ORGANIC CHEMISTRY, 72, 1134, (2007)
Abstract: The enhanced stability of bent or kinked polycyclic benzenoids over linear ones is well established, phenanthrene and anthracene being archetypal representatives. The question why kinked is more stable than linear is, however, still a matter of discussion. Recently, it has been proposed that H-H bonding interactions between the two hydrogen atoms in the bay region of phenanthrene are responsible for the larger stability of this molecule as compared to anthracene. This conclusion conflicts with the vast body of evidence for nonbonded steric repulsion between these hydrogen atoms. In this work, we provide new, complementary evidence for the repulsive character of the H-H interactions in phenanthrene’s bay region. We have traced the origin of phenanthrene’s enhanced stability to the more efficient bonding in the pi-electron system using, among others, a quantitative energy decomposition analysis of the bonding between the two constituting 2-methtriyl-phenyl fragments in both phenanthrene and anthracene (i.e., C14H10 = C6H4 center dot-CH center dot center dot + C6H4 center dot-CH center dot center dot). The scope of our study is extended to polycyclic benzenoids by analyzing also hexacene and various bent isomers of the latter. Our results once more falsify one of the core concepts of the theory of atoms-in-molecules (AIM), namely, that the presence of bond paths and the presence of bond critical points (they exist indeed between the two bay H atoms in phenanthrene) are sufficient indicators for a stabilizing interaction. Instead, our results confirm that these AIM parameters merely diagnose the proximity or contact between charge distributions, be this contact stabilizing or destabilizing.

First author: Furlan, Sara, Ab initio molecular dynamics of heme in cytochrome c, JOURNAL OF PHYSICAL CHEMISTRY B, 111, 1157, (2007)
Abstract: Ab initio molecular dynamics (AIMD) calculations, based on the Car-Parrinello method, have been carried out for three models of heme c that is present in cytochrome c. Both the reduced (Fe(II)) and oxidized (Fe(III)) forms have been analyzed. The simplest models (1R and 1O, respectively) consist of a unsubstituted porphyrin (with no side chains) and two axially coordinated imidazole and ethylmethylthioether ligands. Density functional theory optimizations of these models confirm the basic electronic features and are the starting point for building more complex derivatives. AIMD simulations were performed after reaching the thermal stability at T = 300 K. The evolution of the Fe-L-ax bond strengths is examined together with the relative rotations of the imidazole and methionine about the axial vector, which appear rather independent from each other. The next models (2R and 2O) contain side chains at the heme to better simulate the actual active site. It is observed that two adjacent propionate groups induce some important effects. The axial Fe-S delta bond is only weakened in 2R but is definitely cleaved in the oxidized species 2O. Also the mobility of the Im ligand seems to be reduced by the formation of a strong hydrogen bond that involves the Im N delta 1-H delta 1 bond and one carboxylate group. In 2O the interaction becomes so strong that a proton transfer occurs and the propionic acid is formed. Finally, the models 3 include a free N-methyl-acetamide molecule to mimic a portion of the protein backbone. This influences the orientation of carboxylate groups and limits the amount of their hydrogen bonding with the Im ligand. Residual electrostatic interactions are maintained, which are still able to modulate the dissociation of the methionine from the heme.

First author: Hsu, I-Jui, New members of a class of iron-thiolate-nitrosyl compounds: Trinuclear iron-thiolate-nitrosyl complexes containing Fe3S6 core, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 129, 1151, (2007)
Abstract: The neutral trinuclear iron-thiolate-nitrosyl, [(ON)Fe(mu-S,S-C6H4)](3) (1), and its oxidation product, [(ON)Fe(mu-S,S-C6H4)](3)[PF6] (2), were synthesized and characterized by IR, X-ray diffraction, X-ray absorption, electron paramagnetic resonance (EPR), and magnetic measurement. The five-coordinated, square pyramidal geometry around each iron atom in complex 1 remains intact when complex 1 is oxidized to yield complex 2. Magnetic measurements and EPR results show that there is only one unpaired electron in complex 1 (S-total = (1)/(2)) and no unpaired electron (S-total = 0) in 2. The detailed geometric comparisons between complexes 1 and 2 provide understanding of the role that the unpaired electron plays in the chemical bonding of this trinuclear complex. Significant shortening of the Fe-Fe, Fe-N, and Fe-S distances around Fe(1) is observed when complex 1 is oxidized to 2. This result implicates that the removal of the unpaired electron does induce the strengthening of the Fe-Fe, Fe-N, and Fe-S bonds in the Fe(1) fragment. A significant shift of the nu(NO) stretching frequency from 1751 cm(-1) (1) to 1821, 1857 cm(-1) (2) (KBr) also indicates the strengthening of the N-O bonds in complex 2. The EPR, X-ray absorption, magnetic measurements, and molecular orbital calculations lead to the conclusion that the unpaired electron in complex 1 is mainly allocated in the Fe(1) fragment and is best described as {Fe(1)NO}(7), so that the unpaired electron is delocalized between Fe and NO via d-pi(*) orbital interaction; some contributions from [Fe(2)NO] and [Fe(3)NO] as well as the thiolates associated with Fe (1) are also realized. According to MO calculations, the spin density of complex 1 is predominately located at the Fe atoms with 0.60, -0.15, and 0.25 at Fe(1), Fe(2), and Fe(3), respectively.

First author: Maretti, Luca, Spin coupling in the supramolecular structure of a new tetra(quinoline-TEMPO)yttrium(III) complex, INORGANIC CHEMISTRY, 46, 660, (2007)
Abstract: The newly synthesized tetra(quinoline-TEMPO)yttrium(III) potassium salt shows interesting structural features at the molecular and supramolecular levels, revealed by the analysis of the X-ray diffraction data. The magnetic susceptibility and EPR data corroborated with structural considerations showed that the exchange and dipolar spin coupling interactions are taking place at the nodes assembling the supramolecular 2D structure. The Y(III) center shows antiprismatic octacoordination, close to the idealized D-2 symmetry. The diamagnetic transition metal plays no role in mediating the radical interactions since the TEMPO-type fragments are remote from the chelating moieties of the ligand. In turn, significant interaction occurs on the nodes consisting in the quasi-rectangular coordination of potassium counterions by the spin-bearing TEMPO groups coming from four distinct complex units. The antiferromagnetic susceptibility was consistently modeled by a spin Hamiltonian based on the rectangle topology of four spins S = (1)/(2). The fitted exchange parameters are J(a) = -5.1 cm(-1) and J(b) = -3.4 cm(-1) for the edges, imposing J(d) = 0 for the diagonal. These values are in excellent agreement with the ab initio results J(a) = -4.83 cm(-1), J(b) = -3.44 cm(-1), J(d) = -0.07 cm(-1) obtained in a CASSCF(12,8) calculation. Based on the reliability of the ab initio results we were able to select the presented J parameters among several versions of multiple solutions with acceptable goodness of the fit. A methodological caveat about the artifacts of the automatic use of best fit parameters, in the absence of supplementary criteria, in the context of relative blindness of magnetic susceptibility modeling, is raised. The details of the EPR spectrum at 10 K are also consistent, in the frame of dipolar approximation, with the model of four interacting spins at the nodes of the supramolecular assembling.

First author: Gradinaru, Julieta, Structural, spectral, electric-field-induced second harmonic, and theoretical study of Ni(II), Cu(II), Zn(II), and VO(II) complexes with [N2O2] unsymmetrical schiff bases of S-methylisothiosemicarbazide derivatives,INORGANIC CHEMISTRY, 46, 884, (2007)
Abstract: New unsymmetrical [N2O2] tetradentate Schiff base complexes of Ni(II), Cu(II), Zn(II), and VO(II) were synthesized by template condensation of the tetradentate precursor 1-phenylbutane-1,3-dione mono-S-methylisothiosemicarbazone with o-hydroxybenzaldehyde or its 5-phenylazo derivative. They were characterized by elemental analysis, IR, UV-vis, electron spin resonance, and NMR spectroscopy, mass spectrometry, and magnetic measurements. The crystal structures of five of them have been determined by X-ray diffraction using, in some cases, synchrotron radiation. These compounds are characterized by a large thermal stability; their decomposition temperatures range from 240 up to 310 degrees C. Complexes with the phenylazo substituent were found to possess a large second-order nonlinear optical (NLO) response, as determined both by measurements of solution-phase direct current electric-field-induced second harmonic generation and by theoretical time-dependent density functional theory (TDDFT) calculations. The molecular hyperpolarizability was found to decrease in the order Zn(II) > Cu(II) > Ni(II) similar to VO(II). The active role of the metal in determining the NLO properties of the complexes was shown through an analysis of their UV-vis spectra, which revealed the presence of metal-to-ligand (in closed-shell complexes) and ligand-to-metal (in open-shell complexes) charge-transfer bands together with intra-ligand charge-transfer transitions. Assignment of the bands was based on the analysis of the TDDFT computed spectra.

First author: Hartl, Frantisek, Electronic transitions and bonding properties in a series of five-coordinate “16-electron” complexes [Mn(CO)(3)(L-2)](-) (L-2 = chelating redox-active pi-donor ligand), COORDINATION CHEMISTRY REVIEWS,251, 557, (2007)
Abstract: In this article we present for the first time accurate density functional theory (DFT) and time-dependent (TD) DFT data for a series of electronically unsaturated five-coordinate complexes [Mn(CO)(3)(L-2)](-), where L-2 stands for a chelating strong pi-donor ligand represented by catecholate, dithiolate, amidothiolate, reduced alpha-diimine (1,4-dialkyl-1,4-diazabutadiene (R-DAB), 2,2′-bipyridine) and reduced 2,2′-biphosphinine types. The single-crystal X-ray structure of the unusual compound [Na(BPY)][Mn(CO)(3)(BPY)]center dot Et2O and the electronic absorption spectrum of the anion [Mn(CO)(3)(BPY)](-) are new in the literature. The nature of the bidentate ligand determines the bonding in the complexes, which varies between two limiting forms: from completely pi-delocalized diamagnetic {(CO)(3)Mn-L-2}(-) for L-2 = alpha-diimine or biphosphinine, to largely valence-trapped {(CO)(3)Mn-1-L-2(2-)}(-) for L-2(2-) = catecholate, where the formal oxidation states of Mn and L-2 can be assigned. The variable degree of the pi-delocalization in the Mn(L-2) chelate ring is indicated by experimental resonance Raman spectra of [Mn(CO)(3)(L-2)](-) (L-2=3,5-di-tBu-catecholate and iPr-DAB), where accurate assignments of the diagnostically important Raman bands have been aided by vibrational analysis. The L-2 = catecholate type of complexes is known to react with Lewis bases (CO substitution, formation of six-coordinate adducts) while the strongly pi-delocalized complexes are inert. The five-coordinate complexes adopt usually a distorted square pyramidal geometry in the solid state, even though transitions to a trigonal bipyramid are also not rare. The experimental structural data and the corresponding DFT-computed values of bond lengths and angles are in a very good agreement. TD-DFT calculations of electronic absorption spectra of the studied Mn complexes and the strongly pi-delocalized reference compound [Fe(CO)(3)(Me-DAB)] have reproduced qualitatively well the experimental spectra. Analyses of the computed electronic transitions in the visible spectroscopic region show that the lowest-energy absorption band always contains a dominant (in some cases almost exclusive) contribution from a pi(HOMO) -> pi*(LUMO) transition within the MnL2 metallacycle. The character of this optical excitation depends strongly on the composition of the frontier orbitals, varying from a partial L-2 -> Mn charge transfer (LMCT) through a fully delocalized pi(MnL2) -> pi*(MnL2) situation to a mixed (CO)Mn -> L-2 charge transfer (LLCT/MLCT). The latter character is most apparent in the case of the reference complex [Fe(CO)(3)(Me-DAB)]. The higher-lying, usually strongly mixed electronic transitions in the visible absorption region originate in the three lower-lying occupied orbitals, HOMO – 1 to HOMO – 3, with significant metal-d contributions. Assignment of these optical excitations to electronic transitions of a specific type is difficult. A partial LLCT/MLCT character is encountered most frequently. The electronic absorption spectra become more complex when the chelating ligand L-2, such as 2,2′-bipyridine, features two or more closely spaced low-lying empty pi* orbitals.

