2004 publications citing ADF

First author: Maurer, P, Theoretical studies of the reductive C-S bond cleavage in complexes of the form [M(9S3)(2)](2+) (M = Re, Tc, and Ru; 9S3=1,4,7-trithiacyclononane), JOURNAL OF PHYSICAL CHEMISTRY A, 108, 11494, (2004)
Abstract: We have applied Density Functional Theory (DFT) at the generalized gradient approximation (GGA) level to investigate the C-S bond cleavage in hexathioether complexes of the form [M(9S3)(2)](n+) (with 9S3 = 1,4,7-trithiacyclononane and M = Re, Tc; n = 1, 2; as well as M = Ru; n = 2, 3). The experimental trends in C-S bond lengths of the different compounds’ are reproduced faithfully. Reduction leads to a lowering of the calculated reaction energies by approximate to20 kcal/mol to values of 4, 10, and 44 kcal/mol for M = Re, Tc, Ru, respectively. The corresponding values for the activation energy are 10, 15, and 44 kcal/mol, which is in agreement with the experimental observation that the rhenium and technetium compounds lose an ethene molecule immediately after reduction, while the ruthenium compound is stable toward such a loss. Our calculations suggest that the unique reactivity of the reduced rhenium and technetium complexes is a result of the higher energies of metal t(2g)-orbitals, resulting from the lower overall charge of the complex. pi-Back-donation from t(2g)-orbitals into C-S sigma*-orbitals is another important effect, leading to low activation barriers, as only little electronic rearrangement is necessary upon cleavage of the C-S bonds.

First author: Fratiloiu, S, VIS/NIR absorption spectra of positively charged oligo(phenylenevinylene)s and comparison with time-dependent density functional theory calculations, JOURNAL OF PHYSICAL CHEMISTRY B, 108, 19967, (2004)
Abstract: A combined experimental and theoretical study of the optical properties of positively charged unsubstituted and dialkoxy-substituted phenylenevinylene (PV) oligomers in solution is presented. Cations of PV oligomers were produced by irradiation of a solution with high-energy electron pulses. The optical absorption spectra were measured using time-resolved visible/near-infrared (VIS/NIR) spectroscopy in the range of 500-2100 nm (0.6-2.5 eV). The optical absorption spectra of positively charged PVs are compared with results from time-dependent density functional theory (TDDFT) calculations and previous semiempirical calculations. The experimental spectra of cations of partially dialkoxy-substituted PVs indicate the presence of a transition with a maximum below 0.6 eV. According to earlier semiempirical calculations, the energy of this transition exhibits an oscillating behavior as a function of the length of the oligomer. This was not observed experimentally. However, the monotonic decrease of the low-energy absorption band, as obtained from TDDFT calculations, is in agreement with the experimental findings.

First author: Swart, M, Hydrogen bonds of RNA are stronger than those of DNA, but NMR monitors only presence of methyl substituent in uracil/thymine, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 126, 16718, (2004)
Abstract: A combined experimental and theoretical study of the optical properties of positively charged unsubstituted and dialkoxy-substituted phenylenevinylene (PV) oligomers in solution is presented. Cations of PV oligomers were produced by irradiation of a solution with high-energy electron pulses. The optical absorption spectra were measured using time-resolved visible/near-infrared (VIS/NIR) spectroscopy in the range of 500-2100 nm (0.6-2.5 eV). The optical absorption spectra of positively charged PVs are compared with results from time-dependent density functional theory (TDDFT) calculations and previous semiempirical calculations. The experimental spectra of cations of partially dialkoxy-substituted PVs indicate the presence of a transition with a maximum below 0.6 eV. According to earlier semiempirical calculations, the energy of this transition exhibits an oscillating behavior as a function of the length of the oligomer. This was not observed experimentally. However, the monotonic decrease of the low-energy absorption band, as obtained from TDDFT calculations, is in agreement with the experimental findings.

First author: Bradley, CA, Zirconium sandwich complexes with eta(9) indenyl ligands: Well-defined precursors for zirconocene-mediated coupling reactions, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 126, 16937, (2004)
Abstract: A family of isolable, well-defined bis-indenyl zirconium sandwich complexes, (eta(5)-C9H5-1,3-R-2)-(eta(9)-C9H5-1,3-R-2)Zr (R = silyl, alkyl), have been prepared by either alkane reductive elimination of alkali metal reduction of a suitable zirconium(IV) dihalide precursor. Crystallographic characterization oil two of these derivatives, R = SiMe2CMe3 and CHMe2, reveals unprecedented eta(2) coordination of one of the indanyl ligands. Variable-temperature and EXSY NMR studies establish that the eta(5) and eta(2) rings are rapidly interconverting in solution. The sandwich complexes serve as effective sources of low-valent zirconium, reacting rapidly with both olefins and alkynes at ambient temperature. In contrast to bis-cyclopentadienyl chemistry, the olefin adducts of the bis-indenyl zirconium sandwiches undergo preferential C-H activation to yield the corresponding allyl hydride compounds, although reaction with excess olefin proceeds through, the eta(2)-olefin adduct, forming the corresponding zirconacyclopentane.

First author: Carlsson, H, Nickel complexes of carboxylate-containing polydentate ligands as models for the active site of urease, INORGANIC CHEMISTRY, 43, 8252, (2004)
Abstract: Two new carboxylate-containing polydentate ligands have been synthesized, the symmetric ligand 2,6-bis[N-(N(carboxyl methyl)-N-((1-methylimidazol) methyl)amine)methyl]-4-methylphenolate (BCIMP) and the corresponding asymmetric ligand 2-(N-isopropyl-N-((1-aminomethyl)-4-methylphenol (ICIMP). The ligands have been used to prepare model complexes for the active site of the dinuclear nickel enzyme urease, viz. [Ni-2(BCIMP)Ac-2](-) (6), [Ni-2(BCIMP)(Ph2Ac)(2)](-) (7), [Ni-2(ICIMP)(Ph2Ac)(2)] (14), [Ni-4(ICIMP)(2)(Ph2Ac)(2)][ClO4](2) (15), [Ni-4(ICIMP)(2)(Ph2Ac)(2)(DMF)(2)][ClO4](2) (16), and [Ni-4(ICIMP)(2)(Ph2Ac)(2)(urea)(H2O)][ClO4](2) (17), where the latter complex contains urea coordinated in a unidentate fashion through the carbonyl oxygen. The N2O-N2O2 donor set of ICIMP provides a good framework for the preparation of urease models, but in some cases tetranuclear nickel complexes are formed due to coordination of the carboxylate moiety of one dinickel-ICIMP unit to one or both of the nickels of a second Ni-2 unit. Reactivity and kinetics studies of 7 and 15 show that these model complexes catalyze hydrolysis of 2-hydroxypropyl p-nitrophenyl phosphate (HPNP) at basic pH. In this assay, complexes based on the asymmetric ligand ICIMP exhibit a significantly faster rate of hydrolysis than the corresponding BCIMP complexes. Magnetic measurements indicate that there are weak antiferromagnetic interactions between the nickel ions in complex 16.

First author: Huang, DM, Theoretical study of stable intermolecular complexes of furan with hydrogen halides, JOURNAL OF PHYSICAL CHEMISTRY A, 108, 11375, (2004)
Abstract: The intermolecular complexes of furan with hydrogen halides are examined using ab initio calculations performed at the second-order Moller-Plesset perturbation approximation with the 6-311++G(d,p) basis set. Two types of geometry are observed: the atom-on geometry, featuring a roughly planar complex with C-2v symmetry and a hydrogen bond between the furan oxygen and the hydrogen halide; and the face-on geometry, in which the hydrogen halide lies above the furan ring in an orientation almost perpendicular to the plane of the ring. The furan-HF and furan-HI complexes are each found to have one minimum geometry, of the atom-on and face-on type, respectively. Both geometry types are obtained for the HCl- and HBr-furan complexes. With the exception of furan-HCl, the HX subunits of the atom-on complexes deviate slightly from the furan ring plane. Each of the face-on complexes shows interaction between the hydrogen of the halide subunit and the formal pi-bond between C-2 and C-4 of the furan ring. An electrostatic density potential map of furan was generated for the determination of attractive interaction sites. Interaction energy decomposition reveals that atom-on complex interactions are predominantly electrostatic in nature, while orbital and electrostatic interactions dominate the face-on type complexes.

First author: Wang, F, Time-dependent density functional theory based on a noncollinear formulation of the exchange-correlation potential, JOURNAL OF CHEMICAL PHYSICS, 121, 12191, (2004)
Abstract: In this study we have introduced a formulation of time-dependent density functional theory (TDDFT) based on a noncollinear exchange-correlation potential. This formulation is a generalization of conventional TDDFT. The form of this formulation is exactly the same as that of the conventional TDDFT for the excitation energies of transitions that do not involve spin flips. In addition, this noncollinear TDDFT formulation allows for spin-flip transitions. This feature makes it possible to resolve more fully excited state spin multiplets, while for closed-shell systems, the spin-flip transitions will result in singlet-triplet excitations and this excitation energy calculated from this formulation of TDDFT is exactly the same as that from ordinary TDDFT. This formulation is applied to the dissociation of H-2 in its (1)Sigma(g)(+) ground state and (1)Sigma(u)(+) and (3)Sigma(u)(-) excited states with (3)Sigma(u)(-) (M-s=+1) as the reference state and the multiplets splitting of some atoms.

First author: Zbiri, M, Investigating the (MHe)-He-* exciplexes, M={Li,Na,K,Rb,Cs,Fr}: Density functional approach,JOURNAL OF CHEMICAL PHYSICS, 121, 11625, (2004)
Abstract: Potential curves for the ground and the first lowest excited states of the MHe (where M={Li,Na,K,Rb,Cs,Fr}) exciplexes are calculated using the density functional theory (DFT) formalism. Relativistic calculations are carried out with and without spin-orbit (SO) coupling effect, using a zeroth order regular approximation (ZORA) approach. The depth D-e and position R-e parameters of the potential curves for the case without spin-orbit effect are presented and compared with other works. Potential curves for Li-He, Cs-He, and Fr-He without spin-orbit effect and Cs-He with the spin-orbit effect are shown. A bond analysis is presented too, since the central interest of the study of the exciplexes is the nature and the existence of the bonding states that are the origin of emission spectra observed experimentally for these systems.

First author: Leigh, WJ, Organogermanium reactive intermediates. The direct detection and characterization of transient germylenes and digermenes in solution, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 126, 16105, (2004)
Abstract: Diphenylgermylene (Ph(2)Ge) and its Ge=Ge doubly bonded dinner, tetraphenyldigermene (6a), have been characterized directly in solution for the first time by laser flash photolysis methods. The germylene is formed via (formal) cheletropic photocycloreversion of 3,4-dimethyl-1,1-diphenylgermacyclopent-3-ene (4a), which is shown to proceed in high chemical (>95%) and quantum yield (Phi = 0.62) by steady-state trapping experiments with methanol, acetic acid, isoprene, and triethylsilane. Flash photolysis of 4a in dry deoxygenated hexane at 23degreesC leads to the prompt formation of a transient assigned to Ph(2)Ge (Am = 500 nm; is an element of(max) = 1650 M(-1) cm(-1)), which decays with second-order kinetics (tau approximate to 3 mus), with the concomitant growth of a second transient species that is assigned to cligermene 6a (tau approximate to 40 mus; lambda(max) = 440 nm). Analogous results are obtained from 1,1-dimesityl- and 1,1-dimethyl-3,4-dimethylgermacyclopent-3-ene (4b and 4c, respectively), which afford Mes(2)Ge (tau approximate to 20 mus; lambda(max) = 560 nm) and Me(2)Ge (tau approximate to 2 mus; lambda(max) = 480 nm), respectively, as well as the corresponding digermenes, tetramesityl- (6b; lambda(max) = 410 nm) and tetramethy1cligermene (6c; lambda(max) = 370 nm). The results for the mesityl compound are compared to the analogous ones from laser flash photolysis of the known Mes(2)Ge/6b precursor, hexamesitylcyclotrigermane. The spectra of the three germylenes and two of the digermenes are in excellent agreement with calculated spectra, derived from time-dependent DFT calculations. Absolute rate constants for dimerization of Ph(2)Ge and Mes(2)Ge and for their reaction with n-butylamine and acetic acid in hexane at 23degreesC are also reported.

First author: Sokolov, MN, Synthesis and characterization of a novel tantalum chalcogen-rich molecular cluster with square planar metal core, INORGANIC CHEMISTRY, 43, 7966, (2004)
Abstract: Black single crystals of Ta(4)Se(9)l(8) are obtained in a high yield by heating Ta, Se, and l(2) at 300degreesC in 1:2.2:1.0 molar ratio. In the structure, the tantalum atoms form a square, with four Se-2 ligands bridging the Ta-Ta edges and one capping the square. Each Ta atom has two terminal iodine atoms. The compound is diamagnetic and has only two electrons for metal-metal bonding.

First author: Cooney, JJA, Electronic structure of bent titanocene complexes with chelated dithiolate ligands, INORGANIC CHEMISTRY, 43, 8110, (2004)
Abstract: Gas-phase photoelectron spectroscopy and density functional theory have been utilized to investigate the interactions between the p orbitals of dithiolate ligands and d orbitals of titanium in bent titanocene complexes as minimum molecular models of active site features of pyranopterin Mo/W enzymes. The compounds Cp2Ti(S-S) [where (S-S) is 1,2-ethenedithiolate (S2C2H2), 1, 1,2-benzenedithiolate (bdt), 2, or 1,3-propanedithiolate (pdt), 3, and Cp- is cyclopentadienyl] provide access to a formal 16-electron d(0) electronic configuration at the metal. A “dithiolate-folding-effect” involving an interaction of metal and sulfur orbitals is demonstrated in complexes with arene- and enedithiolates. This effect is not observed for the alkanedithiolate in complex 3.

First author: Belanzoni, P, Atomic-silicon cryptates in siloxanic networks, CHEMICAL PHYSICS LETTERS, 400, 179, (2004)
Abstract: The existence of atomic-silicon cryptates in siloxanic networks has been studied theoretically via high level quantum mechanical calculations. Modeling with model molecules the candidate sites to host atomic silicon, we found that metastable adducts can be formed only in regions where the siloxanic network is not subjected to steric constraints; stationary states are instead impossible in highly reticulated siloxanic networks. This analysis suggests that the atomic silicon injected into the oxide during thermal oxidation of silicon with O-2 may be trapped as a metastable adduct at the oxide surface.

First author: Swart, M, Performance of the OPBE exchange-correlation functional, MOLECULAR PHYSICS, 102, 2467, (2004)
Abstract: In a recent evaluation of density functional theory (DFT) functionals OPBE, which combines Handy’s optimized exchange (OPTX) with the PBE correlation, was shown to correctly predict the spin states (singlet through sextet) of seven different iron complexes (2004, J. Phys. Chem. A, 108, 5479). The present study provides a further test of OPBE as well as that of the OPerdew and OLYP functionals, in which OPTX is combined with the Perdew and LYP correlations, respectively. These three are compared to other pure DFT functionals for their performance in calculating the atomization energies for the G2-set of up to 148 molecules, six reaction barriers Of S(N)2 reactions, geometry optimizations of 19 small molecules and four metallocenes, and zero-point vibrational energies for 13 small molecules. OPBE performs exceptional well in all cases.

First author: Wang, F, Excitation energies of some d(1) systems calculated using time-dependent density functional theory: an implementation of open-shell TDDFT theory for doublet-doublet excitations, MOLECULAR PHYSICS, 102, 2585, (2004)
Abstract: Time-dependent density functional theory has been used extensively to study the excitation energies of closed-shell systems with great success, while its applications to open-shell systems are still limited, especially open-shell transition metal compounds. In the present work, the excitation energies of ligand to metal charge transfer excitations and d–>d excitations of some open-shell d(1) MLX4 transition metal compounds with spin-unrestricted TDDFT were studied. The results demonstrate that TDDFT can be used to study the excitation energies of the title systems accurately. With BP86/ALDA, the errors are mostly around 0.3-0.5 eV, which is similar to the error for TDDFT calculations on closed-shell systems.

First author: Atanasov, M, The calculation of ESR parameters by density functional theory: the g- and A-tensors of Co(acacen), CHEMICAL PHYSICS LETTERS, 399, 433, (2004)
Abstract: The new DFT based ligand field (LF) model is proposed to calculate the g- and A-tensors of [Co(acacen)] that is known to be a difficult case. The results obtained are compared with the ZORA approach implemented in ADF as well as with the experimental values. The calculations are in good agreement with the experimental data and demonstrate the ability of the method to reproduce the large anisotropy typical for this type of complexes. The ligand field-density functional theory method is therefore not simply a method to calculate multiplet structure, ligand field splittings and UV-Vis transitions, but is also appropriate to compute magnetic properties.

First author: Collins, SN, Density functional theory and low-temperature matrix investigations of CO-loss photochemistry from [(C5R5)Ru(CO)(2)](2) ( R = H, Me) complexes, JOURNAL OF CLUSTER SCIENCE, 15, 469, (2004)
Abstract: The photochemical CO-loss products of the diruthenium complexes [CpRu(CO)(2)](2) (5; Cp = eta(5)-C5H5), [Cp*Ru(CO)(2)](2) (5*; Cp* = eta(5)-C-5(CH3)(5)) and CpCp*[Ru(CO)(2)](2) (5′) have been studied experimentally in low-temperature ( 96 K) matrices in 3-methylpentane by using IR spectroscopy. It is proposed that all three complexes undergo single-CO-loss chemistry but that the products have different structures. The single-CO-loss product from 5 is proposed to have one bridging and two terminal carbonyl ligands, whereas 5* and 50 generate triply bridged CO-loss products similar to that observed from [CpFe(CO)(2)](2) and [Cp*Fe(CO)(2)](2). Double-CO-loss from 5* and 5′ is also apparently observed. Relativistic DFT calculations have been carried out on various isomers of the starting materials and on potential CO-loss products from 5. The calculations suggest that the triply bridged product Cp2Ru2 (mu-CO)3 (6) might have a singlet ground state in contrast to the corresponding diiron complex Cp2Fe2(mu-CO)(3) (3), which has a triplet ground state.

First author: McCormack, DA, Improving numerical integration through basis set expansion, THEORETICAL CHEMISTRY ACCOUNTS, 112, 410, (2004)
Abstract: Calculations are presented to assess a theorem presented by S.F. Boys [(1969) Proc. R. Soc. A. 309:195], regarding the accuracy of numerical integration in quantum chemical calculations. The theorem states that the error due to numerical integration can be made proportional to the error due to basis set truncation, and thus goes to zero in the limit of a complete basis. We test this theorem on the hydrogen atom, showing that with a solution-spanning basis, the numerically exact orbital energy can indeed be calculated with a small number of integration points. Moreover, tests for H and H-2(+) demonstrate that even when only a near-complete basis is employed, Boys’ Theorem can significantly reduce integration error. However, for other systems, like the oxygen atom and the CO2 molecule, the theorem yields no advantage for some occupied orbitals. It is concluded that the theorem would be most useful for calculations that demand large basis sets.

First author: Deeth, RJ, The performance of nonhybrid density functionals for calculating the structures and spin states of Fe(II) and Fe(III) complexes, JOURNAL OF COMPUTATIONAL CHEMISTRY, 25, 1840, (2004)
Abstract: The local density approximation and a range of nonhybrid gradient corrected density functionals (PW91, BLYP, PBE, revPBE, RPBE) have been assessed with respect to the prediction of geometries and spin-state energy preferences for a range of homoleptic Fe(II)L-6 and Fe(III)L-6 complexes, where L = Cl-, CN-, NH3, pyridine, imidazole, H2O, O==CH2 and tetrahydrofuran. While the qualitative spin-state energies from in vacuo structure optimizations are reasonable the geometries are relatively poorly treated, especially for [FeCl6](3-)/(4-). Structural results for all the complexes are significantly improved by including environmental effects. The best compromise between structural and spin-state predictive accuracy was obtained for the RPBE functional in combination with the COSMO solvation approach. This approach systematically overestimates the energetic preference for a low spin state, which is partly due to the well-known effect of the lack of exact exchange in nonhybrid functionals and partly due to the larger solvation stabilization of low-spin complexes that have shorter bond lengths and thus smaller molecular volumes than their high-spin partners. Calculations on low spin [Fe(bipy)(3)](2+) and [Fe(phen)(3)](2+) and their ortho methyl substituted analogs, which are high spin at room temperature but cross over to low spin at low temperature, suggest the RPBE/COSMO combination generates low spin states which are too stable by approximately 13 kcal mol(-1).

First author: Seth, M, Theoretical study of the copolymerization of ethylene and propylene by a heterogeneous Ziegler-Natta catalyst, MACROMOLECULES, 37, 9191, (2004)
Abstract: The copolymerization of ethylene and propylene by a heterogeneous Ti/MgCl2 Ziegler-Natta catalyst is studied with density functional theory calculations. One particular model of an active site, the so-called “TiCl3-based slope site”, is looked at in detail. The influence of the previous monomer insertion is allowed for by examining sites where the growing polymer chain is modeled by a methyl, propyl, isobutyl, and 2-butyl group. Propylene is found to form a more stable pi-complex with the active site than ethylene. Propylene is also found to have a lower barrier to insertion into the Ti-C bond than ethylene in most instances and to prefer to insert in a 1-2 orientation rather than a 2-1 orientation. The relative height of the insertion barriers of ethylene and propylene is in contradiction to experimentally observed copolymer compositions. Increasing steric bulk of the polymer chain disfavors propylene insertion relative to ethylene insertion and 1-2 propylene insertion relative to 2-1 insertion. Some of the insertion reactions examined are shown to be significantly stereoselective due to the interaction of propylene and the growing polymer chain. Despite these stereoselective reactions, the active site modeled here will not produce tactic polymer except under some special circumstances which are outlined.

First author: Tahtinen, P, Conformational analysis of saturated trans-fused 1,3,2-benzoxazaphosphinine 2-oxides – DFT calculation of NMR J(PH) coupling constants, EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, 37, 4921, (2004)
Abstract: The (3)J(P,H) and (4)J(P,H) spin-spin coupling constants of a selected test set of organophosphorus compounds, calculated by density functional theory (DFT) methods, were found to correlate well with the experimentally measured coupling constants. The contribution of the spin-dipole (SD) term to the coupling constants was found to be negligible, and the diamagnetic and paramagnetic spin-orbit (DSO and PSO) terms cancelled each other, as in the case of J(H,H). Calculation solely of the Fermi contact (FC) term was found to be sufficient to provide good estimates of the coupling constants. In the second part of the work, the conformational equilibria and coupling constants in 2-bis(2-chloroethyl)amino-trans-octahydro-2H-1,3,2-benzoxazaphosphinine 2-oxide and its 3-methyl derivative were studied. DFT methods failed in predicting the relative stabilities of the conformations but yielded good geometries and coupling constants. Optimization of the conformations at the Moller-Plesset second-order perturbation theory (MP2) level resulted in energy differences compatible with previous experimental observations.

First author: van den Bosch, M, Simulation of the substrate cavity dynamics of quercetinase, JOURNAL OF MOLECULAR BIOLOGY, 344, 725, (2004)
Abstract: Molecular dynamics (MD) simulations have been performed on quercetin 2,3 dioxygenase (2,3QD) to study the mobility and flexibility of the substrate cavity. 2,3QD is the only firmly established Cu-containing dioxygenase known so far. It catalyses the breakage of the O-heterocycle of flavonols. The substrates occupy a shallow and overall hydrophobic cavity proximal to the metal centre of the homo-dimeric enzyme. The linker connecting the C-terminal and N-terminal domains in the monomer is partly disordered in the crystal structure and part of it forms a flexible lid at the entrance of the substrate cavity. This loop has been tentatively assigned a role in the enzyme mechanism: it helps lock the substrate into place. The dynamics of this loop has been investigated by MD simulation. The initial coordinates were taken from the crystal structure of 2,3QD in the presence of the substrate kaempferol (KMP). After equilibration and simulation over 7.2 ns the substrate was removed and another equilibration and simulation of 7.2 ns was performed. The results show that the structures of the free enzyme as well as of the enzyme-substrate complex are stable in MD simulation. The linker shows strongly enhanced mobility in the loop region that is close to the entrance to the substrate cavity (residues 154-169). Movement of the loop takes place on a timescale of 5-10 ns. To confirm the conclusions about the loop dynamics drawn from the 7.2 ns simulation, the simulation was extended with another 8 ns. When substrate binds into the cavity the loop orders remarkably, although mobility is retained by residues 155-158. Some regions of the loop (residues 154-160 and 164-176) move over a considerable distance and approach the substrate closely, reinforcing the idea that they lock the substrate in the substrate cavity The enthalpic component of the interaction of the loop with the protein and the KMP appears to favour the locking of the substrate. Two water molecules were found immobilised in the cavity, one of which exhibited rotation on the picosecond timescale. When the substrate is removed, the empty cavity fills up with water within 200 ps.

First author: de Jong, GT, Ab initio benchmark study for the oxidative addition of CH4 to Pd: Importance of basis-set flexibility and polarization, JOURNAL OF CHEMICAL PHYSICS, 121, 9982, (2004)
Abstract: To obtain a state-of-the-art benchmark potential energy surface (PES) for the archetypal oxidative addition of the methane C-H bond to the palladium atom, we have explored this PES using a hierarchical series of ab initio methods (Hartree-Fock, second-order Moller-Plesset perturbation theory, fourth-order Moller-Plesset perturbation theory with single, double and quadruple excitations, coupled cluster theory with single and double excitations (CCSD), and with triple excitations treated perturbatively [CCSD(T)]) and hybrid density functional theory using the B3LYP functional, in combination with a hierarchical series of ten Gaussian-type basis sets, up to g polarization. Relativistic effects are taken into account either through a relativistic effective core potential for palladium or through a full four-component all-electron approach. Counterpoise corrected relative energies of stationary points are converged to within 0.1-0.2 kcal/mol as a function of the basis-set size. Our best estimate of kinetic and thermodynamic parameters is -8.1 (-8.3) kcal/mol for the formation of the reactant complex, 5.8 (3.1) kcal/mol for the activation energy relative to the separate reactants, and 0.8 (-1.2) kcal/mol for the reaction energy (zero-point vibrational energy-corrected values in parentheses). This agrees well with available experimental data. Our work highlights the importance of sufficient higher angular momentum polarization functions, f and g, for correctly describing metal-d-electron correlation and, thus, for obtaining reliable relative energies. We show that standard basis sets, such as LANL2DZ+1f for palladium, are not sufficiently polarized for this purpose and lead to erroneous CCSD(T) results. B3LYP is associated with smaller basis set superposition errors and shows faster convergence with basis-set size but yields relative energies (in particular, a reaction barrier) that are ca. 3.5 kcal/mol higher than the corresponding CCSD(T) values.

First author: Cohen, AJ, Calculation of nuclear magnetic resonance shielding constants using potential-based methods,CHEMICAL PHYSICS LETTERS, 399, 84, (2004)
Abstract: We present the calculation of nuclear magnetic resonance shielding constants using a range of different methods. In particular we examine two new methods proposed by Yang and Wu which are based on the Kohn-Sham potential. The first is a method which reproduces an accurate input density (WY) and the second is an implementation of the optimised effective potential method. We find that these methods give results which are very similar to each other and when the methods are applied to a hybrid functional (e.g. B3LYP) we obtain good agreement with experiment.

First author: Zhang, JP, Quantum chemical analysis of the chemical bonds in tris(8-hydroxyquinolinato)aluminum as a key emitting material for OLED, JOURNAL OF PHYSICAL CHEMISTRY A, 108, 10296, (2004)
Abstract: The structures of mer-tris(8-hydroxyquinolinato)aluminum (Alq3) in the ground (S-0) and first excited (S-1) states have been optimized at the B3LYP/6-31+G(d) and CIS/6-31G(d) levels of theory. Absorption and emission for Alq3 are predicted with use of CI-ZINDO and TD-DFT. The results of an energy-partitioning analysis of the ground state of Alq3 are discussed. The electronic transition between S-0 and S-1 for mer-Alq3 is found to be mainly localized at the A-quinolate ligand as evidenced by the structural shift between the excited and ground states and the partial charge transfer from the phenoxide side to the pyridyl side within A-quinolate. The calculated optical and structural properties of mer-Alq3 are traced back to the weakest electrostatic attractive energy between the A-quinolate ligand and the Alq2 fragment due to the special arrangement, resulting in geometry change of ligand A upon excitation and the localization of the HOMO on A-quinolate.

First author: Zhang, DY, Density functional theory studies of correlations between structure, binding energy, and dipole polarizability in Si-9 and Si-12, CHEMICAL PHYSICS LETTERS, 398, 283, (2004)
Abstract: Two medium-size silicon clusters, namely, Si-9 and Si-12, have been used as model systems to investigate the correlations between structure, stability, and the static dipole polarizability by theoretical methods. Results show that polarizability correlates with the standard deviation of the atomic distances, and that the binding energy correlates with both the averaged atomic distance and the number of Si-Si bonds formed in the particular cluster. These correlations are significant, since they allow predictions of certain physical properties, i.e., dipole polarizability and stability, based solely on the structural information of the cluster.

First author: Yan, LK, Why does disubstituted hexamolybdate with arylimido prefer to form an orthogonal derivative? Analysis of stability, bonding character, and electronic properties on molybdate derivatives by density functional theory (DFT) study, JOURNAL OF PHYSICAL CHEMISTRY B, 108, 17337, (2004)
Abstract: The bonding character of arylimido molybdate derivatives has been investigated, using density functional theory (DFT). The natural bond orbital analysis reveals that the Moequivalent toN triple bond in the arylimido molybdate derivatives is comprised of a alpha-bond and two pi-bonds. The energy analysis of 2,6-dimethylaniline disubstituted molybdate derivatives [Mo6O17R2](2-) (where R = 2,6-dimethylaniline group) has been performed. The results show that orthogonal [Mo6O17R2](2-) is more stable than diagonal [Mo6O17R2](2-). The bonding capability of the Mo6O17R fragment with arylimido group R is strong for orthogonal [Mo6O17R2](2-). 2,6-Dimethylaniline disubstituted hexamolybdate derivative prefers to form an orthogonal derivative. The analysis of geometrical and electronic properties provides further support. The arylimido effectively modifies the occupied molecular orbitals and extends its organic T-electrons to the polyoxometalate skeleton. The major contributors to the highest occupied molecular orbital (HOMO) are p orbitals centered on the C atoms and N atoms, and d(yz) orbitals centered on Mo atoms linked with the N atom of the organoimido group. The present investigation provides important insight into polyanion-organoimido interactions.

