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

Abstract

Lanthanide complexes of three classes of polyoxoanions have been characterized by multinuclear ( 183 W and 31 P) NMR spectroscopy among other techniques. The tetrabutylammonium salt of the lacunary [α-2-P 2 W 17 O 61 ] 10- , prepared by metathesis of the potassium salt, was isomerically pure according to 183 W and 31 P NMR spectroscopy. The K 13 [Ln(SiW 11 O 39 ) 2 ] family of complexes show a six-line pattern in the 183 W NMR spectrum at 40 °C for the lanthanum derivative, consistent with a symmetrical structure (C 2h or C 2v symmetry), and eleven-line patterns for the ytterbium and lutetium analogues at 23 °C, suggesting a lower symmetry (C 2 ) for complexes of the heavier lanthanide ions. The same phenomenon was observed for the [α-2-Ln(P 2 W 17 O 61 ) 2 ] 17- family of compounds. High-temperature 183 W NMR experiments on the [Lu(SiW 11 O 39 ) 2 ] 13- and the [α-2-Lu(P 2 W 17 O 61 ) 2 ] 17- compounds showed a reversible broadening and coalescence of the resonances, due to a dynamic effect, possibly rotation of the oxoanion ligands.