Synthesis,spectroscopic characterization and redox properties of titanium and vanadium substituted Keggin-type heteropolyanions

The Ti-substituted heteropolytungstates K7TiIVW11–BO40] and K6VVTiIVW10PO40] have been synthesized and characterized by elemental analyses and spectroscopic techniques. Their redox properties have been studied by cyclic voltammetry, and the compounds were found to be more difficult to reduce than the unsubstituted heteropolyanion. The one- and two-electron reduced heteropoly blues of VVTiIVW10PO40]6–, namely VIVTiIVW10PO40]7– and VIVTiIIIW10PO40]8–, have also been prepared by chemical methods. Their optical spectra show low-energy intervalence charge-transfer bands as well as the expected d–d transitions. The optical and e.s.r. investigations indicate that VIV and TiIII are not vicinal in VIVTiIIIW10PO40]8–.