First author: Sherman, David M., Complexation of Cu+ in Hydrothermal NaCl Brines: Ab initio molecular dynamics and energetics, GEOCHIMICA ET COSMOCHIMICA ACTA, 71, 714, (2007)
Abstract: Chloride complexation of Cu+ controls the solubility of copper(l) oxide and sulfide ore minerals in hydrothermal and diagenetic fluids. Solubility measurements and optical spectra of high temperature CuCl solutions have been interpreted as indicating the formation of CuCl CuCl2-, CuCl43- and CuCl43- complexes. However, no other monovalent cation forms tri- and tetrachloro complexes. EXAFS spectra of high temperature Cu-Cl solutions, moreover, appear to show only CuCl and CuCl2- complexes at T > 100 degrees C. To reconcile these results, I investigated the nature and stability of Cu-Cl complexes using ab initio cluster calculations and ab initio (Car-Parrinello) molecular dynamics simulations for CuCl-NaCl-H2O systems at 25 to 450 degrees C. Ab initio molecular dynamic simulations of I m CuCl in a 4 m Cl solution give a stable CuCl3- complex at 25 degrees C over 4 ps but show that the third Cl- is weakly bound. When the temperature is increased along the liquid-vapour saturation curve to 125 degrees C, the CuCl32- complex dissociates into CuCl2- and Cl-; only CuCl2- forms at 325 degrees C and 1 kbar. Even in a 15.6 m Cl brine at 450 degrees C, only the CuCl2- complex forms over a 4 ps simulation run.Cluster calculations with a static dielectric continuum solvation field (COSMO) were used in an attempt directly estimate free energies of complex formation in aqueous solution. Consistent with the MD simulations, the CuCl32- complex is slightly stable at 25 degrees C but decreases in stability with decreasing dielectric constant (epsilon). The CuCl42- complex is predicted to be unstable at 25 degrees C and becomes increasingly unstable with decreasing dielectric constant. In hydrothermal fluids (epsilon < 30) both the CuCl32- and CuCl43- complexes are unstable to dissociation into CuCl2- and Cl-.The results obtained here are at odds with recent equations of state that predict CuCl32- and CuCl43- complexes are the predominant species in hydrothermal brines. In contrast, I predict that only CuCl2- complexes will be significant at T > 125 degrees C, even in NaCl-saturated brines. The high-temperature (T > 125 degrees C) optical spectra of CuCl solutions and solubility measurements of Cu minerals in Cl-brines need to be reinterpreted in terms of only the CuCl and CuCl2- complexes.

First author: Mitoraj, Mariusz, Natural orbitals for chemical valence as descriptors of chemical bonding in transition metal complexes, JOURNAL OF MOLECULAR MODELING, 13, 347, (2007)
Abstract: Natural orbitals for chemical valence (NOCV) are defined as the eigenvectors of the chemical valence operator defined by Nalewajski et al.; they decompose the deformation density (differential density, Delta rho) into diagonal contributions. NOCV were used in a description of the chemical bond between the organometallic fragment and the ligand in example transition-metal complexes: heme-CO ([FeN5C20H15]-CO), [Ni-diimine hydride]-ethylene ([(NN)-N-boolean AND-Ni-H]-C2H4, (NN)-N-boolean AND=-NH-CH-CH-NH-), and [Ni(NH3)(3)]-CO. DFT calculations were performed using gradient-corrected density functional theory (DFT) in the fragments resolution, using the fragment/ligand Kohn-Sham orbitals as a basis set in calculations for the whole fragment-ligand complex. It has been found that NOCV lead to a very compact description of the fragment-ligand bond, with only a few orbitals exhibiting non-zero eigenvalues. Results of NOCV analysis, compared with Mulliken populations analysis and Zigler-Rauk interaction-energy decomposition, demonstrate that the use of the natural valence orbitals allows for a separation of the sigma-donation and pi-back-donation contributions to the ligand-fragment bond. They can be also useful in comparison of these contributions in different complexes.

First author: Wang, Xiaojing, Investigation of the dissociative adsorption for cyclopropane on the copper surface by density functional theory and quantum. chemical molecular dynamics method, SURFACE SCIENCE, 601, 679, (2007)
Abstract: The dissociative adsorption of cyclopropane on the copper surface was studied using quantum chemical molecular dynamics method with “Colors-Excite” code and density functional theory by Amsterdam Density Functional program (ADF2000). The excited state of cyclopropane was used as adsorbate to simulate the dissociated adsorption under an irradiation energy of ca. 10 eV. One of the C-C bonds in cyclopropane was broken and the two new bonds between cyclopropane and copper surface were formed. The electrons transferred from the copper atoms to cyclopropane with a value of about 0.2e. The shorter distances between the carbons and surface copper atoms showed the existence of strong interaction. Consistently, the results indicated metallacyclopentane was the most possible intermediate species in dissociative adsorption by ADF2000 and “Colors-Excite” method.

First author: Sun, Yuming, A TDDFT study on the excitation of P700, CHEMICAL PHYSICS LETTERS, 434, 111, (2007)
Abstract: The excitation property of P700 has been studied using the time-dependent density functional method. It is found that the excitation of P700 is intrinsically asymmetric at its two Chla halves, and this asymmetry may be closely related to the relative use of two electron transfer branches. Based on the calculated results, we also proposed a charge separation mechanism for P700, in which the time evolution of the excited state of P700 is modulated by a quantum beat of period about 75 fs, making the electron transfer of two branches correlated, or complementary effect possible.

First author: Hanmura, Tetsu, Reactions of nitrogen monoxide on cobalt cluster ions: Reaction enhancement by introduction of hydrogen, JOURNAL OF PHYSICAL CHEMISTRY A, 111, 422, (2007)
Abstract: Absolute cross sections for NO chemisorption, NO decomposition, and cluster dissociation in the collision of a nitrogen monoxide molecule, NO, with cluster ions Co-n(+) and ConH+ (n = 2-5) were measured as a function of the cluster size, n, in a beam-gas geometry in a tandem mass spectrometer. Size dependency of the cross sections and the change of the cross sections by introduction of H to Co-n(+) (effect of H-introduction) are explained by a statistical model based on the RRK theory, with the aid of the energetics obtained by a DFT calculation. It was found that the reactions are governed by the energetics rather than dynamics. For instance, Co-3(+) does not react appreciably with NO because the reactions are endothermic, while Co3H+ does because the reaction becomes exothermic by the H-introduction.

First author: Cador, Olivier, Electron-sponge behavior and electronic structures in cobalt-centered pentagonal prismatic Co11Te7(CO)(10) and Co11Te5(CO)(15) cluster anions, INORGANIC CHEMISTRY, 46, 501, (2007)
Abstract: The novel cluster anion [Co11Te5(CO)(15)](-) ([3](-)) has been isolated and structurally characterized as part of the salt [Cp* Nb-2(CO)(2)][3] (Cp* = C5Me5). The cobalt-centered Co-10 pentagonal prism is surrounded by a shell of two mu(5)-Te, three mu(4)-Te ligands, and 15 CO groups in terminal, symmetrical, and sigma-semibridging bonding modes. The hybrid carbonyl-telluride character of the ligand shell is reflected in the solid state by a one-dimensional assembly of polyhedral prisms along a backbone of [Cp*Nb-2(CO)(2)](+) cations. Electrochemical studies reveal the presence of four redox couples of [3](n) (n = – 1 to – 5). The electronic structures of various metal-centered and empty pentagonal-prismatic (PP) M-10 clusters (M = Co, Ni) are calculated and compared to those of pentagonal-antiprismatic (PA) M-10 structures. Closed-shells of 152 and 156 metal valence electrons, respectively, are found to determine the electronic structures and chemical properties of these geometries. From these considerations, magnetic properties have been predicted. They have been verified for the [Co11Te7(CO)(10)](-) cluster anion, which exhibits a singlet triplet gap of 0.318 kcal/mol.

First author: Osorio, Edgar A., Addition energies and vibrational fine structure measured in electromigrated single-molecule junctions based on an oligophenylenevinylene derivative, ADVANCED MATERIALS, 19, 281, (2007)
Abstract: Transport trough electromigrated molecular junctions that contain an individual thiol end-capped oligophenylenevinylene molecule has been studied. At low temperatures more than fifteen excitations appear in the differential conductance map (see figure). Their energies agree with energies obtained from optical measurements on the same molecule, and are therefore attributed to vibrational modes. Addition energies are consistently an order of magnitude smaller than the optical HOMO-LUMO gap.

First author: Lecea, Begona, Theoretical study on the mechanism of the [2+1] thermal cycloaddition between alkenes and stable singlet (phosphino)(silyl)carbenes, JOURNAL OF ORGANIC CHEMISTRY, 72, 357, (2007)
Abstract: [graphics]The mechanism and the origins of the stereocontrol observed in the reaction between differently substituted alkenes and stable (phosphino)(silyl)carbenes giving cyclopropanes have been studied computationally. These cyclopropanation reactions proceed via asynchronous concerted mechanisms involving early transition structures with a significant charge transfer from the carbene to the alkene moiety. The geometric features of these transition structures preclude a significant overlap between the orbitals required for secondary orbital interactions between the reactants. The stereoselectivity observed experimentally stems from favorable electrostatic and steric interactions between the reactants leading to the stereoisomers in which the phosphanyl and carbonyl or aryl groups are cis to each other.

First author: Pietrzyk, Piotr, Computational spectroscopy and DFT investigations into nitrogen and oxygen bond breaking and bond making processes in model deNO(x) and deN(2)O reactions, CATALYSIS TODAY, 119, 219, (2007)
Abstract: Molecular DFT modeling combined with computational spectroscopy (EPR and IR) were applied for analysis of the N-O bond breaking and N-N and O-O bond making in the context of deNO(x) and deN(2)O reactions. Interaction of NO, N2O and NO2 with cationic (transition metals) and anionic (surface O2- ions) centers was explored at the molecular level. The elementary events such as reactant coordination, charge and spin redistributions, which are principal molecular constraints for efficient decomposition of the nitrogen oxides (N2O and NO) were discussed. Particular attention was paid to dynamics of the N-O bond cleavage in N2O molecule through electron and oxygen atom transfer routes, evaluation of preferable coordination modes of NO, discrimination between inner- and outer-sphere mechanism of N-N bond formation, and the influence of spin and electronic redistribution on the reaction course (spin catalysis). Owing to their simplicity and well known surface chemistry, model systems selected for studies of such processes include MoOx/SiO2, MgO and ZSM-5 zeolite exchanged with various transition metal ions (TMI) of different electron configuration and spin multiplicity: Mo5+ (d(1), D-2) Fe3+, Mn2+, Cr+ (d(5), S-6), Fe2+ (d(6), D-5), CO2+ (d(7), F-4), Ni2+ (d(8), F-3), Cu2+ (d(9), D-2) and Cu+, Zn2+ (d(10), S-1).

First author: Frenking, Gernot, Unicorns in the world of chemical bonding models, JOURNAL OF COMPUTATIONAL CHEMISTRY, 28, 15, (2007)
Abstract: The appearance and the significance of heuristically developed bonding models are compared with the phenomenon of unicorns in mythical saga. It is argued that classical bonding models played an essential role for the development of the chemical science providing the language which is spoken in the territory of chemistry. The advent and the further development of quantum chemistry demands some restrictions and boundary conditions for classical chemical bonding models, which will continue to be integral parts of chemistry.

First author: Frenking, Gernot, Electronic structure of CO – An exercise in modern chemical bonding theory, JOURNAL OF COMPUTATIONAL CHEMISTRY, 28, 117, (2007)
Abstract: This paper discusses recent progress that has been made in the understanding of the electronic structure and bonding situation of carbon monoxide which was analyzed using modern quantum chemical methods. The new results are compared with standard models of chemical bonding. The electronic charge distribution and the dipole moment, the nature of the HOMO and the bond dissociation energy are discussed in detail.

First author: Bickelhaupt, F. M., Covalent versus ionic bonding in alkalimetal fluoride oligomers, JOURNAL OF COMPUTATIONAL CHEMISTRY, 28, 238, (2007)
Abstract: The most polar bond in chemistry is that between a fluorine and an alkalimetal atom. Inspired by our recent finding that other polar bonds (C-M and H-M) have important covalent contributions (i.e., stabilization due to bond overlap), we herein address the question if covalency is also essential in the F-M bond. Thus, we have theoretically studied the alkalimetal fluoride monomers, FM, and (distorted) cubic tetramers, (FM)(4), with M = Li, Na, K, and Rb, using density functional theory at the BP86/TZ2P level. Our objective is to determine how the structure and thermochemistry (e.g., F-M bond lengths and strengths, oligomerization energies, etc.) of alkalimetal fluorides depend on the metal atom, and to understand the emerging trends in terms of quantitative Kohn-Sham molecular orbital theory. The analyses confirm the extreme polarity of the F-M bond (dipole moment, Voronoi deformation density and Hirshfeld atomic charges), and they reveal that bond overlap-derived stabilization (ca. -6, -6, and -2 kcal/mol) contributes only little to the bond strength (-136, -112, and -114 kcal/mol) and the trend therein along Li, Na, and K. According to this and other criteria, the F-M bond is not only strongly polar, but also has a truly ionic bonding mechanism. Interestingly, the polarity is reduced on tetramerization. For the lithium and sodium fluoride tetramers, the F-4 tetrahedron is larger than and surrounds the M-4 cluster (i.e., F-F > M-M). But in the potassium and rubidium fluoride tetramers, the F-4 tetrahedron is smaller than and inside the M-4 cluster (i.e., F-F < M-M).