First author: Baik, MH, Theoretical investigation of the metal-metal interaction in dimolybdenum complexes with bridging hydride and methyl ligands, POLYHEDRON, 23, 2879, (2004)
Abstract: DFT calculations on dinuclear molybdenum complexes with bridging hydride and methyl ligands, namely [CpMo(mu-O2CH)](2)(mu-PH2)(mu-H) and [CP*MO(mu-O2CMe)](2)(mu-PMe2)(mu-Me), indicate that the bonding is best described in terms of. (i) a 2-center-2-electron Mo-Mo single bond and (ii) a 3-center-2-electron Mo-H-Mo or Mo-Me-Mo bond. The presence of a 2-center-2-electron Mo-Mo single bond is in accord with an electron counting procedure that views the bridging hydride and methyl ligands as mu-LX ligands; in contrast, an electron counting procedure which apportions half of the valence electron of the hydrogen atom or methyl radical to each metal dictates a Mo=Mo double bond, a result that is contrary to the theoretical calculations. Consideration of a variety of other bridging hydride complexes indicates that the mu-LX electron counting method provides the best general description of the bonding by clearly distinguishing between the number of 3-center-2-electron M-H-M interactions and direct 2-center-2-electron M-M interactions.

First author: Brett, CM, Theoretical studies of 18-electron M(CnHn)(C-10 (- n) H10-n) (M = Fe, Ru, Os; n=3, 4, 5) sandwich complexes, POLYHEDRON, 23, 2993, (2004)
Abstract: Density functional theory has been used to explore the energetics and bonding of the symmetric and unsymmetric isomeric sandwich complexes (eta(5)-C5H5)(2)M, (eta(4)-C4H4)M(eta(6)-C6H6), and (eta(3)-C3H3)M(eta(7)-C7H7) (M = Fe, Ru, Os). For each metal atom, the symmetric “5-5” metallocene was found to be the most stable isomer, with the “4-6” and “3-7” isomers ca. 40 and 80 kcal/mol higher in energy, respectively. Bonding analysis shows that (eta(4)-C4H4)Fe(eta(6)-C6H6) is best considered as a (eta(4)-C4H4)Fe fragment interacting with a C6H6 ligand, although the interactions become less separable as the metal is changed to Ru and Os. Similarly, the dominant bonding in (eta(3)-C3H3)M(eta(7)-C7H7) is that of a M(eta(7)-C7H7) perturbed by the interaction with a C3H3 ligand.

First author: Rajapakshe, A, Pentadienyls vs cyclopentadienyls and reversal of metal-ligand bonding affinity with metal oxidation state: Synthesis, molecular structures, and electronic structures of high-valent zirconium pentadienyl complexes,JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 126, 14105, (2004)
Abstract: Molecules of the form Cp(6,6-dmch)ZrX2 (Cp = eta(5)-cyclopentadienyl, X = Cl, Br, 1; 6,6-dmch = eta(5)-6,6-dimethylcyclohexadienyl) have been synthesized, and the molecular and electronic structures have been investigated. These molecules allow direct comparison of the bonding and properties of pentadienyl and cyclopentadienyl ligands in the same high-oxidation-state metal complexes. Unlike the well-known Cp2ZrX2 analogues, these Cp(6,6-dmch)ZrX2 Molecules are intensely colored, indicating significantly different relative energies of the frontier orbitals. Also unusual, the average Zr-C distances to the 6,6-dmch pentadienyl ligand are about 0.1 Angstrom longer than the average Zr-C distances to the cyclopentadienyl ligand for these Zr(IV) complexes, opposite of what is observed for the Zr(II) complex Cp(2,6,6-tmch)Zr(PMe3)(2) (tmch = eta(5)-2,6,6-trimethylcyclohexadienyl), reflecting a dramatic reversal in the favorability of the bonding depending on the metal oxidation state. The experimental and computational results indicate that the color of the Cp(6,6-dmch)ZrX2 complexes is due to a 6,6-dmch ligand-to-metal charge-transfer band. Compared to the Cp2ZrX2 analogues, the Cp(6,6-dmch)ZrX2 molecules have a considerably less stable HOMO that is pentadienyl-based and an essentially unchanged metal-based LUMO. Also, the lowest unoccupied orbital of pentadienyl is stabilized relative to cyclopentadienyl and becomes a better potential delta electron acceptor, thus contributing to the differences in structure and reactivity of the low-valent and high-valent metal complexes.

First author: Volkov, A, Response to the paper A comparison between experimental and theoretical aspherical-atom scattering factors for charge-density refinement of large molecules, by Pichon-Pesme, Jelsch, Guillot & Lecomte (2004),ACTA CRYSTALLOGRAPHICA SECTION A, 60, 638, (2004)
Abstract: Molecules of the form Cp(6,6-dmch)ZrX2 (Cp = eta(5)-cyclopentadienyl, X = Cl, Br, 1; 6,6-dmch = eta(5)-6,6-dimethylcyclohexadienyl) have been synthesized, and the molecular and electronic structures have been investigated. These molecules allow direct comparison of the bonding and properties of pentadienyl and cyclopentadienyl ligands in the same high-oxidation-state metal complexes. Unlike the well-known Cp2ZrX2 analogues, these Cp(6,6-dmch)ZrX2 Molecules are intensely colored, indicating significantly different relative energies of the frontier orbitals. Also unusual, the average Zr-C distances to the 6,6-dmch pentadienyl ligand are about 0.1 Angstrom longer than the average Zr-C distances to the cyclopentadienyl ligand for these Zr(IV) complexes, opposite of what is observed for the Zr(II) complex Cp(2,6,6-tmch)Zr(PMe3)(2) (tmch = eta(5)-2,6,6-trimethylcyclohexadienyl), reflecting a dramatic reversal in the favorability of the bonding depending on the metal oxidation state. The experimental and computational results indicate that the color of the Cp(6,6-dmch)ZrX2 complexes is due to a 6,6-dmch ligand-to-metal charge-transfer band. Compared to the Cp2ZrX2 analogues, the Cp(6,6-dmch)ZrX2 molecules have a considerably less stable HOMO that is pentadienyl-based and an essentially unchanged metal-based LUMO. Also, the lowest unoccupied orbital of pentadienyl is stabilized relative to cyclopentadienyl and becomes a better potential delta electron acceptor, thus contributing to the differences in structure and reactivity of the low-valent and high-valent metal complexes.

First author: Zhai, HJ, Icosahedral gold cage clusters: M@Au-12(-) (M = V, Nb, and Ta), JOURNAL OF CHEMICAL PHYSICS, 121, 8369, (2004)
Abstract: We report the observation and characterization of a series of stable bimetallic 18-valence-electron clusters containing a highly symmetric 12-atom icosahedral Au cage with an encapsulated central heteroatom of Group VB transition metals, M@Au-12(-) (M=V,Nb,Ta). Electronic and structural properties of these clusters were probed by anion photoelectron spectroscopy and theoretical calculations. Characteristics of the M@Au-12(-) species include their remarkably high binding energies and relatively simple spectral features, which reflect their high symmetry and stability. The adiabatic electronic binding energies of M@Au-12(-) were measured to be 3.70+/-0.03, 3.77+/-0.03, and 3.76+/-0.03 eV for M=V, Nb, and Ta, respectively. Comparison of density-functional calculations with experimental data established the highly symmetric icosahedral structures for the 18-electron cluster anions, which may be promising building blocks for cluster-assembled nanomaterials in the form of stoichiometric [M@Au-12(-)]X+ salts.

First author: Bagno, A, Calculation of NMR parameters an van der Waals complexes involving organic systems and xenon, JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, 17, 945, (2004)
Abstract: Some of our recent results concerning the prediction of NMR parameters for van der Waals (vdW) complexes are reviewed. Through-space coupling constants, in organic molecules stabilized by CH-pi interaction, are calculated to be of the order of 0.3 Hz, therefore above the current experimental resolution. Through-space coupling constants between hydrocarbons and xenon are also calculated to be relatively large, of the order of a few Hz at the vdW contact distance. Finally, we present some preliminary data on the dependence of the chemical shift of xenon in vdW complexes with alkyl chains. These results will serve as a tool in molecular dynamics simulations of xenon dissolved in membranes.

First author: Qiu, YX, A time-dependent DFT study on the electronic excitation states of polycyclic aromatic compound of phenanthrene, ACTA CHIMICA SINICA, 62, 2030, (2004)
Abstract: The time-dependent DFF (TD-DFT), CIS and TD-HF studies have been performed on the UV-spectrum of phenanthrene. Based on the optimized geometries, the vertical excitation energies were calculated. The effect of basis sets is important on the excitation energies. Different exchange-correlation potentials hardly affected the excitation energies due to that the systematic errors of orbital energies were cancelled each other. The deviations between our theoretical results and experimental ones are in the same order of magnitude as that between different experimental methods. TD-DFT is more satisfactory than CIS and TD-HF on the electronic excitation energy calculations.

First author: Bart, SC, Preparation and molecular and electronic structures of iron(0) dinitrogen and silane complexes and their application to catalytic hydrogenation and hydrosilation, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 126, 13794, (2004)
Abstract: Reduction of the five-coordinate iron(II) dihalide complexes ((iPr)PDI)FeX(2) ((iPr)PDI = ((2,6-CHMe(2))(2)C(6)H(3)N=CMe)(2)C(5)H(3)N; X = Cl, Br) with sodium amalgam under 1 atm of dinitrogen afforded the square pyramidal, high spin iron(0) bis(dinitrogen) complex ((iPr)PDI)Fe(N(2))(2). In solution, ((iPr)PDI)Fe(N(2))(2) loses 1 equiv of N(2) to afford the mono(dinitrogen) adduct ((iPr)PDI)Fe(N(2)). Both dinitrogen compounds serve as effective precatalysts for the hydrogenation and hydrosilation of olefins and alkynes. Effecient catalytic reactions are observed with low catalyst loadings (less than or equal to0.3 mol %) at ambient temperature in nonpolar media. The catalytic hydrosilations are selective in forming the anti-Markovnikov product. Structural characterization of a high spin iron(0) alkyne and a bis(silane) sigma-complex has also been accomplished and in combination with isotopic labeling studies provides insight into the mechanism of both catalytic C-H and catalytic C-Si bond formation.

First author: Cavigliasso, G, Density functional investigation of metal-metal interactions in mixed-valence d(2)d(3) (Cr, Mo, W) and d(3)d(4) (Mn, Tc, Re) face-shared [M2Cl9](2-) systems, INORGANIC CHEMISTRY, 43, 6734, (2004)
Abstract: The molecular and electronic structures of mixed-valence face-shared (Cr, Mo, W) d(2)d(3) and (Mn, Tc, Re) d(3)d(4) [M2Cl9](2-) dimers have been calculated by density functional methods in order to investigate metal-metal bonding in this series. The electronic structures of these systems have been analyzed using potential energy curves for the broken-symmetry and other spin states arising from the d(2)d(3) and d(3)d(4) coupling modes. In (d(2)d(3)) [Mo2Cl9](2-) and [W2Cl9](2-), the global minimum has been found to be a spin-doublet state characterized by delocalization of the metal-based electrons in a multiple metal-metal bond (with a formal bond order of 2.5). In contrast, weak coupling between the metal centers and electron localization are favored in (d(2)d(3)) [Cr2Cl9](2-), the global minimum for this species being a ferromagnetic S = 5/2 state with a relatively long Cr-Cr separation. The (d(3)d(4)) [Re2Cl9](2-) system also exhibits a global minimum corresponding to a metal-metal bonded spin-doublet state with a formal bond order of 2.5, reflecting the electron-hole equivalence between d(2)d(3) and d(3)d(4) configurations. Double minima behavior is predicted for (d(3)d(4)) [Tc2Cl9](2-) and [Mn2Cl9](2-) due to two energetically close low-lying states (these being S = 3/2 and S = 5/2 states for the former, and S = 5/2 and S = 7/2 states for the latter). A comparison of computational results for the d(2)d(2), d(2)d(3), and d(3)d(3) [W2Cl9](2-) Series and the d(3)d(3), d(3)d(4), and d(4)d(4) [Re2Cl9](2-) series indicates that the observed trends in metal-metal distances can only be rationalized if changes in both the strength of a bonding and metal-metal bond order are taken into consideration. These two factors act conjointly in the W series but in opposition to one another in the Re series. In the case of the [Cr2Cl9](z-) and [Mn2Cl9](z-) climers, the metal-metal bond lengths are significantly shorter for mixed-valence (d(2)d(3) or d(3)d(4)) than d(3)d(3) systems. This result is consistent with the fact that some degree of metal-metal bonding exists in the former (due to partial delocalization of a single a electron) but not in the latter (where all metal-based electrons are completely localized).

First author: Campanera, JM, Organometallic derivatives of fullerenes: A DFT study of (eta(2)-C-x){Pt(PH3)(2)}(n) (x=60, 70, 84; n=1-6), INORGANIC CHEMISTRY, 43, 6815, (2004)
Abstract: To determine the relationship among curvature, patch type, and reactivity of the C-C site, a series of density functional calculations were performed on several substituted fullerenes. [6:6] pyracylene-type sites are the most reactive sites in all analyzed cages: C-60, C-70, and C-84. The binding energy between the Pt(PH3)(2) unit and fullerene is almost independent of the size of the cage and of the number of metals coordinated on the fullerene surface. Contrarily, curvature and type of carbon-carbon bond are determinant for the coordination strength. The use of relatively large basis sets is necessary to have consistent energies.

First author: Hoggan, PE, Choice of atomic orbitals to evaluate sensitive properties of molecules: an example of NMR chemical shifts, INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 100, 214, (2004)
Abstract: Now ab initio or density functional theory (DFT) molecular property calculations over a Slater-type orbital basis are available in several software packages. In this work, the relative merits of various exponential-type orbitals (ETOs) are investigated for solving problems of interest to nuclear magnetic resonance (NMR), while showing how they are related mathematically. The preferred ETOs will be shown to be the hydrogenic orbitals and similar Coulomb Sturmians. Slater-type functions (STFs) will be compared with them, and suitable equivalent (seldom used) combinations given. The correct shielding of the nucleus, resulting from radial factors of hydrogenic orbitals, is finally shown to be essential in the evaluation of precise nuclear shielding tensors for NMR spectroscopy of molecules using ab initio or DFT methods.

First author: Miljacic, L, Structural analysis of porphyrin molecular squares using molecular mechanics and density-functional methods, JOURNAL OF CHEMICAL PHYSICS, 121, 7228, (2004)
Abstract: “Molecular squares” formed from Re(CO)(3)Cl corners and porphyrin sides have potential applications as hosts for catalytic sites and as building blocks for membranes. In these materials, knowledge of the conformations of the squares is important. Molecular-mechanics (MM) and density-functional (DF) calculations have been used iteratively in this work to find the minimum-energy configurations of several porphyrin molecular squares. MM predicts that the steric and torsional interactions at connecting junctures of the square framework determine the overall geometry. Torsional degrees of freedom around these junctures were therefore analyzed using DF methods, giving further insight and helping choose among MM force-field options. Single-point DF calculations on the entire squares showed that the energy and conformation of the entire square could be reliably obtained by performing DF calculations on the critical elements of the square and then piecing them together. This “piecewise” strategy allows for both the major torsional motions and the most important local relaxations of large supramolecular species such as molecular squares.

First author: Kordas, G, FT-EPR spectroscopy in the borate system, JOURNAL OF NON-CRYSTALLINE SOLIDS, 345, 45, (2004)
Abstract: 80-mol% B2O3 20-mol% Li2O glass has been subjected to gamma-irradiation at room temperature and subsequently studied by CW EPR (continuous wave electron paramagnetic resonance), ECHO-fs (field sweep), 4p-ESEEM (electron spin echo envelop modulation spectroscopy), 2D-HYSCORE (hyperfine sublevel correlation) spectroscopy and pulse ENDOR (electron nuclear double resonance) spectroscopies. The variation of the EPR signal with the conditions of measurements suggests that several centers contribute to the signal. The A(iso)-couplings of the next neighbor have been determined by these methods. One may suggest on this ground the existence of the tetraborate, diborate and boron network non-bridging oxygen (BN-nbo) structures, though this preliminary effort needs supplementary investigational work to be convinced about it.

First author: Al Natsheh, A, Sulfuric acid and sulfuric acid hydrates in the gas phase: A DFT investigation, JOURNAL OF PHYSICAL CHEMISTRY A, 108, 8914, (2004)
Abstract: The gaseous sulfuric acid and its hydrates play an essential role in the formation and evolution of atmospheric aerosols via nucleation of binary sulfuric acid-water vapors. Recently, it has been pointed out that the dipole moment of vapor molecules and small preexisting clusters is a new parameter controlling the nucleation rates. In this paper, the dipole moments of the mono-, di, and trihydrates of the sulfuric acid are calculated for the first time. We also report on the molecular structures, energies, vibrational frequencies, absorption intensities and dipole moments of the hydrates and compare our model predictions with the results of other studies. The density functional theory (DFT) calculations have been carried out using the PW91 method and TZP basis set. We have determined the optimized conformations of gas-phase sulfuric acid and mono-, di-, and trihydrates of sulfuric acid using different starting scenarios and computed their dipole moments. The obtained results can be utilized directly in the modeling of the atmospheric aerosol formation and they are applied for the analysis of the hydration thermodynamics.

First author: Grozema, FC, Electronic structure of thienylene vinylene oligomers: Singlet excited states, triplet excited states, cations, and dications, JOURNAL OF PHYSICAL CHEMISTRY B, 108, 16139, (2004)
Abstract: This paper describes a quantum chemical study of the electronic structure of thienylene vinylene oligomers ranging in size from two thienylene rings (2TV) to 12TV. The geometries of the TV oligomers in the ground state, the lowest triplet state, and the singly and doubly oxidized states were optimized using density functional theory calculations. The electronic absorption spectra were obtained from configuration interaction calculations with an INDO/s reference wave function. Comparison with experimental data shows that the agreement is satisfactory, except for the triplet-triplet absorption spectra. For closed shell systems (ground state and doubly occupied state), the spectra were also calculated by time dependent density functional theory (TDDFT). TDDFT considerably underestimates the neutral singlet-singlet excitation energies for longer chains. The nature of the excited states for the TV radical cations was found to be more similar to that of thiophenes than to that of phenylene vinylenes, indicating that the sulfur atom has a marked influence on the pi-electron system. For the (singlet) absorption spectra of doubly oxidized TVs, the results from TDDFT calculations are surprisingly Good; they are also good for long chains. TDDFT calculations for doubly charged TVs also confirm the existence of a second, weak absorption band as has been found experimentally.

First author: Alia, Photochemically induced dynamic nuclear polarization in photosystem I of plants observed by C-13 magic-angle spinning NMR, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 126, 12819, (2004)
Abstract: Photochemically induced dynamic nuclear polarization (photo-CIDNP) has been observed in photosystem I of spinach by C-13 magic angle spinning solid-state NMR under continuous illumination with white light. An almost complete set of chemical shifts of the aromatic ring carbons of a single Chl a molecule has been obtained which is assigned to the P2-cofactor of the primary electron donor P700. Since all light-induced C-13 NMR signals appear to be emissive, a predominance of the three-spin mixing mechanism over the differential decay mechanism is proposed. The origin of the strong contribution of the three-spin mixing mechanism and the differences with photosystem II are discussed.

First author: Zurek, E, Density functional calculations of the C-13 NMR chemical shifts in (9,0) single-walled carbon nanotubes, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 126, 13079, (2004)
Abstract: The electronic structure and C-13 NMR chemical shift of (9,0) single-walled carbon nanotubes (SWNTs) are investigated theoretically. Shielding tensor components are also reported. Density functional calculations were carried out for C-30-capped and H-capped fragments which serve as model systems for the infinite (9,0) SWNT. Based on the vanishing HOMO-LUMO gap, H-capped nanotube fragments are predicted to exhibit “metallic” behavior. The C-13 chemical shift approaches a value of approximate to133 ppm for the longest fragment studied here. The C-30-capped SWNT fragments of D-3d/D-3h symmetry, on the other hand, are predicted to be small-gap semiconductors just like the infinite (9,0) SWNT. The differences in successive HOMO-LUMO gaps and HOMO and LUMO energies, as well as the C-13 NMR chemical shifts, converge slightly faster with the fragment’s length than for the H-capped tubes. The difference between the H-capped and C-30-capped fragments is analyzed in some detail. The results indicate that (at least at lengths currently accessible to quantum chemical computations) the H-capped systems represent less suitable models for the (9,0) SWNT because of pronounced artifacts due to their finite length. From our calculations for the C-30-capped fragments, the chemical shift of a carbon atom in the (9,0) SWNT is predicted to be about 130 ppm. This value is in reasonably good agreement with experimental estimates for the C-13 chemical shift in SWNTs.

First author: Wang, XJ, A theoretical study on the cyclopropane adsorption onto the copper surfaces by density functional theory and quantum chemical molecular dynamics methods, JOURNAL OF MOLECULAR CATALYSIS A-CHEMICAL,220, 189, (2004)
Abstract: We report a theoretical study on the cyclopropane adsorption onto Cu(111) surfaces by density functional theory (DFT) and quantum chemical molecular dynamics methods. The equilibrium geometry of the physisorbed species was obtained using both periodic and cluster models by DFT methods that employ Cambridge serial total energy package (CASTEP), DMol ab initio quantum chemistry software of Accelrys’ materials studio (DMol), and Amsterdam density functional (ADF) program. It was found that the adsorbate molecule was tilted towards the metal surface with one C-C bond (upwards) parallel to the surface and that the physisorption occurred via a third carbon atom pointing (downwards) towards the surface. The electronic distribution and geometrical structure of physisorbed cyclopropane were slightly deviated from its gas phase molecule. The calculated vibrational frequencies and adsorption energies are close to experimental data, confirming the reliability of our DFT results. The adsorption process was simulated using our novel tight-binding quantum chemical molecular dynamics program, ‘Colors’. The calculation results indicated that both the adsorption and desorption processes of cyclopropane took place molecularly. The electron transfer and structural properties of equilibrium position obtained by ‘Colors’ are consistent with those by the first principles DFT methods.

First author: Langlet, J, Decomposition of intermolecular interactions: comparison between SAPT and density-functional decompositions, JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM, 685, 43, (2004)
Abstract: We try to decompose the interaction energy of the hydrogen bonded dimer systems HOH…NH3, H2O…HNH2, and H2O…HNH3+ into several well-defined quantities, using the fragment-based density-functional calculations, Symmetry-adapted perturbation theory, and as well the Heitler-London approach to interaction energies. The theoretical considerations and the numerical results show that despite the different nature of the decomposition schemes common terms beyond the electrostatic interaction of the unperturbed monomers can be extracted. For the Perdew-Wang 91 exchange-correlation functional, the Pauli repulsion implicitely contains an intermolecular correlation part which is numerically close to the SAPT dispersion.

First author: Diefenbach, A, Activation of H-H, C-H, C-C, and C-Cl bonds by Pd(0). Insight from the activation strain model, JOURNAL OF PHYSICAL CHEMISTRY A, 108, 8460, (2004)
Abstract: To achieve more insight into palladium-catalyzed H-H, C-H, C-C, and C-Cl bond activation and the mutual competition between these processes, several mechanistic pathways for oxidative addition of Pd(0) to H-2 (H-H), CH4 (C-H), C2H6 (C-C and C-H), and CH3Cl (C-Cl) were studied uniformly at the ZORA-BP86/TZ(2)P level of relativistic nonlocal density functional theory (DFT). Oxidative addition is overall exothermic for all model reactions studied, with 298 K reaction enthalpies (DeltaH(r,298)) of -35.7 kcal/mol (C-Cl) through -9.7 kcal/mol (C-H in CH4). The lowest barrier pathway is the direct oxidative insertion of Pd into the C-X or H-H bond (X = H, CH3, Cl), with 298 K activation enthalpies (DeltaH(298)(double dagger)) that increase in the order H-H (-21.7 kcal/mol) < C-Cl (-6.0 kcal/mol) approximate to C-H (-5.0 and -4.1 kcal/mol for CH4 and C2H6) < C-C (9.6 kcal/mol). The “straight” S(N)2 substitution resulting in PdCH3+ + X- or PdH+ + H- is highly endothermic (144-237 kcal/mol) and thus not competitive. Only in the case of Pd + CH3Cl is a third pathway found in which S(N)2 substitution occurs in concert with a rearrangement of the Cl- leaving group from C to Pd (S(N)2/Cl-ra) leading, in one step, to CH3PdCl via an activation barrier DeltaH(double dagger)298 of 21.2 kcal/mol. The competition between the various bond activation processes is analyzed using the activation strain model in which activation energies (DeltaE(double dagger)) are decomposed into the activation strain (DeltaE(strain)(double dagger)) of and the stabilizing transition state (TS) interaction (DeltaE(int)(double dagger)) between the reactants in the activated complex: DeltaE(double dagger) = DeltaE(strain)(double dagger) + DeltaE(int)(double dagger). Interestingly, the activation strain DeltaE(strain)(double dagger) adopts characteristic values for each type of bond and reaction mechanism. The trend in TS interaction DeltaE(int)(double dagger) turns out to be mainly determined by the donor-acceptor orbital interactions between occupied Pd 4d atomic orbitals and the empty sigma*(C-X) (or sigma*(H-H)) acceptor orbital associated with the bond to be activated in the substrate.

First author: Jackson, TA, Spectroscopic and computational studies of the azide-adduct of manganese superoxide dismutase: Definitive assignment of the ligand responsible for the low-temperature thermochromism, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 126, 12477, (2004)
Abstract: A variety of spectroscopic and computational techniques have been used to examine the thermochromic transition previously reported for the oxidized state of Mn-dependent superoxide dismutase from E. coli in the presence of substrate analog azide (N-3-Mn3+SOD).[Whittaker, M. M.; Whittaker, J. W. Biochemistry 1996, 35, 6762-6770.] Although previous spectroscopic studies had shown that this thermochromic event corresponds to a change in coordination number of the active-site Mn3+ ion from 6 to 5 as temperature is increased, the ligand that dissociates in this conversion had yet to be identified. Through the use of electronic absorption, circular dichroism (CD), and magnetic CD (MCD) spectroscopies, both d-d and ligand-to-metal charge-transfer (LMCT) transition energies have been determined for native (MnSOD)-S-3divided by (possessing a five-coordinate Mn3+ center) and Y34F N-3-Mn3+SOD (forming a six-coordinate N-3-Mn3+ adduct at all temperatures). These two systems provide well-defined reference points from which to analyze the absorption and CD data obtained for N-3-(MnSOD)-S-3divided by at room temperature (RT). Comparison of excited-state spectroscopic data reveals that Mn3+SOD and RT N-3-Mn3+SOD exhibit virtually identical d-d transition energies, suggesting that these two species possess similar geometric and electronic structures and, thus, that azide does not actually coordinate to the active-site Mn3+ ion at RT. However, resonance Raman spectra of both N-3-Mn3+SOD and Y34F N-3-Mn3+SOD at 0 degreesC exhibit azide-related vibrations, indicating that azide does interact with the active site of the native enzyme at this temperature. To gain further insight into the nature of the azide/Mn3+ interaction in RT N-3-Mn3+SOD, several viable active-site models designed to promote either dissociation of coordinated solvent, Asp167, or azide were generated using DFT computations. By utilizing the time-dependent DFT method to predict absorption spectra for these models of RT N3-Mn3+SOD, we demonstrate that only azide dissociation is consistent with experimental data. Collectively, our spectroscopic and computational data provide evidence that the active site of N-3-Mn3+SOD at RT exists in a dynamic equilibrium, with the azide molecule either hydrogen-bonded to the second-sphere Tyr34 residue or coordinated to the Mn3+ ion. These results further highlight the role that second-sphere residues, especially Tyr34, play in tuning substrate (analog)/metal ion interactions.

First author: Asthagiri, D, On the role of the conserved aspartate in the hydrolysis of the phosphocysteine intermediate of the low molecular weight tyrosine phosphatase, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 126, 12677, (2004)
Abstract: The usual rate-determining step in the catalytic mechanism of the low molecular weight tyrosine phosphatases involves the hydrolysis of a phosphocysteine intermediate. To explain this hydrolysis, general base-catalyzed attack of water by the anion of a conserved aspartic acid has sometimes been invoked. However, experimental measurements of solvent deuterium kinetic isotope effects for this enzyme do not reveal a rate-limiting proton transfer accompanying dephosphorylation. Moreover, base activation of water is difficult to reconcile with the known gas-phase proton affinities and solution phase pK(a)’s of aspartic acid and water. Alternatively, hydrolysis could proceed by a direct nucleophilic attack by a water molecule. To understand the hydrolysis mechanism, we have used high-level density functional methods of quantum chemistry combined with continuum electrostatics models of the protein and the solvent. Our calculations do not support a catalytic activation of water by the aspartate. Instead, they indicate that the water oxygen directly attacks the phosphorus, with the aspartate residue acting as a H-bond acceptor. In the transition state, the water protons are still bound to the oxygen. Beyond the transition state, the barrier to proton transfer to the base is greatly diminished; the aspartate can abstract a proton only after the transition state, a result consistent with experimental solvent isotope effects for this enzyme and with established precedents for phosphomonoester hydrolysis.

