Keggin (K5, H3O)[SiV3W9O40H]·xH2O: Characterization and crystal structure

Abstract

Single crystals of the potassium salt (K5, H3O)[SiV3W9O40H]·xH2O of the vanadium tri-substituted α-Keggin dodecatungstosilicate were prepared and analyzed by vibrational, EPR and 51V NMR spectroscopy. Varying the synthesis conditions allows crystallization of partially reduced anions. The crystal structure was determined for both oxidized (V5+) and partially reduced (V4+/5+) potassium salts. Single crystal X-ray diffraction data and solid state 51V-NMR spectra confirm the occurrence of a single vanadium site in a cubic structure due to rotational disorder of the Keggin ion. Partially reduced compounds crystallize within the same structure as fully oxidized ones. EPR experiments confirm strong interaction of V4+ with two V5+ ions, in accordance with insertion of a V3 subunit into the lacunary Keggin ion as designed in the synthesis method. The 3D-edifice is composed of K+/H2O counter-sublattice with evidence of tunable water occupancy.