Tungsten NMR spin-spin couplings in polyoxometalates

Polyoxometalates (POM) are a class of clusters based on MO₆ octahedra where M is tungsten or molybdenum, often containing a further heteroatom at the center. POMs are finding extensive application in materials chemistry, catalysis and pharmacology, and their complex structure is probed by means of NMR spectroscopy of the W-183 nucleus. Empirical criteria are often employed to interpret experimental spectra, but computational chemistry is now capable to predict the NMR spectrum of species as large as gamma-[SiW₁₀O₃₆]^8- (see Figure) with great accuracy ( Angew. Chem. Int. Ed. 2005, in press).

Prof. Bagno of the University of Padova in Italy comments "Through the unique capability of ADF (and associated CPL module) to compute the electronic structure of molecules containing heavy atoms in a relativistic DFT framework we have been able to address a puzzling issue - why is one vicinal coupling constant in gamma-[SiW₁₀O₃₆]^8- so small?