First author: Hocking, Rosalie K., Fe L-edge x-ray absorption spectroscopy of low-spin heme relative to non-heme Fe complexes: Delocalization of Fe d-electrons into the porphyrin ligand, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 129, 113, (2007)
Abstract: Hemes (iron porphyrins) are involved in a range of functions in biology, including electron transfer, small-molecule binding and transport, and O-2 activation. The delocalization of the Fe d-electrons into the porphyrin ring and its effect on the redox chemistry and reactivity of these systems has been difficult to study by optical spectroscopies due to the dominant porphyrin pi ->pi* d transitions, which obscure the metal center. Recently, we have developed a methodology that allows for the interpretation of the multiplet structure of Fe L-edges in terms of differential orbital covalency (i.e., differences in mixing of the d-orbitals with ligand orbitals) using a valence bond configuration interaction (VBCI) model. Applied to low-spin heme systems, this methodology allows experimental determination of the delocalization of the Fe d-electrons into the porphyrin (P) ring in terms of both P -> Fe sigma and pi-donation and Fe -> P pi back-bonding. We find that d- donation to Fe(III) is much larger than pi back-bonding from Fe(II), indicating that a hole superexchange pathway dominates electron transfer. The implications of the results are also discussed in terms of the differences between heme and non-heme oxygen activation chemistry.

First author: Louwerse, Manuel J., Oxidative properties of FeO2+: electronic structure and solvation effects, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 9, 156, (2007)
Abstract: An electronic structure analysis is provided of the action of solvated FeO2+, [FeO(H2O)(5)](2+), as a hydroxylation catalyst. It is emphasized that the oxo end of FeO2+ does not form hydrogen bonds (as electron donor and H-bond acceptor) with H-bond donors nor with aliphatic C H bonds, but it activates C-H bonds as an electron acceptor. It is extremely electrophilic, to the extent that it can activate even such poor electron donors as aliphatic C-H bonds, the C-H bond orbital acting as electron donor in a charge transfer type of interaction. Lower lying O-H bonding orbitals are less easily activated. The primary electron accepting orbital in a water environment is the 3 sigma*alpha orbital, an antibonding combination of Fe-3d(z2) and O-2p(z), which is very low-lying relative to the pi*alpha compared with, for example, the sigma* orbital in O-2 relative to its pi*. This is ascribed to relatively small Fe-3d(z2) With O-2p(z) overlap, due to the nodal structure of the 3d(z2).The H-abstraction barrier is very low in the gas phase, but it is considerably enhanced in water solvent. This is shown to be due to strong screening effects of the dielectric medium, leading to relative destabilization of the levels of the charged [FeO(H2O)(5)](2+) species compared to those of the neutral substrate molecules, making it a less effective electron acceptor. The solvent directly affects the orbital interactions responsible for the catalytic reaction.

First author: Huerta, Elisa, Selective binding and easy separation C-70 by nanoscale self-assembled capsules,ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 46, 202, (2007)
Abstract: An electronic structure analysis is provided of the action of solvated FeO2+, [FeO(H2O)(5)](2+), as a hydroxylation catalyst. It is emphasized that the oxo end of FeO2+ does not form hydrogen bonds (as electron donor and H-bond acceptor) with H-bond donors nor with aliphatic C H bonds, but it activates C-H bonds as an electron acceptor. It is extremely electrophilic, to the extent that it can activate even such poor electron donors as aliphatic C-H bonds, the C-H bond orbital acting as electron donor in a charge transfer type of interaction. Lower lying O-H bonding orbitals are less easily activated. The primary electron accepting orbital in a water environment is the 3 sigma*alpha orbital, an antibonding combination of Fe-3d(z2) and O-2p(z), which is very low-lying relative to the pi*alpha compared with, for example, the sigma* orbital in O-2 relative to its pi*. This is ascribed to relatively small Fe-3d(z2) With O-2p(z) overlap, due to the nodal structure of the 3d(z2).The H-abstraction barrier is very low in the gas phase, but it is considerably enhanced in water solvent. This is shown to be due to strong screening effects of the dielectric medium, leading to relative destabilization of the levels of the charged [FeO(H2O)(5)](2+) species compared to those of the neutral substrate molecules, making it a less effective electron acceptor. The solvent directly affects the orbital interactions responsible for the catalytic reaction.

First author: Halime, Zakaria, Bismuth and lead hanging-carboxylate porphyrins: An unexpected homobimetallic lead (II) complex, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 46, 5120, (2007)
Abstract: An electronic structure analysis is provided of the action of solvated FeO2+, [FeO(H2O)(5)](2+), as a hydroxylation catalyst. It is emphasized that the oxo end of FeO2+ does not form hydrogen bonds (as electron donor and H-bond acceptor) with H-bond donors nor with aliphatic C H bonds, but it activates C-H bonds as an electron acceptor. It is extremely electrophilic, to the extent that it can activate even such poor electron donors as aliphatic C-H bonds, the C-H bond orbital acting as electron donor in a charge transfer type of interaction. Lower lying O-H bonding orbitals are less easily activated. The primary electron accepting orbital in a water environment is the 3 sigma*alpha orbital, an antibonding combination of Fe-3d(z2) and O-2p(z), which is very low-lying relative to the pi*alpha compared with, for example, the sigma* orbital in O-2 relative to its pi*. This is ascribed to relatively small Fe-3d(z2) With O-2p(z) overlap, due to the nodal structure of the 3d(z2).The H-abstraction barrier is very low in the gas phase, but it is considerably enhanced in water solvent. This is shown to be due to strong screening effects of the dielectric medium, leading to relative destabilization of the levels of the charged [FeO(H2O)(5)](2+) species compared to those of the neutral substrate molecules, making it a less effective electron acceptor. The solvent directly affects the orbital interactions responsible for the catalytic reaction.

First author: Braunschweig, Holger, Synthesis and electronic structure of a ferroborirene, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 46, 5215, (2007)
Abstract: An electronic structure analysis is provided of the action of solvated FeO2+, [FeO(H2O)(5)](2+), as a hydroxylation catalyst. It is emphasized that the oxo end of FeO2+ does not form hydrogen bonds (as electron donor and H-bond acceptor) with H-bond donors nor with aliphatic C H bonds, but it activates C-H bonds as an electron acceptor. It is extremely electrophilic, to the extent that it can activate even such poor electron donors as aliphatic C-H bonds, the C-H bond orbital acting as electron donor in a charge transfer type of interaction. Lower lying O-H bonding orbitals are less easily activated. The primary electron accepting orbital in a water environment is the 3 sigma*alpha orbital, an antibonding combination of Fe-3d(z2) and O-2p(z), which is very low-lying relative to the pi*alpha compared with, for example, the sigma* orbital in O-2 relative to its pi*. This is ascribed to relatively small Fe-3d(z2) With O-2p(z) overlap, due to the nodal structure of the 3d(z2).The H-abstraction barrier is very low in the gas phase, but it is considerably enhanced in water solvent. This is shown to be due to strong screening effects of the dielectric medium, leading to relative destabilization of the levels of the charged [FeO(H2O)(5)](2+) species compared to those of the neutral substrate molecules, making it a less effective electron acceptor. The solvent directly affects the orbital interactions responsible for the catalytic reaction.

First author: Tonner, Ralf, C(NHC)(2): Divalent carbon(0) compounds with N-heterocyclic carbene ligands – Theoretical evidence for a class of molecules with promising chemical properties, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 46, 8695, (2007)
Abstract: An electronic structure analysis is provided of the action of solvated FeO2+, [FeO(H2O)(5)](2+), as a hydroxylation catalyst. It is emphasized that the oxo end of FeO2+ does not form hydrogen bonds (as electron donor and H-bond acceptor) with H-bond donors nor with aliphatic C H bonds, but it activates C-H bonds as an electron acceptor. It is extremely electrophilic, to the extent that it can activate even such poor electron donors as aliphatic C-H bonds, the C-H bond orbital acting as electron donor in a charge transfer type of interaction. Lower lying O-H bonding orbitals are less easily activated. The primary electron accepting orbital in a water environment is the 3 sigma*alpha orbital, an antibonding combination of Fe-3d(z2) and O-2p(z), which is very low-lying relative to the pi*alpha compared with, for example, the sigma* orbital in O-2 relative to its pi*. This is ascribed to relatively small Fe-3d(z2) With O-2p(z) overlap, due to the nodal structure of the 3d(z2).The H-abstraction barrier is very low in the gas phase, but it is considerably enhanced in water solvent. This is shown to be due to strong screening effects of the dielectric medium, leading to relative destabilization of the levels of the charged [FeO(H2O)(5)](2+) species compared to those of the neutral substrate molecules, making it a less effective electron acceptor. The solvent directly affects the orbital interactions responsible for the catalytic reaction.

First author: Li, Jun, Chirality, agostic interactions, and pyramidality in actinide methylidene complexes, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 46, 9045, (2007)
Abstract: An electronic structure analysis is provided of the action of solvated FeO2+, [FeO(H2O)(5)](2+), as a hydroxylation catalyst. It is emphasized that the oxo end of FeO2+ does not form hydrogen bonds (as electron donor and H-bond acceptor) with H-bond donors nor with aliphatic C H bonds, but it activates C-H bonds as an electron acceptor. It is extremely electrophilic, to the extent that it can activate even such poor electron donors as aliphatic C-H bonds, the C-H bond orbital acting as electron donor in a charge transfer type of interaction. Lower lying O-H bonding orbitals are less easily activated. The primary electron accepting orbital in a water environment is the 3 sigma*alpha orbital, an antibonding combination of Fe-3d(z2) and O-2p(z), which is very low-lying relative to the pi*alpha compared with, for example, the sigma* orbital in O-2 relative to its pi*. This is ascribed to relatively small Fe-3d(z2) With O-2p(z) overlap, due to the nodal structure of the 3d(z2).The H-abstraction barrier is very low in the gas phase, but it is considerably enhanced in water solvent. This is shown to be due to strong screening effects of the dielectric medium, leading to relative destabilization of the levels of the charged [FeO(H2O)(5)](2+) species compared to those of the neutral substrate molecules, making it a less effective electron acceptor. The solvent directly affects the orbital interactions responsible for the catalytic reaction.

First author: Schnegg, A., High-field EPR, ENDOR and ELDOR on bacterial photosynthetic reaction centers, APPLIED MAGNETIC RESONANCE, 31, 59, (2007)
Abstract: We report on recent 95 and 360 GHz high-field electron paramagnetic resonance (EPR), electron-nuclear double resonance (ENDOR) and pulsed electron-electron double resonance (PELDOR) studies of wild-type and mutant reaction centers (RCs) from the photosynthetic bacterium Rhodobacter sphaeroides. Taking advantage of the excellent spectral and temporal resolution of EPR at 95 and 360 GHz, the electron-transfer (ET) cofactors radical ions and spin-correlated radical pairs were characterized by their g- and hyperfine-tensor components, their anisotropic T-2 relaxation as well as by the dipolar interaction between P(865)(center dot+)Q(A)(center dot-) radical pairs. The goal of these studies is to better understand the dominant factors determining the specificity and directionality of transmembrane ET processes in photosynthetic RC proteins. In particular, our multifrequency experiments elucidate the subtle cofactor-protein interactions, which are essential for fine-tuning the ET characteristics, e.g., the unidirectionality of the light-induced ET pathways along the A branch of the RC protein. By our high-field techniques, frozen-solution RCs of novel site-specific single and double mutants of R. sphaeroides were studied to modulate the ET characteristics, e.g., even to the extent that dominant B branch ET prevails. The presented multifrequency EPR work culminates in first 360 GHz ENDOR results from organic nitroxide radicals as well as in first 95 GHz high-field PELDOR results from orientationally selected spin-polarized radical pairs P(865)(center dot+)QA(center dot-), which allow to determine the full geometrical structure of the pairs even in frozen-solution RCs.

First author: Roy, E., Magnetic field dependence of C-13 photo-CIDNP MAS NMR in plant photosystems I and II,APPLIED MAGNETIC RESONANCE, 31, 193, (2007)
Abstract: Photochemically induced dynamic nuclear polarization is observed in the two photosynthetic reaction centers of plants, photosystem I (PSI) and photosystem 11 (PSII) by `C magic-angle spinning nuclear magnetic resonance (NMR) at three different magnetic fields 17.6, 9.4, and 4.7 T. There is a significant difference in field dependence detected in the light-induced signal pattern of the two photosystems. For PSII the optimal NMR enhancement factor of about 5000 is observed at 4.7 T. On the other hand, the maximal light-induced signals of PSI are observed at 9.4 T.

First author: Senn, Hans Martin, QM/MM methods for biological systems, ATOMISTIC APPROACHES IN MODERN BIOLOGY: FROM QUANTUM CHEMISTRY TO MOLECULAR SIMULATIONS, 268, 173, (2007)
Abstract: Thirty years after the seminal contribution by Warshel and Levitt, we review the state of the art of combined quantum-mechanics/molecular-mechanics (QM/MM) methods, with a focus on biomolecular systems. We provide a detailed overview of the methodology of QM/MM calculations and their use within optimization and simulation schemes. A tabular survey of recent applications, mostly to enzymatic reactions, is given.