First author: Neugebauer, J, Vibronic coupling and double excitations in linear response time-dependent density functional calculations: Dipole-allowed states of N-2, JOURNAL OF CHEMICAL PHYSICS, 121, 6155, (2004)
Abstract: The present study serves two purposes. First, we evaluate the ability of present time-dependent density functional response theory (TDDFRT) methods to deal with avoided crossings, i.e., vibronic coupling effects. In the second place, taking the vibronic coupling effects into account enables us, by comparison to the configuration analysis in a recent ab initio study [J. Chem. Phys. 115, 6438 (2001)], to identify the neglect of double excitations as the prime cause of limited accuracy of these linear response based TDDFRT calculations for specific states. The “statistical averaging of (model) orbital potentials (SAOP)” Kohn-Sham potential is used together with the standard adiabatic local-density approximation (ALDA) for the exchange-correlation kernel. We use the N-2 molecule as prototype, since the TDDFRT/SAOP calculations have already been shown to be accurate for the vertical excitations, while this molecule has a well-studied, intricate vibronic structure as well as significant double excitation nature in the lowest (1)Pi(u) state at elongated bond lengths. A simple diabatizing scheme is employed to obtain a diabatic potential energy matrix, from which we obtain the absorption spectrum of N-2 including vibronic coupling effects. Considering the six lowest dipole allowed transitions of (1)Sigma(u)(+) and (1)Pi(u) symmetry, we observe a good general agreement and conclude that avoided crossings and vibronic coupling can indeed be treated satisfactorily on the basis of TDDFRT excitation energies. However, there is one state for which the accuracy of TDDFRT/ALDA clearly breaks down. This is the state for which the ab initio calculations find significant double excitation character. To deal with double excitation character is an important challenge for time-dependent density functional theory.

First author: Bagno, A, Relativistic DFT calculation of Ru-99 NMR parameters: Chemical shirts and spin-spin coupling constants, MAGNETIC RESONANCE IN CHEMISTRY, 42, S79, (2004)
Abstract: The nuclear shielding of Ru-99 in a wide variety of complexes was investigated computationally by DFT methods, including relativistic effects (by means of the Pauli and ZORA approximations), up to spin-orbit coupling and Slater all-electron or frozen-core basis sets. Mononuclear complexes, a trinuclear cluster and a ruthenium-substituted polyoxometalate were included. Chemical shifts calculated in this way correlated very satisfactorily with experimental values, with fit lines having slopes close to unity. In the few cases where a comparison was possible, spin-spin coupling constants involving Ru-99 were also successfully calculated.

First author: Feindel, KW, A relativistic DFT study of one-bond fluorine-X indirect spin-spin coupling tensors, MAGNETIC RESONANCE IN CHEMISTRY, 42, S158, (2004)
Abstract: The relativistic zeroth-order regular approximation (ZORA) DFT method was employed to investigate indirect spin-spin coupling tensors involving fluorine, (1)J(X, F). The relative contributions of the mechanisms contributing to (1)J(X, F) are discussed, with special attention paid to the magnitude and origin of the anisotropy in this tensor, DeltaJ. This quantum chemical study demonstrates that, for the systems investigated, the ZORA-DFT method reproduces the magnitude of (1)J(X, F)(iso) and indicates that DeltaJ(X, F) is of the same order of magnitude as (1)J(X, F)(iso). Several examples are provided that demonstrate the importance of considering contributions of DeltaJ to the experimental measurement of effective dipolar coupling constants, R-eff. Given the difficulties with determining DeltaJ experimentally and the promising computational results, we suggest that the quantum chemical calculation of (1)J(X, F) be used as a complementary tool to aid in the analysis of data from NMR experiments designed to measure dipolar coupling constants.

First author: Le Guennic, B, NMR properties of platinum-thallium bonded complexes: analysis of relativistic density functional theory results, MAGNETIC RESONANCE IN CHEMISTRY, 42, S99, (2004)
Abstract: The metal NMR parameters of the complexes [(NC)(5)Pt-Tl(CN)(n)](n-) (n = 0-3, I-IV) and [(NC)(5)Pt-Tl-Pt(CN)(5)](3-) (V), as well as [{Pt(NO3)(NH3)(2)L-2}Tl(NO3)(2)(MeOH)] (VI) and [{Pt(NO3)(NH3)(2)L-2}(2)](+) (VII) with L = (NHCOBu)-Bu-t, were computationally investigated by relativistic density functional theory. Complexes I-V were previously studied by us. We briefly review the main findings here. Their spin-spin coupling constants are analyzed in terms of molecular orbital and fragment orbital contributions which demonstrate the various influences of the solvent and of the ligands on the extraordinarily large metal-metal coupling constants. Complexes VI and VII and various model systems were investigated in more detail. It is shown that the same computational model which performs best for I-V yields too large metal-metal coupling constants for VI and VII. The analysis shows that this is likely to be attributable to a strong sensitivity of the coupling constants to the rather small Pt 6s contributions in the occupied metal-metal sigma-bonding orbitals. Bulk solvent effects on the metal-metal couplings are sizeable and should be considered in the computational model. Both calculated and experimental Pt-TI coupling constants for VI and VII are substantially larger than those for I-V, thereby representing the largest heteronuclear coupling constants known so far experimentally. Metal chemical shifts for VI and VII were also investigated. The computational results indicate that the choice of the Pt reference is rather problematic. Tl chemical shifts agree much better with experimental data.

First author: Mawhinney, RC, NMR quantum computing: applying theoretical methods to designing enhanced systems,MAGNETIC RESONANCE IN CHEMISTRY, 42, S88, (2004)
Abstract: Density functional theory results for chemical shifts and spin-spin coupling constants are presented for compounds currently used in NMR quantum computing experiments. Specific design criteria were examined and numerical guidelines were assessed. Using a field strength of 7.0 T, protons require a coupling constant of 4 Hz with a chemical shift separation of 0.3 ppm, whereas carbon needs a coupling constant of 25 Hz for a chemical shift difference of 10 ppm, based on the minimal coupling approximation. Using these guidelines, it was determined that 2,3-dibromothiophene is limited to only two qubits; the three qubit system bromotrifluoroethene could be expanded to five qubits and the three qubit system 2,3-dibromopropanoic acid could also be used as a six qubit system. An examination of substituent effects showed that judiciously choosing specific groups could increase the number of available qubits by removing rotational degeneracies in addition to introducing specific conformational preferences that could increase (or decrease) the magnitude of the couplings. The introduction of one site of unsaturation can lead to a marked improvement in spectroscopic properties, even increasing the number of active nuclei.

First author: Yoshida, Y, Living copolymerization of ethylene with norbornene catalyzed by bis(pyrrolide-imine) titanium complexes with MAO, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 126, 12023, (2004)
Abstract: Bis(pyrrolide-imine) Ti complexes in conjunction with methylalumoxane (MAO) were found to work as efficient catalysts for the copolymerization of ethylene and norbornene to afford unique copolymers via an addition-type polymerization mechanism. The catalysts exhibited very high norbornene incorporation, superior to that obtained with Me2Si(Me4CP)(N-tert-Bu)TiCl2 (CGC). The sterically open and highly electrophilic nature of the catalysts is probably responsible for the excellent norbornene incorporation. The catalysts displayed a marked tendency to produce alternating copolymers, which have stereoirregular structures despite the C-2 symmetric nature of the catalysts. The norbomene/ethylene molar ratio in the polymerization medium had a profound influence on the molecular weight distribution of the resulting copolymer. At norbomene/ethylene ratios larger than ca. 1, the catalysts mediated room-temperature living copolymerization of ethylene and norbornene to form high molecular weight monodisperse copolymers (M-n > 500 000, M-w/M-n < 1.20).C-13 NMR spectroscopic analysis of a copolymer, produced under conditions that gave low molecular weight, demonstrated that the copolymerization is initiated by norbornene insertion and that the catalyst mostly exists as a norbornene-last-inserted species under living conditions. Polymerization behavior coupled with DFT calculations suggested that the highly controlled living polymerization stems from the fact that the catalysts possess high affinity and high incorporation ability for norbornene as well as the characteristics of a living ethylene polymerization though under limited conditions (M-n 225 000, M-w/M-n 1.15, 10-s polymerization, 25degreesC). With the catalyst, unique block copolymers [i.e., poly(ethylene-co-norbornene)(1)-b-poly(ethylene-co-norbornene)(2), PE-b-poly(ethylene-co-norbornene)] were successfully synthesized from ethylene and norbomene. Transmission electron microscopy (TEM) indicated that the PE-b-poly(ethylene-co-norbornene) possesses high potential as a new material consisting of crystalline and amorphous segments which are chemically linked.

First author: Kovacs, A, Theoretical study of UX6 and UO2X2 (X = f, cl, br, I), JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM, 684, 35, (2004)
Abstract: In the present study the structural, vibrational and bonding properties of the uranium(VI) halide and oxyhalide molecules UX6 and UO2X2 (X = F, Cl, Br, 1) have been investigated by quantum chemical calculations. The title molecular properties have been computed using quasi-relativistic density functional theory in conjunction with a polarised triple-zeta basis set. The bonding interactions between the fragments U…X-6 and UO2… X-2 have been investigated using the extended transition state energy partitioning method. Our quantitative analysis revealed an increase of the electrostatic interactions in UO2X2 with respect to UX6 as a result of the oxygen substitution. Analogously to previous results on uranyl, the bonding Kohn-Sham orbitals Of UO2X2 showed a clear triple-bond character of the formally U=O double bonds. The population analysis results are in agreement with a predominant role of the uranium 5f orbitals in the orbital interactions, whereas a slight strengthening of the 6d contributions toward the heavier halides.

First author: Wang, JH, Chemistry of C-trimethylsilyl-substituted heterocarboranes. 30. Synthetic and structural studies on oxide ion encapsulating tetralanthanide tetrahedra surrounded by “carbons apart” C2B4-carborane Ligands (Ln(III) = La, Nd, Gd, Tb, Ho, Lu), ORGANOMETALLICS, 23, 4621, (2004)
Abstract: The reactions of closo-exo-5,6-Na(THF)(2)-1-Na(THF)(2)-2,4-(SiMe3)(2)-2,4-C2B4H4 (1) with anhydrous LnCl(3) (Ln = La, Nd, Gd, Tb, Ho, Lu) and freshly distilled H2O in molar ratios of 5:4:1 gave crystalline solids, identified as the new oxolanthanacarboranes {[eta(5)-1-Ln(THF)(n)-2,4-(SiMe3)(2)-2,4-C2B4H4](4)(mu-Cl)(2)( mu(4)-O)}.yTHF (Ln = La (2), n = 0, y = 1; Ln = Nd (3), n = 1, y = 0; Ln = Gd (4), n = 0, y = 1; Ln = Tb (5), n = 1, y = 0; Ln = Ho (6), n = 0, y = 1; Ln = Lu (7), n = 1, y = 0), in 73-86% yields. All new compounds were characterized by IR spectroscopy and elemental analyses. While the diamagnetic compounds 2 and 7 were also studied by H-1, C-13, and B-11 NMR spectroscopy, the lanthanacarboranes 3 and 5-7 were further characterized by single-crystal X-ray diffraction analyses. The species 3, 5, and 7 were found to be isostructural, all containing oxide ion encapsulating tetralanthanide cores, Ln(mu(4)-O), that are stabilized by coordinating two carborane ligands: one in an eta(5) fashion via the C2B3-bonding face and the other via two Ln-H-B bridges to a neighboring cage. Complexes 3 and 5-7 crystallized in the monoclinic space group C2/c with a = 23.748(5), 23.577(5), 28.403(5), and 23.544(5) Angstrom, b = 18.632(5), 18.513(5), 12.835(2), and 18.440(5) Angstrom, c = 22.798(5), 22.602(5), 27.879(5), and 22.480(5) Angstrom, beta = 104.338(5), 104.092(5), 117.820(3), and 104.153(5)degrees, and V = 9774(64), 9568(4), 8989(13), and 9464(4) Angstrom(3), respectively (Z = 4). The final refinements of 3 and 5-7 converged at R1 = 0.0795, 0.0703, 0.0367, and 0.0904; wR2 = 0.1793, 0.1686, 0.794, and 0.1844, and GOF = 1.401, 1.305, 1.446, and 1.498, respectively. The room-temperature magnetic susceptibility of the holmium compound 6 was found to be 10.3 mu(B) per lanthanide metal.

First author: Venkatesan, K, Synthetic access to half-sandwich manganese C-4 cumulenic complexes,ORGANOMETALLICS, 23, 4661, (2004)
Abstract: The vinylalkynyl complexes Mn(C5H4R’)(R”2PCH2CH2PR”(2))(=C CSnPh3C=-CSnPh3) (5, 6) were obtained in good yields by treatment of Mn(C5H4R’)(eta(6)-cycloheptatriene) (R’ = H (1a), Me (1b)) with 1 equiv of Ph(3)SnCdropCCdropCSnPh(3) and R”2PCH2CH2PR”(2) (R” = CH3 (dmpe), C2H5 (depe)). The theoretically characterized (DFT) C-4 cumulenic species Mn(C5H4R’)(R”2PCH2CH2PR”(2)){=C=C=C C(SnPh3)(2)} (7, 8) were obtained by photolysis of the tin-substituted vinylalkynyl complexes 5 and 6. Subsequently 7 and 8 could be converted into the parent cumulenic species Mn(C5H4R’)(R”2PCH2CH2PR”(2)){=C=C=C=C(H)(2)} (9, 10) by reacting complexes 7 and 8 with TBAF (5% H2O) at -40 degreesC. The difference in the thermodynamic stabilities between the complexes 7 and 8 and complexes 9 and 10 was traced by DFT calculations using Mn(C5H5)(dHpe){=C=C=C=C(SnMe3)(2)} (4-H) and Mn(C5H5)(dHpe){=C=C=C=CH2} (9-H) as model complexes. Treatment of the vinylalkynyl complex with an excess of MeOH led to the formation of a dinuclear complex with a C-8 chain between two manganese centers. The cumulenic complexes and the vinylalkynyl complexes were characterized by NMR and vibrational spectroscopy and elemental analyses. An X-ray diffraction study has been performed on complex 4b.

First author: Infante, I, The importance of spin-orbit coupling and electron correlation in the rationalization of the ground state of the CUO molecule, JOURNAL OF CHEMICAL PHYSICS, 121, 5783, (2004)
Abstract: We present calculations at the relativistic coupled cluster theory that predict the (1)Sigma(0)(+) ground state of CUO to lie 58.2 kJ/mol below the first excited state, (3)Phi(2). This can be contrasted with the outcome of earlier density functional theory and complete active space second order perturbation theory (CASPT2) calculations that both predicted a (3)Phi(2) ground state upon inclusion of spin-orbit coupling in the calculations. Our result gives further justification to the interpretation of the measured frequency shifts of this species in various noble gas matrices as being caused by significant interaction between the uranium and the heavier noble gas atoms.

First author: Wesolowski, TA, Hydrogen-bonding-induced shifts of the excitation energies in nucleic acid bases: An interplay between electrostatic and electron density overlap effects, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 126, 11444, (2004)
Abstract: We present calculations at the relativistic coupled cluster theory that predict the (1)Sigma(0)(+) ground state of CUO to lie 58.2 kJ/mol below the first excited state, (3)Phi(2). This can be contrasted with the outcome of earlier density functional theory and complete active space second order perturbation theory (CASPT2) calculations that both predicted a (3)Phi(2) ground state upon inclusion of spin-orbit coupling in the calculations. Our result gives further justification to the interpretation of the measured frequency shifts of this species in various noble gas matrices as being caused by significant interaction between the uranium and the heavier noble gas atoms.

First author: Cho, HM, Temperature and isotope substitution effects on the structure and NMR properties of the pertechnetate ion in water, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 126, 11583, (2004)
Abstract: The uniquely well-resolved Tc-99 NMR spectrum of the pertechnetate ion in liquid water poses a stringent test of the accuracy of ab initio calculations. The displacement of the Tc-99 chemical shift as a function of temperature has been measured over the range 10-45 degreesC for the three isotopomers Tc(O-16)(4)(-), Tc(O-16)(3)(O-18)(-), and Tc(O-16)(3)(O-17)(-) at natural oxygen isotope abundance levels, and in addition the temperature dependence of the Tc-O scalar coupling was determined for the Tc(O-16)(3)(O-17)(-) isotopomer. Values for these parameters were computed using relativistic spin-orbit density functional theory with an unsolvated ion approximation and with treatments of the solvated ion based on the COnductor-like Screening MOdel (COSMO) approach. The temperature and isotope dependence of Tc-99 NMR parameters inferred by these methods were in good quantitative agreement with experimental observations. The change in the Tc-O bond length associated with the changes in temperatures considered here was determined to be of the order of 10(-4) Angstrom. Vibrational energies and Tc-O bond lengths derived from these models also compare favorably with previous experimental studies.

First author: Salomon, A, Stable room-temperature molecular negative differential resistance based on molecule-electrode interface chemistry, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 126, 11648, (2004)
Abstract: We show reproducible, stable negative differential resistance (NDR) at room temperature in molecule-controlled, solvent-free devices, based on reversible changes in molecule-electrode interface properties. The active component is the cyclic disulfide end of a series of molecules adsorbed onto mercury. As this active component is reduced, the Hg-molecule contact is broken, and an insulating barrier at the molecule-electrode interface is formed. Therefore, the alignment of the molecular energy levels, relative to the Fermi levels of the electrodes, is changed. This effect results in a decrease in the current with voltage increase as the reduction process progresses, leading to the so-called NDR behavior. The effect is reproducible and repeatable over more than 50 scans without any reduction in the current. The stability of the system, which is in the “solid state” except for the Hg, is due to the molecular design where long alkyl chains keep the molecules aligned with respect to the Hg electrode, even when they are not bound to it any longer.

First author: Gryff-Keller, A, Systematic discrepancy of theoretical predictions of NMR chemical shifts for chlorinated aromatic carbons using the GIAO DFT method, MOLECULAR PHYSICS, 102, 1903, (2004)
Abstract: Theoretical calculations of carbon-13 NMR chemical shifts using the gauge including atomic orbitals (GIAO) DFT approach with a moderately large set of basis functions usually yield quite satisfactory results. In the case of chlorinated aromatic carbons, however, abnormally large differences between experimental and calculated values have been noticed. This discrepancy has been proven not to be caused by improper referencing, or the basis set effect, and probably not by neglect of vibrational corrections. One of the possible sources of the chlorine effect could be the impact of relativistic phenomena on electrons moving about the chlorine nucleus. The second, probably more important factor is the influence of electron correlations, ignored in Hartree-Fock SCF and only partially included in DFT calculations. Surprisingly, however, the observed divergence has been significantly larger for DFT than for Hartree-Fock results. In the latter case the observed divergence between theoretical and experimental C-13 NMR chemical shifts of chlorine-bonded carbons is systematic but rather small (3.4-4.4 ppm).

First author: Burland, MC, Proton as the simplest of all catalysts for [2+2] cycloadditions: DFT study of acid-catalyzed imine metathesis, JOURNAL OF ORGANIC CHEMISTRY, 69, 6173, (2004)
Abstract: The mechanism of imine metathesis was studied as a prototype reaction for the impact that heteroatom substitution has on thermally forbidden [2 + 2] addition reactions using high-level density functional theory in combination with a continuum solvation model. The intuitively expected high activation barriers were confirmed for N-alkyl- and N-aryl-substituted imine reactants with transition state free energies of 78.8 and 68.5 kcal/mol, respectively, in benzene. The computed reaction energy profiles were analyzed to discover possible strategies for lowering the transition state energy. Protonation of the imine nitrogen was proposed as a possible catalytic route and was explicitly modeled. The computed reaction energy profile shows that protonation of one of the imine reactants has an enormous effect on the overall rate of metathesis and lowers the activation barrier by as much as 37.3 and 30.6 kcal/mol for the N-alkyl and N-aryl reactants, respectively. These results suggest that acid-catalyzed imine metathesis should be amenable at elevated temperatures. Furthermore, the protonation of both reactants of the metathesis reaction is predicted to be not productive owing to electrostatic repulsion of the reactants, thus suggesting that there should be an optimum pH for the catalytic turnover. A detailed analysis of the catalytic mechanism is presented, and the primary driving force for the catalysis is identified. Upon protonation of the imine nitrogen, the key [2 + 2]-addition step becomes asynchronous and one of the two intermolecular N-C bonds is formed before traversing the transition state, resulting in a substantial net decrease of the overall energy requirement. The general applicability of this intuitively understandable mechanism for designing structural features for lowering the energy of transition state structures is explored.

First author: Soo, HS, A homoleptic molybdenum(IV) enolate complex: Synthesis, molecular and electronic structure, and NCN group transfer to form a terminal cyanoimide of molybdenum(VI), JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 126, 11370, (2004)
Abstract: A monomeric molybdenum(IV) tetrakis enolate complex Mo(OC[Ad]MeS)(4), 1, where Ad = 2-adamantylidene and Mes = 2,4,6-Me3C6H2, has been synthesized and characterized structurally by X-ray diffraction, chemically through NCN group-transfer reactivity, and computationally to investigate the origins of the observed structure that is intermediate between tetrahedral and square planar. No prior examples of Mo(OR)(4) have been structurally characterized despite having been the subject of both experimental and theoretical interest. Complex 1 has a singlet ground state and thus a metal-based lone pair of electrons. The latter has been visualized with the aid of the electron localization function (ELF) and appears as a two-bladed propeller with D-2d symmetry. Complex 1 makes a simple 1:1 adduct with t-BuNC that is trigonal bipyramidal with an axial isocyanide as demonstrated by X-ray crystallography. This trigonal bipyramidal 1:1 adduct has a triplet ground state and provides a model for the way in which 1 interacts with NCN group donor dbabhCN prior to NCN group transfer to form the terminal cyanoimide complex 1-NCN. The calculated Mo-N bond dissociation enthalpy for 1-NCN is 104 kcal mol(-1), 30 kcal mol(-1) greater than that for the corresponding dissociation of NCN from cyanophosphiniminato NCNPMe3.

First author: van Faassen, M, Size-scaling of the polarizability of tubular fullerenes investigated with time-dependent (current)-density-functional theory, CHEMICAL PHYSICS LETTERS, 395, 274, (2004)
Abstract: We present a study of the static polarizability for the tubular fullerenes C-60 + (i x 10), where i= 0-5, and the closely related [5,5] carbon nanotube, using time-dependent (current)-density-functional theory. Comparing the results obtained within the conventional adiabatic local-density approximation with those obtained using the Vignale-Kohn current-dependent exchange-correlation functional it is found that the extra long-range exchange-correlation effects described by the current-density functional are important to consider, especially for the longest fullerenes. For all systems studied the current-density functional results are in good agreement with experiment, and the agreement with available ab initio self-consistent-field results and results from a point-dipole interaction model is much better than when using the adiabatic local-density functional.

First author: Pouchan, C, Between geometry, stability, and polarizability: Density functional theory studies of silicon clusters Si-n (n=3-10), JOURNAL OF CHEMICAL PHYSICS, 121, 4628, (2004)
Abstract: The relationship between the polarizability, stability, and the geometry of small-size silicon clusters has been investigated by the density functional theory methods. Results obtained at local density approximation/Vosko-Wilk-Nusair and general gradient approximation/BLYP levels with polarized even-tempered basis set of quadruple zeta quality are presented and compared with those obtained by the B3LYP method, as well as with the ab initio results in recent literature. We have found that the polarizability is directly related to the size of the energy gap between symmetry-compatible bonding and antibonding molecular orbitals, but not necessarily to the size of the HOMO-LUMO (highest occupied molecular orbital-lowest unoccupied molecular orbital) gap. Furthermore, we have defined two structural parameters, namely, the averaged Si-Si distances and the standard deviation of the Si-Si distances, which were found to correlate remarkably well with the binding energy of the clusters and the HOMO-LUMO gap, respectively. These straightforward correlations would, therefore, provide a means to predict the physical properties, in particular, the polarizability and the stability, simply based on the structural information of the cluster.

First author: Sugiyama, H, Preparation, characterization, and magnetic behavior of the in derivatives (Ln = Nd, La) of a 2,6-diiminepyridine ligand and corresponding dianion, INORGANIC CHEMISTRY, 43, 5771, (2004)
Abstract: An unprecedented Nd[2,6-{[2,6-(i-Pr)(2)C6H5]N=C(CH3)}(2)(C5H3N)]Ndl(2)(THF) (1) complex was prepared by oxidizing metallic Nd with 12 in THF and in the presence of 2,6-{[2,6-(i-Pr)(2)C6H5]N=C(CH3)}(2)(C5H3N). The magnetic behavior at variable T clearly indicated that the complex should be regarded as a trivalent Nd atom antiferromagnetically coupled to a radical anion. By using the doubly deprotonated form of the diimino pyridine ligand {[2,6-{[2,6-(i-Pr)(2)C6H5]N-C=CH2}(2)(C5H3N)](2-) (2) the corresponding trivalent complexes {[2,6-{[2,6-(i-Pr)(2)C6H5]N-C=CH2}(2)(C5H3N)]Ln (THF)}(mu-Cl)(2)[Li(THF)(2)].0.5 (hexane) [Ln = Nd (3), La (4)] were obtained and characterized. Reduction of these species afforded electron transfer to the ligand system which gave ligand dimerization via C-C bond formation through one of the two ene-amido functions of each molecule. The resulting dinuclear {[{[2,6-(i-Pr)(2)C6H5]N-C=(CH2)}(C5H3N){[2,6-(i-Pr)(2)C6H5]N=CCH2}]Ln(TH F)(2)(mu-CI)[Li(THF)(3)]}(2).2(THF) [Ln = Nd (5), La (6)] were isolated and characterized.

First author: Coppens, P, The interplay between experiment and theory in charge-density analysis, ACTA CRYSTALLOGRAPHICA SECTION A, 60, 357, (2004)
Abstract: The comparison of theory and experiment remains a cornerstone of scientific inquiry. Various levels of such comparison applicable to charge-density analysis are discussed, including static and dynamic electron densities, topological properties, d-orbital occupancies and electrostatic moments. The advantages and drawbacks of the pseudoatom multipole are discussed, as are the experimentally constrained wavefunctions introduced by Jayatilaka and co-workers, which combine energy minimization with the requirement to provide a reasonable fit to the X-ray structure factors. The transferability of atomic densities can be exploited through construction of a pseudoatom databank, which may be based on analysis of ab initio molecular electron densities, and can be used to evaluate a host of physical properties. Partitioning of theoretical energies with the Morokuma-Ziegler energy decomposition scheme allows direct comparison with electrostatic interaction energies obtained from electron densities represented by the pseudoatom formalism. Compared with the Buckingham expression for the interaction between non-overlapping densities, the agreement with theory is much improved when a newly developed hybrid EP/MM (exact potential/multipole model) method is employed.

First author: Zouchoune, B, Bonding analysis of square-antiprismatic and fused square-antiprismatic copper(I)-selenium clusters, JOURNAL OF CLUSTER SCIENCE, 15, 267, (2004)
Abstract: The electronic structure of the Cu2(4n+2)Se4n+2(PH3)(8)(n=1-4) D-4h series of model clusters has been analyzed by means of density functional theory calculations. The fused square antiprismatic structure of the metal framework is found to be always preferred over the fused cuboctahedral one because it reinforces the Cu-P bonds. Thus, the presence of the terminal phosphine ligands tends to strengthen the Cu…Cu (d(10)…d(10)) bonding by mixing bonding combinations of the vacant Cu 4s and 4p orbitals into the occupied 3d combinations. The calculations indicate that the compounds corresponding to n=3 and 4 should be easily two-electron-reduced, leading to stable dianionic species.

First author: Kordas, G, g-Factor calculations for the species occurring in borate glasses, JOURNAL OF NON-CRYSTALLINE SOLIDS, 343, 159, (2004)
Abstract: The g-factors expected for the various structures reported in borate glasses were calculated to predict the spectra observed in these glasses. The g-factors were calculated by DFT methods (ADF and G03w). Based on these calculations, the BOHC(1) and BOHC(2) were attributed to non-bridging oxygen bonded to threefold coordinated boron attached to a boroxol ring and an unpaired electron trapped by an orthoborate unit, respectively.

First author: Bowmaker, GA, Solid-state Ag-109 CP/MAS NMR spectroscopy of some diammine silver(I) complexes,MAGNETIC RESONANCE IN CHEMISTRY, 42, 819, (2004)
Abstract: Solid-state cross-polarization magic-angle spinning (CP/MAS) NMR spectra were recorded for the compounds [Ag(NH3)(2)](2)SO4, [Ag(NH3)(2)](2)SeO4 and [Ag(NH3)(2)]NO3, all of which contain the linear or nearly linear two-coordinate [Ag(NH3)(2)](+) ion. The Ag-109 CP/MAS NMR spectra show centrebands and associated spinning sideband manifolds typical for systems with moderately large shielding anisotropy, and splittings due to indirect (1)J(Ag-109,N-14) spin-spin coupling. Spinning sideband analysis was used to determine the Ag-109 shielding anisotropy and asymmetry parameters Deltasigma and eta from these spectra, yielding anisotropies in the range 1500-1600 ppm and asymmetry parameters in the range 0-0.3. Spectra were also recorded for N-15 and (for the selenate) Se-77. In all cases the number of resonances observed is as expected for the crystallographic asymmetric units. The crystal structure of the selenate is reported for the first time. One-bond (Ag-107,Ag-109,N-15) coupling constants are found to have magnitudes in the range 60-65 Hz. Density functional calculations of the Ag shielding tensor for model systems yield results that are in good agreement with the experimentally determined shielding parameters, and suggest that in the solid compounds Deltasigma and eta are reduced and increased, respectively, from the values calculated for the free [Ag(NH3)(2)](+) ion (1920 ppm and 0, respectively), primarily as a result of cation-cation interactions, for which there is evidence from the presence of metal-over-metal stacks of [Ag(NH3)(2)](+) ions in the solid-state structures of these compounds.

