| Polyoxometalates are attractive for design of new materials, due to their diverse chemistry and favorable structural, and electronic properties. In this thesis, we examine a series of vanadium and lanthanide substituted polyoxotungstate solids prepared with different counter cations by 51V and 31P solid-state magic angle spinning NMR spectroscopy.;In one study, we have established 51V solid-state MAS NMR spectroscopy as a sensitive probe of the cationic environment and morphology in vanadium-substituted polyoxotungstates. For Lindqvist-type polyoxotungstates, the counter cations alone dictate the electronic environment of vanadium in the oxoanion. In contrast, for the Keggin family the counter cations have a milder effect on the quadrupolar interaction presumably due to the larger unit cells and longer vanadium-cation distances. The degree of vanadium substitution has a pronounced effect on the quadrupolar and chemicalshielding anisotropy interactions for both vanadium substituted Keggin- and Wells-Dawson-type polyoxotungstates.;In another study, we present the first results demonstrating the REAPDOR NMR technique for measurement of dipolar interaction and internuclear distances in a spin-1/2 - spin-7/2 nuclear pair. An accurate distance between 31P and 51V of mono-vanadium substituted polyoxotungstates (K4PVW11O40, alpha2-K7 P2VW17O61 and alpha1-K 7P2VW17O61) can be determined with REAPDOR NMR, while X-ray diffraction yields average P-W/V distances only, because of orientational disorder. The comparison of the two methods indicates that the distances by REAPDOR NMR are generally consistent with the average estimates by X-ray diffraction.;In a third study, we have investigated a series of paramagnetic Eu(III) and lanthanide(III) substituted polyoxotungstates prepared as salts of different counter cations, as well as the corresponding diamagnetic vanadium-substituted compounds by 31P magic angle spinning solid state NMR spectroscopy. We have demonstrated that the electron-nuclear dipolar interaction and the spin-lattice relaxation times in these compounds are very sensitive to the effective magnetic moments and the local geometry of the paramagnetic centers. Subtle variations in the crystal packing of these solids give rise to pronounced differences in the spectroscopic observables. The spinning sideband patterns, calculated from the X-ray crystallographic coordinates using a thermally averaged magnetic moment and a point dipole approximation, agree with the experimental spectra to within 10-15%. Overall, the results suggest that 31P magic angle spinning NMR spectroscopy is a quick and sensitive probe of local geometry in paramagnetic Keggin polyoxometalates and may be particularly useful in the absence of long-range order. |