First author: Cariati, Elena, Tuning second-order NLO responses through halogen bonding, CHEMICAL COMMUNICATIONS, 268, 2590, (2007)
Abstract: As a function of the ability of the solvent to behave as acceptor of halogen bonding, the NLO-phores under study give rise to mu beta(lambda) values ranging from +192 x 10(-48) esu to -465 x 10(-48) esu.

First author: Dragonetti, Claudia, Cyclometallated iridium(III) complexes with substituted 1,10-phenanthrolines: a new class of highly active organometallic second order NLO-phores with excellent transparency with respect to second harmonic emission, CHEMICAL COMMUNICATIONS, 268, 4116, (2007)
Abstract: [Ir( ppy)(2)( 5- R- 1,10- phen)][ PF6] ( ppy = cyclometallated 2- phenylpyridine, phen = phenanthroline, R = H, Me, NMe2, NO2) and [ Ir( ppy)(2)( 4- R’,7- R’- 1,10- phen)][ PF6] ( R’ = Me, Ph) complexes are characterized by one of the highest second order NLO response ( measured by the EFISH technique) reported for a metal complex, mainly due ( as suggested by a theoretical SOS- TDDFT investigation) to MLCT processes from the ppy Ir based moiety acting as donor push system to pi* orbitals of phen, acting as an acceptor pull system; the good transparency to the second harmonic emission renders these NLO- phores appealing as building blocks for molecular materials with second harmonic generation.

First author: Valencia, Ramon, Large fullerenes stabilized by encapsulation of metallic clusters, CHEMICAL COMMUNICATIONS, 268, 4161, (2007)
Abstract: Structures are proposed for six endohedral metallofullerenes with large carbon cages ( from C-92 to C-100) on the basis of sizeable ( LUMO-4) -( LUMO-3) gap and the formal transfer of six electrons to the cages.

First author: Santi, Saverio, Tuning the electronic communication in heterobimetallic mixed-valence ions of (1-ferrocenyl)- and (2-ferrocenyl)indenyl rhodium isomers, CHEMISTRY-A EUROPEAN JOURNAL, 13, 1955, (2007)
Abstract: A series of heterobimetallic complexes of general structure [RhL2-{eta(5)-(2-ferrocenyl)indenyl}] (L-2 = cod, nbd, L = CO; cod = cyclooctadiene; nbd = norbornadiene) has been synthesised with the aim of tuning the metal-metal interaction in their mixed-valence ions generated both by chemical and electrochemical oxidation, and the results are compared with those obtained for [RhL2{eta(5)-(1-ferrocenyl)indenyl}] isomers. Crystallographic studies and DFT calculations provide a detailed description of the structural and electronic features of these complexes evidencing a significant difference in the extent of planarity of the flexible bridging ligand between the 1- and 2-ferrocenyl isomers. Independent experimental probes, in particular the potential splitting in the cyclic voltammograms and the IT bands in the near-IR spectra, are rationalised in the framework of Marcus-Hush theory and at quantum chemistry level by DFT and TD-DFT methods. These methods allow us to establish a trend based on the magnitude of iron-rhodium electronic coupling H-ab ranging from valence trapped to almost delocalised ions. The quasi planar bridge and the olefin ancillary ligands make [Rh(nbd)-{eta(5)-(2-ferrocenyl)indenyl}](+) and [Rh(cod){eta(5)-(2-ferrocenyl)indenyl}](+) rare examples of heterobimetallic systems which can be classified as borderline Class II/Class III species.

First author: Christian, Gemma, Breaking chemistry’s strongest bond: Can three-coordinate [M{N(R)Ar}3] complexes cleave carbon monoxide?, CHEMISTRY-A EUROPEAN JOURNAL, 13, 4264, (2007)
Abstract: The reaction pathway for the interaction of CO with three-coordinate Ta-III, W-III and Re-III complexes (modelled on the experimental [M{N(tBu)Ar}(3)] system) has been explored by using density functional methods. Calculations show that CO binds without a barrier to [Re(NH2)(3)], forming the encounter complex [OC-Re(NH2)(3)], which is stabilized by approximate to 280 kJ mol(-1) relative to the reactants. The binding of [Ta(NH2)(3)] to the oxygen terminus of CO is inhibited by a barrier of only 20 kJ mol(-1) and is followed by spontaneous cleavage of the C-O bond to form the products [C-Re(NH2)(3)] and [O-Ta(NH2)(3)]. The salient features of the potential energy surface are more favourable to CO cleavage than the analogous N-2 cleavage by [Mo(NH2)(3)], which is less exothermic (335 vs. 467 kJ mol(-1)) and is impeded by a significant barrier (66 kJ mol(-1)). The Re-III/Ta-III/CO system therefore appears to be an excellent candidate for cleaving the exceptionally strong C-O bond under mild laboratory conditions. The related W-III/Ta-III dimer, which significantly weakens but does not cleave the CO bond, may be a suitable alternative when the chemistry is to be performed on activated CO rather than on the strongly bound oxide and carbide cleavage products.

First author: Kuo, Ming-Yu, Cyanation: Providing a three-in-one advantage for the design of n-type organic field-effect transistors, CHEMISTRY-A EUROPEAN JOURNAL, 13, 4750, (2007)
Abstract: The theoretical work presented here demonstrates that, when substitution takes place at appropriate positions, cyanation could be a useful tool for reducing the internal reorganization energy of molecules. A molecular-orbital-based explanation is given for this fundamentally important phenomenon. Some of the cyanated pentacene derivatives (nCN-PENT-n) not only have internal reorganization energies for electron transfer (lambda(-)) smaller than that of pentacene, but the lambda(-) values are even of the same magnitude as the internal reorganization energy for hole transfer (lambda(+)) of pentacene, a small value that few organic compounds have surpassed. In addition, cyanation raises the electron affinity of the parent compound and may afford good electronic couplings between neighboring molecules, because of its ability in promoting pi-stacking. For the design of high performance n-Type Or-game field-effect transistors, high electron affinities, large intermolecular electronic couplings, and small reorganization energies are necessary. Cyanation may help in all three aspects. Two cyanated trialkylsilylethynyl pentacene derivatives with known it-stacking structures are predicted to provide reasonably small internal reorganization energies, large electronic couplings, and high electron affinities. They have the potential to outperform N-fluoroalkylated dicyanoperylene-3,4:9,10-bis(-dicarboximides) (PDI-FCN2) in terms of electron mobility.

First author: Shamov, Grigory A., A comparative relativistic DFT and ab initio study on the structure and thermodynamics of the oxofluorides of uranium(IV), (V) and (VI), CHEMISTRY-A EUROPEAN JOURNAL, 13, 4932, (2007)
Abstract: All the possible uranium(VI, V, IV) oxides, fluorides and oxofluorides were studied theoretically by using density functional theory (DFT) in the generalised gradient approximation (GGA), and three different relativistic methods (all-electron scalar four component Dyall RESC method (AE), relativistic small-core ECPs, and zeroth order regular approximation ZORA). In, order to test different correlation methods, for the two former relativistic methods hybrid DFT, and, for the AE method, MP2 molecular orbital calculations were performed as well. Single-point AE-CCSD(T) energies were calculated on MP2 geometries as well. Energies of the uranium(VI) and (V) oxofluorides dissociation, uranium(VI) fluoride hydrolysis and oxofluoride disproportionation were calculated and compared against the available experimental thermochemical data. AE-CCSD(T) energies were the closest to the experiment. For GGA DFT methods, all the relativistic methods used yield similar results. For thermochemistry, the best quantitative agreement with the experimental and CCSD(T) values for both U=O and U-F bond strengths was obtained with hybrid DFT methods, provided that a reliable basis set was used. Both the GGA DFT and MP2 MO methods show overbinding of these bonds; moreover, this overbinding was found to be not uniform but strongly dependent on the coordination environment of the uranium atom in each case. U=O vibrational frequencies given by hybrid DFT, however, are systematically overestimated, and are better reproduced by GGA DFT; MP2 values usually fall in-between. Reaction enthalpics, U=O frequencies and complex geometries given by the PBE, MPBE, BPBE, BLYP and OLYP GGA functionals are quite similar, with OLYP performing slightly better than the others but still not as good as hybrid DFT. The geometries of the molecules are found to be influenced by the following factors: the inverse transinfluence (ITI) of the oxygen ligand and, for U-V, and U-IV, the Jahn-Teller distortion.

First author: Petrie, Simon, Bridge over troubled water: Resolving the competing photosystem II crystal structures,CHEMISTRY-A EUROPEAN JOURNAL, 13, 5082, (2007)
Abstract: Density functional theory (DFT) calculations, at the Becke-Perdew/TZP level of theory, were used to investigate a set of CaMn4-containing clusters that model the active site of the water-oxidizing complex (WOC) of photosystem II (PSII). Metal-atom positions for three representative isomeric clusters of the formula [CaMn4C9N2O16H10]+center dot 4H(2)O are in good agreement with the disparate Mn-4 geometries of the three most recent Xray crystal structures. Remarkably, interconversion between these three isomeric clusters is found to be facile, resulting from subtle changes in the coordination environment around the CaMn4 centre. Ibis result provides a clear rationalisation of the marked differences in reported crystal structures. Recent concerns have been raised regarding the opportunity for X-ray-damage-induced distortion of the metal-containing active centre during crystallographic analysis. Our calculations suggest. that an even greater problem may be presented by the apparent fluxionality of the CaMn4 skeleton within the active centre. Structural rearrangement may well precede crystallographic analysis, for example by the preferential “freezing-out” of one of several near-isoenergetic structures during the workup for crystallisation. This prospect, which our calculations cannot exclude, highlights the difficulties that will continue to be faced by experimentalists seeking unambiguous structural information on the WOC’s active site.

First author: Fernandez, Israel, Aromaticity in metallabenzenes, CHEMISTRY-A EUROPEAN JOURNAL, 13, 5873, (2007)
Abstract: The electronic structure and bonding situation in 21 metallabenzenes (metal=Os, Ru, Ir, Rh, Pt, and Pd) were investigated at the DFT level (BP86/TZ2P) by using an energy decomposition analysis (EDA) of the interaction energy between various fragments. The aim of the work is to estimate the strength of the at bonding and the aromatic character of the metallacyclic compounds. Analysis of the electronic structure shows that the metallacyclic moiety has five occupied pi orbitals, two with b(1), symmetry and three with a(2) symmetry, which describe the pi-bonding interactions. The metallabenzenes are thus 10 at-electron systems. This holds for 16-electron and for 18-electron complexes. The pi bonding in the metallabenzenes results mainly from the b(1), contribution, but the a(2) contribution is not negligible. Comparison of the at-bonding strength in the metallacyclic compounds with acylic reference molecules indicates that metallabenzenes should be considered as aromatic compounds whose extra stabilization due to aromatic conjugation is weaker than in benzene. The calculated aromatic stabilization energies (ASEs) are between 8.7 kcal mol(-1) for 13 and 37.6 kcalmol(-1) for 16 which is nearly as aromatic as benzene (ASE =42.5 kcal mol(-1)). The classical metallabenzene model compounds 1 and 4 exhibit intermediate aromaticity with ASE values of 33.4 and 17.6 kcal mol(-1). The greater stability of the 5d complexes compared with the 4d species appears not to be related to the strength of at conjugation. From the data reported here there is no apparent trend or pattern which indicates a correlation between aromatic stabilization and particular ligands, metals, coordination numbers or charge. The lower metal-C(5)H(5) binding energy of the 4d complexes correlates rather with weaker sigma-orbital interactions.

First author: Weiss, Andre, Diboryl and diboranyl porphyrin complexes: Synthesis, structural motifs and redox chemistry: Diborenyl porphyrin or diboranyl isophlorin?, CHEMISTRY-A EUROPEAN JOURNAL, 13, 5982, (2007)
Abstract: The syntheses of diboryl porphyrin complexes [(BX2)(2)(ttp)] (ttp: dianion of tetra-p-tolylporphyrin) and the B-B single-bond diboranyl complexes [(BX)(2)(ttp)] (X=F, Cl, Br, I) are given. The former are prepared from the reactions of BX3 (X=F, Cl) with [Li-2(ttp)] and the latter from B2Cl4 (X=Cl), the reaction of SbF3 with [(BCl)(2)(ttp)] (for X=F), and, in the cases of X=Br or I, in a remarkable reductive coupling reaction resulting directly from the reaction of BBr3 or BI3 with [Li-2(ttp)]. Density functional theory (DFT) calculations on the thermochernical parameters for the reductive coupling reactions (and those calculated for related dipyrromethene complexes) indicate that a combination of the reducing ability of bromide and iodide ions combined with the constrained environment of the porphyrin ligand contribute to the driving force. The reductive coupling is also observed in the reaction of [(BCl2)(2)(ttp)] with nBuLi to give [(BnBU)(2)(ttp)], which was characterised crystallographically. The reaction of [(BCl)(2)(ttp)] with catechol gives a boron catecholato porphyrin complex, [B-2(O2C6H4)(ttp)] Chloride abstraction from [(BCl)(2)(ttp)] gives the planar dication [B-2(ttp)](2+), whereas chemical reduction of [(BCl)(2)-(ttp)] by using magnesium anthracenide gives a neutral complex, [B-2(ttp)], in which the ttp ligand has been reduced by two electrons to give an unusual example of an isophlorin complex. The cationic and neutral complexes [B-2(ttp)](2+) and [B-2(ttp)] were characterised through a combination of spectroscopic data that is supported by DFT calculations on the porphine analogues.