First author: Petrie, S, On the mechanism of dioxygen formation from a Di-mu-oxo-bridged manganese dinuclear complex,INORGANIC CHEMISTRY, 43, 5237, (2004)
Abstract: Density functional theory (DFT) calculations, using the Becke-Perdew gradient-corrected functional with a triple-plus-polarization basis set, have been used to characterize the [(H2O)(H3N)(3)Mn(mu-O)(2)Mn(NH3)(3)(OH2)(q+) (q = 2-5) complexes. This structure has been proposed as a possible model for the oxygen-releasing site of the photosystern II (PSII) reaction center. We have performed full optimizations to locate stationary points in various spin states for each of the +2 to +5 charge states. Our calculations indicate that 02 release from the vacuum-phase +5 charge state complex is barrier inhibited, in contrast to the results of a recent DFT study. We report several new di-mu-oxo-bridged stationary points with spin multiplicities of S = 1/2, 3/2, and 5/2 and effective metal oxidation states of (MnMnV)-Mn-IV for the +5 charge state. Finally, calculations employing the ‘conductorlike screening model’ (COSMO), to address the inclusion of solvent effects, indicate that dissociative O-2 release from the +5 charge state model complex is inhibited by a major barrier and is therefore apparently highly disfavored.

First author: Orian, L, Rh-103 NMR chemical shifts in organometallic complexes: A combined experimental and density functional study, CHEMISTRY-A EUROPEAN JOURNAL, 10, 4029, (2004)
Abstract: Experimental Rh-103 NMR chemical shifts of mono- and binuclear rhodium(I) complexes containing s- or as-hydroindacenide and indacenediide bridging ligands with different ancillary ligands (1,5-cyclooctadiene, ethylene, carbonyl) are presented. A protocol, based on density functional theory calculations, was established to determine Rh-103 NMR shielding constants in order to rationalise the effects of electronic and structural variations on the spectroscopic signal, and to gain insight into the efficiency of this computational method when applied to organometallic systems. Scalar and spin-orbit relativistic effects based on the ZORA (zeroth order regular approximation) level have been taken into account and discussed. A good agreement was found for model compounds over a wide range of chemical shifts of rhodium (approximate to 10000 ppm). This allowed us to discuss the experimental and calculated delta(Rh-103) in larger complexes and to relate it to their electronic structure.

First author: Termaten, AT, Generating and dimerizing the transient 16-electron phosphinidene complex [Cp*Ir=PAr]: A theoretical and experimental study, CHEMISTRY-A EUROPEAN JOURNAL, 10, 4063, (2004)
Abstract: The properties of the 16-electron phosphinidene complex [CpRIr=PR] were investigated experimentally and theoretically. Density functional theory calculations show a preferred bent geometry for the model complex [CpIr=PH], in contrast to the linear structure of [CpIr=NH]. Dimerization to give [{CpIr=PH}(2)] and ligand addition to afford [Cp(L)Ir=PH] (L=PH3, CO) were calculated to give compounds that were energetically highly favorable, but which differed from the related imido complexes. Transient 16-electron phosphinidene complex [Cp*Ir=PAr] could not be detected experimentally. Dehydrohalogenation of [Cp*IrCl2(PH2Ar)] in CH2Cl2 at low temperatures resulted in the novel fused-ring systems 17 (Ar=Mes*) and 20 (Ar=Mes), with dimeric [{Cp*Ir=PAr}(2)] being the likely intermediate. Intramolecular C-H bond activation induced by steric factors is considered to be the driving force for the irreversible formation of 17 and 20. ONIOM calculations suggest this arises because of the large steric congestion in [{Cp*Ir=PAr}2], which forces it toward a more reactive planar structure that is apt to rearrange.

First author: Guillaumont, D, Quantum chemistry study of actinide(III) and lanthanide(III) complexes with tridentate nitrogen ligands, JOURNAL OF PHYSICAL CHEMISTRY A, 108, 6893, (2004)
Abstract: The structure and bonding in large complexes of actinide(III) and lanthanide(III) with tridentate N-donor ligands and water molecules have been investigated through quantum chemistry calculations in order to characterize the nature of the lanthanide-ligand and actinide-ligand bonds. Calculations have been performed using relativistic density functional theory on [M(L)(H2O)(6)](3+), [M(L)(H2O)(5)Cl](2+), and [M(H2O)(9)](3+) clusters where M = La, Ce, Nd, U, Pu, Am, or Cm and L = 2,2′:6’2″terpyridine (Terpy) or 2,6-bis(5,6-dimethyl-1,2,4-triazin-3-yl)pyridine (MeBtp). Calculated M-L distances compare well with X-ray crystal data obtained on related systems. In particular, calculations correctly reproduce the experimentally observed shortening of the uranium-ligand bond in comparison with the cerium-ligand bond. The calculated evolution of the M-L bond as a function of the cation shows that lanthanide-ligand distances decrease with the diminution of the ionic radius, whereas the actinide-ligand distances increase from uranium to americium and are shorter than Ln-N distances. These trends are explained by the presence of slightly stronger covalent effects in the metal-ligand bond for the actinides, decreasing in the order U > Pu > Am Cm, compared to lanthanides. The participation of 5f orbitals in the bonding is found to be significant only for uranium.

First author: Chang, CJ, Targeted proton delivery in the catalyzed reduction of oxygen to water by bimetallic Pacman porphyrins, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 126, 10013, (2004)
Abstract: A combined experimental and theoretical investigation of the role of proton delivery in determining O-2 reduction pathways catalyzed by cofacial bisporphyrins is presented. A homologous family of dicobalt(II) Pacman porphyrins anchored by xanthene [Co-2(DPX) (1) and Co-2(DPXM) (3)] and dibenzofuran [Co-2(DPD) (2) and Co2(DPDM) (4)] have been synthesized, characterized, and evaluated as catalysts for the direct four-proton, four-electron reduction of O-2 to H2O. Structural analysis of the intramolecular diiron(III) mu-oxo complex Fe2O(DPXM) (5) and electrochemical measurements of 1-4 establish that Pacman derivatives bearing an aryl group trans to the spacer possess structural flexibilities and redox properties similar to those of their parent counterparts; however, these trans-aryl catalysts exhibit markedly reduced selectivities for the direct reduction of O-2 to H2O over the two-proton, two-electron pathway to H2O2. Density functional theory calculations reveal that trans-aryl substitution results in inefficient proton delivery to O-2-bound catalysts compared to unsubstituted congeners. In particular, the HOMO of [Co-2(DPXM)(O-2)](+) disfavors proton transfer to the bound oxygen species, funneling the O-O activation pathway to single-electron chemistry and the production of H2O2, whereas the HOMO of [Co-2(DPX)(O-2)](+) directs protonation to the [Co2O2] core to facilitate subsequent multielectron O-O bond activation to generate two molecules of H2O. Our findings highlight the importance of controlling both proton and electron inventories for specific O-O bond activation and offer a unified model for O-O bond activation within the clefts of bimetallic porphyrins.

First author: Dai, XL, Discrete bridging and terminal copper carbenes in copper-catalyzed cyclopropanation, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 126, 10085, (2004)
Abstract: The Cu(I) beta-diketiminate [Me(2)NN]Cu(eta(2)-ethylene) (2) catalyzes the cyclopropanation of styrene with N(2)CPh(2) to give 1,1,2-triphenylcyclopropane in 67% yield. Addition of N(2)CPh(2) to 2 equiv of 2 allows for the isolation of the dicopper carbene {[Me(2)NN]Cu}(2)(mu-CPh(2)) (3) in which the diphenylcarbene moiety is symmetrically bound between two [Me(2)NN]Cu fragments (Cu-C = 1.922(4) and 1.930(4) Angstrom) with a Cu-Cu separation of 2.4635(7) Angstrom. In toluene-d(8) solution, 3 reversibly dissociates a [Me(2)NN]Cu fragment to give [Me(2)NN]Cu(toluene) and the terminal carbene [Me(2)NN]Cu=CPh(2). Dicopper carbene 3 reacts with 3 equiv of styrene to give 1,1,2-triphenylcyclopropane and 2 equiv of [Me(2)NN]Cu(eta(2)-styrene) within minutes. DFT studies with simplified ligands indicate a stronger Cu-C pi-back-bonding interaction from two Cu(I) centers to the carbene acceptor orbital in a dicopper carbene than that present in a monocopper carbene. Nonetheless, the terminal carbene [Me(3)NN]Cu=CPh(2) (8) that possesses a p-methyl group on each beta-diketiminato N-aryl ring may be isolated and exhibits a shortened Cu-C distance of 1.834(3) Angstrom. The stoichiometric cyclopropanation of styrene by 8 in 1,4-dioxane is first-order in both copper carbene 8 and styrene with activation parameters DeltaH(not similar or equal to) = 10.4(3) kcal/mol and DeltaS(not similar or equal to) = -32.3(9) cal/mol-K. In 1,4-dioxane, 8 decomposes to Ph(2)C=CPh(2) via first-order kinetics with activation parameters DeltaH(not similar or equal to) = 21(1) kcal/mol and DeltaS(not similar or equal to) = -8(3) cal/mol-K. Arene solutions of thermally sensitive terminal carbene 8 decompose to [Me(3)NN]-Cu(arene), which reacts with 8 still present in solution to give the more thermally stable {[Me(3)NN]Cu}(2)-(mu-CPh(2)).

First author: Zhang, JP, Quantum chemical analysis of the chemical bonds in Mq3 (M = A(III), Ga-III) as emitting material for OLED, CHEMICAL PHYSICS LETTERS, 394, 120, (2004)
Abstract: Geometries of ground and first excited states of mer-tris(8-hydroxyquinolinato)metal (Mq3, M=Al-III, Ga-III) are optimized at B3LYP/6-31G(d) and CIS/6-31G level, respectively. In order to investigate the difference for individual ligands in mer-Mq3, the energy partitioning analysis has been carried out at the BP86 level using TZ2P basis functions for the bonding interactions between each fragment Mq2 and single ligand q. HOMO and LUMO distribution fashion can be traced back to the lowest electrostatic attractive and highest orbital interaction energy between fragments A-quinolate ligand and Mq2 and B-ligand and Mq2, respectively.

First author: Costabile, C, Origin of enantioselectivity in the asymmetric Ru-catalyzed metathesis of olefins, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 126, 9592, (2004)
Abstract: The mechanism of enantioselectivity in the asymmetric Ru-catalyzed metathesis of olefins is investigated with a theoretical approach. The models are based on the chiral N-heterocyclic (NHC)-based catalysts developed by Grubbs. Our analysis indicates that the origin of enantioselectivity in the ring-closing metathesis of achiral trienes is correlated to the chiral folding of the N-bonded aromatic groups, which is imposed by the Ph groups in positions 4 and 5 of the imidazole ring of the NHC ligand. This chiral folding of the catalyst imposes a chiral orientation around the Ru=C bond, which, in turn, selects between the two enantiofaces of the substrate. In the ring-closing transition state, the geometry in which additional groups on the forming ring are in pseudoequatorial positions is favored over transition states in which this additional group is in a pseudoaxial position. These combined effects rationalize the enantiomeric excesses experimentally obtained.

First author: Wang, Q, The synthesis and electronic structure of a novel [NiS4Fe2(CO)(6)] radical cluster: Implications for the active site of the [NiFe] hydrogenases, CHEMISTRY-A EUROPEAN JOURNAL, 10, 3384, (2004)
Abstract: A novel [Ni’S-4’Fe-2(CO)(6)] cluster (1: ‘S-4’=(CH3C6H3S2)(2)(CH2)(3)) has been synthesised, structurally characterised and has been shown to undergo a chemically reversible reduction process at -1.31 V versus Fc(+)/Fc to generate the EPR-active monoanion 1(-). Multifrequency Q-, X- and S-band EPR spectra of Ni-61-enriched 1(-) show a well-resolved quartet hyperfine splitting in the low-field region due to the interaction with a single Ni-61 (I = 3/2) nucleus. Simulations of the EPR spectra require the introduction of a single angle of non-coincidence between g, and A(1), and g(3) and A(3) to reproduce all of the features in the S- and X-band spectra. This behaviour provides a rare example of the detection and measurement of non-coincidence effects from frozen-solution EPR spectra without the need for single-crystal measurements, and in which the S-band experiment is sensitive to the non-coincidence. An analysis of the EPR spectra of 1(-) reveals a 24% Ni contribution to the SOMO in 1(-), supporting a delocalisation of the spin-density across the NiFe2 cluster. This observation is supported by IR spectroscopic results which show that the CO stretching frequencies, v(CO), shift to lower frequency by about 70 cm(-1) when 1 is reduced to 1(-). Density functional calculations provide a framework for the interpretation of the spectroscopic properties of 1(-) and suggest that the SOMO is delocalised over the whole cluster, but with little S-centre participation. This electronic structure contrasts with that of the Ni-A, -B, -C and -L forms of [NiFe] hydrogenase in which there is considerable S participation in the SOMO.

First author: Frantz, S, EPR insensitivity of the metal-nitrosyl spin-bearing moiety in complexes [LnRuII-NO.](k),EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 10, 2902, (2004)
Abstract: A survey of 18 paramagnetic species [LnRu(NO)](k), including seven new examples studied by in situ electrolysis, reveals a surprisingly narrow range of EPR parameters despite a wide variety of ligands such as pyridine, polypyridines, imines, amines, nitriles, phosphanes, carbonyl, cyclopentadienides, halides, hydride, hydroxide, thiocyanate or cyanide: g(1) = 2.015 +/- 0.02, g(2) = 1.990 +/- 0.015, g(3) = 1.892 +/- 0.03, g(av) = 1.968 +/- 0.02, Deltag = g(1) – g(3) = 0.122 +/- 0.037, A(2)(N-14) = 3.3 +/- 0.5 mT. This rather small variability, smaller still if the organometallic compounds are excluded, differs from the wider range of EPR data reported for nitrosyliron species with S = 1/2; apparently, the {RuNO}(7) configuration involves a rather invariant and relatively covalent metal-NO interaction. DFT calculations were employed for [(NC)(5)Ru(NO)](3-) to reproduce the EPR data, to evaluate the spin distribution (58% spin density on NO), and to reveal structural changes on reduction such as the Ru-N-O bending and Ru-NO bond lengthening. In addition, the possibility of staggered and eclipsed conformations is discussed.

First author: Nemcsok, D, The significance of pi interactions in group 11 complexes with N-heterocyclic carbenes,ORGANOMETALLICS, 23, 3640, (2004)
Abstract: The nature of the chemical bond in mixed carbene-halogen complexes (1)TMX (X = F-I) and bis(carbene) complexes (1)(2)TM+ of group 11 metals (TM = Cu, Ag, Au) with imidazol-1-ylidene (1) as ligand has been investigated at the BP86 level of theory using an energy decomposition analysis (EDA). The metal-carbene bonds are mainly held together by classical electrostatic attraction, which contributes >65% of the binding interactions. The metal-carbene bonds are very strong. In the bis(carbene) complexes, the N-heterocyclic carbene ligand 1 is bonded even more strongly than in the mixed carbene-halogen complexes. In the bis(carbene) complexes, orbital interactions are slightly more important than in the mixed carbene-halogen complexes but the covalent contribution is always <35% of the total attractive interaction. The orbital interaction part of the bonding has only similar to20% pi backbonding. The calculated data are not very different from previous EDA results for the Fischer carbene complex (CO)(5)W-C(OH)(2). The EDA results suggest that R2C<–MLn pi back-donation in complexes with N-heterocyclic carbenes is not substantially smaller than in classical Fischer carbene complexes bearing two pi donor groups R.

First author: Patchkovskii, S, Theoretical analysis of singlet and triplet excited states of nickel porphyrins, JOURNAL OF CHEMICAL PHYSICS, 121, 1317, (2004)
Abstract: Local density and generalized gradient approximation time-dependent density functional methods have been used for calculation of the singlet and triplet excited states of nickel-porphine, Ni-tetraphenyloporphine, and Ni-octaethyloporphyrine. Special attention is paid to metal-ligand transitions and d-d transitions. It is shown that the lowest exited singlet states of the three compounds can be described as a transfer of an electron from the porphine ring to the d(x 2-y 2) orbital of the nickel atom. On the other hand, the lowest excited triplet state arises from promotion of an electron between two nickel d orbitals, an occupied d(z)2 and an empty d(x 2-y 2). It is proposed that a rapid quenching of the excited singlet states is due to an ultrafast intersystem crossing between E-1(g) and E-3(g) or B-3(1g) states.

First author: van Eijck, L, A quantative study of the charge-transfer between conjugated thiophene rings in vibrationally excited states, PHYSICA B-CONDENSED MATTER, 350, 220, (2004)
Abstract: The charge transfer integral (CTI) between monomers in polythiophene is important for the electrical properties of the polymer. Torsional oscillations of the monomers are thought to play a key role in reducing the CTI, but the present study shows that other out-of-plane vibrational modes may play an even more important role between 10(-12) and 10(-14) See timescale on which charge-transfer occurs.

First author: Hanna, TE, Synthesis of a base-free titanium imido and a transient alkylidene from a titanocene dinitrogen complex. Studies on Ti=NR hydrogenation, nitrene group transfer, and comparison of 1,2-addition rates,ORGANOMETALLICS, 23, 3448, (2004)
Abstract: The synthesis and reactivity of the end-on bound dinitrogen complex [(eta(5)-C5H3-1,3-(SiMe3)(2))(2)Ti](2)(mu(2),eta(1),eta(1)-N-2) is described. The solid state structure of the dinitrogen compound reveals a weakly activated end-on bound N-2 ligand with an N-N bond length of 1.164(5) Angstrom. Displacement of the N2 ligand by organic azides has been used to prepare monomeric, base-free titanocene imido complexes, (eta(5)-C5H3-1,3-(SiMe3)(2))(2)Ti=NR (R = SiMe3, 2,4,6-Me-3-C6H2). While unreactive toward C-H bonds, the Ti-N linkage is readily hydrogenated and participates in group transfer reactions with unsaturated organic molecules such as carbon monoxide and benzophenone. Reaction of the N-2 complex with Ph2CN2 allowed isolation of (eta(5)-C5H3-1,3-(SiMe3)(2))(2)Ti(N2CPh2), which exists as a mixture of interconverting eta(2) and eta(1) isomers in solution. The diazoalkane complex also participates in “imido-like” reactivity, producing (eta(5)-C5H3-1,3-(SiMe3)(2))(2)Ti(NHN=CPh2)H upon addition of H-2. Changing the diazoalkane to Me3SiCHN2 resulted in isolation of the double cyclometalated titanocene (eta(5)-C5H3-eta(1)-1-SiMe2CH2-3-SiMe3)(2)Ti, arising from facile intramolecular C-H activation of the cyclopentadienyl substituent by a transient titanocene alkylidene.

First author: Matveev, AV, Efficient symmetry treatment for the nonrelativistic and relativistic molecular Kohn-Sham problem. The symmetry module of the program ParaGauss, COMPUTER PHYSICS COMMUNICATIONS, 160, 91, (2004)
Abstract: We describe a general strategy for exploiting spatial symmetry in density functional (DF) calculations of molecules and clusters. following the implementation in the parallel DF program PARAGAUSS. Point group elements are defined via a quaternion parametrization. Symmetrized irreducible bases of vector and projective representations as well as Clebsch-Gordan coefficients are constructed with the help of the eigenfunction method. We discuss the symmetrization of molecular orbitals for nonrelativistic and scalar relativistic DF calculations and molecular two- and four-component spinors for relativistic DF calculations that account for spin-orbit interaction. In addition, we present a strategy to symmetrize spinors simultaneously according to a double group and the corresponding point group. In relativistic DF calculations, this approach allows full exploitation of the symmetry of spin-free operators, e.g., in the numerical integration of the exchange-correlation potential.

First author: Clough, CR, Organic nitriles from acid chlorides: An isovalent N for (O)CI exchange reaction mediated by a tungsten nitride complex, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 126, 7742, (2004)
Abstract: We describe a general strategy for exploiting spatial symmetry in density functional (DF) calculations of molecules and clusters. following the implementation in the parallel DF program PARAGAUSS. Point group elements are defined via a quaternion parametrization. Symmetrized irreducible bases of vector and projective representations as well as Clebsch-Gordan coefficients are constructed with the help of the eigenfunction method. We discuss the symmetrization of molecular orbitals for nonrelativistic and scalar relativistic DF calculations and molecular two- and four-component spinors for relativistic DF calculations that account for spin-orbit interaction. In addition, we present a strategy to symmetrize spinors simultaneously according to a double group and the corresponding point group. In relativistic DF calculations, this approach allows full exploitation of the symmetry of spin-free operators, e.g., in the numerical integration of the exchange-correlation potential.

First author: Swart, M, Validation of exchange – Correlation functionals for spin states of iron complexes, JOURNAL OF PHYSICAL CHEMISTRY A, 108, 5479, (2004)
Abstract: Spin state energies of iron complexes are important for biochemical applications such as the catalytic cycle of cytochrome P450. Due to the size of these systems and the presence of iron, accurate computational results can be obtained only with density functional theory (DFT). Validation of exchange-correlation (xc) DFT functionals for predicting the correct spin ground state of iron complexes is a rather unexplored area. In this contribution we report a systematic study on the performance of several xc functionals for seven iron complexes that are experimentally found to have either a low, intermediate, or high spin ground state. Standard xc functionals like LDA, BLYP, and PBE are found to disfavor high spin states, whereas hybrid and some meta-GGA functionals do provide the correct spin ground state for all molecules. Recently improved pure DFT functionals such as Handy’s optimized exchange (OPTX) also perform well. The origin for the apparent performance of the DFT functionals has been addressed and seems to be related to the inclusion of fourth-order terms (s(4)) of the dimensionless (or reduced) density gradient s in the exchange functional.

First author: Bridgeman, AJ, Computational study of the vibrational spectra of alpha- and beta-Keggin polyoxometalates,CHEMISTRY-A EUROPEAN JOURNAL, 10, 2935, (2004)
Abstract: The structures and vibrational frequencies of the alpha- and beta-isomers of the phosphomolybdate Keggin anion [PMo12O40](3-) have been calculated by using density functional theory. Good agreement between the calculated un-scaled vibrational frequencies and those determined experimentally and between the calculated and observed IR traces has been obtained allowing the IR and Raman spectra to be assigned. For the alpha-isomer, the agreement with experiment using the current level of theory is superior to that obtained previously. For the beta-isomer, for which no non-empirical study has previously been reported, the agreement with experiment is slightly poorer but still allows the spectrum to be assigned unambiguously. To calculate the structure and vibrational spectra of these large molydate cluster ions requires large basis sets and a good treatment of electron correlation and relativistic effects. For the 53-atoms [PMo12O40](3-) ions, the computational demands are very high, requiring several months computational time. ne calculated IR spectral traces for the two isomers are quite similar due to the relative flexibility of the molybdates, where the slight weakening of the bonding of the rotated trimetallic unit to the rest of the cluster in the beta-isomer is compensated by contraction of the bonds within the unit, and the structure of the [MO6] and [PO4] units in the two isomers is nearly identical. The vibrations characteristic of the bridging Mo-O-Mo bonds involve both the “2-2” junctions between rotated [M3O13] units and the “1-2” junctions between rotated and unrotated units. The separation of “ligand” and “interligand” vibrations is not clear. The vibrational analyses confirm the high symmetry, namely T-d and C-3nu for the alpha- and beta-isomers, respectively, assumed by previous workers in this field. The characteristic group frequencies for the Type I polyoxometalates containing both edge and corner-sharing I octahedra have been identified.

First author: van Oort, B, Electronic structure of transition metal-isocorrole complexes: A first quantum chemical study,EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 10, 2442, (2004)
Abstract: DFT calculations indicate that the broad electronic-structural features of metalloisocorroles are rather similar to those of analogous metallocorroles. Thus, like their corrole analogues, many metalloisocorroles feature substantially non-innocent ligands. Another key point is that both corroles and isocorroles can exhibit at least two kinds of radical character, a(2) and b(1). However, corrole and isocorrole derivatives also differ significantly in a few ways: for example, the S = 1/2 CoPh complexes of corrole and isocorrole exhibit ground states of different symmetries ((2)A” and (2)A’, respectively, in C-s notation), reflecting different interplays of metal(d(pi))-ligand(p(pi)) interactions in corrole versus isocorrole derivatives. The ligand non-innocence phenomena encountered in this study are broadly reminiscent of similar phenomena in peroxidase compound I intermediates and their synthetic models. It seems reasonable, therefore, to adopt the view that this study, along with related studies on corrole derivatives, provides a broader chemical context for appreciating the electronic structures of high-valent heme protein intermediates.

First author: Stephens, FH, Small-molecule activation by molybdaziridine hydride complexes: Mechanistic sequence of the small-molecule binding and molybdaziridine ring-opening steps, ORGANOMETALLICS, 23, 3126, (2004)
Abstract: The relationship between molybdaziridine hydride Mo(H)(Me2C=NAr)(N[i-Pr]Ar)(2) (1, Ar = 3,5-C6H3Me2) and its three-coordinate isomer Mo(N[i-Pr]Ar)(3) (2) has been probed via an investigation of the coordination chemistry of 1 and Mo(N[t-Bu]Ar)(3) (3) with 1-adamantylisocyanide (AdNC). One or two equivalents of AdNC react with 1 to form the adducts 2-AdNC and 2-(AdNC)(2), respectively. One equivalent of AdNC coordinates to 3, forming 3-AdNC. Similarly, tert-butylisocyanide (t-BuNC) reacts with 1 to form 2-t-BuNC and 2-(t-BuNC)(2) and with 3 to form 3-t-BuNC. An X-ray crystal structure of 2-(AdNC)(2) reveals a trigonal bipyramidal core with a trans disposition of the isocyanide ligands (C-Mo-C, 172.8(4)degrees; Mo-C, 2.135(11) and 2.083(11) Angstrom). The structure of 3-t-BuNC features a bent isocyanide ligand with a C-N-C angle of 137.8(7)degrees, and the compound has a solution IR stretch of 1759 cm(-1), revealing Mo-C multiple-bond character. The fast reactions of AdNC with 1, 1-d(3), and 3 were studied by stopped-flow spectrophotometry in a wide temperature range (-80 to 25 degreesC). A comparison of the reaction rates and activation parameters indicates that 2 is not an intermediate on the pathway from I to 2-AdNC, but rather that the molybdaziridine hydride opens upon AdNC binding in an associative process. The enthalpies of reaction to generate the compounds of interest were measured using solution calorimetry: 2-AdNC, -24.6 kcal.mol(-1); 3-AdNC, -29.1 kcal.mol(-1). The enthalpy of binding of the second equivalent of AdNC to generate 2-(AdNC)(2) is -10.2 kcal.mol(-1).

First author: Casalbore-Miceli, G, A correlation between electrochemical properties and geometrical structure of some triarylamines used as hole transporting materials in organic electroluminescent devices, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 6, 3092, (2004)
Abstract: Two new compounds with four tertiary arylamine moieties connected in a fully para-conjugated system have been synthesised in order to obtain new molecules having low ionisation potentials, as required for hole transporting materials in organic light emitting diodes (OLEDs). Their electrochemical properties have been measured and compared to seven different commercial triarylamines tested in the same experimental conditions. Using the AM I geometries and the statistical average of orbital potential method (SAOP), the redox potentials of the molecules have been estimated and found to be in good agreement with the experimental data. An evident correlation between the molecular geometry and the electrochemical potential of the first oxidation exists and shows that, for equal number of para-conjugated triarylamine moieties, the starburst configuration is more efficient than the linear one in lowering the oxidation potential and that the amine moieties of the inner sphere play a more important role than those of the outer sphere. Besides, amine moieties connected by a biphenyl bridge show generally higher ionisation potentials than those connected via one phenylene.

First author: Solans-Monfort, X, Can Cu+-exchanged zeolites store molecular hydrogen? An ab-initio periodic study compared with low-temperature FTIR, JOURNAL OF PHYSICAL CHEMISTRY B, 108, 8278, (2004)
Abstract: Cu+-exchanged Si/Al 11: 1 chabazite has been studied ab initio using the periodic CRYSTAL03 computer code with Hartree-Fock and the hybrid B3LYP Hamiltonians to characterize the structures and energetics of the Cu+ ion sitting preference and its interaction with H-2. Two sites (I and IV) have been found to be stable for Cu+ ion: site 1, the most stable one, envisaging coordination in a six-membered zeolite ring and site IV in which the Cu+ ion sits in the largest eight-membered ring. Interaction of H-2 gives adsorption energies at B3LYP of -13 and -56 kJ/mol for sites I and IV, respectively. The B3LYP bathochromic harmonic H-2 frequency shifts are 847 and 957 cm(-1) for adsorption at sites I and IV, respectively, in good agreement with the shifts measured (1030 and 1081 cm(-1)) in the Cu-ZSM-5 system in which Cu+ ion is, respectively, three and bi-coordinated by the oxygen atoms of the zeolite framework. Analysis of the components of the adsorption energy, carried out within the cluster approach, revealed that charge transfer from the Cu(3d(pi)) orbital through the antibonding H-2(sigma(u)) and orbital polarization play a significant role in the H-2 adsorption energy, and cause the large bathochromic H-2 frequency shift.

First author: Lo, WY, Synthesis, photophysics, electrochemistry, theoretical, and transient absorption studies of luminescent copper(I) and silver(I) diynyl complexes. X-ray crystal structures of [Cu-3(mu-dppm)(3)(mu(3)-eta(1)-C CC CPh)(2)]PF6 and [Cu-3(mu-dppm)(3)(mu(3)-eta(1)-C CC CH)(2)]PF6, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 126, 7300, (2004)
Abstract: A series of soluble trinuclear copper(I) and silver(I) complexes containing bicapped diynyl ligands, [M-3(mu-dppm)(3)(mu(3)-eta(1)-CdropCCdropCR)(2)]PF6 (M = Cu, R = Ph, C6H4-CH3-p C6H4-OCH3-p, (C6H13)-C-n, H; M = Ag, R = Ph, C6H4-OCH3-P), has been synthesized and their electronic, photophysical, and electrochemical properties studied. The X-ray crystal structures of [Cu-3(mu-dppm)(3)(mu(3)-eta(1)-CdropCCdropCPh)(2)]PF6 and [Cu-3(mu-dPPM)(3)(mu(3)-eta(1)-CdropCCdropCH)(2)]PF6 have been determined.

