Mixed-valence fluoropolytungstates

Abstract

Electrochemical reduction of fluoropolytungstates leads to a new series of mixed-valence compounds. Valence trapping and electron delocalization have been studied by optical spectroscopy and e.s.r. in the temperature range 4–300 K. This shows that at low temperature the unpaired electrons are trapped on a single tungsten site. Electron delocalization occurs above 50 K. A detailed analysis of the e.s.r. linewidth dependence with temperature leads to thermal activation energies of 0.03–0.04 eV. The transfer integral J was estimated from e.s.r. and optical spectroscopy leading to J= 0.4 eV, which shows that the reduced fluoropolytungstates belong to the class II according to the usual classification of mixed-valence compounds.