First author: Pierrefixe, Simon C. A. H., Aromaticity: Molecular-orbital picture of an intuitive concept, CHEMISTRY-A EUROPEAN JOURNAL, 13, 6321, (2007)
Abstract: Geometry is one of the primary and most direct indicators of aromaticity and anti aromaticity: a regular structure with delocalized double bonds (e.g., benzene) is symptomatic of aromaticity, whereas a distorted geometry with localized double bonds (e.g., 1,3-cyclobutadiene) is characteristic of anti aromaticity. Here, we present a molecular-orbital (MO) model of aromaticity that explains, in terms of simple orbital-overlap arguments, why this is so. Our MO model is based on accurate Kohn-Sham DFT analyses of the bonding in benzene, 1,3-cyclobuta-diene, cyclohexane, and cyclobutane, and how the bonding mechanism is affected if these molecules undergo geometrical deformations between regular, delocalized ring structures, and distorted ones with localized double bonds. We show that the propensity of the pi electrons is always, that is, in both the aromatic and antiaromatic molecules, to localize the double bonds, against the delocalizing force of the sigma electrons. More importantly, we show that the pi electrons nevertheless decide about the localization or delocalization of the double bonds. A key component of our model for uncovering and resolving this seemingly contradictory situation is to analyze the bonding in the various model systems in terms of two interpenetrating fragments that preserve, in good approximation, their geometry along the localization/delocalization modes.

First author: Soave, Raffaefla, Progress in the understanding of drug-receptor interactions, part 2: Experimental and theoretical electrostatic moments and interaction energies of an angiotensin II receptor antagonist (C(30)H(30)N(6)O(3)S),CHEMISTRY-A EUROPEAN JOURNAL, 13, 6942, (2007)
Abstract: A combined experimental and theoretical charge density study of an angiotensin II receptor antagonist (1) is presented focusing on electrostatic properties such as atomic charges, molecular electric moments up to the fourth rank and energies of the intermolecular interactions, to gain an insight into the physical nature of the drug-receptor interaction. Electrostatic properties were derived from both the experimental electron density (multipole refinement of X-ray data collected at T = 17 K) and the ab initio wave-function (single molecule and fully periodic calculations at the DFT level). The relevance of S center dot center dot center dot O and S center dot center dot center dot N intramolecular interactions on the activity of I is highlighted by using both the crystal and gas-phase geometries and their electrostatic nature is documented by means of QTAIM atomic charges. The derived electrostatic properties are consistent with a nearly spherical electron density distribution, characterised by an intermingling of electropositive and -negative zones rather than by a unique electrophilic region opposed to a nucleophilic area. This makes the first molecular moment scarcely significant and ill-determined, whereas the second moment is large, significant and highly reliable. A comparison between experimental and theoretical components of the third electric moment shows a few discrepancies, whereas the agreement for the fourth electric moment is excellent. The most favourable intermolecular bond is show to be an NH center dot center dot center dot N hydrogen bond with an energy of about 50 kJ mol(-1). Key pharmacophoric features responsible for attractive electrostatic interactions include CH center dot center dot center dot X hydrogen bonds. It is shown that methyl and methylene groups, known to be essential for the biological activity of the drug, provide a significant energetic contribution to the total binding energy. Dispersive interactions are important at the thiophene and at both the phenyl fragments. The experimental estimates of the electrostatic contribution to the intermolecular interaction energies of six molecular pairs, obtained by a new model proposed by Spackman, predict the correct relative electrostatic energies with no exceptions.

First author: Krapp, Andreas, Is this a chemical bond? A theoretical study of Ng(2)@C-60 (Ng = He, Ne, Ar, Kr, Xe),CHEMISTRY-A EUROPEAN JOURNAL, 13, 8256, (2007)
Abstract: Quantum-chemical calculations using DFT (BP86) and ab initio methods (MP2, SCS-MP2) have been carried out for the endohedral fullerenes Ng(2)@C-60 (Ng=He-Xe). The nature of the interactions has been analyzed with charge- and energy-partitioning methods and with the topological analysis of the electron density (Atoms-in-Molecules (AIM)). The calculations predict that the equilibrium geometries of Ng(2)@C-60, have D-3d sym metry when Ng=Ne, Ar, Kr, while the energy-minimum structure of Xe-2@C-60 has D-5d symmetry. The precession movement of He-2 in He-2@C-60 has practically no barrier. The Ng-Ng distances in Ng(2)@C-60 are much shorter than in free Ng(2). All compounds N-92@C-60 are thermodynamically unstable towards loss of the noble gas atoms. The heavier species Ar-2@C-60, Kr-2@C-60, and Xe-2@C-60 are high energy compounds which are at the BSSE corrected SCS-MP2/TZVPP level in the range 96.7-305.5 kcalmol(-1) less stable than free C-60+2Ng. The AIM method reveals that there is always an Ng-Ng bond path in Ng(2)@C-60. There are six Ng-C bond paths in (D-3d) Ar-2@C-60, Kr-2@C-60, and Xe-2@C-60, whereas the lighter D3d homologues He-2@C-60 and Ne-2@C-60 have only three Ng-C-2 paths. The calculated charge distribution and the orbital analysis clearly show that the bonding situation in Xe-2@C-60 significantly differs from those of the lighter homologues. The atomic partial charge of the [Xe-2] moiety is +1.06, whereas the charges of the lighter dimers [Ng(2)] are close to zero. The a,, HOMO of (D3d) Xe2@C60 in the (1)A(1g) state shows a large mixing of the highest lying occupied sigma* orbital of [Xe2] and the orbitals of the C-60 cage. There is only a small gap between the a(2u) HOMO of Xe-2@C-60 and the e(u) LUMO and the a(2u) LUMO+1. The calculations show that there are several triplet states which are close in energy to each other and to the (1)A(1g) state. The bonding analysis suggests that the interacting species in Xe-2@C-60 are the charged Species Xe-2(q+) and C-60(q-), where 1 < q < 2. The calculated Xe-Xe distance in the endohedral fullerene (2.494 angstrom) is even shorter than the calculated value for free Xe-2(2+) (2.746 angstrom). Thus, the Xe-C and Xe-Xe interactions in Xe2@C60 should be considered as genuine chemical bonds which are enforced by the compression energy. The Ng-Ng and Ng-C interactions in the lighter homologues Ar-2@C-60 and Kr-2@C-60 may also be considered as chemical bonds because the theoretically predicted properties of the endohedral fullerenes are significantly different from the free C60 and noble gas atoms. According to the bonding analysis, He-2@C-60 and Ne-2@C-60 are weakly bonded van der Waals complexes.

First author: Zheng, Shao-Liang, The nature of the Ag-I center dot center dot center dot Ag-I interaction in different Ag(NH3)(2) dimers embedded in supramolecular, CHEMISTRY-A EUROPEAN JOURNAL, 13, 8583, (2007)
Abstract: An isolated silver(I) ammonia monomer, a dimer, and a novel dimer containing an intercalated water molecule have been embedded as guests in supramolecular frameworks, [Ag(NH3)(2)][(H(2)thpe)(H(3)thpe)]center dot MeCN (1), [{Ag(NH3)(2)}(2)][(H(2)thpe)(2)]center dot 4.25H(2)O (2), and [{Ag(NH3)(2)}-H2O-{Ag(NH3)(2)}]- [(H(2)thpe)(2)]center dot benzene (3) (H3THPE= tris(hydroxyphenyl)ethane). The [{Ag(NH3)(2)}(2)](2+) dimer is not stable as an isolated entity, but is stabilized by hydrogen bonding in the supramolecular framework. The water-intercalated silver(I) ammonia dimer, which constitutes a novel species, is also subject by hydrogen bonding in concentrated solutions. The destabilization energy of the dimer relative to isolated monomers is calculated to be 300 kJ mol(-1) by both perturbation methods and DFT theory. For the water-intercalated dimer it is calculated to be approximate to 200 kJ mol(-1) according to the BSSE-corrected MP2 calculation. The different aggregate states show a dramatic variation of absorption and emission properties, in accordance with the concentration dependent red-shift observed in solutions. Natural-bond-orbital analysis shows that the disilver-ammonium-aquo “sandwich” cation in 3 is stabilized by interaction between the it lone pair orbital on the oxygen atom of the water molecule and Ag-1-N o antibonding molecular orbital.

First author: Fernandez, Israel, Stable pentacoordinate carbocations: Structure and bonding, CHEMISTRY-A EUROPEAN JOURNAL, 13, 8620, (2007)
Abstract: We report that only elements more electropositive than carbon (Group 13, 14, and Be) form stable symmetrical HnE-CH3-EHn+ structures (E = Group 1, 2, 13, or 14 element) with a planar CH3 group symmetrically bonded to two EHn moieties, in analogy with prototypical S(N)2 transition structures. Analysis of the bonding situation of these pentacoordinate carbon molecules was studied by means of an energy decomposition analysis (EDA) of the interaction energy. This shows that HnE-CH3EH3- molecules can be viewed as being composed of one CH3 group that is sigma-covalently bonded to two EHn groups forming a three-center, two-electron bond.

First author: Hebben, Nicole, The electronic structure of the tris(ethylene) complexes [M(C2H4)(3)] (M=Ni, Pd, and Pt): A combined experimental and theoretical study, CHEMISTRY-A EUROPEAN JOURNAL, 13, 10078, (2007)
Abstract: In this article we analyze in detail the electronic properties of the D-3h-Symmetric tris(ethylene) complexes of nickel, palladium, and platinum ([M(C2H4)(3)] M=Ni, Pd, Pt). In the case of [Pd(C2H4)(3)] the analysis is based on new experimental IR and Raman spectra for the matrix-isolated molecules and in all cases on the results of quantum-chemical (DFT) calculations. The experimental spectra collected for [Pd(C2H4)(3)] provide evidence for several previously unobserved vibrational modes, including the in-phase and out-of-phase nu(C-C) and delta(CH2) modes, and the in-phase nu(M-C) mode. Special consideration is given to possible inter-ligand interactions. The interaction force constant f(CC,CC) between two C2H4 ligands can be directly estimated from the spectra, and its very small value (0.002 Nm(-1)) indicates the absence of any significant inter-ligand interaction. An analysis of the topology of the theoretical electron density distribution, rho(r), and the corresponding Laplacian, del(2)rho(r), for [Pd(C2H4)(3)] and its lighter and heavier homologues [Ni(C2H4)(3)] and [Pt(C2H4)(3)], respectively, is in full agreement with the conclusions drawn from the experimental results. The combined experimental and quantum-chemical results provide detailed insights in the electronic properties of these prototypical ethylene complexes.

First author: Maurer, Jorg, Towards new organometallic wires: Tetraruthenium complexes bridged by phenylenevinylene and vinylpyridine ligands, CHEMISTRY-A EUROPEAN JOURNAL, 13, 10257, (2007)
Abstract: The tetranuclear complexes [{(PiPr(3))(2)(CO)ClRu(mu-CH=CHpy)Ru Cl(CO)(PPh3)(2)}(2)(mu-CH=CH-C6H4-CH=CH-1,4)] (3a) and [{(PiPr(3))(2)(CO)- ClRu(mu-CH=CHpy)RuCl(CO)(PPh3)(2)}(2)-(mu-CH=CH-C6H4-CH=CH-1,3)] (3b), which contain vinylpyridine ligands that connect peripheral Ru(PiPr(3))(2)(CO)Cl units to a central di-vinylphenylene-bridged diruthenium core, have been prepared and investigated. These complexes, in various oxidation states up to the tetracation level, have been characterized by standard electrochemical and spectroelectrochemical techniques, including IR, UV/Vis/NIR and ESR spectroscopy. A comparison with the results for the vinylpyridine-bridged dinuclear complex [PiPr(3))(2)(CO)ClRu(mu-CH=CHpy)RuCl-(CO)(PPh3)(2)(CH=CHPh)] (6) and the divinylphenylene-bridged complexes [{(EtOOCpy)(CO)Cl(PPh3)(2)Ru}(2)(mu- CH=CH-C6H4-CH=CH-1,4)] (8a) and [{(EtOOCpy)(CO)Cl(PPh3)(2)Ru}(2)(mu-CH=CH-C6H4-CH=CH-1,3)] (8 b), which represent the outer sections (6) or the inner core (8a,b) of complexes 3a,b, and with the mononuclear complex [(EtOOCpy)(CO)(PPh3)(2)RuCl(CH=CHPh)] (7) indicate that every accessible oxidation process is primarily centred on one of the vinyl ligands, with smaller contributions from the metal centres. The experimental results and quantum chemical calculations indicate charge- and spin-delocalization across the central divinylphenylenediruthenium part of 3a,b or the styrylruthenium unit of 6, but not beyond. The energy gap between the higher lying styryl- or divinylphenylenediruthenium-based and the lower occupied vinylpyridineruthenium-based orbitals increases in the order 6 < 3b < 3a and thus follows the conjugation within the non-heteroatom-substituted aromatic vinyl ligand.