First author: Tohi, Y, Polyethylenes having well-defined bimodal molecular weight distributions formed with bis(phenoxy-imine) Zr complexes, MACROMOLECULAR CHEMISTRY AND PHYSICS, 205, 1179, (2004)
Abstract: Bis(phenoxy-imine) Zr complexes with MAO activation can produce polyethylenes with well-defined bimodal molecular weight distributions. Polymerization behavior indicates that minor changes in the ligand structures can have a significant effect on the modality of the resulting polyethylenes. Although there is no direct relationship between the bimodal catalytic behavior and the structure of a precatalyst complex in solution, a precatalyst complex having a methyl or methoxy group para to the phenoxy-oxygen inclined to exhibit bimodal behavior whereas that with a pentafluorophenyl group on the imine-nitrogen displayed unimodal behavior. Polymerization results suggest that bimodal behavior is linked to the presence of two kinds of cationic active species, which arise from different modes of ligand coordination. A qualitative correlation was found between the calculated amounts of possible cationic active species and the uni- and bimodal catalytic behavior. Based on the results obtained, we concluded that the bimodal polyethylenes are produced by two kinds of cationic active species having two available cis-located sites with cis-N, trans-O and cis-N, cis-O arrangements. The results introduced herein are rare examples of the production of well-defined bimodal polyethylenes using a single precatalyst.

First author: Seth, M, Calculation of the A term of magnetic circular dichroism based on time dependent-density functional theory I. Formulation and implementation, JOURNAL OF CHEMICAL PHYSICS, 120, 10942, (2004)
Abstract: A procedure for calculating the A term and the A/D ratio of magnetic circular dichroism (MCD) within time-dependent density functional theory (TD-DFT) is described. Utilizing an implementation of the MCD theory within the Amsterdam Density Functional program, the A term contributions to the MCD spectra of MnO4-, CrO42-, VO43-, MoO42-, VO43-, MoS42-, Se-4(2+), Te-4(2+), Fe(CN)(6)(4-), Ni(CN)(4)(2-), trichlorobenzene, hexachlorobenzene, tribromobenzene, and hexabromobenzene are calculated. For the most part, agreement between theory and experiment for A/D ratios and the relative magnitude of A terms is found to be good, leading to simulated spectra that are similar in appearance to those derived from measurements. The A terms are found to be too small whenever comparison with experiment was possible, probably due to the neglect of environment effects on the incident radiation and the relative low accuracy of dipole strengths calculated within TD-DFT.

First author: Manke, DR, Eclipsed M2X6 compounds exhibiting very short metal-metal triple bonds, INORGANIC CHEMISTRY, 43, 3618, (2004)
Abstract: The preparation, characterization, and electronic structure of homoleptic complexes of molybdenum and tungsten bridged by bis(alkylamido)phenylboranes, M-2[RN-B-Ph-NR](3) (M = Mo, R = Et (1), Pr-i (2); M = W, R = Et (3), Pr-i (4)), are described. These triple metal-metal bond species (i) exhibit a nearly eclipsed ligand geometry and (ii) possess the shortest metal-metal bonds of neutral dimolybdenum and ditungsten M2X6 complexes observed to date (d(Mo-Mo) = 2.1612(6) Angstrom (1); d(W-W) = 2.2351(7) Angstrom (4)).

First author: Volkov, A, Combination of the exact potential and multipole methods (EP/MM) for evaluation of intermolecular electrostatic interaction energies with pseudoatom representation of molecular electron densities, CHEMICAL PHYSICS LETTERS, 391, 170, (2004)
Abstract: A new method (EP/MM) for calculation of intermolecular electrostatic interaction energies from pseudoatom expansions of molecular densities is presented. It combines numerical evaluation of the exact Coulomb integral for the short-range with the Buckingham-type multipole approximation for the long-range interatomic interactions. In first instance the method is combined with the pseudoatom representation of the atomic densities as derived from theoretical wavefunctions. The resulting electrostatic interaction energies of monomers in molecular dimers are in very good agreement with Morokuma-Ziegler decompositioning of triple-zeta DFT energies. The combination of EP/MM with densities from the theoretical databank of aspherical pseudoatoms provides more accurate results than the MMFF94 force-field at a moderate increase in computing time. EP/MM is also applicable to experimental electron densities.

First author: Coombs, DL, Fe=B double bonds: Synthetic, structural, and reaction chemistry of cationic terminal borylene complexes, ORGANOMETALLICS, 23, 2911, (2004)
Abstract: Application of halide abstraction chemistry to asymmetric haloboryl complexes (eta(5)-C(5)Me(5))Fe(CO)(2)B(ER(n))X leads to the first synthetic route to cationic multiply bonded group 13 diyl species, [(eta(5) -C(5)Me(5))Fe(CO)(2)B(ER(n))](+). The roles of steric bulk and pi electron release within the ER(n) substituent in generating tractable borylene complexes have been probed, as has the nature of the counterion. A combination of spectroscopic, structural, and computational techniques leads to the conclusion that the bonding in complexes such as [(eta(5)-C(5)Me(5))Fe(CO)(2)B(Mes)](+) is best described as an Fe=B double bond composed of B–>Fe sigma donor and Fe–>B pi back-bonding components. An extended study of the fundamental reactivity of cationic borylene systems reveals that this is dominated not only by nucleophilic addition at boron but also by iron-centered substitution chemistry leading to overall displacement of the borylene ligand.

First author: Pandey, KK, Where are the hydrogen atoms in [(eta(5)-C5H5)(PH3)(2)W(H2SiMe2)]+? A theoretical study,ORGANOMETALLICS, 23, 2944, (2004)
Abstract: Quantum-chemical DFT calculations of the tungsten silylene complex [Cp(PH3)(2)W(H2SiMe2)](+) have been carried out with the aim to elucidate the structure and bonding situation of the molecule. The W-SiMe2 interactions have been examined with an energy decomposition analysis. The geometry optimization with the constraint of C-s symmetry gives a classical dihydride structure as the lowest-lying energy minimum form. Four other structures which have up to two bridging hydrogen atoms are only <5 kcal/mol higher in energy than the classical form. The results suggest that the model complex [Cp(PH3)(2)W(H2SiMe2)](+) and the real complex [Cp*(dmpe)W(H)(2)SiMe2][B(C6F5)(4)], which was synthesized by Tilley, have a very fluxional W(H2SiMe2) moiety, which makes it meaningless to classify the structure as classical or nonclassical. The energy decomposition analysis indicates that, in all binding modes, W-SiMe2 pi-back-donation is very weak. The silylene complex should therefore be considered as a W(d(2)) compound, where the formal oxidation state of the metal is +4.

First author: Senn, HM, Oxidative addition of aryl halides to palladium(0) complexes: A density-functional study including solvation, ORGANOMETALLICS, 23, 2980, (2004)
Abstract: Using density-functional theory calculations in combination with an electrostatic continuum solvation model, we have investigated the oxidative addition of phenyl halides PhX to palladium(0) complexes of bidentate phosphanes [Pd(PP)], yielding aryl halo complexes [(PP)Pd(Ph)(X)], with X = Cl, Br, I and PP = 1,2-bis(dimethylphosphino)ethane or (P)-2,2′-bis(dimethylphosphino)-1,1′-biphenyl. We have considered the formation of the reactive 14-electron species from the saturated [Pd(PP)(2)] as well as different prereaction complexes [(PP)Pd(PhX)] with an intact phenyl halide. We find that ligand dissociation is the limiting reaction step, while the formation of the prereaction complex and the oxidative addition itself are energetically (very) favorable. The concerted transition state for oxidative addition known in the gas phase could not be found in solution. Instead, we propose a pathway involving the very facile dissociation of the halide from the prereaction complex, with subsequent collapse to the product.

First author: Calimet, N, The influence of a transmembrane pH gradient on protonation probabilities of bacteriorhodopsin: The structural basis of the back-pressure effect, JOURNAL OF MOLECULAR BIOLOGY, 339, 571, (2004)
Abstract: Bacteriorhodopsin pumps protons across a membrane using the energy of light. The proton pumping is inhibited when the transmembrane proton gradient that the protein generates becomes larger than four pH units. This phenomenon is known as the back-pressure effect. Here, we investigate the structural basis of this effect by predicting the influence of a transmembrane pH gradient on the titration behavior of bacteriorhodopsin. For this purpose we introduce a method that accounts for a pH gradient in protonation probability calculations. The method considers that in a transmembrane protein, which is exposed to two different aqueous phases, each titratable residue is accessible for protons from one side of the membrane depending on its hydrogen-bond pattern. This method is applied to several ground-state structures of bacteriorhodopsin, which residues already present complicated titration behaviors in the absence of a proton gradient. Our calculations show that a pH gradient across the membrane influences in a non-trivial manner the protonation probabilities of six titratable residues which are known to participate in the proton transfer: D85, D96, D115, E194, E204, and the Schiff base. The residues connected to one side of the membrane are influenced by the pH on the other side because of their long-range electrostatic interactions within the protein. In particular, D115 senses the pH at the cytoplasmic side of the membrane and transmits this information to D85 and the Schiff base. We propose that the strong electrostatic interactions found between D85, D115, and the Schiff base as well as the interplay of their respective protonation states under the influence of a transmembrane pH gradient are responsible for the back-pressure effect on bacteriorhodopsin.

First author: Kubo, M, Design of new catalysts for ecological high-quality transportation fuels by combinatorial computational chemistry and tight-binding quantum chemical molecular dynamics approaches, CATALYSIS TODAY, 89, 479, (2004)
Abstract: Recently, we introduced a concept of combinatorial chemistry to computational chemistry and proposed a new method called “combinatorial computational chemistry”, which enables us to perform a theoretical high-throughput screening of catalysts. In the present paper, we reviewed our recent application of our combinatorial computational chemistry approach to the design of new catalysts for high-quality transportation fuels. By using our combinatorial computational chemistry techniques, we succeeded to predict new catalysts for methanol synthesis and Fischer-Tropsch synthesis. Moreover, we have succeeded in the development of chemical reaction dynamics simulator based on our original tight-binding quantum chemical molecular dynamics method. This program realizes more than 5000 times acceleration compared to the regular first-principles molecular dynamics method. Electronic- and atomic-level information on the catalytic reaction dynamics at reaction temperatures significantly contributes the catalyst design and development. Hence, we also summarized our recent applications of the above quantum chemical molecular dynamics method to the clarification of the methanol synthesis dynamics in this review.

First author: Peacock, CL, Copper(II) sorption onto goethite, hematite and lepidocrocite: A surface complexation model based on ab initio molecular geometries and EXAFS spectroscopy, GEOCHIMICA ET COSMOCHIMICA ACTA, 68, 2623, (2004)
Abstract: We measured the adsorption of Cu(II) onto goethite (alpha-FeOOH), hematite (alpha-Fe2O3) and lepidocrocite (gamma-FeOOH) from pH 2-7. EXAFS spectra show that Cu(II) adsorbs as (CuO4Hn)(n-6) and binuclear (Cr2O6Hn)(n-8) complexes. These form inner-sphere complexes with the iron (hydr)oxide surfaces by corner-sharing with two or three edge-sharing Fe(O,OH)(6) polyhedra. Our interpretation of the EXAFS data is supported by ab initio (density functional theory) geometries of analogue Fe-2(OH)(2)(H2O)(8)Cu(OH),and Fe-3(OH)(4)(H2O)(10)Cu-2(OH)(6) clusters. We find no evidence for surface complexes resulting from either monodentate corner-sharing or bidentate edge-sharing between (CuO4Hn)(n-6) and Fe(O,OH), polyhedra. Sorption isotherms and EXAFS spectra show that surface precipitates have not formed even though we are supersaturated with respect to CuO and Cu(OH)(2). Having identified the bidentate (dropFeOH),Cu(OH)O, and tridentate (dropFe(3)O(OH)(2))Cu-2(OH)(3)(0) surface complexes, we are able to fit the experimental copper(II) adsorption data to the reactions3(dropFeOH) + 2Cu(2+) + 3H(2)O = (dropFe(3)O(OH)(2))Cu-2(OH)(3)(0) + 4H(+)and2(dropFeOH) + Cu2+ + 2H(2)O = (dropFeOH)(2)Cu(OH)(2)(0) + 2H(+).The two stability constants are similar for the three iron (hydr)oxide phases investigated.

First author: Hoggan, PE, Note on hydrogenic atomic orbitals to evaluate sensitive properties of molecules: An example of NMR chemical shifts, JOURNAL OF THEORETICAL & COMPUTATIONAL CHEMISTRY, 3, 163, (2004)
Abstract: Now that the problems surrounding ab initio calculations over a Slater Type Orbital basis have been solved, it is available in several software packages.For general structures the STOP package (Slater Type Orbital Package) has offered ab initio SCF molecular properties since 1996, the requisite integrals all being evaluated analytically, including the four center term available since 1994. SMILES (Slater Molecular Integrals for Large Electronic Systems) has offered various basis sets, geometry optimization and CI since 2001. For density functional work, ADF, the Amsterdam Density Functional suite of programs, is a project dating from the 1970s with a 2003 edition.In this work the preferred ETOs (Exponential Type Orbitals) will be shown to be the hydrogenic orbitals and similar Coulomb Sturmians. Slater Type Functions (STFs) will be compared to them and suitable equivalent combinations, which are rarely used, given.The correct shielding of the nucleus, resulting from radial factors of hydrogenic orbitals is shown to be essential in the evaluation of precise nuclear shielding tensors for NMR spectroscopy of molecules using ab initio or DFT methods.The case study of benzothiazoles using natural abundance N-15 is re-examined and compared with previous work including measurements.

First author: Pons, V, Structure and dynamics of a dihydrogen/hydride ansa molybdenocene complex, INORGANIC CHEMISTRY, 43, 3475, (2004)
Abstract: In contrast to [Cp2MoH3](+), which is a thermally stable trihydride complex, the ansa-bridged analogue [(eta-C5H4)(2)-CMe2MoH(H-2)](+) (1) is a thermally labile dihydrogen/hydride complex. Partial deuteration of the hydride ligands allows observation of J(H-D) = 11.9 Hz in 1-d(1) and 9.9 Hz in 1-d(2) (245 K), indicative of a dihydrogen/hydride structure. There is a slight preference for deuterium to concentrate in the dihydrogen ligand. A rapid dynamic process interchanges the hydride and dihydrogen moieties in complex 1. Low temperature H-1 NMR spectra of 1 give a single hydride resonance, which broadens at very low temperature due to rapid dipole-dipole relaxation (T-1 = 23 ms (750 MHz, 175 K) for the hydride resonance in 1). Low temperature H-1 NMR spectra of 1-d(2) allow the observation of decoalescence at 180 K into two resonances. The bound dihydrogen ligand exhibits hindered rotation with DeltaG(150)(double dagger) = 7.4 kcal/mol, but H atom exchange is still rapid at all accessible temperatures (down to 130 K). Density functional calculations confirm the dihydrogen/hydride structure as the ground state for the molecule and give estimates for the energy of two hydrogen exchange processes in good agreement with experiment. The presence of the C ansa bridge is shown to decrease the ability of the metallocene fragment to donate to the hydrogens, thus stabilizing the (eta(2)-H-2) unit and modulating the barrier to H-2 rotation.

First author: Herbert, BJ, Hydrogen transfer between ligands: A density functional study of the rearrangement of M(eta(6)-C7H8)(2) into M(eta(7)-C7H7)(eta(5)-C7H9) [M = Mo, Mo+, Zr], ORGANOMETALLICS, 23, 2658, (2004)
Abstract: The electronic structure of the family of sandwich complexes M(eta(6)-C7H8)(2) and M(eta(7)-C7H7)-(eta(5)-C7H9) (M = Mo, Mo+, Zr) was investigated using density functional theory, and their geometries were accounted for. The mechanism for conversion of M(eta(6)-(CH8)-H-7)(2) into M(eta(7)-C7H7)(eta(5)-C7H9) by hydrogen transfer was investigated, and the experimental trends were reproduced. The neutral Mo species was calculated to have an activation free energy 13 kJ mol(-1) lower than the cationic Mo+. The rate-limiting step for the transfer in the neutral molybdenum species is breaking of the C-H bond to form a molybdenum hydride intermediate, which rapidly converts into the rearranged product. The transition state is late on the reaction coordinate, and C-H bond breaking occurs after ring slippage to form an (eta(6), eta(4)) 16-electron species. The cationic molybdenum species has a similar reaction profile. The zirconium species is found to have two competing pathways both with higher activations energies: one with an (eta(7), eta(5)) Zr-H intermediate, the other occurring by direct transfer of the hydrogen without forming Zr-H species. The effect of adding PH3 to the zirconium system has also been studied, which has the effect of lowering the barrier to the direct transfer of hydrogen between the ligands.

First author: Balcells, D, Polyene cyclization by a double intramolecular Heck reaction. A DFT study,ORGANOMETALLICS, 23, 2784, (2004)
Abstract: A density functional theory (DFT) model study has been carried out on the cyclization of aryl polyene triflate catalyzed by a Pd(II)-BINAP complex in a Heck type reaction. In the model study, the catalyst was represented by Pd(PH(2)(CH)(4)PH(2)), whereas the aryl polyene triflate substrate was simplified by replacing the dimethoxy naphthalene fragment with hydrogens. Formally, this cyclization reaction consists Of an intramolecular Heck reaction with two olefin insertions, also known as a double or cascade Heck reaction. The postulated cationic pathway for aryl triflate substrates has been explored as the reaction mechanism. The study has mainly focused on the two migratory insert ion steps, where the identity of the final reaction products is decided. At both steps two distinct insertions may occur: exo, or 1,2-insertion, and endo, or 2,1-insertion. The computation of the possible intermediates and transition states demonstrated that the first insertion is exo-selective, with an energy barrier of only 4.1 kcal/mol, while the second insertion is endo-selective, involving a much higher energy barrier of 22.8 kcal/mol. The calculated subsequent preference for exo and endo selectivity is in good agreement with qualitative experimental observation. According to our results, the main factor controlling the exo/endo selectivity, at both the thermodynamic and the kinetic levels, is the relative stability of the cyclic system resulting from the migratory insertion. Furthermore, a furan ring present in the substrate can play an important role by forming a stable and inert pi-complex that is able to suppress subsequent migratory insertion steps. On the other hand, taking into account the solvent effects using a continuum model, we found that the exo/endo selectivity of the first insertion step is solvent-dependent. As the polarity of the solvent increases, the relative stability of the endo intermediate also increases, in good agreement with the available experimental data. The beta-elimination steps affording the final reaction products were also investigated. The results show that the beta-elimination on the endo intermediates is thermodynamically favored over the beta-elimination on the exo intermediates. On the other hand, the results for the beta-elimination on the endo intermediates show that this reaction is highly reversible.

First author: Gruning, M, Improved description of chemical barriers with generalized gradient approximations (GGAs) and meta-GGAs, JOURNAL OF PHYSICAL CHEMISTRY A, 108, 4459, (2004)
Abstract: The performance of exchange and correlation (xc) functionals of the generalized gradient approximation (GGA) type and of the meta-GGA type in the calculation of chemical reactions is related to topological features of the electron density which, in turn, are connected to the orbital structure of chemical bonds within the Kohn-Sham (KS) theory. Seventeen GGA and meta-GGA xc functionals are assessed for 15 hydrogen abstraction reactions and 3 symmetrical S(N)2 reactions. Systems that are problematic for standard GGAs characteristically have enhanced values of the dimensionless gradient argument s(sigma)(2) with local maxima in the bonding region. The origin of this topological feature is the occupation of valence KS orbitals with an antibonding or essentially nonbonding character. The local enhancement of s(sigma)(2) yields too negative exchange-correlation energies with standard GGAs for the transition state of the S(N)2 reaction, which leads to the reduced calculated reaction barriers. The unwarranted localization of the effective xc hole of the standard GGAs, i.e., the nondynamical correlation that is built into them but is spurious in this case, wields its effect by their s(sigma)(2) dependence. Barriers are improved for xc functionals with the exchange functional OPTX as x component, which has a modified dependence on s(sigma)(2). Standard GGAs also underestimate the barriers for the hydrogen abstraction reactions. In this case the barriers are improved by correlation functionals, such as the Laplacian-dependent (LAP3) functional, which has a modified dependence on the Coulomb correlation of the opposite- and like-spin electrons. The best overall performance is established for the combination OLAP3 of OPTX and LAP3.

First author: Damrauer, NH, Observation of proton-coupled electron transfer by transient absorption spectroscopy in a hydrogen-bonded, porphyrin donor-acceptor assembly, JOURNAL OF PHYSICAL CHEMISTRY B, 108, 6315, (2004)
Abstract: Proton-coupled electron transfer (PCET) kinetics of a Zn(II) porphyrin donor noncovalently bound to a naphthalene-diimide acceptor through an amidinium-carboxylate interface have been investigated by time-resolved spectroscopy. The S, singlet excited-state of a Zn(II) 2-amidinium-5,10,15,20-tetramesitylporphyrin chloride (ZnP-beta-AmH+) donor is sufficiently energetic (2.04 eV) to reduce a carboxylate-diimide acceptor (DeltaGdegrees = -460 mV, THF). Static quenching of the porphyrin fluorescence is observed and time-resolved measurements reveal more than a 3-fold reduction in the S, lifetime of the porphyrin upon amidinium-carboxylate formation (THF, 298 K). Picosecond transient absorption spectra of the free ZnP-beta-AmH+ in THF reveal the existence of an excited-state isosbestic point between the S-1 and T-1 states at probe = 650 nm, providing an effective ‘zero-kinetics’ background on which to observe the formation of PCET photoproducts. Distinct rise and decay kinetics are attributed to the build-up and subsequent loss of intermediates resulting from a forward and reverse PCET reaction, respectively (k(PCET)(fwd) = 9 x 10(8) s(-1) and k(PCET)(rev) = 14 x 101 s-1). The forward rate constant is nearly 2 orders of magnitude slower than that measured for covalently linked Zn(II) porphyrin-acceptor dyads of comparable driving force and D-A distance, establishing the importance of a proximal proton network in controlling charge transport.

First author: Deubel, DV, Road maps for nitrogen-transfer catalysis: The challenge of the osmium(VIII)-catalyzed diamination, CHEMISTRY-A EUROPEAN JOURNAL, 10, 2475, (2004)
Abstract: Although the Sharpless dihydroxylation has been used on laboratory and industrial scales for several decades, an analogous osmium-catalyzed diamination is unknown. To explore the reaction of osmium(VIII) oxo-imido complexes with C=C bonds, density functional calculations have been performed. The calculations predict a chemoselective and perispecific [3+2] addition of the NH=Os=NH moiety of diimidodioxoosmium(VIII) to ethylene, yielding dioxoosma-2,5-diazolidine. At first sight, this metallacycle seems extremely stable; it is more stable than diimidoosma-2,5-dioxolane by 40 kcal mol(-1). However, a comparison of the thermodynamic reaction profiles for catalytic model cycles of dihydroxylation, ammohydroxylation, and diamination reveals that, contrary to common belief, the instability of the metal=N bond in the osmium(VIII) imido complex rather than the stability of the metal-N bond in the osmium(vi) intermediate causes most of the energy difference between the metallacycles. Substituents on the substrate have a small effect on the thermodynamic reaction profiles, whereas substituents on the imido ligands allow steric and electronic control of the reaction free enthalpies in the range of up to 25 kcal-mol(-1). The results of this study help identify potential challenges in the development of the as-yet hypothetical title reaction and provide a modular concept for exploring novel catalytic routes.

First author: Autschbach, J, Solvent effects on Pt-195 and Tl-205 NMR chemical shifts of the complexes [(NC)(5)Pt-Tl(CN)(n)](n-) (n=0-3), and [(NC)(5)Pt-Tl-Pt(CN)(5)](3-) studied by relativistic density functional theory, CHEMISTRY-A EUROPEAN JOURNAL, 10, 2581, (2004)
Abstract: ne Pt-295 and Tl-205 NMR chemical shifts of the complexes [(NC)(5)Pt-Tl(CN)(n)](n-) n = 0-3, and of the related system [(NC)(5)Pt-Tl-Pt(CN)(5)](3-) have been computationally investigated. It is demonstrated that based on relativistically optimized geometries, by applying an explicit first solvation shell, an additional implicit solvation model to represent the bulk solvent effects (COSMO model), and a DFT exchange-correlation potential that was specifically designed for the treatment of response properties, that the experimentally observed metal chemical shifts can be calculated with satisfactory accuracy. The metal chemical shifts have been computed by means of a two-component relativistic density functional approach. The effects of electronic spin-orbit coupling were included in all NMR computations. The impact of the choice of the reference, which ideally should not affect the accuracy of the computed chemical shifts, is also demonstrated. Together with recent calculations by us of the Pt and Tl spin-spin coupling constants, all measured metal NMR parameters of these complexes are now computationally determined with sufficient accuracy in order to allow a detailed analysis of the experimental results. In particular, we show that interaction of the complexes with the solvent (water) must be an integral part of such an analysis.

First author: Volkov, A, Ab initio quality electrostatic atomic and molecular properties including intermolecular energies from a transferable theoretical pseudoatom databank, JOURNAL OF PHYSICAL CHEMISTRY A, 108, 4283, (2004)
Abstract: The development of a theoretical databank of transferable pseudoatoms for fast prediction of the electron densities and related electronic properties of proteins is described. Chemically unique pseudoatoms identified on the basis of common connectivity and bonding are extracted from ab initio molecular densities of a large number of small molecules using a least-squares projection technique in Fourier transform space. The performance of the databank is evaluated by comparison of the electron densities and electrostatic properties of the amino acids GLN, SER, and LEU and their dimers with those obtained from molecular calculations on the same test compounds. It is found that deformation density bond peaks are reproduced to within 0.02-0.10 e/Angstrom(3), whereas electrostatic potentials, bond critical point indices, atomic charges, and molecular moments show differences with results from calculations performed directly on the test molecules which are comparable with or smaller than the spread of the values between different ab initio methods (Hamiltonian, basis set, etc.). The order of intermolecular electrostatic interaction energies for selected dimers of the test compounds are well reproduced, though the results are always smaller, by about 25 kJ/mol on average, than electrostatic energies from Morokuma-Ziegler decomposition of the total interaction energy evaluated with the ADF program. The difference is attributed to the limitations of the Buckingham-type approximation for electrostatic interactions, used in the current study, which assumes nonoverlapping charge densities. The consistency achieved by the pseudoatom databank is much better than that obtained with the AMBER99, CHARMM27, MM3, and MMFF94 force fields, which sometime overestimate, sometimes underestimate, the electrostatic interaction energy. The electrostatic component of the binding energies (directly related to the enthalpy of sublimation) of molecules in crystals, calculated based on the databank parameters, agree within 25-60 kJ/mol with the total binding energies evaluated ab initio at the Density Functional level of theory, even though the exchange-repulsion and dispersion terms have not been taken into account in the databank values.

First author: Krishna, GG, A computational study of ligand interactions with hafnium and zirconium metal complexes in the liquid-liquid extraction process, JOURNAL OF PHYSICAL CHEMISTRY B, 108, 6112, (2004)
Abstract: In this paper we present a computational study of ligand interactions with hafnium and zirconium metal complexes which occur in the liquid-liquid extraction of these metals from their aqueous solutions. Separation of Hf and Zr has been a challenge in liquid-liquid extraction technologies and the existing methodologies, namely the MIBK (methyl isobutyl ketone) process, are used to extract hafnium into the organic phase while on the contrary the TBP (tributyl phosphate) process is used to extract Zr into the organic phase. Understanding the actual interactions taking place, including an estimate of the binding energies and conformations of the guest-host system of the metal complexes and the solvents, would help us to design better and safer extractants. Recent studies in the literature have shown that the quantum chemical based DFT methods have proven to be good tools for such types of studies. Thus in this work we have carried out high-level DFT studies using the hybrid B3LYP/Lanl2dz and BLYP/TZP (with the relativistic corrections) on tetravalent Hf and Zr metal complexes interacting with neutral ligands and compared the results to the experimental observations. These studies show that at the molecular level it is the Hf complex that has larger interaction energy with the ligands, thus indicating that in the mixture of Hf and Zr complexes in solutions which are not complicated by aggregation and polymerization, Hf would be extracted preferably into the organic solvent, in agreement with the experimental observation. We conclude from this study that primary interaction energies (gas-phase stabilization) are sufficient to significantly discriminate Hf and Zr complexes and thus can be used to explain Hf and Zr separation.

First author: Funk, T, X-ray magnetic circular dichroism of Pseudomonas aeruginosa nickel(II) azurin, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 126, 5859, (2004)
Abstract: We show that X-ray magnetic circular dichroism (XMCD) can be employed to probe the oxidation states and other electronic structural features of nickel active sites in proteins. As a calibration standard, we have measured XMCD and X-ray absorption (XAS) spectra for the nickel(II) derivative of Pseudomonas aeruginosa azurin (NiAz). Our analysis of these spectra confirms that the electronic ground state of NiAz is high-spin (S = 1); we also find that the L-3-centroid energy is 853.1 (1) eV, the branching ratio is 0.722(4), and the magnetic moment is 1.9(4) mu(B). Density functional theory (DFT) calculations on model NiAz structures establish that orbitals 3d(x2-y2) and 3d(z2) are the two valence holes in the high-spin Ni(II) ground state, and in accord with the experimentally determined orbital magnetic moment, the DFT results also demonstrate that both holes are highly delocalized, with 3d(x2-y2) having much greater ligand character.

