[The synthesis and spectral study of multicomponent heteropoly compounds with Keggin structure. II]

The multicomponent heteropoly compounds [Me4N]4 + x[SiVxMoyW12 - x - yO40].n H2O with Keggin structure have been synthesized and characterized by FTIR. The vibrational frequencies of containing-oxygen bonds (Si-Oa,M=Od, M-Ob-M and M-Oc-M) in these heteropoly compounds have been studied. The vibrational frequencies nu as(M=Od) and nu as(M-Ob-M) are demonstrated to explain why the acidity of the heteropoly compounds becomes weaker and the oxidative ability becomes stronger when W atoms are substituted by V atoms. The rule of the change is similar with [PVxMoyW12 - x - yO40](3 + x)-. In addition, the acidity of P series is stronger than the acidity of the corresponding Si series.