First author: Tonner, Ralf, Bonding analysis of N-heterocyclic carbene tautomers and phosphine Ligands in transition-metal complexes: A theoretical study, CHEMISTRY-AN ASIAN JOURNAL, 2, 1555, (2007)
Abstract: DFT calculations at the BP86/TZ2P level were carried out to analyze quantitatively the metal-ligand bonding in transition-metal complexes that contain imidazole (IMID), imidazol-2-ylidene (nNHC), or imidazol-4-ylidene (aNHC). The calculated complexes are [Cl4TM(L)] (TM=Ti, Zr, Hf), [(CO)(5)TM(L)] (TM=Cr, Mo, W), [(CO)(4)TM(L)] (TM=Fe, Ru, Os), and [CITM(L)] (TM=Cu, Ag, Au). The relative energies of the free ligands increase in the order IMID < nNHC < aNHC. ne energy levels of the carbon a lone-pair orbitals suggest the trend aNHC > nNHC > IMID for the donor strength, which is in agreement with the progression of the metal-ligand bond-dissociation energy (BDE) for the three ligands for all metals of Groups 4, 6, 8, and 10. The electrostatic attraction can also be decisive in determining trends in ligand-metal bond strength. The comparison of the results of energy decomposition analysis for the Group 6 complexes [(CO)(5)TM(L)] (L=nNHC, aNHC, IMID) with phosphine complexes (L=PMe3 and PCl3) shows that the phosphine ligands are weaker sigma donors and better pi acceptors than the NHC tautomers nNHC, aNHC, and IMID.

First author: Costa, Paulo J., Remote metal-arene pi bonding in organometallic complexes: A DFT study, COLLECTION OF CZECHOSLOVAK CHEMICAL COMMUNICATIONS, 72, 703, (2007)
Abstract: The observation that the 14-electron cation [Rh(PPh3)(3)](+) is more electron-rich than expected, as a result of coordination of a C = C bond in one phenyl group, opened the way to a search for more examples of this behavior. We used DFT calculations and energy decomposition analysis to study this M -eta(2)-arene interaction and to calculate its strength. For this purpose, we have chosen two formally unsaturated complexes, viz. [Mo(eta(5)-C5H5)(CO)(2)(PPh3)](+) (1) and [Ru(eta(5)-C5H5)(binap)](+) (2). In the former complex, the PPh3 ligand can be easily moved away from the metal, destroying the Mo -eta(2)-arene interaction, while in 2 this is achieved by a distortion of the Binap ligand. The experimental parameters, namely the distortion of the aryl-containing ligand, have been well reproduced by the calculated coordination geometry; the M -eta(2)-arene interaction was estimated as 13.4 kcal mol(-1) for Mo and 21.4 kcal mol(-1) for Ru. The energy decomposition analysis revealed the formation of a covalent bond between the metal and the C = C bond, which made the global process favorable, regardless the energy required to reorganize the geometry of the ligand in the new environment.

First author: Voznicova, Radka, On the reaction of hexachlorocyclotriphosphazene with heptamethyldisilazane. Crystal structure of P3N3Cl5{N(CH3)[Si(CH3)(3)]}, COLLECTION OF CZECHOSLOVAK CHEMICAL COMMUNICATIONS, 72, 1407, (2007)
Abstract: The reaction of P3N3Cl6 (1) with heptamethyldisilazane in the molar ratio 1:1 leads to the formation of 2,4,4,6,6-pentachloro-N-methyl-N-(trimethylsilyl) cyclotriphosphazen-2-amine, P3N3Cl5{N(CH3)[Si(CH3)(3)]} (2). Compound 2 was characterized by elemental analysis and spectroscopically. Molecular and crystal structures of 2 were determined by X-ray diffraction. 2 is monoclinic, space group P2(1)/n. Experimental data were compared with results of DFT calculations.

First author: Brayshaw, Simon K., A DFT based investigation into the electronic structure and properties of hydride rich rhodium clusters, DALTON TRANSACTIONS, 72, 1781, (2007)
Abstract: Density functional theory has been used to investigate the structures, bonding and properties of a family of hydride rich late transition metal clusters of the type [Rh-6(PH3)(6)H-12](x)(x=0,+1,+2,+3 or +4), [Rh-6(PH3)(6)H-16](x)(x=+1or+2) and [Rh-6(PH3)(6)H-14](x)(x=0,+1or+2). The positions of the hydrogen atoms around the pseudo-octahedral Rh-6 core in the optimized structures of [Rh-6(PH3)(6)H-12](x) (x=0,+1,+2,+3 or +4) varied depending on the overall charge on the cluster. The number of semi-bridging hydrides increased (semi-bridging hydrides have two different Rh-H bond distances) as the charge on the cluster increased and simultaneously the number of perfectly bridging hydrides ( equidistant between two Rh centers) decreased. This distortion maximized the bonding between the hydrides and the metal centers and resulted in the stabilization of orbitals related to the 2T(2g) set in a perfectly octahedral cluster. In contrast, the optimized structures of the 16-hydride clusters [Rh-6(PH3)(6)H-12](x)(x=+1 or +2) were similar and both clusters contained an interstitial hydride, along with one terminal hydride, ten bridging hydrides and two coordinated H-2 molecules which were bound to two rhodium centers in an eta(2): eta(1)-fashion. All the hydrides were on the outside of the Rh-6 core in the lowest energy structures of the 14-hydride clusters [Rh-6(PH3)(6)H-14] and [Rh-6(PH3)(6)H-14](+), which both contained eleven bridging hydrides, one terminal hydride and one coordinated H-2 molecule. Unfortunately, the precise structure of [Rh-6(PH3)(6)H-14](2+) could not be determined as structures both with and without an interstitial hydride were of similar energy. The reaction energetics for the uptake and release of two molecule of H-2 by a cycle consisting of [ Rh-6(PH3)(6)H-12](2+), [ Rh6( PH3) 6H16](2+), [ Rh-6(PH3)(6)H-14](+), [Rh-6(PH3)(6)H-12](+) and [ Rh-6( PH3)(6)H-14](2+) were modelled, and, in general, good agreement was observed between experimental and theoretical results. The electronic reasons for selected steps in the cycle were investigated. The 12-hydride cluster [Rh-6(PH3)(6)H-12](2+) readily picks up two molecules of H-2 to form [Rh-6(PH3)(6)H-16](2+) because it has a small HOMO-LUMO gap (0.50 eV) and a degenerate pair of LUMO orbitals available for the uptake of four electrons (which are provided by two molecules of H-2). The reverse process, the spontaneous release of a molecule of H-2 from [ Rh-6( PH3)(6)H-16](+) to form [Rh-6(PH3)(6)H-14](+) occurs because the energy gap between the anti-bonding SOMO and the next highest energy occupied orbital in [Rh-6(PH3)(6)H-16](+) is 0.9 eV, whereas in Rh-6(PH3)(6)H-14](+) the energy gap between the anti-bonding SOMO and the next highest energy occupied orbital is only 0.3 eV. At this stage the factors driving the conversion of [Rh-6(PH3)(6)H-14](+) to [Rh-6(PH3)(6)H-12](2+) are still unclear.

First author: Christian, Gemma, Rationalizing the different products in the reaction of N-2 with three-coordinate MoL3 complexes, DALTON TRANSACTIONS, 72, 1939, (2007)
Abstract: The reaction of N-2 with three-coordinate MoL3 complexes is known to give rise to different products, N-MoL3, L3Mo-N-MoL3 or Mo2L6, depending on the nature of the ligand L. The energetics of the different reaction pathways are compared for L = NH2, NMe2, N(Pr-i)Ar and N(Bu-t)Ar (Ar = 3,5-C6H3Me2) using density functional methods in order to rationalize the experimental results. Overall, the exothermicity of each reaction pathway decreases as the ligand size increases, largely due to the increased steric crowding in the products compared to reactants. In the absence of steric strain, the formation of the metal-metal bonded dimer, Mo2L6, is the most exothermic pathway but this reaction shows the greatest sensitivity to ligand size varying from significantly exothermic, -403 kJ mol(-1) for L = NMe2, to endothermic, + 78 kJ mol(-1) for L = N(Bu-t)Ar. For all four ligands, formation of N-MoL3 via cleavage of the N-2 bridged dimer intermediate, L3Mo-N-N-MoL3, is strongly exothermic. However, in the presence of excess reactant MoL3, formation of the single atom-bridged complex L3Mo-N-MoL3 from N-MoL3 + MoL3 is both thermodynamically and kinetically favoured for L = NMe2 and N( iPr) Ar, in agreement with experiment. In the case of L = N( tBu) Ar, the greater steric bulk of the tBu group results in a much less exothermic reaction and a calculated barrier of 66 kJ mol(-1) to formation of the L3Mo-N-MoL3 dimer. Consequently, for this ligand, the energetically and kinetically favoured product, consistent with the experimental data, is the nitride complex L3Mo-N.

First author: Starynowicz, Przemyslaw, An ytterbium(II) complex with dimethyl ester of oxydiacetic acid, DALTON TRANSACTIONS, 72, 2779, (2007)
Abstract: An Yb( II) complex with dimethyl ester of oxydiacetic acid, [Yb(CH3OOCCH2OCH2COOCH3)(3)]-( ClO4)(2), has been obtained by electrochemical reduction and its crystal structure has been determined. The complex cations have the D-3 (32) crystallographic symmetry. The compound shows a very broad absorption band, starting from 500 nm towards the UV region, and traces of luminescence with a maximum at 545 nm. The performed density functional theory ( DFT) calculations have shown that the absorption band results from mixed f-d and charge transfer transitions, and the empty antibonding pi* orbitals of the ester groups quench the luminescence.

First author: Lemonnier, Jean-Francois, Host-guest adaptability within oxothiomolybdenum wheels: structures, studies in solution and DFT calculations, DALTON TRANSACTIONS, 72, 3043, (2007)
Abstract: The formation of host-guest cyclic architectures, built up through the self-condensation process of [Mo2O2S2](2+) oxothiocations around linear dicarboxylate ions such as adipate (Adip(2-)), suberate (Sub(2-)) and azelaate (Azel(2-)) anions is reported. The complexes [Mo(12)Adip](2-), [Mo(12)Sub](2-) and [Mo(14)Azel](2-) have been characterized in the solid state by X-ray diffraction and in solution by H-1 NMR in different solvents (D2O, DMF, DMSO and CD3CN). The host-guest dynamics appear to be dependent on the nature of the system and are mainly governed by mutual adaptability between the host and the guest. H-1 NMR DOSY experiments show systematic differences, either positive or negative between the experimental and calculated molecular weights which appear to be correlated with the charge of the anion. The relative stabilities of the twelve-membered rings containing the Adip(2-), Pim(2-) (pimelate) or Sub(2-) anions were determined experimentally and decrease according to the order [Mo(12)Adip](2-) > [Mo(12)Pim](2-) > [Mo(12)Sub](2-). The host-guest adaptability depends on the length of the carbon chain and gives rise to selective encapsulation processes. Finally, theoretical DFT investigations in the gas phase yielded conformations whose symmetry and geometrical parameters proved consistent with X-ray structures and 1H NMR spectra recorded in DMSO or DMF. Energy calculation highlights the high flexibility of the ring showing that only 3.1 kJ mol(-1) accompanies the conformational change from circular to elliptical. The host-guest bond energy ( DE) calculated for the Mo-12-based clusters is consistent with the experimental stability scale, major variations being due to some constraints undergone by the central alkyl chain.

First author: McRobbie, Graeme, Probing key coordination interactions: configurationally restricted metal activated CXCR4 antagonists, DALTON TRANSACTIONS, 72, 5008, (2007)
Abstract: The syntheses of configurationally restricted mono- and bis-macrocyclic copper( II) perchlorate complexes ( copper( II) 5-benzyl-1,5,8,12-tetraazabicyclo[10.2.2]hexadecane and dicopper( II) 5,5 ‘-[ 1,4-phenylenebis(methylene)]-bis(1,5,8,12-tetraazabicyclo[10.2.2]hexadec ane)) are reported and the X-ray structure of the copper( II) mono- macrocyclic complex has been determined. EXAFS studies on the bis-macrocyclic species in aqueous solution show that the copper coordination spheres are essentially identical to the solid state structure, and do not vary in the presence of 20 equivalents of sodium acetate per metal centre. DFT calculations were carried out at the BP86/TZP level to determine the nature of potential binding interactions with CXCR4 aspartate residues. The alkylated single macrocyclic compound was modelled with an acetate included to represent the aspartate residue, demonstrating that the predicted macrocycle configuration has the lowest energy and the acetate interaction is effectively monodentate giving a distorted trigonal bipyramidal geometry at the copper centre. In vitro anti-HIV infection assays show that the configurationally restricted dicopper( II) complex is more active ( average EC50 = 0.026 lM against HIV-1) than the non-constrained dicopper( II) 1,1 ‘-[1,4-phenylenebis(methylene)]-bis(1,4,8,11-tetraazacyclotetradecane) ( average EC50 = 0.047 mu M against HIV-1) although it is an order of magnitude less active than the configurationally restricted dizinc( II) complex.