First author: Tai, HC, Organometallics versus P-4 complexes of group 11 cations: Periodic trends and relativistic effects in the involvement of (n-1)d, ns, and np orbitals in metal-ligand interactions, ORGANOMETALLICS, 23, 2343, (2004)
Abstract: The nature of the bonding in ethylene and eta(2)-P4 complexes, M(C2H4)(2)(+) and M(eta(2)-P-4)(2)(+), of group 11 metal cations (M = Cu, Ag, Au) has been explored by density functional calculations. On the basis of the evaluation of symmetry orbitals, the contributions from the interactions of ligand orbitals with metal ns, np, and (n-1)d orbitals have been investigated. The analysis shows that the metal-ligand bonds in the organometallics and phosphorus complexes fit to a unified scheme, whereas traditional concepts such as the isolobality principle would hardly predict such a bonding analogy between C2H4 and P-4 complexes. Bond energies increasing in the order Ag < Cu < Au have been predicted. The stronger metal-ligand bonds in the gold(l) compounds compared to those in the silver(l) compounds can be elucidated by the relativistic stabilization of the orbital interactions, particularly of those involving 6s and 5d orbitals. The stronger metal-ligand bonds in Cu(eta(2)-P-4)(2)(+) compared to those in the experimentally known Ag(eta(2)-P-4)(2)(+) can be attributed partly to the strong back-donation from metal 3d orbitals to vacant ligand orbitals. This result stands in sharp contrast to the common belief that first-row transition metals form weaker bonds to ligands than do their second-row analog-Lies because of a comparably small overlap between ligand orbitals and metal 3d orbitals.

First author: Volkov, A, Calculation of electrostatic interaction energies in molecular dimers from atomic multipole moments obtained by different methods of electron density partitioning, JOURNAL OF COMPUTATIONAL CHEMISTRY,25, 921, (2004)
Abstract: Accurate and fast evaluation of electrostatic interactions in molecular systems is still one of the most challenging tasks in the rapidly advancing field of macromolecular chemistry, including molecular recognition, protein modeling and drug design. One of the most convenient and accurate approaches is based on a Buckingham-type approximation that uses the multipole moment expansion of molecular/atomic charge distributions. In the mid-1980s it was shown that the pseudoatom model commonly used in experimental X-ray charge density studies can be easily combined with the Buckingham-type approach for calculation of electrostatic interactions, plus atom-atom potentials for evaluation of the total interaction energies in molecular systems. While many such studies have been reported, little attention has been paid to the accuracy of evaluation of the purely electrostatic interactions as errors may be absorbed in the semiempirical atom-atom potentials that have to be used to account for exchange repulsion and dispersion forces. This study is aimed at the evaluation of the accuracy of the calculation of electrostatic interaction energies with the Buckingham approach. To eliminate experimental uncertainties, the atomic moments are based on theoretical single-molecule electron densities calculated at various levels of theory. The electrostatic interaction energies for a total of I I dimers of a-glycine, N-acetylglycine and L-(+)-lactic acid structures calculated according to Buckingham with pseudoatom, stockholder and atoms-in-molecules moments are compared with those evaluated with the Morokuma-Ziegler energy decomposition scheme. For a-glycine a comparison with direct “pixel-by-pixel” integration method, recently developed Gavezzotti, is also made. It is found that the theoretical pseudoatom moments combined with the Buckingham model do predict the correct relative electrostatic interactions energies, although the absolute interaction energies are underestimated in some cases. The good agreement between electrostatic interaction energies computed with Morokuma-Ziegler partitioning, Gavezzotti’s method, and the Buckingham approach with atoms-in-molecules moments demonstrates that reliable and accurate evaluation of electrostatic interactions in molecular systems of considerable complexity is now feasible.

First author: Rapta, P, ESR/UV-Vis-NIR cyclovoltammetry of macrocyclic complex [Cu-I(bite)]BF4 at different temperatures, JOURNAL OF ELECTROANALYTICAL CHEMISTRY, 566, 123, (2004)
Abstract: Using in situ ESR/UV-Vis-NIR cyclovoltammetry at different temperatures, model systems for blue copper proteins like [Cu-1(bite)]BF4 and [Cu-11(bite)](BF4)(2) (bite = biphenyldiimino dithioether) were studied with respect to their redox behavior. Chemically reversible processes in the electrode reaction were observed by ESR and UV-Vis-NIR spectroscopy during the repetitive redox cycling of [Cu-1(bite)]BF4. The complex cyclovoltammetric feature of the compounds in acetonitrile can be explained by adsorption and a slow heterogeneous electron transfer with rate constant k(s) = 2 x 10(-4) cm s(-1). Spectroelectrochemical studies of the redox products at 77 K confirmed the formation of a metastable pseudo-tetrahedral [Cu-11 (bite)](2+) intermediate. This is direct experimental proof of processes in redox reactions of the [Cu-1(bite)](+) within a dual-pathway square reaction scheme indicating preferable electron transfer from the pseudo-tetrahedral [Cu-1(bite)](+) as the initial step. The DFT optimized geometries of quasi-tetrahedral and quasi-planar [Cu-1(bite)](+/2+) complexes are in reasonable agreement with experimental data.

First author: Fernandez, PG, Cu2+ impurities in fluorite-type crystals: Mechanisms favoring an off-center motion,PHYSICAL REVIEW B, 69, 123, (2004)
Abstract: Magnetic resonance data on Cu2+-doped lattices with fluorite structure reveal that the equilibrium geometry for SrCl2:Cu2+ involves an important off-center displacement of Cu2+ along <001> type directions (Z(0)approximate to1.3 Angstrom) while in CaF2:Cu2+ the impurity remains on-center though with a orthorhombic distortion of the ligand shell. In the case of SrF2:Cu2+ an off-center motion is also observed though the estimated displacement (Z(0)approximate to0.8 Angstrom) is substantially smaller than that for SrCl2:Cu2+. A microscopic explanation of these challenging facts has been attempted through calculations in the density functional theory framework on clusters involving up to 51 atoms. Total energy calculations using the hybrid nonlocal B3LYP functional on clusters of only 21 atoms are shown to reproduce reasonably main experimental features leading to Z(0)=0, 0.3, and 1.1 Angstrom for Cu2+-doped CaF2, SrF2, and SrCl2, respectively. The well depth delta=0.12 eV obtained for SrF2:Cu2+ is substantially smaller than that for SrCl2:Cu2+ (delta=0.29 eV) and is consistent with the incoherent hopping observed in the former case upon temperature raising leading to an isotropic EPR spectrum. The origin of these surprising facts is shown to come mainly from a competition between the electrostatic barrier due to the rest of lattice ions upon the impurity ion and the electronic energy gain from bonding when the coordination number of the d(9) impurity changes from 8 to 4. This simple argument explains that keeping the same d(9) ion, an increase of the host lattice parameter and a decrement of ligand electronegativity favor the occurrence of an off-center motion. Following these ideas calculations on SrL2:Mn2+ (L=F, Cl) give Z(0)=0 in agreement with available EPR data. At variance with what happens for Jahn-Teller distortions off-center displacements are shown to be related from the beginning to modifications of involved wavefunctions as described by the pseudo Jahn-Teller theory.

First author: Costuas, K, Electron-rich piano-stool iron sigma-acetylides. Theoretical and phenomenological investigation of electronic substituent effects in iron(II) acetylides, ORGANOMETALLICS, 23, 2053, (2004)
Abstract: The electronic structures of the electron-rich Fe(II) acetylide complexes (eta(2)-dppe)(eta(5)-C(5)Me(5))Fe(C=CC(6)H(4)-X) (1a-j: dppe = 1,2-bis(diphenylphosphino)ethane; X = NO(2), CN, CF(3), Br, F, H, Me, (t)Bu, OMe, NH(2)) have been investigated using density functional theory calculations. The crystal structures of the bromo- (1d), methyl- (1g), methoxy- (1i), and amino-substituted complexes (1j) are reported to complement the available structural data. The structural data, the first ionization potentials, and the relevant electronic and vibronic transitions calculated for the model complexes are compared to the experimental data for the corresponding Fe(II) complexes among 1a-j. The influence of the X substituent on the electronic properties is then more specifically investigated by means of linear free-energy relationships (LFERs). Correlations between the experimental data gathered for 1a-j and electronic substituent parameters (ESP’s) provide additional information on the way the remote para substituent influences the electronic properties of these Fe(II) acetylide complexes. This dual theoretical/phenomenological approach gives a consistent picture of the bonding between the Fe(II) center and the functional phenylacetylide fragment.

First author: Watson, MA, Density-functional generalized-gradient and hybrid calculations of electromagnetic properties using Slater basis sets, JOURNAL OF CHEMICAL PHYSICS, 120, 7252, (2004)
Abstract: In this paper we extend our density-functional theory calculations, with generalized gradient approximation and hybrid functionals, using Slater-type orbitals (STOs), to the determination of second-order molecular properties. The key to the entire methodology involves the fitting of all STO basis function products to an auxiliary STO basis, through the minimization of electron-repulsion integrals. The selected properties are (i) dipole polarizabilities, (ii) nuclear magnetic shielding constants, and (iii) nuclear spin-spin coupling constants. In all cases the one-electron integrals involving STOs were evaluated by quadrature. The implementation for (ii) involved some complexity because we used gauge-including atomic orbitals. The presence of two-electron integrals on the right-hand side of the coupled equations meant that the fitting procedure had to be implemented. For (iii) in the hybrid case, fitting procedures were again required for the exchange contributions. For each property we studied a number of small molecules. We first obtained an estimate of the basis set limit using Gaussian-type orbitals (GTOs). We then showed how it is possible to reproduce these values using a STO basis set. For (ii) a regular TZ2P quality STO basis was adequate; for (i) the addition of one set of diffuse functions (determined by Slater’s rules) gave the required accuracy; for (iii) it was necessary to add a set of 1s functions, including one very tight function, to give the desired result. In summary, we show that it is possible to predict second-order molecular properties using STO basis sets with an accuracy comparable with large GTO basis sets. We did not encounter any major difficulties with either the selection of the bases or the implementation of the procedures. Although the energy code (especially in the hybrid case) may not be competitive with a regular GTO code, for properties we find that STOs are more attractive.

First author: Liu, TQ, Density functional vertical self-consistent reaction field theory for solvatochromism – Studies of solvent-sensitive dyes, JOURNAL OF PHYSICAL CHEMISTRY A, 108, 3545, (2004)
Abstract: On the basis of the Franck-Condon principle, a density functional vertical self-consistent reaction field (VSCRF) solvation model for vertical excitation and emission processes is established. The principles and implementation of the VSCRF model are presented. The predicted blue shifts of the vertical excitation energies of diazines in different solvents from n-heptane to water solutions are compared with the corresponding time dependent density functional calculations and are in very good agreement with experiment. We have also applied this method to predict the blue shifts and the vertical excitation and emission energies of Brooker’s merocyanine dye with increasing solvent polarities from CHCI3 to H2O solutions. Overall, our calculations predicted the relative excitation and emission energy orderings for Brooker’s merocyanine in different solvents with different polarities. Also, the calculated Stokes shift is fairly well represented for different solvents, and the calculations correctly show that the absorption energies have a much stronger solvent dependence than the emission energies. The importance of both relaxation of the molecular structures and consideration of explicit H-bonding H2O and CH3OH molecules in water and methanol solvents in predicting the solvatochromic shifts is also discussed.

First author: de Pater, BC, Strongly nucleophilic Rh-1 centre in square-planar complexes with terdentate (kappa(3)) 2,2 ‘: 6 ‘,2 ”-terpyridine ligands: Crystallographic, electrochemical and density functional theoretical studies, EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 108, 1675, (2004)
Abstract: Rh-I-terpyridine complexes have been unambiguously formed for the first time. The 2,21:6′,2″-terpyridine (tpy), 4′-chloro-2,2′:6′,2″-terpyridine (4′-Cl-tpy) and 4′-(tert-butyldimethylsilyl-ortho-carboranyl)-2,2′:6′,2″-terpyridine (carboranyl-tpy) ligands were used for successful syntheses and characterisation of the corresponding Rh-I complexes with halide coligands, [Rh(X)(4′-Y-terpyridine)] (X = Cl, Y = H, Cl, carboranyl; X = Br, Y = H). All four neutral Rh-tpy complexes are square planar, with Rh-X bonds in the plane of the 4′-Y-terpyridine ligands. Full characterisation of these dark blue, highly air-sensitive compounds was hampered by their poor solubility in various organic solvents. This is mainly due to the formation of pi-stacked aggregates, as evidenced by the crystal structure of [Rh(Cl)(tpy)]; in addition, [Rh(Cl)(carboranyl-tpy)] merely forms discrete dimers. The (bonding) properties of the novel Rh-I-terpyridine complexes have been studied with single-crystal X-ray diffraction, (time-dependent) density functional theoretical (DFT) calculations, far-infrared spectroscopy, electronic absorption spectroscopy and cyclic voltammetry. From DFT calculations, the HOMO of the studied Rh-I-terpyridine complexes involves predominantly the metal centre, while the LUMO resides on the terpyridine ligand. Absorption bands of the studied complexes in the visible region (400-900 nm) can be assigned to MLCT and MLCT/XLCT transitions. The relatively low oxidation potentials of [Rh(X)(tpy)] (X = Cl, Br) point to a high electron density on the metal centre. This makes the Rh-I-terpyridine complexes strongly nucleophilic and (potentially) highly reactive towards various (small) substrate molecules containing carbon-halide bonds.

First author: Petrie, S, DFT and metal-metal bonding: A dys-functional treatment for multiply charged complexes?,INORGANIC CHEMISTRY, 43, 2597, (2004)
Abstract: Density functional theory (DFT) calculations are reported for 16 binuclear transition-metal complexes. Structural motifs studied include face-shared and edge-shared bioctahedra, carboxylate-bridged “paddlewheel” complexes, and nonbridged dimers possessing direct metal-metal bonds. Most of these structure types are represented both by multiply charged (tri- and tetra-anionic, and tetracationic) and by neutral or singly charged examples. Geometry optimizations for these species, in the vacuum phase, use the “broken-symmetry” approach coupled with nine different DFT methods, We find a clear dichotomy in the performance of different DFT approaches. For the eight neutral or singly charged complexes, orthodox gradient-corrected DFT methods such as BP and PBE perform generally very well in reproducing in vacuo the complex geometries obtained from X-ray crystallographic studies. In contrast, these orthodox approaches fail to reliably mimic the crystalline geometries for more highly charged complexes such as Mo2Cl93-, Cr-2(CH3)(8)(4-), and Rh-2(NCCH3)(10)(4+). Much closer agreement with experimental condensed-phase structures for the multiply charged dinuclear complexes is seen for two “local-density-approximation” approaches, Xalpha and VWN, and for VWN+B-LYP, an unorthodox combination of the VWN local and B-LYP nonlocal density functionals. The very good performance of the latter approaches arises from an essentially fortuitous cancellation of errors: while the generally overbinding nature of these approaches suggests that they will not reliably describe true gas-phase structures, this overbinding compensates very well for the coulombic distortion expected when complexes are removed from the charge-stabilizing environment of the crystalline or solvated state. We recommend that, as an alternative to the (computationally expensive) incorporation of solvent-field corrections, VWN+B-LYP is the preferred method for structural characterization of triply or more highly charged dinuclear complexes, while orthodox approaches such as PBE perform best for neutral or mildly charged complexes.

First author: Guerra, CF, Hydrogen bonding in mimics of Watson-Crick base pairs involving C-H proton donor and F proton acceptor groups: A theoretical study, CHEMPHYSCHEM, 5, 481, (2004)
Abstract: We have theoretically analyzed mimics of Watson-Crick adenine-thymine (AT) and guanine-cytosine (GC) base pairs in which N-H…O and N…H-N hydrogen bonds ore replaced by N-H…F and N…H-C, respectively, by using the generalized gradient approximation of density functional theory at BP86/TZ2P. The general effect of the above substitutions is an elongation and weakening of the hydrogen bonds that hold together the base pairs. However, the precise effects depend on how many and, in particular, on which hydrogen bonds are substituted in AT and GC Another purpose of this work is to clarify the relative importance of electrostatic attraction versus orbital interaction in the weak hydrogen bonds involved in the mimics, by using a quantitative bond-energy decomposition scheme. At variance with widespread believe, the orbital interaction component in these weak hydrogen bonds is found to contribute 34-42% of the attractive interactions and is thus of the some order of magnitude as the electrostatic component, which provides the remaining attraction component.

First author: Nechaev, MS, Energy partitioning analysis of the bonding in ethylene and acetylene complexes of group 6, 8, and 11 metals: (CO)(5)TM-C2Hx and Cl4TM-C2Hx (TM = Cr, Mo, W), (CO)(4)TM-C2Hx (TM = Fe, Ru, Os), and TM+-C2Hx (TM = Cu, Ag, Au), JOURNAL OF PHYSICAL CHEMISTRY A, 108, 3134, (2004)
Abstract: Quantum chemical calculations at the DFT level have been carried out for the title compounds. The equilibrium geometries and bond dissociation energies are reported. The nature of the bonding between the metal and the pi ligands ethylene and acetylene has been investigated by means of an energy partitioning analysis. The nature of the metal-ligand interactions is not very different from each other in the donor-acceptor complexes (CO)(5)TM-C2Hx (TM = Cr, Mo, W), (CO)(4)TM-C2Hx (TM = Fe, Ru, Os), and TM+-C2Hx (TM = Cu, Ag, An). The metal-C2Hx bonds have a slightly more electrostatic than covalent character. The covalent bonding comes mainly from the metal <– ligand sigma donation and the metal –> ligand pi(ll) in-plane back-donation. The contributions from the out-of-plane pi(perpendicular to) and delta orbitals are negligible. The main difference of the bonding interactions in the metallacyclic compounds Cl4TM-C2Hx (TM = Cr, Mo, W) is that they are clearly more covalent than electrostatic. The covalent interactions come also mainly from a(1)(sigma) and b(2)(pi(ll)) interactions. The a(2)(delta) orbital interactions are negligible but the interactions of the out-of-plane pi orbitals in the acetylene complexes Cl4TM-C2H2 contribute similar to11% to the total orbital term.

First author: Yuan, DW, Saturated adsorption of CO and coadsorption of CO and O-2 on Au-N(-) (N=2-7) clusters,JOURNAL OF CHEMICAL PHYSICS, 120, 6574, (2004)
Abstract: A first-principles quantum chemistry method, based on the Kohn-Sham density-functional theory, is used to investigate the adsorption of CO and O-2 on small gas-phase gold cluster anions. The saturated adsorption of carbon monoxide on gold cluster anions Au-N(-) (N=2-7) is discussed. The adsorption ability of CO reduces with the increase of the number of CO molecules bound to gold cluster anions, resulting in saturated adsorption at a certain amount of absorbed CO molecules, which is determined by geometric and electronic properties of gold clusters cooperatively. The effect of CO preadsorption on the electronic properties of gold cluster anions depends on the cluster size and the number of adsorbed CO, and the vertical detachment energies of CO-adsorbed gold cluster anions show a few changes with respect to corresponding pure gold cluster anions. The results indicate that the impinging adsorption of CO molecules may lead to geometry structure transformation on Au-3(-) cluster. For the coadsorption of CO and O-2 on Au-2(-), Au-3(-) isomers, Au-4(-), and Au-6(-), we describe the cooperative adsorption between CO and O-2, and find that the O-2 dissociation is difficult on gas-phase gold cluster anions even with the preadsorption of CO.

First author: Cavigliasso, G, Density functional investigation of metal-metal interactions in d(4)d(4) face-shared [M2Cl9](3-) (M = Mn, Tc, Re) systems, INORGANIC CHEMISTRY, 43, 2368, (2004)
Abstract: The molecular and electronic structures of the d(4)d(4) face-shared [M2Cl9](3-) (M = Mn, Tc, Re) dimers have been calculated by density functional methods in order to investigate metal-metal bonding in this series. The electronic structures of these systems have been analyzed using potential energy curves for the broken-symmetry and other spin states arising from the various d(4)d(4) coupling modes, and closed energy cycles have been utilized to identify and quantify the parameters which are most important in determining the preference for electron localization or delocalization and for high-spin or low-spin configurations. In [Tc2Cl9](3-) and [Re2Cl9](3-), the global minimum has been found to be a spin-triplet state arising from the coupling of metal centers with low-spin configurations, and characterized by delocalization of the metal-based electrons in a double (delta and delta(pi)) bond with a metal-metal separation of 2.57 Angstrom. In contrast, high-spin configurations and electron localization are favored in [Mn2Cl9](3-), the global minimum for this species being the ferromagnetic S = 4 state with a rather long metal-metal separation of 3.43 Angstrom. These results are consistent with metal-metal overlap and ligand-field effects prevailing over spin polarization effects in the Tc and Re systems, but with the opposite trend being observed in the Mn complex. The ground states and metal-metal bonding observed for the d(4)d(4) systems in this study parallel those previously found for the analogous d(2)d(2) complexes of V, Nb, and Ta, and can be rationalized on the basis that the d4d4 dimer configuration is the hole equivalent of the d(2)d(2) configuration.

First author: Peacock, CL, Vanadium(V) adsorption onto goethite (alpha-FeOOH) at pH 1.5 to 12: A surface complexation model based on ab initio molecular geometries and EXAFS spectroscopy, GEOCHIMICA ET COSMOCHIMICA ACTA, 68, 1723, (2004)
Abstract: We measured the adsorption of V(V) onto goethite (alpha-FeOOH) under oxic (P-O2 = 0.2 bar) atmospheric conditions. EXAFS spectra show that V(V) adsorbs by forming inner-sphere complexes as VO2(OH)(2) and VO3(OH). We predicted the relative energies and geometries of VO2(O, OH)(2)-FeOOH surface complexes using ab initio calculations of the geometries and energetics of analogue Fe-2(OH)(2)(H2O)(6)O2VO2(O, OH)(2) clusters. The bidentate corner-sharing complex is predicted to be substantially (57 kJ/mol) favoured energetically over the hypothetical edge-sharing bidentate complex. Fitting the EXAFS spectra using multiple scattering shows that only the bidentate corner-sharing complex is present with Fe-V and V-O distances in good agreement with those predicted. We find it important to include multiple scattering in the fits of our EXAFS data otherwise spurious V-Fe distances near 2.8 Angstrom result which may be incorrectly attributed to edge-sharing complexes. We find no evidence for monodentate complexes; this agrees with predicted high energies of such complexes. Having identified the Fe2O2V(OH)(2)(+) Fe2O2VO(OH)(O) surface complexes, we are able to fit the experimental vanadium(V) adsorption data to the reactions2FeOH(2)(+) + VO2+ Fe2O2V(OH)(2)(+) + 2H(+)and2FeOH + HVO42- = Fe2O2VO(OH)(0) + 2OH(-)also determined the first acid dissociation constant of the Fe2O2VO2H2+ surface complex. Fits of sorption edges to surface complexation models are ambiguous. This is one of the first studies to provide a surface complexation model of sorption edges that is consistent with both spectroscopic and quantum mechanical constraints.

First author: Luo, Y, Ligand effect on the periodic properties of trivalent organolanthanide complexes: a density functional study, INORGANIC CHEMISTRY COMMUNICATIONS, 7, 566, (2004)
Abstract: For the first time, density functional calculations on a series of organolanthanides of the type Cp(3)Ln, Cp(2)LnCl, Cp(2)LnCl(THF) and CpLnCl(2) (Ln = La, Ce, Eu, Gd, Yb and Lu; Cp = cyclopentadienyl, C5H5; THF = tetrahydrofuran, OC4H8), which showed a periodic trend and the influence of ligands on the molecular properties for a set of tailored lanthanide complexes. The replacement of the ligands by another alters the bond lengths and has irregular trends along the lanthanide series. The increase in the (Hirshfeld) charges on going from La to Lu indicates an increase in ionic character, which is in line with the chemical hardness and softness concept while Mulliken charges failed to describe the same.

First author: Seda, J, Estimation of electron spectr transitions of free-based porphin and Mg-porphin using various quantum chemical approaches, INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES, 5, 196, (2004)
Abstract: For optimized molecules of free-base porphin and magnesium-porphin (at Hartree-Fock level and 6-31G* basis set) excitation spectra were determined using several ab initio methods: CIS, RPA, CASSCF, and TDDFT. Obtained values were compared with semiempirical ZINDO method, other calculations found recently in literature and experimental data. It was demonstrated that for qualitatively correct spectra description the AO basis must include both the polarization and diffuse functions. The later play an important role in formation of Rydberg MOs. Estimated energies of the spectra transitions using the CIS method remain relatively far from the measured values. RPA method can be already considered as a quantitatively accurate method when sufficiently large basis set is used. For CASSCF approach, it was shown that even the lowest energy transitions are insufficiently described in CAS formalism and much larger active space or inclusion of more inactive orbitals in correlation treatment would be necessary for obtaining sufficient accuracy. It can be stated that without sufficiently large correlation contributions, the determined spectra are not able to reach quantitative agreement with experimental data. From the methods treated in this study, only TDDFT can be considered as a useful tool for spectra prediction, at least for calculations of lower excited states. It is relatively fast and feasible for calculation of middle-size molecules. ZINDO approximation is also relatively successful for such large systems. Acceptable predictions of experimentally observed energy transitions in the range of Q and B bands were obtained. Until higher (UV) part of spectra is examined where the excitations to Rydberg orbital will happen, it can be considered as a good candidate for electron spectra calculations.

First author: Bagno, A, Fries rearrangement of aryl formates promoted by BCl3. Mechanistic evidence from B-11 NMR spectra and DFT calculations, ZEITSCHRIFT FUR NATURFORSCHUNG SECTION B-A JOURNAL OF CHEMICAL SCIENCES, 59, 386, (2004)
Abstract: The Fries rearrangement of model aryl formate esters, promoted by boron trichloride, has been investigated by means of NMR spectroscopy (both experimental and computational) and by DFT calculations. Firstly, the B-11 NMR chemical shifts of a series of model boron compounds have been predicted by GIAO-B3LYP/6-31G(d,p) calculations, in order to make predictions of the chemical shifts of transient reaction intermediates observable by B-11 NMR. Such B-11 spectra for the reaction of two esters (phenyl and 3-methyoxyphenyl formates) have been obtained, and are found to follow different patterns which can be rationalized on the basis of computed chemical shifts. Secondly, DFT calculations (B3LYP/6-31G(d,p) level) have been employed to investigate several mechanistic pathways of the rearrangement of phenyl formate. It is found that the pathways leading to the lowest activation energies are those in which formyl chloride is generated from a complex between phenyl formate and BCl3, which then acts as the formylating agent.

First author: Qiu, YX, Theoretical studies on the structure of Hg(I)-hydroiddic compounds, ACTA CHIMICA SINICA, 62, 556, (2004)
Abstract: Geometries, vibrational frequencies and stability of Hg-2(OH)(2) as well as Hg2F2 and Hg2Cl2 have been investigated by means of ab initio HF, MP2 and density functional theory methods with LanL2DZ, SDD basis sets. The 5s, 5p semi-core of Hg has significant contribution to Hg-Hg bonding. HF method is not suitable for the [ Hg-Hg](2+) system due to the strong correlation effects. The non-local exchange correction of Becke functional gives too long Hg-Hg distances. Local spin density functional theory and MP2 may reproduce die spectroscopic constants reasonably. Relativistic effects reduce the Hg-Hg bond lengths by about 24 pm and stabilize the Hg-Hg bond significantly by about 20%. Although Hg2L2 (L = OH, F, Cl) in disproportionation reaction Hg2L2–>HgL + Hg is stable in the gas phase, relativistic effects reduce the tendency. The stability of Hg-2(OH)(2) is comparable to that of mercurous halides.

First author: Wei, YQ, Basisset effects in the DFT calculations of hyperpolarizability, ACTA CHIMICA SINICA, 62, 578, (2004)
Abstract: Diffuse functions were added based on DZP set in ADF, which was called DZP + df set. The first hyperpolarizability calculations of five selected molecules show that the calculated results by using DZP + df set are much better than those by DZP set. Diffuse functions in the basis set were found to be important to calculate molecular hyperpolarizability.

First author: Kelly, E, Calculation of free energy profiles for elementary bimolecular reactions by a initio molecular dynamics: Sampling methods and thermostat considerations, JOURNAL OF PHYSICAL CHEMISTRY A, 108, 2167, (2004)
Abstract: A study designed to refine the procedure for performing ab initio molecular dynamics calculations (AIMD) on chemical reactions is presented. Of key interest is the calculation of changes in free energy along the entire reaction path. Several simple elementary reactions are studied with the Car-Parrinello projector augmented-wave (CP-PAW) density-functional theory (DFT) methodology. The illustrative gas-phase bimolecular addition reactions are (i) a sigma complexation of BH3 + H2O.H2O-BH3, (ii) the Diels-Alder reactions of butadiene with ethene, C4H6 + C2H4 –> cyclohexene, 1,3-cyclopentadiene (CP) and ethene, CP + C2H4 –> norbornene, and the stereoselective reaction of 5-amino-CP with ethene, amino-CP + C2H4 –> amino-norbornene, (iii) the carbene cyclopropanation Cl2C + C2H4 –> Cl2C3H4, and (iv) the dimerization of ketene. These reactions were used to test both the slow-growth and point-wise thermodynamic integration (STI and PTI) methods of phase-space sampling as well as the Nose-Hoover and Andersen thermostats. It is found that the PTI technique is potentially superior to the slow-growth method in terms of computational expense and is at least as accurate. The Nose-Hoover thermostat appears to be inadequate for most of the reactions modeled here, whereas the stochastic Andersen thermostat affords more accurate results.

