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.