First author: Bruce, Michael I., Syntheses, structures and redox properties of some complexes containing the Os(dppe)Cp* fragment, including [{Os(dppe)Cp*}(2)(mu-C CC C)], DALTON TRANSACTIONS, 72, 5387, (2007)
Abstract: The sequential conversion of [OsBr(cod)Cp*] (9) to [OsBr(dppe)Cp*] (10), [Os(=C=CH2)(dppe)Cp*] PF6 ([11]PF6), [Os(C CH)(dppe)Cp*] (12), [{Os(dppe)Cp*}(2){mu-(=C=CH-CH=C=)}][PF6](2) ([13](PF6)(2)) and finally [{Os(dppe)Cp*}(2)(mu-C CC C)] (14) has been used to make the third member of the triad [{M(dppe)Cp*}(2)(mu-C CC C)] (M = Fe, Ru, Os). The molecular structures of [11]PF6, 12 and 14, together with those of the related osmium complexes [Os(NCMe)(dppe)Cp*]PF6 ([15]PF6) and [Os(C CPh)(dppe)Cp*] (16), have been determined by single-crystal X-ray diffraction studies. Comparison of the redox properties of 14 with those of its iron and ruthenium congeners shows that the first oxidation potential E-1 varies as: Fe approximate to Os < Ru. Whereas the Fe complex has been shown to undergo three sequential 1-electron oxidation processes within conventional electrochemical solvent windows, the Ru and Os compounds undergo no fewer than four sequential oxidation events giving rise to a five-membered series of redox related complexes [{M(dppe)Cp*}(2)(mu-C-4)](n+) (n = 0, 1, 2, 3 and 4), the osmium derivatives being obtained at considerably lower potentials than the ruthenium analogues. These results are complimented by DFT and DT DFT calculations.

First author: Fernandez, Israel, Direct estimate of conjugation and aromaticity in cyclic compounds with the EDA method,FARADAY DISCUSSIONS, 135, 403, (2007)
Abstract: The nature of the interatomic interactions in cyclic conjugated molecules has been investigated with the Energy Decomposition Analysis ( EDA). The focus of this work is on the strength of the pi bonding and pi conjugation in carbocyclic and heterocyclic molecules. The calculated Delta E-pi values suggest that the EDA may be used directly for estimating the strength of pi conjugation in aromatic, homoaromatic, homoantiaromatic and antiaromatic compounds. The theoretical data show a pattern which agrees with the 4n + 2 rule. The extra aromatic stabilization energy has been obtained by comparing cyclic conjugation with the strength of pi conjugation in acyclic reference compounds. The Delta E-pi values indicate that benzene is significantly stabilized by aromatic stabilization, but the total pi bonding contribution to the carbon – carbon bonding becomes even more stabilizing when the geometry is distorted toward a D-3h form which has three long and three short C – C bonds. The D-6h equilibrium structure is enforced by the sigma orbital interactions and by the quasiclassical electrostatic attraction. The VRE and ASE values suggest that pyridine is more strongly stabilized by aromatic conjugation than benzene. The EDA data of the six-membered cyclic 6 pi species C5H5E (E=CH, N-Bi) and (HB=NH)(3) predicts strength of aromatic stabilization in the order N > CH > P > As > Bi >> borazine. The ASE values of the five-membered heterocyclic systems C4H4E (E=NH, O, S) are smaller than for the benzene analogues showing the order NH similar to S > O. The ASE value for Cp- is very small which probably comes from the choice of the reference system. The VRE results indicate that Cp- is strongly stabilized by cyclic conjugation. The ASE values for the cyclic singlet carbenes indicate weak aromatic stabilization in the 2 pi system cyclopropenylidene which is much stronger in the 6 pi compound cycloheptatrienylidene while the 4 pi molecule cylopentadienylidene is clearly antiaromatic. The triplet states of all three cyclic carbenes are antiaromatic. The strength of the p conjugation in the homoconjugated cyclic compounds suggests weak aromatic stabilization in the 6 pi compounds 1,3-cyclobutene and 1,3-cyclopentadiene but weak antiaromatic destabilization in the 2 pi compound cyclopropene and in the 8 pi molecules 1,3-cyclohexadiene and 1,3,5-cycloheptatriene. The 4n + 2 rule thus holds also for homoconjugated systems. A large negative value for the ASE is calculated for 1,3-cyclobutadiene.

First author: Bickelhaupt, F. Matthias, Highly polar bonds and the meaning of covalency and ionicity – structure and bonding of alkali metal hydride oligomers, FARADAY DISCUSSIONS, 135, 451, (2007)
Abstract: The hydrogen-alkali metal bond is simple and archetypal, and thus an ideal model for studying the nature of highly polar element-metal bonds. Thus, we have theoretically explored the alkali metal hydride monomers, HM, and ( distorted) cubic tetramers, (HM)(4), with M = Li, Na, K, and Rb, using density functional theory (DFT) at the BP86/TZ2P level. Our objective is to determine how the structure and thermochemistry ( e. g., H-M bond lengths and strengths, oligomerization energies, etc.) of alkali metal hydrides depend on the metal atom, and to understand the emerging trends in terms of quantitative Kohn-Sham molecular orbital (KS-MO) theory. The H-M bond becomes longer and weaker, both in the monomers and tetramers, if one descends the periodic table from Li to Rb. Quantitative bonding analyses show that this trend is not determined by decreasing electrostatic attraction but, primarily, by the weakening in orbital interactions. The latter become less stabilizing along Li-Rb because the bond overlap between the singly occupied molecular orbitals (SOMOs) of H-. and M-. radicals decreases as the metal ns atomic orbital (AO) becomes larger and more diffuse. Thus, the H – M bond behaves as a text-book electron-pair bond and, in that respect, it is covalent, despite a high polarity. For the lithium and sodium hydride tetramers, the H-4 tetrahedron is larger than and surrounds the M-4 cluster (i.e., H – H 4 M – M). Interestingly, this is no longer the case in the potassium and rubidium hydride tetramers, in which the H4 tetrahedron is smaller than and inside the M4 cluster ( i.e., H-H < M-M).

First author: Periyasamy, Ganga, The dithiolene ligand – ‘innocent’ or ‘non-innocent’? A theoretical and experimental study of some cobalt-dithiolene complexes, FARADAY DISCUSSIONS, 135, 469, (2007)
Abstract: As Jorgensen pointed out in 1966 ( Coord. Chem. Rev., 1966, 1, 164), a ligand is to be regarded as ‘innocent’ if it allows the oxidation state of a metal in a complex to be defined. In this respect, the vast majority of ligands are ‘innocent’ and, therefore, ligands that are ‘non-innocent’ have received special attention. Dithiolenes have been regarded as ‘non-innocent’ ligands since it is possible to consider a ligand of this type to be present in a complex as either: (i) an ene-1,2-dithiolate dianion or (ii) a neutral dithioketone. On this basis, the electronic structure of a dithiolene complex can be described by a set of resonance structures, each of which involves the dithiolene in one of the two forms with the oxidation state of the metal centre being adjusted accordingly. The relative importance of these structures is expected to be reflected in the corresponding molecular structure and spectroscopic properties. In this paper we present a theoretical study of the pair of related eta(5)-cyclopentadienyl cobalt dithiolene complexes, [CpCo(S2C2(H)Ph)] and [CpCo(S2C2(H)Ph)(PMe3)]. Density functional theory calculations successfully predict their different structures and NMR chemical shifts, which we have measured. These wavefunctions have been analysed, particularly in terms of Natural Bond Orbitals and Nucleus Independent Chemical Shifts in an attempt to understand how “innocence” or otherwise is reflected in the experimental data. To this end, a similar analysis is applied to the gold complexes [Au(S2C2(H)Ph)(2)](-) and [Au(S2C2(H)Ph)(2)].

First author: Swart, Marcel, Metal-ligand bonding in metallocenes: Differentiation between spin state, electrostatic and covalent bonding, INORGANICA CHIMICA ACTA, 360, 179, (2007)
Abstract: We have analyzed metal-ligand bonding in metallocenes using density functional theory (DFT) at the OPBE/TZP level. This level of theory was recently shown to be the only DFT method able to correctly predict the spin ground state of iron complexes, and similar accuracy for spin ground states is found here. We considered metallocenes along the first-row transition metals (Sc-Zn) extended with alkaline-earth metals (Mg, Ca) and several second-row transition metals (Ru, Pd, Ag, Cd). Using an energy decomposition analysis, we have studied trends in metal-ligand bonding in these complexes. The OPBE/TZP enthalpy of heterolytic association for ferrocene (-658 kcal/mol) as obtained from the decomposition analysis is in excellent agreement with benchmark CCSD(T) and CASPT2 results. Covalent bonding is shown to vary largely for the different metallocenes and is found in the range from -155 to -635 kcal/mol. Much smaller variation is observed for Pauli repulsion (55-345 kcal/mol) or electrostatic interactions, which are however strong (-480 to -620 kcal/mol). The covalent bonding, and thus the metal-ligand bonding, is larger for low spin states than for higher spin states, due to better suitability of acceptor d-orbitals of the metal in the low spin state. Therefore, spin ground states of transition metal complexes can be seen as the result of a delicate interplay between metal-ligand bonding and Hund’s rule of maximum multiplicity.

First author: Autschbach, Jochen, Analyzing and interpreting NMR spin-spin coupling constants using molecular orbital calculations, JOURNAL OF CHEMICAL EDUCATION, 84, 156, (2007)
Abstract: We have analyzed metal-ligand bonding in metallocenes using density functional theory (DFT) at the OPBE/TZP level. This level of theory was recently shown to be the only DFT method able to correctly predict the spin ground state of iron complexes, and similar accuracy for spin ground states is found here. We considered metallocenes along the first-row transition metals (Sc-Zn) extended with alkaline-earth metals (Mg, Ca) and several second-row transition metals (Ru, Pd, Ag, Cd). Using an energy decomposition analysis, we have studied trends in metal-ligand bonding in these complexes. The OPBE/TZP enthalpy of heterolytic association for ferrocene (-658 kcal/mol) as obtained from the decomposition analysis is in excellent agreement with benchmark CCSD(T) and CASPT2 results. Covalent bonding is shown to vary largely for the different metallocenes and is found in the range from -155 to -635 kcal/mol. Much smaller variation is observed for Pauli repulsion (55-345 kcal/mol) or electrostatic interactions, which are however strong (-480 to -620 kcal/mol). The covalent bonding, and thus the metal-ligand bonding, is larger for low spin states than for higher spin states, due to better suitability of acceptor d-orbitals of the metal in the low spin state. Therefore, spin ground states of transition metal complexes can be seen as the result of a delicate interplay between metal-ligand bonding and Hund’s rule of maximum multiplicity.

First author: Schmidt, Andreas, Studies on photocatalytically active materials containing structure elements of a pyridinium alkaloid from Punica granatum, JOURNAL OF MATERIALS CHEMISTRY, 17, 2793, (2007)
Abstract: The alkaloid punicin from Punica granatum, N-(2 ‘,5 ‘- dihydroxyphenyl) pyridinium chloride, forms heterocyclic mesomeric betaines and radicals, which were examined by ESR measurements and DFT calculations, in aqueous solution. By reaction of poly(4-vinylpyridine) with p-benzoquinone under two different reaction conditions, polymeric structures with punicin constituents were prepared and characterized. The ESR signals of these polymers were calculated and discussed. The 4,4 ‘-bipyridine derivative of these polymers was prepared starting from Merrifield resin which was subsequently reacted with 4,4 ‘-bipyridine and p-benzoquinone, or, alternatively, with N-(2 ”-5 ”-dihydroxyphenyl)-4-(4 ‘-pyridine) pyridinium chloride. The properties of these new materials in reversible photocatalytic processes via radical species were examined. Therefore, solutions or suspensions were irradiated in water in the presence of proflavinium as a sensitizer, and EDTA as a sacrificial donor under an inert atomsphere. Oxygen (air) recovers the starting materials by formation of hydroxide ions which were determined by pH measurements.

