The effect of water-miscible organic solvents on the substitution reaction of Keggin-type heteropolysilicates and -germanates with vanadium(V) ion

The substitution reaction of Keggin-type polyoxometalates, [XM12O40]n− (X = Si, Ge, P, or As; M = Mo or W), with vanadium(V) ion was investigated with cyclic voltammetry, Raman spectroscopy, and 31P NMR. The effect of organic solvents, such as acetonitrile (ACN), tetrahydrofuran (THF), formamide (FA), N-methylformamide (NMF), and N-methylacetoamide (NMA) on their substitution reactions was examined. In aqueous and aqueous-FA, -NMF, and -NMA solutions, the molybdenum or tungsten unit in the Keggin-anions was substituted with vanadium(V) ion to form V(V)-substituted polyoxometalates, while no substitution reaction occurred in aqueous-ACN and -THF solutions. It is suggested that this results from the relationship between the total anion charge and the permittivity of organic solvents.

Graphical abstractThe substitution reaction of Keggin-type polyoxometalates, [XM12O40]n− (X = Si, Ge, P, or As; M = Mo or W), with vanadium(V) ion was investigated with cyclic voltammetry, Raman spectroscopy, and 31P NMR. The effect of organic solvents, such as acetonitrile, tetrahydrofuran, formamide, N-methylformamide, and N-methylacetoamide, on their substitution reactions was examined.Figure optionsDownload full-size imageDownload as PowerPoint slide