First author: Hinderberger, D, Dynamics, site binding, and distribution of counterions in polyelectrolyte solutions studied by electron paramagnetic resonance spectroscopy, JOURNAL OF PHYSICAL CHEMISTRY B, 108, 3698, (2004)
Abstract: A microscopic picture of counterion condensation in liquid and glassy frozen solutions of the cationic polyelectrolyte poly(diallyldimethylammonium chloride) (PDADMAC is derived from data obtained by a combination of continuous-wave and pulse electron paramagnetic resonance techniques. The condensation of such divalent anions to the polyelectrolyte chain in the presence of a large excess of polyelectrolyte and monovalent counterions can be described by a dynamic equilibrium between specifically site-bound and nonspecifically territorially bound counterions with exchange between the two states proceeding on time scales significantly shorter than 1 ns. No free divalent counterions are detected. The dynamic electrostatic attachment is manifest in an axially symmetric rotational diffusion tensor, with the unique axis of fast rotation corresponding to the electrostatic bond between one sulfonate group of Fremy’s salt and the quaternary ammonium group of the PDADMAC repeat unit. A distance of 0.43 nm between the electron spin and the N-14 nucleus of the ammonium group is found by electron spin-echo envelope modulation spectroscopy, suggesting that the site-bound state corresponds to contact ion pairs. The same experiment provides an estimate of 20% site-bound and 80% territorially bound divalent counterions in glycerol/water glassy frozen solution. Pulse electron-electron double resonance measurements show that on nanometer length scales the counterions are virtually homogeneously distributed in three dimensions for high polyelectrolyte concentration but linearly distributed along stretched chains at low polyelectrolyte concentrations where no overlap of chains is expected.

First author: Atanasov, M, DFT-based pseudo-Jahn-Teller coupling studies on the steric and energetic lone pair effect of four- and five-coordinate halide molecules and complexes with central ions from the fifth, sixth, and seventh main groups,INORGANIC CHEMISTRY, 43, 1998, (2004)
Abstract: The energetical and stereochemical effect of the s(2) lone pair in the title molecules and complexes is investigated using a pseudo-Jahn-Teller coupling model with parameters adjusted to energies and wave functions from DFT calculations. Vibronic coupling parameters were calculated and compared with those of the coordination number (CN) 3. Inspecting the correlation between the chemical hardness and the vibronic coupling energy (hardness rule), it is found that the tendency to distort decreases with increasing CN. While all considered molecules AX(3) (A(III) = P to Bi; X- = F to 1) undergo lone pair deformations (D-3h –> C-3v), only part of the AX(4)(-) and BX4 species (B-IV = S to Po) do so (T-d –> C-2v)-and even less the ones with CN = 5 (D-3h –> C-2v (congruent toC4(v))), AX(5)(2-), BX5-, and CF5 (C-v; Cl to l). The distorted polyhedra of minimum energy possess usually the butterfly C-2v shape (CN = 4, tau(2)(zeta) displacement path) and a C-2v = C-4v geometry (CN = 5, epsilon’ (epsilon) distortion path). A further symmetry lowering to C, occurs, if the central ion becomes too small with respect to the ligands (ionic size influence, PCl(Br)(4)(-), pCl(5)(2-)), with the tendency to reduce the CN toward 3 + 1 and 4 + 1, respectively. For CN = 4 the various stationary points of, for example, compressed and elongated C-3v, C-4v, etc. in the multidimensional ground-state potential surface have been characterized. Though of higher energy than the absolute C-2v minimum, they are shown to govern the dynamics and reactivity of the CN = 4 species to a large extent. To simulate the chemical environment (positively charged counterions, polar solvents), the DFT calculations were performed using the polarizable continuum model COSMO (conductor-like screening model). Though the electronic energy gain upon distortion is not significantly affected by the solvent, the total stabilization energy is distinctly enhanced, frequently leading to lone pair deformations of otherwise electronically stable species. All results obtained by the combined vibronic/DFT approach are well in accord with available experimental data.

First author: Le Guennic, B, Synthesis and characterization of hypoelectronic rhenaboranes. Analysis of the geometric and electronic structures of species following neither borane nor metal cluster electron-counting paradigms, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 126, 3203, (2004)
Abstract: The reaction of (Cp*ReH2)(2)B4H4 With monoborane leads to the sequential formation of (Cp*Re)(2)BnHn (n = 7-10, 1-4). These species adopt closed deltahedra with the same total connectivities as the closo-borane anions [BnHn](2-), n = 9-12, but with flattened geometries rather than spherical shapes. These rhenaborane clusters are characterized by high metal coordination numbers, Re-Re cross-cluster distances within the Re-Re single bond range, and formal cluster electron counts three skeletal electron pairs short of that required for a canonical closo-structure of the same nuclearity. An open cluster, (Cp*ReH)(2)B7H9 (5), is isolated that bears the same structural relationship to arachno-B9H15 as 1-4 bear to the closo-borane anions. Chloroborane permits the isolation of (Cp*ReH)(2)B5C15 (6), an isoelectronic chloroanalogue of known open (Cp*WH2)(2)B5H5 and (Cp*Re)(2)B6H4CI2 (7), a triple-decker complex containing a planar, six-membered 1,2-B6H4CI2 ring. Both are putative five- and six-boron intermediates in the formation of 1. Electronic structure calculations (extended Huckel and density functional theory) yield geometries in agreement with the structure determinations, large HOMO-LUMO gaps in accord with the high stabilities, and B-11 chemical shifts accurately reflecting the observed shifts. Analyses of the bonding in 1-4 reveal that the Cp*(ReCp)-Cp-…*Re interaction generates fragment orbitals that are able to contribute the “missing” three skeletal electron pairs required for skeletal bonding. The necessity of a (ReRe)-Re-… interaction for strong cluster bonding requires a borane fragment shape change to accommodate it, thereby explaining the noncanonical geometries. Application of the debor principle of borane chemistry to the shapes of 1-4 readily rationalizes the observed geometries of 5 and 6. This evidence of the scope of transition metal fragment control of borane geometry suggests the existence of a large class of metallaboranes with structures not found in known borane or metal clusters.

First author: Lemaur, V, Charge transport properties in discotic liquid crystals: A quantum-chemical insight into structure-property relationships, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 126, 3271, (2004)
Abstract: We describe at the quantum-chemical level the main parameters that control charge transport at the molecular scale in discotic liquid crystals. The focus is on stacks made of triphenylene, hexaazatriphenylene, hexaazatrinaphthylene, and hexabenzocoronene molecules and derivatives thereof. It is found that a subtle interplay between the chemical structure of the molecules and their relative positions within the stacks determines the charge transport properties; the molecular features required to promote high charge mobilities in discotic materials are established on the basis of the calculated structure-property relationships. We predict a significant increase in the charge mobility when going from triphenylene to hexaazatrinaphthylene; this finding has been confirmed by measurements carried out with the pulse-radiolysis time-resolved microwave conductivity technique.

First author: Xie, RH, Excitations, optical absorption spectra, and optical excitonic gaps of heterofullerenes. 1. C-60, C59N+, and C48N12: Theory and experiment, JOURNAL OF CHEMICAL PHYSICS, 120, 5133, (2004)
Abstract: Low-energy excitations and optical absorption spectrum of C-60 are computed by using time-dependent (TD) Hartree-Fock, TD-density functional theory (TD-DFT), TD DFT-based tight-binding (TD-DFT-TB), and a semiempirical Zerner intermediate neglect of diatomic differential overlap method. A detailed comparison of experiment and theory for the excitation energies, optical gap, and absorption spectrum of C-60 is presented. It is found that electron correlations and correlation of excitations play important roles in accurately assigning the spectral features of C-60, and that the TD-DFT method with nonhybrid functionals or a local spin density approximation leads to more accurate excitation energies than with hybrid functionals. The level of agreement between theory and experiment for C-60 justifies similar calculations of the excitations and optical absorption spectrum of a monomeric azafullerene cation C59N+, to serve as a spectroscopy reference for the characterization of carborane anion salts. Although it is an isoelectronic analogue to C-60, C59N+ exhibits distinguishing spectral features different from C-60: (1) the first singlet is dipole-allowed and the optical gap is redshifted by 1.44 eV; (2) several weaker absorption maxima occur in the visible region; (3) the transient triplet-triplet absorption at 1.60 eV (775 nm) is much broader and the decay of the triplet state is much faster. The calculated spectra of C59N+ characterize and explain well the measured ultraviolet-visible (UV-vis) and transient absorption spectra of the carborane anion salt [C59N][Ag(CB11H6Cl6)(2)] [Kim et al., J. Am. Chem. Soc. 125, 4024 (2003)]. For the most stable isomer of C48N12, we predict that the first singlet is dipole-allowed, the optical gap is redshifted by 1.22 eV relative to that of C-60, and optical absorption maxima occur at 585, 528, 443, 363, 340, 314, and 303 nm. We point out that the characterization of the UV-vis and transient absorption spectra of C48N12 isomers is helpful in distinguishing the isomer structures required for applications in molecular electronics. For C59N+ and C48N12 as well as C-60, TD-DFT-TB yields reasonable agreement with TD-DFT calculations at a highly reduced cost. Our study suggests that C-60, C59N+, and C48N12, which differ in their optical gaps, have potential applications in polymer science, biology, and medicine as single-molecule fluorescent probes, in photovoltaics as the n-type emitter and/or p-type base of a p-n junction solar cell, and in nanoelectronics as fluorescence-based sensors and switches.

First author: Venkatesan, K, Carbon-carbon bonds of manganese half-sandwich complexes for electron reservoir functions, ORGANOMETALLICS, 23, 1183, (2004)
Abstract: Vinylidene species of the type Mn(C5H4CH3)[(H3C)(2)PCH2CH2P(CH3)(2)](=C=(CRR2)-R-1) (R-1 = R-2 = H; RI = H, R2 = Ph) can be fully reversibly coupled to yield the dinuclear complexes [(C5H4CH3)(dmpe)Mnequivalent to CC(R-1)(R-2)C(R-1)(R-2)Cequivalent toMn(dmpe)(C5H4CH3)][PF6](2) (R-1, R-2 = H; R-1 = H, R-2 = Ph) by an oxidation/reduction cycle involving formation and cleavage of a C-C sigma bond.

First author: Vargas, A, Adsorption of activated ketones on platinum and their reactivity to hydrogenation: a DFT study,JOURNAL OF CATALYSIS, 222, 439, (2004)
Abstract: The adsorption of several ketones interesting for the enantioselective hydrogenation on cinchona-modified platinum has been modeled using relativistically corrected density functional theory. Two metal clusters, containing 19 and 31 Pt atoms, respectively, have been used to model a Pt(111) surface. The two adsorption modes eta(1) and eta(2) have been described, and their importance for the mechanism of hydrogenation has been pointed out. The effect of an ester group in alpha position and of alpha-fluorination of a ketone on its adsorption has been studied, and an explanation for the reactivity enhancement due to the ketone substitution has been proposed.

First author: Bachmann, J, Multielectron chemistry of zinc porphyrinogen: A ligand-based platform for two-electron mixed valency, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 126, 2829, (2004)
Abstract: The synthesis, electronic structure, and oxidation-reduction chemistry of a homologous series of Zn(II) porphyrinogens are presented. The fully reduced member of the series, [LZn](2-), was prepared in two steps from pyrrole and acetone. The compound undergoes consecutive two-electron, ligand-based, oxidations at +0.21 and +0.63 V vs NHE to yield [(LZn)-Zn-Delta] and [(LZn)-Zn-DeltaDelta](2+), which also have been independently prepared by chemical means. X-ray diffraction analysis of the redox intermediary, [(LZn)-Zn-Delta], shows that the partly oxidized macrocycle is composed of a methylene-bridged dipyrrole that is doubly strapped to a two-electron oxidized dipyrrole bridged by a cyclopropane ring (L-Delta). The localization of two hole equivalents on the oxidized side of the porphyrinogen framework is consistent with a two-electron mixed valency formulation for the [(LZn)-Zn-Delta] species. Electronic structure calculations and electronic spectroscopy support this formalism. Density functional theory computations identify the HOMO to be localized on the reduced half of the macrocycle and the LUMO to be localized on its oxidized half. As implicated by the energy level diagram, the lowest energy transition in the absorption spectrum of [(LZn)-Zn-Delta] exhibits charge-transfer character. Taken together, these results establish the viability of using a ligand framework as a two- and four-electron/hole reservoir in the design of multielectron redox schemes.

First author: Sinnecker, S, Calculating the electron paramagnetic resonance parameters of exchange coupled transition metal complexes using broken symmetry density functional theory: Application to a Mn-III/Mn-IV model compound,JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 126, 2613, (2004)
Abstract: The capability of the density functional broken symmetry approach for the calculation of various EPR parameters of exchange coupled metal clusters is demonstrated by studying the experimentally well-investigated [(MnMnIV)-Mn-III(mu-O)(2)(mu-OAc)DTNE](2+) complex. Geometry optimizations of the complex in its broken symmetry and high spin states yielded structures with two distinct manganese sites and geometrical parameters in good agreement with the X-ray structure. Exchange coupling constants were calculated from the energy differences between the high spin and broken symmetry states using the Heisenberg spin Hamiltonian. Very good agreement between theory and experiment was achieved with the B3LYP hybrid functional. The g-tensor calculations were performed employing the coupled perturbed Kohn-Sham equations. A strategy for the computation of g-tensor site values is presented and provides single-site g-tensors that are in good agreement with the expectations for Mn-III and Mn-IV, respectively. Spin projection gave the g-tensor of the coupled manganese complex in very good agreement with the experimental results. Complete Mn-55 hyperfine tensors, including spin-orbit contributions, were calculated and spin-projected. The source of anisotropy in this system could be traced back to the Mn-III ion in line with the experimental results. The isotropic manganese hyperfine coupling constants were underestimated by factors between 1.4 and 2.5. It is shown that this deficiency is systematic in character and not anchored in the broken symmetry approach. Nuclear quadrupole splitting of the Mn-55 nuclei is shown to be small in this system. In addition, N-14 and H-1 ligand hyperfine data were calculated and compared well with the experimental results. The quality of the extended point-dipole model was demonstrated in application to H-1 anisotropic hyperfine coupling constants.

First author: Deeth, RJ, A molecular mechanics study of copper(II)-catalyzed asymmetric Diels-Alder reactions,ORGANOMETALLICS, 23, 1042, (2004)
Abstract: A simple molecular mechanics force field for the study of complexes important in the bis-(oxazoline) copper(II)-catalyzed Diels-Alder reaction of cyclopentadiene with acrylimide dienophiles has been developed. The parameter set has been based on the MMFF94 force field as implemented in the Molecular Operating Environment (MOE) and supplemented by available experimental and DFT calculated data. Control over the electronic preference for a square-planar complex geometry has been achieved by introducing a dummy bond. Catalyst-substrate complexes and approximate transition states have been studied by stochastic conformational searches to investigate conformational preferences and to estimate regio- and enantioselectivities based on the steric characteristics of different bis(oxazoline) ligands. While prediction of regioselectivity is reliable, factors determining enantioselectivity are more subtle, and predictions have been only moderately successful. Further computational experiments have been used to elucidate the source of some of these discrepancies.

First author: Esterhuysen, C, The nature of the chemical bond revisited. An energy partitioning analysis of diatomic molecules E-2 (E=N-Bi, F-I), CO and BF, THEORETICAL CHEMISTRY ACCOUNTS, 111, 381, (2004)
Abstract: The nature of the chemical bonds in the diatomic molecules E-2 (E=N-Bi, F-I), CO and BF has been studied with an energy partitioning analysis using gradient-corrected density functional theory calculations. The results make it possible to estimate quantitatively the strength of covalent and electrostatic attractions and the Pauli repulsion between the atoms. The data suggest that some traditional explanations regarding the strength of the molecules should be modified. The energy partitioning analysis shows that the chemical bonds in the group 15 diatomic molecules have significant electrostatic character, which increases from 30.1% in N-2 to 58.3% in Bi-2. The contribution of the electrostatic attraction to the binding interactions in Sb-2 and Bi-2 is larger than the covalent bonding. The strength of the pi bonding in the triply bonded dinitrogen is less than that of the sigma bonding. The calculations indicate that DeltaE(pi) is between 32.2% (Bi-2) and 40.0% (P-2) of the total orbital interaction energy (DeltaE(orb)). The much stronger bond of N-2, as compared with the heavier group 15 E-2 homologues, is not caused by a particularly strong contribution by the pi bonding, but rather by the relatively large sigma interactions. The comparison of N-2 with isoelectronic CO shows that the electrostatic character in the heteroatomic molecule is slightly smaller (28.8%) than in the homoatomic molecule. The contribution of the pi bonding in CO is larger (49.2%) than in N-2 (34.3%). The reason why CO has a stronger bond than N-2 is the significantly weaker Pauli repulsion in CO. The electrostatic character of the bonding in BF is slightly larger (32.0%) than in CO and N-2. BF has much weaker pi-bonding contributions that provide only 11.2% of the covalent interactions, which is why BF has a much weaker bond than CO and N-2. The chemical bonds in the dihalogen molecules have much higher covalent than electrostatic character. The DeltaE(orb) term contributes between 74.4% (Br-2) and 79.7% (F-2) to the total attractive interactions. The relatively weak bond in F-2 comes from the rather large Pauli repulsion.

First author: Spiegel, K, Cisplatin binding to DNA oligomers from hybrid Car-Parrinello/molecular dynamics simulations,JOURNAL OF PHYSICAL CHEMISTRY B, 108, 2699, (2004)
Abstract: The structure and binding of cisplatin to DNA in aqueous solution are investigated via a QM/MM methodology. In our approach, the platinated moiety is treated at the density functional level and the biomolecular frame with the AMBER force field. The calculations are based on X-ray structures of platinated DNA in the free form (cispt-d(CCTCTG*G*TCTCC)-d(GGAGACCAGAGG) [Takahara, et al. Nature 1995,377,649-652](1)) and in complex with HMG protein domain A (cispt-d(CCUCTCTG*G*ACCTTCC)-d(GGAGAGACCTG-GAAGG) [Ohndorf et al. Nature 1999, 399, 708 -712](2) as well as on a cisplatin docked DNA model. During the QM/MM simulation, the structure of the platinated DNA dodecamer rearranges significantly toward structural determinants of the solution structure as obtained by NMR spectroscopy [Gelasco et al. Biochemistry 1998, 37, 9230-9239].(3) The calculated (195)Pt chemical shifts of the QM/MM structure relative to cisplatin in aqueous solution are in qualitative agreement with the experimental data [Bancroft et al. J. Am. Chem. Soc. 1990, 112, 6860-6871. Miller et al. Inorg. Chem. 1985, 24, 2421-2425].(4,5) The QM/MM structure of the platinated/DNA HMG complex, on the other hand, remains rather similar to the X-ray structure, consistent with its relatively low flexibility. Docking of Pt(NH(3))(2)(2+) onto DNA in its canonical B-conformation causes a large axis bend and a rearrangement of DNA as experimentally observed in the platinated adducts, with NMR chemical shifts in qualitative agreement with the values in aqueous solution(4,5).

First author: Hoggard, PE, The photohydrochlorination of platinum(IV) chloride in chloroform, INORGANICA CHIMICA ACTA, 357, 639, (2004)
Abstract: When irradiated at 240 nm. PtCl4 in CHCl3 is converted to H2PtCl6. When irradiated at wavelengths longer than 265 nm, PtCl4 is converted to H2PtCl4 and H2PtCl6 in equal amounts. The latter reaction is suggested to proceed by dissociation of chlorine from a ligand to metal charge transfer excited state of Pt(IV) through a Pt(III) intermediate that disproportionates. The 240 nm photoreaction includes a second, solvent-initiated pathway, suggested to involve CCl3 radicals from the photolysis of chloroform, which attack the PtCl4 oligomer to create a Pt(V) intermediate.

First author: Hu, XL, Group 11 metal complexes of N-heterocyclic carbene ligands: Nature of the metal-carbene bond,ORGANOMETALLICS, 23, 755, (2004)
Abstract: When irradiated at 240 nm. PtCl4 in CHCl3 is converted to H2PtCl6. When irradiated at wavelengths longer than 265 nm, PtCl4 is converted to H2PtCl4 and H2PtCl6 in equal amounts. The latter reaction is suggested to proceed by dissociation of chlorine from a ligand to metal charge transfer excited state of Pt(IV) through a Pt(III) intermediate that disproportionates. The 240 nm photoreaction includes a second, solvent-initiated pathway, suggested to involve CCl3 radicals from the photolysis of chloroform, which attack the PtCl4 oligomer to create a Pt(V) intermediate.

First author: Saeys, M, Kinetic models for catalytic reactions from first principles: benzene hydrogenation, MOLECULAR PHYSICS, 102, 267, (2004)
Abstract: A fundamental kinetic model was constructed from first principles for the hydrogenation of benzene over a Pt(111) catalyst. Benzene adsorbs at the hollow and the bridge sites of the Pt(111) surface. Benzene at the hollow site is the reactive species, whereas benzene at the bridge site is too strongly bound. Hydrogenation follows a Horiuti-Polanyi mechanism. A reaction path analysis based on quantum chemical density functional theory calculations indicates that the fifth hydrogenation step is the rate determining step with an activation energy of 104 kJ mol(-1) . From the first principles reaction path analysis, a Langmuir-Hinshelwood-Hougen-Watson rate equation was constructed using first principles kinetic and thermodynamic data. Only the coverage-dependent hydrogen adsorption enthalpy was regressed to accurately (F value of 38 500) model laboratory scale data for the hydrogenation of toluene over a Pt-ZSM-22 catalyst. The optimized hydrogen adsorption enthalpy of -68.8 +/- 2 kJ mol(-1) is intermediate between the low and high coverage value of -94.0 and -45.0 kJ mol(-1) respectively.

First author: Garcia-Lastra, JM, Jahn-Teller impurities in tetragonal lattices: Why is the ligand octahedron of Cu2+ in layered perovskites compressed?, CHEMICAL PHYSICS LETTERS, 385, 286, (2004)
Abstract: Cu2+ impurities in tetragonal layered perovskites display a compressed geometry (R-eq > R-ax) along the crystal c-axis. Searching the microscopic origin of this fact DFT calculations have been performed on clusters simulating K2MgF4:Cu2+. Results for a 37 atoms cluster indicate that the difference, 6,c, between the energies for elongated and compressed minima along the c-axis is around 0.2 eV while R-eq – R-ax < 0.10 Angstrom. This result is shown to come mainly from the tetragonal electrostatic potential due to the rest of ions on CuF64- which provides a gap, Delta, between similar tox(2)-y(2) and similar to3z(2)-r(2) orbitals when R-eq = R-ax. Although delta(ec) < Delta this gap is shown to play a key role for understanding the equilibrium geometry in tetragonal perovskites.

First author: Gao, GH, Divalent molybdenum complexes of the dipyrrolide ligand system. Isolation of a Mo-2 unit with a 45 degrees twist angle, INORGANIC CHEMISTRY, 43, 1108, (2004)
Abstract: The preparation of divalent(.)Mo’complexes of dipyrrolide dianions was carried out by reacting Mo-2(acetate)4 with the dipotassium salts of Ph2C(2-C4H3NH)(2) and 2-[1,1-bis(1H-pyrrol-2-yl)ethyl]pyridine. The two reactions respectively afforded the diamagnetic {[Ph2C(C4H3N)(2)](2)Mo-2(OAc)(2)[K(THF)(3)][K(THF)]}(THF)-T-. (1) and {[(2-C5H4 N)(CH3)C(2-C4H3N)(2)]-Mo(OAc)[K(THF)]}(2)(THF)-T-. (2). Both compounds retained two acetate units in the dimetallic structure. Conversely, the reaction of Me8Mo2Li4(THF)(4) with Et2C(2-C4H3NH)(2) afforded the paramagnetic dimer {[Et2C(C4H3N)(2)](4)Mo2Li2}- {Li(THF)(4)}(2)(.)0.5THF (3). The paramagnetism is most likely caused by the 45degrees rotation of the two Mo(dipyrrolide) units with respect to each other and which, in turn, is caused by the presence of two lithium cations in the molecular structure.

First author: Hager, JS, Raman under nitrogen. The high-resolution Raman spectroscopy of crystalline uranocene, thorocene, and ferrocene, JOURNAL OF CHEMICAL PHYSICS, 120, 2708, (2004)
Abstract: The utility of recording Raman spectroscopy under liquid nitrogen, a technique we call Raman under nitrogen (RUN), is demonstrated for ferrocene, uranocene, and thorocene. Using RUN, low-temperature (liquid nitrogen cooled) Raman spectra for these compounds exhibit higher resolution than previous studies, and new vibrational features are reported. The first Raman spectra of crystalline uranocene at 77 K are reported using excitation from argon (5145 Angstrom) and krypton (6764 Angstrom) ion lasers. The spectra obtained showed bands corresponding to vibrational transitions at 212, 236, 259, 379, 753, 897, 1500, and 3042 cm(-1), assigned to ring-metal-ring stretching, ring-metal tilting, out-of-plane CCC bending, in-plane CCC bending, ring-breathing, C-H bending, CC stretching and CH stretching, respectively. The assigned vibrational bands are compared to those of uranocene in THF, (COT)(2-), and thorocene. All vibrational frequencies of the ligands, except the 259 cm(-1) out-of-plane CCC bending mode, were found to increase upon coordination. A broad, polarizable band centered about similar to460 cm(-1) was also observed. The 460 cm(-1) band is greatly enhanced relative to the vibrational Raman transitions with excitations from the krypton ion laser, which is indicative of an electronic resonance Raman process as has been shown previously. The electronic resonance Raman band is observed to split into three distinct bands at 450, 461, and 474 cm-1 with 6764 Angstrom excitation. Relativistic density functional theory is used to provide theoretical interpretations of the measured spectra.

First author: Suzuki, Y, Phenoxy-ether ligated Ti complexes for the polymerization of ethylene, MACROMOLECULAR RAPID COMMUNICATIONS, 25, 493, (2004)
Abstract: Bis(phenoxy-ether) Ti complexes were investigated as ethylene polymerization catalysts. The complexes, combined with iBu(3)Al/Ph3CB(C6F5)(4) or methylaluminoxane (MAO) cocatalysts, can be highly active single site catalysts, which display activities (turnover frequency, max. 2065 min(-1)) comparable with that of a highly active bis(phenoxy-imine) Ti complex/MAO system and provide very high molecular weight polyethylenes (M-v 2040 000 5 420 000) at 25degreesC under atmospheric pressure.

First author: Solomon, EI, Electronic structures of metal sites in proteins and models: Contributions to function in blue copper proteins, CHEMICAL REVIEWS, 104, 419, (2004)
Abstract: Bis(phenoxy-ether) Ti complexes were investigated as ethylene polymerization catalysts. The complexes, combined with iBu(3)Al/Ph3CB(C6F5)(4) or methylaluminoxane (MAO) cocatalysts, can be highly active single site catalysts, which display activities (turnover frequency, max. 2065 min(-1)) comparable with that of a highly active bis(phenoxy-imine) Ti complex/MAO system and provide very high molecular weight polyethylenes (M-v 2040 000 5 420 000) at 25degreesC under atmospheric pressure.

First author: Noodleman, L, Quantum chemical studies of intermediates and reaction pathways in selected enzymes and catalytic synthetic systems, CHEMICAL REVIEWS, 104, 459, (2004)
Abstract: Bis(phenoxy-ether) Ti complexes were investigated as ethylene polymerization catalysts. The complexes, combined with iBu(3)Al/Ph3CB(C6F5)(4) or methylaluminoxane (MAO) cocatalysts, can be highly active single site catalysts, which display activities (turnover frequency, max. 2065 min(-1)) comparable with that of a highly active bis(phenoxy-imine) Ti complex/MAO system and provide very high molecular weight polyethylenes (M-v 2040 000 5 420 000) at 25degreesC under atmospheric pressure.

First author: Williams, SD, Scalar relativistic study of the structure of rhodium acetate, INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES, 5, 67, (2004)
Abstract: Rhodium acetate, related rhodium carboxylates, and rhodium amide complexes are powerful catalysts for carbene chemistry. They readily promote the decomposition of diazo compounds and transfer the resulting carbene to a variety of substrates. There have been several quantum chemistry studies of these compounds, particularly of the acetate. These have all used non-relativistic methods, and all have shown optimized Rh-Rh bond lengths significantly longer than the experimental value. In this study we have surveyed several scalar relativistic DFT methods using Gaussian, Slater, and numerical basis functions (in DGAUSS, ADF, and DMOL3). Several combinations of exchange-correlation functionals with relativistic and non-relativistic effective core potentials (ECP) were investigated, as were non-relativistic and all electron scalar relativistic methods. The combination of the PW91 exchange and PW91 correlation functional with the Christiansen-Ermler ECP gave the best results: 2.3918 Angstrom compared to the experimental value of 2.3855+/-0.0005 Angstrom.

First author: Infante, I, QM/MM study of aqueous solvation of the uranyl fluoride [UO2F42-] complex, JOURNAL OF COMPUTATIONAL CHEMISTRY, 25, 386, (2004)
Abstract: The aqueous solvation of the uranylfluoride complex [UO2F42-] was studied using full quantum mechanical (QM) and hybrid QM/molecular mechanics (MM) methods. Inclusion of a complete first solvation shell was found necessary to reproduce the experimentally observed heptacoordination of uranium. An efficient and accurate computational model is proposed that consists of structure optimization of the coordinated uranium complex as QM region, followed by single-point full QM calculations to compute relative energies. This method is proven feasible for studies of large solvated actinide complexes.

First author: Rizzuti, B, Active site modeling in copper azurin molecular dynamics simulations, JOURNAL OF MOLECULAR MODELING, 10, 25, (2004)
Abstract: Active site modeling in molecular dynamics simulations is investigated for the reduced state of copper azurin. Five simulation runs (5 ns each) were performed at room temperature to study the consequences of a mixed electrostatic/constrained modeling for the coordination between the metal and the polypeptide chain, using for the ligand residues a set of charges that is modified with respect to the apo form of the protein by the presence of the copper ion.The results show that the different charge values do not lead to relevant effects on the geometry of the active site of the protein, as long as bond distance constraints are used for all the five ligand atoms. The distance constraint on the O atom of Gly45 can be removed without altering the active site geometry. The coordination between Cu and the other axial ligand Met121 is outlined as being flexible. Differences are found between the bonds of the copper ion with the two apparently equivalent N-delta1 atoms of His46 and His117.The overall findings are discussed in connection with the issue of determining a model for the active site of azurin suitable to be used in molecular dynamics simulations under unfolding conditions.