First author: Fang, Hua, Density functional study of closed-shell attraction on X(ML)(3)(+)(X = O, S, Se; M = Au, Ag, Cu) systems, JOURNAL OF MOLECULAR MODELING, 13, 255, (2007)
Abstract: With the help of quantum mechanical calculations, we have examined the series of central system X(ML)(3)(+)(X = O, S, Se; M = Au, Ag, Cu). Using a scalar-relativistic density functional approach, we studied the geometry structures, Mulliken populations and charges of the systems. Structure parameters of the experimental systems are reproduced well with X alpha method. The metallophilic interaction energy is analyzed and decomposed. For the systems with different central atoms and different metal atoms, the nature of the metallophilic attraction interaction is analyzed.

First author: Miyamoto, Akira, Electronic structure and electrical conductivity of MgO protecting layer in plasma-display panels: A tight-binding quantum chemical study, JOURNAL OF THE SOCIETY FOR INFORMATION DISPLAY, 15, 307, (2007)
Abstract: The tight-binding quantum chemical molecular dynamics code, Colors, has been successfully applied to the electronic-structure calculations of the MgO-protecting-layer model in plasma-display panels (PDPs). The code succeeded in reproducing the band-gap energy of the MgO crystal structure. The energy gap between the bottom of the conduction band (CB) and the top of valence band (VB) was 7.45 eV, which is in quantitative agreement with the experimental and previous theoretical results. The electronic structure of the undoped MgO model and Si-doped MgO model was also calculated. The impurity level was 2.15 eV lower than that for the bottom of the CB. This result was in qualitative agreement with recent cathodoluminescence measurements. In addition, we have already succeeded in developing a novel electrical conductivity simulator using the spatial distribution of the probability density of wave functions obtained from the tight-binding quantum chemical molecular dynamics code, Colors. The electrical conductivity of the MgO-protecting-layer model was estimated with and without an oxygen defect and a significant change in the electrical conductivity of the MgO-protecting-layer materials was observed with the introduction of oxygen defects.

First author: Pazderski, Leszek, H-1, C-13 and N-15 NMR coordination shifts in gold(III), cobalt(III), rhodium(III) chloride complexes with pyridine, 2,2 ‘-bipyridine and 1,10-phenanthroline, MAGNETIC RESONANCE IN CHEMISTRY, 45, 24, (2007)
Abstract: Au(III), Co(III) and Rh(III) chloride complexes with pyridine (py), 2,2′-bipyridine (bpy) and 1,10-phenanthroline (phen) of the general formulae [(MLCl3)-L-1], trans-[(ML4Cl2)-L-2](+), mer-[(ML3Cl3)-L-2], [M-1(LL)Cl-2](+), cis-[M-2(LL)(2)Cl-2](+), where M-1 = Au; M-2 = Co, Rh; L = py; LL = bpy, phen, were studied by H-1-C-13 HMBC and H-1-N-15 HMQC/HSQC. The H-1, C-13 and N-15 coordination shifts (the latter from ca -78 to ca -10 7 ppm) are discussed in relation to the type of metal, electron configuration, coordination sphere geometry and the type of ligand. The C-13 and N-15 chemical shifts were also calculated by quantum-chemical NMR methods, which reproduced well the experimental tendencies concerning the coordination sphere geometry and the ligand type.

First author: Zalis, Stanislav, Electronic structures of two kinds of oligoborane radical anions: mixed-valence description of a reduced p-phenylenediborane and spin density distributions in distorted octahedral clusters [B(6)Hal(6)](center dot-), Hal = Cl, Br, I, MAIN GROUP CHEMISTRY, 5, 267, (2007)
Abstract: Density-functional theory (DFT) calculations have been carried out for the radical anions 1,4[Mes(2)B-(C6H4)-BMes(2)](center dot-) (1) (Mes, mesityl), and for [B6Cl6](center dot-) (2a), [B6Br6](center dot-) (2b) and [B6I6](center dot-) (2c). Previous EPR experiments had indicated significant spin delocalisation based on H-1, B-10 and B-11 hyperfine structure (1) and on g factor anisotropy (2a – c). Starting from optimized geometries the calculations confirmed this notion and yielded quantitative information on the spin distribution. While 1 with about 1/3 of spin density on each of the B atoms and on the organic bridge can be well-formulated as a delocalised (Class III) diboron(III,II) mixed-valent species with a p-phenylene spacer, similarly as the p-phenylenediamine radical cations, the paramagnetic anions 2 are trigonally Jahn-Teller distorted octahedral clusters with variable contributions from the halide substituents to the accommodation of the unpaired electron. While the chloride substituents in 2a participate rather little at the spin distribution, the iodide 2c is calculated with about equal contributions of 8% from individual B and I atoms to the singly occupied MO (SOMO).

First author: Kadantsev, Eugene S., The formulation and implementation of analytic energy gradients for periodic density functional calculations with STO/NAO Bloch basis set, MOLECULAR PHYSICS, 105, 2583, (2007)
Abstract: Analytic energy gradients with respect to atomic coordinates for systems with translational invariance are formulated within the framework of Kohn-Sham Density Functional Theory. The energy gradients are implemented in the BAND program for periodic DFT calculations which directly employs a Bloch basis set made up of Slater-type (STOs) and numeric atomic orbitals (NAOs). The details of our implementation are described including the use of symmetry in the reciprocal and direct spaces, as well as the application of the frozen core approximation.

First author: Jechow, Jason, Role of rotational entropy in benzyl isocyanide isomerization, MOLECULAR PHYSICS, 105, 2919, (2007)
Abstract: We present here a detailed analysis of benzyl isocyanide isomerization as a test case for the ability of different theoretical methods to treat changes in internal rotational degrees of freedom during a reaction. In this reaction, the phenyl rotates freely in the reactant, but has hindered rotation at the transition state; this yields a negative contribution to the reaction entropy. Free energy of activation, internal energy of activation, and entropy of activation were quantified using both thermodynamic integration and harmonic frequency analysis. Compared with experiment, thermodynamic integration generated more accurate activation parameters than the harmonic frequency analysis. A hindered rotor model was also applied to retrieve thermodynamic properties of phenyl rotation at the reactant and at the transition state. The results from this hindered rotor calculation were used to improve the results from the harmonic frequency analysis as well as to verify that the decrease in entropy from the phenyl rotation hindered at the transition state is a major contributor to the entropy of activation seen experimentally in this reaction.

First author: Herrmann, Carmen, Finding a needle in a haystack: direct determination of vibrational signatures in complex systems, NEW JOURNAL OF CHEMISTRY, 31, 818, (2007)
Abstract: Vibrational spectroscopy is a powerful tool to investigate the structure and dynamics of molecular systems. When large molecules are studied, quantum chemical calculations are used to interpret the spectra. In many cases, experimentally driven questions are related to specific regions of a vibrational spectrum, so that an assignment is only required for a subset of vibrations. This holds true in particular for biomolecules, inorganic compounds which are stabilized by many bulky ligands, or other extended systems. In standard quantum chemical calculations of the vibrational spectrum, all normal modes and frequencies of the molecule under study are determined. However, the selective calculation of only relevant information can be made much more efficient by using mode-selective techniques as provided by the mode-tracking algorithm. A critical point for the performance of the mode-tracking scheme is the preparation of a guess vibration, which is then iteratively refined. The guess defines the scientific problem which is to be studied. Various examples are presented to highlight this aspect and the features of the mode-tracking algorithm in general.

First author: Kaczmarzyk, Tomasz, Asymmetry in Mossbauer spectra of Fe-III-azaporphyrin complexes, NUKLEONIKA,52, S93, (2007)
Abstract: Temperature dependence of asymmetry as well as isomer shift and quadrupole splitting values of Mossbauer spectra of trivalent iron complexes coordinated to porphyrin ligands such as octaethylporphyrin, monoazaethioporphyrin, diazaoctaethylporphyrin and phthalacyanine is discussed in this paper. All the above mentioned complexes have the chloride axial ligand at the fifth coordination site. Different temperature changes of asymmetry and other parameters of Mossbauer spectra of these complexes can be correlated with a number of methine bridges CH substituted by nitrogen atoms in the porphyrin macrocycle. The form of this asymmetry is such that the higher-energy component of the doublet is more broadened than the lower-energy one, while the areas (intensities) under each of two components are the same. The most distinct asymmetry is observed at room temperature. When temperature is decreasing, the spectrum becomes successively more symmetrical and at liquid helium temperature linewidths of both components of the quadrupole splitting are very close one another. The Mossbauer spectrum of the FeCl-monoazaethioporphyrin complex exhibits reversed asymmetry at liquid helium temperature in comparison with the spectra of the remaining complexes i.e. the lower-energy component of the doublet is slightly more broadened than the higher-energy one. The spin-spin and spin-lattice relaxation mechanisms in the context of quantum mechanically mixed spin states S = 5/2 + 3/2 of Fe-III ions are considered as a source of the observed asymmetry.

First author: Feindel, Kirk W., A solid-state Mn-55 NMR spectroscopy and DFT investigation of manganese pentacarbonyl compounds, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 9, 1226, (2007)
Abstract: Central transition Mn-55 NMR spectra of several solid manganese pentacarbonyls acquired at magnetic field strengths of 11.75, 17.63, and 21.1 T are presented. The variety of distinct powder sample lineshapes obtained demonstrates the sensitivity of solid-state Mn-55 NMR to the local bonding environment, including the presence of crystallographically unique Mn sites, and facilitates the extraction of the Mn chemical shift anisotropies, CSAs, and the nuclear quadrupolar parameters. The compounds investigated include molecules with approximate C-4v symmetry, LMn(CO)(5) (L = Cl, Br, I, HgMn(CO)(5), CH3) and several molecules of lower symmetry (L = PhCH2, Ph3-nClnSn (n = 1, 2, 3)). For these compounds, the Mn CSA values range from < 100 ppm for Cl3SnMn(CO)(5) to 1260 ppm for ClMn(CO)(5). At 21.1 T the Mn-55 NMR lineshapes are appreciably influenced by the Mn CSA despite the presence of significant Mn-55 quadrupolar coupling constants that range from 8.0 MHz for Cl3SnMn(CO)(5) to 35.0 MHz for CH3Mn(CO)(5). The breadth of the solid-state Mn-55 NMR spectra of the pentacarbonyl halides is dominated by the CSA at all three applied magnetic fields. DFT calculations of the Mn magnetic shielding tensors reproduce the experimental trends and the magnitude of the CSA is qualitatively rationalized using a molecular orbital, MO, interpretation based on Ramsey’s theory of magnetic shielding. In addition to the energy differences between symmetry-appropriate occupied and virtual MOs, the d-character of the Mn MOs is important for determining the paramagnetic shielding contribution to the principal components of the magnetic shielding tensor.

First author: Berger, J. A., Analysis of the Vignale-Kohn current functional in the calculation of the optical spectra of semiconductors, PHYSICAL REVIEW B, 75, 1226, (2007)
Abstract: In this work, we investigate the Vignale-Kohn current functional when applied to the calculation of optical spectra of semiconductors. We discuss our results for silicon. We found qualitatively similar results for other semiconductors. These results show that there are serious limitations to the general applicability of the Vignale-Kohn functional. We show that the constraints on the degree of nonuniformity of the ground-state density and on the degree of the spatial variation of the external potential under which the Vignale-Kohn functional was derived are almost all violated. We argue that the Vignale-Kohn functional is not suited to use in the calculation of optical spectra of semiconductors since the functional was derived for a weakly inhomogeneous electron gas in the region above the particle-hole continuum, whereas the systems we study are strongly inhomogeneous and the absorption spectrum is closely related to the particle-hole continuum.

First author: Magarill, S. A., Crystal chemistry and features of structure formation of mercury oxo- and chalcohalides,USPEKHI KHIMII, 76, 115, (2007)
Abstract: Characteristic features of the crystal structure of mercury oxohalides, chalcohalides and related compounds are considered. The structures of compounds are described both in the traditional way and using a modern approach relying on isolation of stable building blocks and analysis of their packing. Crystallographic and crystal chemical data for the title compounds are given.

First author: Tonner, Ralf, (Ph4P)(2)[Be2F6]center dot 2CH(3)CN: Synthesis, IR spectra, crystal structure, and quantum chemical calculations, ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE, 633, 1183, (2007)
Abstract: The hexafluorodiberyllate (Ph4P)(2)[Be2F6](.)2CH(3)CN (1) was prepared by the reaction of (Ph4P)(2)[Be2Cl6] with excess silver(I) fluoride in acetonitrile solution. According to the IR spectra and to the X-ray crystal structure determination, 1 contains isolated [Be2F6](2-) ions of symmetry Ci, which is very close to symmetry D-2h. 1 crystallizes triclinically in space group P1 with one formula unit per unit cell. Lattice dimensions at 193 K: a = 950.5(2), b = 1016.1(2), c 1305.2(2) pm, alpha = 101.04(2)degrees, beta = 110.83(2)’, gamma = 96.85(2)degrees, R-1 = 0.0354. DFT (BP86) and ab initio (CCSD(T)) calculations with large basis sets provide the picture of an intrinsically unstable molecule stabilized by solvent and solid state effects.