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

The Ti-substituted heteropolytungstates K-7[(TiW11BO40)-W-IV] and K-6[(VTiW10PO40)-Ti-V-W-IV] 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 [(VTiW10PO40)-Ti-V-W-IV](6-), namely [(VTiW10PO40)-Ti-IV-W-IV](7-) and [(VTiW10PO40)-Ti-IV-W-III](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 V-IV and Ti-III are not vicinal in [(VTiW10PO40)-Ti-IV-W-III](8-).