Lanthanide complexes of polyoxometalates: Characterization by tungsten-183 and phosphorus-31 nuclear magnetic resonance spectroscopy

Lanthanide complexes of three classes of polyoxoanions have been characterized by multinuclear (W-183 and P-31) NMR spectroscopy among other techniques. The tetrabutylammonium salt of the lacunary [alpha-2-P2W17O61](10-), prepared by metathesis of the potassium salt, was isomerically pure according to W-183 and P-31 NMR spectroscopy. The K-13[Ln(SiW11O39)(2)] family of complexes show a six-line pattern in the W-183 NMR spectrum at 40 degrees C for the lanthanum derivative, consistent with a symmetrical structure (C-2h or C-2r symmetry), and eleven-line patterns for the ytterbium and lutetium analogues at 23 degrees C, suggesting a lower symmetry (C-2) for complexes of the heavier lanthanide ions. The same phenomenon was observed for the [alpha-2-Ln(P2W17O61)(2)](17-) family of compounds. High-temperature W-183 NMR experiments on the [Lu(SiW11O39)(2)](13-) and the [alpha-2-Lu(P2W17O61)(2)](17-) compounds showed a reversible broadening and coalescence of the resonances, due to a dynamic effect, possibly rotation of the oxoanion ligands.