First author: Halcrow, MA, Temperature dependence of the electronic ground states of two mononuclear, six-coordinate copper(II) centres, NEW JOURNAL OF CHEMISTRY, 28, 228, (2004)
Abstract: Powdered [Cu((LNH2)-N-2)(2)]ClO4](2) (1; L-2 NH2 = 2,6-bis{hydrazonomethyl)pyridine) and [Cu((LOH)-O-2)(2)][ClO4](2) (2; (LOH)-O-2 = 2,6-bis{oximomethyl)pyridine) exhibit EPR spectra that are consistent with (d(z)2}(1) Cu(II) centres at 295 K. These slowly transform upon cooling to 5 K, to show g-values that more closely resemble {d(y2-z2)}(1), pseudo-Jahn-Teller elongated structures. Single crystal X-ray structures of 1.2(CH3)(2)CO and 22(CH3)(2)CO show the expected six-coordinate Cu(II) centres, with Cu-N bond lengths that are consistent with a {d(z2)}(1) configuration according to DF calculations. Importantly, the structure of 2 is temperature-dependent between 100-300 K, its Cu-N bond lengths varying in a manner consistent with the EPR data. The EPR spectra, and TLS analyses of the crystal structures, strongly imply that these changes are not a consequence of dynamic Jahn-Teller disorder. These results contrast with [Cu((LMe)-Me-2)(2)](2+) ((LMe)-Me-2 = 2,6-bis {N-methylcarbaldimino}pyridine) and other [Cu((LR)-R-2)(2)](2+) complexes with small alkyl or aryl ‘R’ substituents, which adopt the more usual {d(y2-z2)}(1) ground states at all temperatures.

First author: Guerra, CF, Voronoi deformation density (VDD) charges: Assessment of the Mulliken, Bader, Hirshfeld, Weinhold, and VDD methods for charge analysis, JOURNAL OF COMPUTATIONAL CHEMISTRY, 25, 189, (2004)
Abstract: We present the Voronoi Deformation Density (VDD) method for computing atomic charges. The VDD method does not explicitly use the basis functions but, calculates the amount of electronic density that flows to or from a certain atom due to bond formation by spatial integration of the deformation density over the atomic Voronoi cell. We compare our method to the well-known Mulliken, Hirshfeld, Bader, and Weinhold [Natural Population Analysis (NPA)] charges for a variety of biological, organic, and inorganic molecules. The Mulliken charges are (again) shown to be useless due to heavy basis set dependency, and the Bader charges (and often also the NPA charges) are not realistic, yielding too extreme values that suggest much ionic character even in the case of covalent bonds. The Hirshfeld and VDD charges, which prove to be numerically very similar, are to be recommended because they yield chemically meaningful charges. We stress the need to use spatial, integration over an atomic domain to get rid of basis set dependency, and the need to integrate the deformation density in order to obtain a realistic picture of the charge rearrangement upon bonding. An asset of the VDD charges is the transparency of the approach owing to the simple geometric partitioning of space. The deformation density based charges prove to conform to chemical experience.

First author: Han, WG, Density functional study of a mu-1,1-carboxylate bridged Fe(III)-O-Fe(IV) model complex. 2. Comparison with ribonucleotide reductase intermediate X, INORGANIC CHEMISTRY, 43, 613, (2004)
Abstract: Using broken-symmetry density functional theory, we have studied an experimentally proposed model for ribonucleotide reductase (RNR) intermediate X, which contains a single oxo bridge, one terminal H(2)O or OH(-) ligand, a bidentate carboxylate from Glu115, and a mono-oxygen bridge provided by Glu238. For the models proposed here, the terminal H(2)O/OH(-) ligand binds to site Fe1 which is closer to Tyr122. The diiron centers are assigned as high-spin Fe(III)Fe(IV) and antiferromagnetically coupled to give the S(total) = 1/2 ground state. Calculations show that the model with a terminal hydroxide in the antiferromagnetic {S(Fe1) = 2, S(Fe2.) = 5/2} state (Fe1 = Fe(IV), Fe2 = Fe(III)) is the lowest energy state, and the calculated isomer shift and quadrupole splitting values for this cluster are also the best among the four clusters studied here when compared with the experimental values. However, the DFT-calculated (1)H proton and (17)O hyperfine tensors for this state do not show good agreement with the experiments. The calculated Fe1-Fe2 distances for this and the other three clusters at > 2.9 Angstrom are much longer than the 2.5 Angstrom which was predicted by the EXAFS measurements. The mono-oxygen bridge provided by Glu238 tends to be closer to one of the Fe sites in all clusters studied here, and it does not function as a bridge in helping to produce a short Fe-Fe distance. Overall, the models tested here are not likely to represent the core structure of RNR intermediate X. The model with the terminal OH(-) binding to the Fe1 (III) center shows the best calculated (1)H proton and 110 hyperfine tensors compared with the experimental values. This supports the earlier proposal based on analysis of ENDOR spectra (Willems et al.(16)) that the terminal oxygen group binds to the Fe(III) site in RNR-X.

First author: Yang, XZ, Spectroscopic constants of gallium monohalides: a DFT study, JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM, 668, 209, (2004)
Abstract: Density-functional theory studies on the ground and the first excited states of gallium monohalide diatomic molecules are carried out, by using two local density approximations (LDAs) and four generalized gradient approximations (GGAs). The results obtained from different functionals are compared with the observed values and the theoretical results. The calculation results with and without zero-order regular approximation (ZORA) scalar relativistic corrections are compared at the same time. All of our results showing that the LDA Vosko-Wilk-Nusair with the Stoll correction are much better than the Xalpha in energy calculation, and the revPBE and RPBE are rather successful GGAs for energy calculation. Furthermore, the ZORA is suggested as a good approximate correction approach for scalar relativistic effects.

First author: Luo, Y, Density functional theory and tight-binding quantum chemical molecular dynamics calculations on Ce1-xCuxO2-delta catalyst and the adsorptions of CH3OH and CH3O on Ce1-xCuxO2-delta, CHEMICAL PHYSICS LETTERS, 384, 30, (2004)
Abstract: For the first time, both density functional and quantum chemical molecular dynamics calculations suggested orbital overlap between Cu and Ce in Ce1-xCuxO2-delta catalyst. The adsorptions of CH3OH and CH3O on Ce1-xCuO2-delta were described using cluster model. CH3OH passed a low energy barrier (2.38 kcal/mol) to achieve the stable adsorption structure. Dissociative adsorption was observed for CH3O but not for CH3OH in the present study. The dissociation of CH3O may produce oxygen vacancy in the catalyst surface. The results indicated that charge transfers from CH3OH or dissociated CH3O to catalyst.

First author: Marconi, G, A circular dichroism and structural study of the inclusion complex artemisinin-beta-cyclodextrin,CHEMICAL PHYSICS LETTERS, 383, 566, (2004)
Abstract: The inclusion complex between the powerful antimalarial agent Artemisinin and beta-cyclodextrin has been studied by means of Circular Dichroism and elucidated by Density Functional Theory calculations on the isolated molecule combined to a statistical Monte Carlo search of the most stable geometry of the complex. The results evidence a host-guest structure in full agreement with the almost unaffected functionality of the drug, which is found to experience a significant hydrophilic environment when complexed.

First author: Shen, JY, A DFT study of the interstitial chemical shifts in main group element centered hexazirconium halide clusters, JOURNAL OF PHYSICAL CHEMISTRY A, 108, 350, (2004)
Abstract: A density functional theoretical study aimed at correlating the chemical shifts of interstitial atoms and electronic structures of main-group-centered hexazirconium halide clusters has been performed and analyzed within the framework of perturbation theory. The influence of bridging halides on electronic structure was studied with two series of model compounds [(Zr(6)Z)X-12](H2O)6(n+) (Z = B, C; X = Cl, Br, I). The effect of terminal ligands on electronic structure was investigated with model compounds [(Zr6B)Cl-12]L-6(+) (L = H2O, PH3, HCN, and OPHA There is a qualitative inverse proportionality between the chemical shifts and the calculated energy gaps between two Kohn-Sham orbitals, DeltaE(t(lu)*-t(lu)), where t(lu) and t(lu)* orbitals are the bonding and antibonding orbitals that result from the interaction between the zirconium cage bonding orbitals and the interstitial 2p orbitals. Chemical shielding properties of the interstitial atoms were further calculated with the gauge-including atomic orbitals (GIAO) method.

First author: Guidoni, L, Green oxidation catalysts: Computational design of high-efficiency models of galactose oxidase,ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 43, 3286, (2004)
Abstract: A density functional theoretical study aimed at correlating the chemical shifts of interstitial atoms and electronic structures of main-group-centered hexazirconium halide clusters has been performed and analyzed within the framework of perturbation theory. The influence of bridging halides on electronic structure was studied with two series of model compounds [(Zr(6)Z)X-12](H2O)6(n+) (Z = B, C; X = Cl, Br, I). The effect of terminal ligands on electronic structure was investigated with model compounds [(Zr6B)Cl-12]L-6(+) (L = H2O, PH3, HCN, and OPHA There is a qualitative inverse proportionality between the chemical shifts and the calculated energy gaps between two Kohn-Sham orbitals, DeltaE(t(lu)*-t(lu)), where t(lu) and t(lu)* orbitals are the bonding and antibonding orbitals that result from the interaction between the zirconium cage bonding orbitals and the interstitial 2p orbitals. Chemical shielding properties of the interstitial atoms were further calculated with the gauge-including atomic orbitals (GIAO) method.

First author: Patzschke, M, Darmstadtium carbonyl and carbide resemble platinum carbonyl and carbide, CHEMICAL COMMUNICATIONS, 43, 1982, (2004)
Abstract: DsC and DsCO are calculated to be very similar to PtC and PtCO, suggesting that even the latest 6d elements resemble the corresponding 5d elements chemically.

First author: Sharrad, CA, Embracing ligands. Synthesis, characterisation and the correlation between Co-59 NMR and ligand field parameters of Co(III) complexes with a new class of nitrogen-thioether multidentate ligand, DALTON TRANSACTIONS, 43, 767, (2004)
Abstract: The syntheses of the hexadentate ligands 2,2,10,10-tetra(methyleneamine)-4,8-dithiaundecane (PrN(4)S(2)amp), 2,2,11,11-tetra(methyleneamine)-4,9-dithiadodecane (BuN(4)S(2)amp), and 1,2-bis(4,4-methyleneamine)-2-thiapentyl)benzene (XyN(4)S(2)amp) are reported and the complexes [Co(RN(4)S(2)amp)](3+) (R = Pr, Bu, Xy) characterised by single crystal X-ray study. The low-temperature (11 K) absorption spectra have been measured in Nafion films. From the observed positions of both spin-allowed (1)A(1g) –> T-1(1g) and (1)A(1g) –> T-1(2g) and spin forbidden (1)A(1g) –> T-3(1g) and (1)A(1g) –> T-3(2g) bands, octahedral ligand-field parameters (10D(q), B and C) have been determined. DFT calculations suggest that significant interaction between the d-d and CT excitations occurs for the complexes. The calculations offer an explanation for the observed deviations from linearity of the relationship between Co-59 magnetogyric ratio and beta(DeltaE)(-1) (beta = the nephelauxetic ratio; DeltaE the energy of the (1)A(1g) –> T-1(1g) transition) for a series of amine and mixed amine/thioether donor complexes.

First author: Sharrad, CA, Synthesis, characterization and DFT studies of the cobalt(III) complex of a tetrapodal pentadentate N4S donor ligand, DALTON TRANSACTIONS, 43, 1166, (2004)
Abstract: The synthesis of the pentadentate ligand 2,6-bis(3,3-dimethyl-2,4-dioxocyclohexanyl)-4-thiaheptane (N(4)Samp) is described. The synthetic pathway involves the coupling of two 1,3-(dimethylenedioxy)-2-methyl-2-(methylene-p-toluenesulfonyl)propane moieties with sodium sulfide and subsequent synthetic elaboration to prepare the final N4S donor system. The cobalt(III) complex [Co(N(4)Samp)Cl](2+) has been prepared and subsequently crystallized as the tetrachlorozincate salt. The X-ray structure analysis confirms the pentadentate nature of the ligand and shows the thioether donor occupying one apex with four equivalent amine donors effectively occupying the equatorial plane of the molecule. The sixth coordination site is occupied by a chloro ligand. The electronic absorption and C-13 NMR spectra have been studied. DFT calculations have been employed to explore structural and mechanistic comparisons between [Co(N(4)Samp)Cl](2+) and an analogous pentaamine complex.

First author: Christian, G, Activation and cleavage of dinitrogen by three-coordinate metal complexes involving Mo(III) and Nb(II/III), DALTON TRANSACTIONS, 43, 2492, (2004)
Abstract: Density functional calculations have been employed to rationalize why the heteronuclear N-2-bridged (MoNbIII)-Nb-III dimer, [Ar(Bu-t)N](3)Mo(mu-N-2)Nb[N(Pr-i)Ar](3) (Ar = 3,5-C6H3Me2), does not undergo cleavage of the dinitrogen bridge in contrast to the analogous (MoMoIII)-Mo-III complex which, although having a less activated N-N bond, undergoes spontaneous dinitrogen cleavage at room temperature. The calculations reveal that although the overall reaction is exothermic for both systems, the actual cleavage step is endothermic by 144 kJ mol(-1) for the (MoNbIII)-Nb-III complex whereas the (MoMoIII)-Mo-III system is exothermic by 94 kJ mol(-1). The reluctance of the (MoNbIII)-Nb-III system to undergo N-2 cleavage is attributed to its d(3)d(2) metal configuration which is one electron short of the d(3)d(3) configuration necessary to reductively cleave the dinitrogen bridge. This is confirmed by additional calculations on the related d(3)d(3) (MoNbII)-Nb-III and (NbNbII)-Nb-II systems for which the cleavage step is calculated to be substantially exothermic, accounting for why in the presence of the reductant KC8, the [Ar(tBu)N](3)Mo(mu-N-2)Nb[N(Pr-i)Ar](3) complex was observed to undergo spontaneous cleavage of the dinitrogen bridge. On the basis of these results, it can be concluded that the level of activation of the N-N bond does not necessarily correlate with the ease of cleavage of the dinitrogen bridge.

First author: Aldridge, S, Carbonyl analogues? Analysis of Fe-E (E = B, Al, Ga) bonding in cationic terminal diyl complexes by density functional theory, DALTON TRANSACTIONS, 43, 2649, (2004)
Abstract: A series of DFT calculations has been carried out with the aim of characterizing the metal-group 13 element interaction in the novel cationic borylene complex [(eta(5)-C5Me5)Fe(CO)(2)(BMes)](+) (1) and related species of the type [(eta(5)-C5R5) M(L)(2)(EX)](n+). In addition, comparisons have been made with charge neutral borylene complexes and with related group 14 based ligand systems (e.g. cationic metal carbonyls, carbenes and vinylidenes) for which models of bonding have previously been established. In this regard particular attention has been focused on the interpretation of (i) molecular orbital composition; (ii) bond dissociation energies (BDEs) and the ratio of ionic to covalent contributions (DeltaE(elstat)/DeltaE(orb)); and (iii) sigma and pi symmetry covalent contributions. The molecular orbital compositions for the prototype borylene complex 1 and for related cationic and neutral systems {e.g.[(eta(5)-C5H5)Fe(PMe3)(2)(BMes)](+) and [(eta(5)-C5H5)Mn(CO)(2)(BMes)]} are consistent with the presence of bonding interactions between metal and borylene fragments of both sigma and pi symmetry. Furthermore, on the basis of BDEs, DeltaE(orb) values and sigma/pi covalent ratios, the bonding in cationic terminal borylene complexes such as 1 appears to have as much right to be termed a M=E double bond as does that in archetypal Fischer carbene and related complexes such as [(eta(5)-C5R5)Fe(CO)(2)(CCMe2)](+) and [(eta(5)-C5R5)Fe(CO)(2)(CH2)](+).

First author: Poleshchuk, OK, DFT study of HFI in halogen-containing gold, silver and copper complexes, HYPERFINE INTERACTIONS, 159, 293, (2004)
Abstract: We have analyzed the nuclear quadrupole coupling constants in copper, silver and gold halides and related compounds an the basis of the calculations with use of pseudo-potentials. The geometrical parameters and NQR halogen quadrupole constants obtained by these calculations substantially corresponded to the data of microwave spectroscopy in the gas phase. The analysis of the quality of the calculations with use of pseudo-potentials and the expanded basis set for the copper compounds was carried out. The ZORA model is shown to be a viable alternative to the computationally demanding B3LYP/SDD model for the calculation of halogen coupling constants in molecules. Besides the ZORA model as against BXYP/SDD model have been caused to realistic values of gold nuclear quadrupole coupling constants. In this case of the gold compounds the main contribution of the chemical Mossbauer shift comes from the 6s-orbiral population of the gold atoms.

First author: Heinrich, F, Are LCAO-MO models useful estimators for electric field gradients in simple molecules?,HYPERFINE INTERACTIONS, 158, 71, (2004)
Abstract: In this tutorial paper we compare the ab-initio calculations of electronic charge densities and related electric field gradients in simple molecules like H-2 as well as the triangular H-3 with variable bond distance and bond angle using the Amsterdam Density Functional (ADF) code With calculations based on a simple linear combination or hydrogen 1s-orbitals. In order to gain more insight into ADF- or other ab-initio-calculations it is rather useful to vary structural parameters. In addition to geometry optimisations we propose to vary bond distances and bond angles over extended ranges in order to arrive at a better interpretation of the results.

First author: Heinrich, F, The electric field gradient of Ag-111 in macrocyclic crown thioethers, HYPERFINE INTERACTIONS, 158, 79, (2004)
Abstract: Time differential perturbed angular correlation experiments and ab-initio density functional theory calculation were used to determine the electric field gradients of the metal centres of the macrocyclic crown thioethers Ag(15S5)[BF4], Ag(18S6-CH2OH)[CF3SO3], Ag(18S6)(+), Ag(19S6-OH)[Tosylat] and Ag(20S6-OH)[CF3SO3]. The density functional theory calculations have been performed with the Amsterdam Density Functional code ADF A “fingerprint systern” is introduced, which allows to assign electric field gradients to certain Ag coordinations in these crown thioether complexes.

First author: Seda, J, Estimation of electron spectra transitions of free-based porphin and Mg-porphin using various quantum chemical approaches, INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES, 5, 196, (2004)
Abstract: For optimized molecules of free-base porphin and magnesium- porphin (at HartreeFock level and 6-31G* basis set) excitation spectra were determined using several ab initio methods: CIS, RPA, CASSCF, and TDDFT. Obtained values were compared with semiempirical ZINDO method, other calculations found recently in literature and experimental data. It was demonstrated that for qualitatively correct spectra description the AO basis must include both the polarization and diffuse functions. The later play an important role in formation of Rydberg MOs. Estimated energies of the spectra transitions using the CIS method remain relatively far from the measured values. RPA method can be already considered as a quantitatively accurate method when sufficiently large basis set is used. For CASSCF approach, it was shown that even the lowest energy transitions are insufficiently described in CAS formalism and much larger active space or inclusion of more inactive orbitals in correlation treatment would be necessary for obtaining sufficient accuracy. It can be stated that without sufficiently large correlation contributions, the determined spectra are not able to reach quantitative agreement with experimental data. From the methods treated in this study, only TDDFT can be considered as a useful tool for spectra prediction, at least for calculations of lower excited states. It is relatively fast and feasible for calculation of middle-size molecules. ZINDO approximation is also relatively successful for such large systems. Acceptable predictions of experimentally observed energy transitions in the range of Q and B bands were obtained. Until higher (UV) part of spectra is examined where the excitations to Rydberg orbital will happen, it can be considered as a good candidate for electron spectra calculations.

First author: Den Auwer, C, Theoretical chemical contribution to the simulation of the L-III X-ray absorption edges of uranyl, neptunyl and osmyl hydrates and hydroxides, NEW JOURNAL OF CHEMISTRY, 28, 929, (2004)
Abstract: XANES spectroscopy has long been used as a structural and electronic probe of a selected element. Phenomenological application of this technique to actinide cations has proved fruitful to characterize the actinide environment in both solid state and solution compounds. Although powerful XANES simulation codes have been developed, the use of such simulations in order to describe the valence orbitals of the actinide cation is still scarce. The very short life time of the core hole at the L-III edge as well as the low symmetry and large size of the coordination polyhedron are difficulties to be overcome in the analysis of the edge spectra. In this work, three simple molecules have been selected for their similar geometry that is typical of the trans dioxo actinyl compounds: [UO2(H2O)(5)](2+), [NpO2(H2O)(5)](2+), [NpO2(OH)(4)](2+). Additional comparison with a transition metal, the osmyl cation [OsO2(OH)(4)](2+), is also made. The cation L-III edges have been recorded and compared to edge calculations using FEFF8.2 code. This article is structured in two parts. In the first one, elaboration and optimization of a valid structural model cluster is carried out using molecular dynamics calculations. The influence of the water solvent molecules as well as the hydrogen atoms of the cations’ first coordination sphere are discussed. In the second part, Amsterdam quantum chemical calculations have been carried out on the four clusters and molecular energy levels are qualitatively compared to the data obtained from calculated XANES spectra.

First author: Lein, M, Christian Klixbull Jorgensen and the nature of the chemical bond in HArF, OPTICAL SPECTRA AND CHEMICAL BONDING IN INORGANIC COMPOUNDS, VOL 1, 106, 181, (2004)
Abstract: The chemical bond in HArF is investigated with the help of the topological analysis of the electron density distribution and with an energy partitioning analysis. The results give quantitative insight into the nature of the interatomic interactions. The H-ArF bond is mainly covalent while the most important contributions to the argon-fluorine bond come from the electrostatic attraction between HAr(+) and P. The strong interatomic attractions in HArF arise from the concerted hydrogen-argon and argon-fluorine interactions. It is the concert of the two forces which leads to chemically bonded argon. The diatomic species ArH and ArF are only weakly bonded van der Waals complexes.

First author: Anthon, C, Elucidation of ligand-field theory. Reformulation and revival by density functional theory, OPTICAL SPECTRA AND CHEMICAL BONDING IN TRANSITION METAL COMPLEXES, 107, 207, (2004)
Abstract: Constrained by the use of an “average-of-configuration” computation, Kohn-Sham-DFT allows identification of the complete set of d(q) states of the ligand field plus repulsion model, LFR. A one-to-one correspondence is assumed between states defined by integer occupation numbers of real KS spin orbitals and single-determinant ligand-field states of a hierarchic cubic-tetragonal-orthorhombic strong-field approximation. The energies of these LFR states are parameterized by using mutually orthogonal parametrical operators. This orthogonality secures optimal meaningfulness of the parameters. The DFT state energies are taken as computed “data”. For d(2), each parameter is defined by a 45-dimensional coefficient vector, which is orthogonal to that of all the other parameters. By forming the scalar products of the coefficient vectors and the “data” vector, the values of the parameters are determined. identically the same parameter values may be obtained by performing the “data” reduction using a linear least squares procedure. The Amsterdam Density Functional program package (ADF) is constrained and then its shortcomings in reproducing the LFR models is quantified. Small “random errors” and “spatial errors” are identified and eliminated. Thereafter, the KS-DFT model for atomic ions is equivalent to the five-parameter Parametrical Multiplet Term model, PMT. This model is finally contracted to the three-parameter Slater-Condon-Shortley model, SCS. This “data” reduction has substantial errors. The computed sum square splitting, SSSADF, which for systems with two electrons in the partially filled shell is the sum of the squares of the 45 barycentered ADF energies, was taken as a measure of the integrated information contents of the 44 independent computed energy differences. Then, for atomic ions, by discarding 0.05% of unsystematic information a 1:1 relationship between the constrained ADF model and the PMT model was obtained. By discarding another 2% of systematic information, a 1: 1 relationship with the SCS model resulted. The SCS model is parameterized in terms of Jorgensen’s spin-pairing energy parameter D and the Racah parameter B. Even though KS-DFT does not lend itself to the direct determination of non-diagonal elements, the present parameterization procedure allows the full dq spaces to be explored.Experimental and computed parameter values have been compared satisfactorily for all the atomic d(2) and d(8) systems for which all J levels have been observed. Moreover, (VX4-)-X-III and (CrX4)-X-IV (X=F, Cl, Br, I) have served as molecular illustrations of the method. The spectrochemical and the nephelauxetic series of ligands as well as the large gap between P and the other halide ions are borne out by our computations and for VX4- (X=Cl and Br) the computed parameter values compare well with published semi-empirical ligand-field data. The philosophy of the cellular ligand-field model is contradicted and that of the angular overlap model supported by the computational result that the covalency of the central ion d orbitals is of dominant importance in the analysis of the frontier orbitals. The spectrochemical parameter A may be obtained as the appropriate KS-DFT orbital energy difference as well as from the combined KS-DFT/LFR model. The nephelauxetic ratio beta may analogously be obtained in two almost independent ways, whose only common feature is the “average-of-configuration” computation. In this computation the ten spin-orbitals of the partially filled shell are equally populated, a constraint forming the basis of this whole comparative study.

First author: Autschbach, J, Properties of WAu12, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 6, 11, (2004)
Abstract: The icosahedral cluster-compound WAu12 was recently predicted by Pyykko and Runeberg and experimentally prepared in the gas phase by the group of Lai-Sheng Wang. The photoelectron spectra and electron affinity were reported; the other physical properties remain unknown. Anticipating further experimental studies on it, we report here predicted vibrational spectra, NMR chemical shifts, spin-spin coupling constants and quadrupole coupling constants as well as optical spectra at the level of single and double excitations. The population analysis is non-trivial. By direct numerical integration, a charge of roughly +1 is obtained for the central tungsten atom. The charge distribution is strongly delocalised but bonding regions are clearly seen. A considerable electric field gradient exists at the gold nuclei. Although the radial bonds are strong, the system is quite elastic. The DFT activation energy for rotating one hemisphere against the other one, at a D-5h transition state, is only about 20 kJ mol(-1). The corresponding h(u) vibrational frequency is predicted to be slightly below 30 cm(-1).

First author: Petrie, S, Theoretical analysis of the [Mn-2(mu-oxo)(2)(mu-carboxylato)(2)](+) core, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 6, 4871, (2004)
Abstract: The first example of a dinuclear manganese complex containing two oxo and two carboxylate bridges, [Mn-2 (mu-O)(2)(mu-O2CArTol)(2)(bpy)(2)](+) (where bpy = 2,2′-bipyridine, and (ArCO2-)-C-Tol = 2,6-di(p-tolyl)benzoate), was reported recently (J. Ani. Chem. Soc. 2003, 125, 13010). X-ray crystallographic analysis performed on this complex reveals a trapped mix-valence species as evidenced, for example, by very different metal-ligand bond distances at the Mn-III and Mn-IV centers. The fact that there are rather bulky bridging carboxylate ligands present in this recently reported dinuclear species raises the question as to whether they affect the extent of valence trapping and the metrical parameters in general. Specifically, it was thought that intramolecular nonbonded contacts could play an important role. In the work reported here, density functional theory calculations were used to address this issue. Structural parameters obtained from calculations on a model compound bearing sterically small bridging carboxylates, [Mn-2(mu-O)(2)(mu-O2CH)(2)(bpy)(2)](+), are in good agreement with the experimentally determined single crystal X-ray structure. Thus, the sterically large carboxylate bridges in [Mn-2(mu-O)(2)(mu-O2CArTol)(2)(bpy)(2)](+) appear not to have a significant effect on the metal-ligand bond distances and angles. There is calculated to be minimal Mn…Mn bonding despite contraction of the Mn…Mn distance relative to related complexes. In addition to calculations on the mixed-valence (MnMnIV)-Mn-III complex, various electronic configurations of the corresponding (MnMnIII)-Mn-III and (MnMnIV)-Mn-IV complexes are explored. Although our calculations support assignment of [Mn-2(mu-O)(2)(mu-O2CH)(2)(bpy)(2)](+) as a valence-trapped (MnMnIV)-Mn-III configuration involving high-spin Mn-III, a delocalized configuration arising from low-spin Mn-III is calculated to lie very close in energy. The energetic proximity of the delocalized configuration is attributed to an effective crossed-exchange mechanism, which permits mixing of an e(g)-based orbital (nominally on high-spin Mn-III) with a vacant t(2g)-based orbital (nominally on Mn-IV).

First author: Deeth, RJ, Computational bioinorganic chemistry, PRINCIPLES AND APPLICATIONS OF DENSITY IN INORGANIC CHEMISTRY II, 113, 37, (2004)
Abstract: Selected examples of density functional theory applied to modelling the active site structures and mechanisms of metalloenzymes are discussed. Factors influencing the design of suitable structural models and the theoretical strategies for computing their structures, energies and properties are presented before describing the calculations on a number of redox-active enzymes containing one or more of Cu, Co, Ni, Fe and Mo.

First author: Yatsenko, AV, Static influence of ligands: Comparison of DFT calculations with experimental data, RUSSIAN JOURNAL OF COORDINATION CHEMISTRY, 30, 1, (2004)
Abstract: The possibility of reproducing regularities of static mutual influence of ligands in of Period V and VI elements of the Periodic Table (Pd, Sn, Sb, Pt, Pb) using the density functional theory (DFT) L calculations is studied. Relativistic effects are taken into account by means of the Dirac equation approximation (zero-order regular approximation, ZORA). The calculations reproduced trans-influence in Pt complexes and trans-shortening and cis-elongation in the nontransition metal complexes. At the same time, Pb chloride complexes and Sn iodide complexes exhibit substantial differences between experimental and calculation bond lengths. When solvation was accounted for by COSMO method, DFT calculations reproduce the relative stability of the cis- and trans-Pt(NH3)(2)X-2 Complexes (X is halogen) and of the sulfur-containing Ni and Pd chelate complexes. The calculated geometry of the cis-Pt(NH3)(2)X-2 molecule noticeably differs from the experimental geometry due to the overestimated strength of intramolecular N-H…X hydrogen bonds.