Mixed-valence complexes of vanadium with 1,10-phenanthroline and 2,2′-bipyridine

Abstract

The electronic structures of some intense purple vanadium complexes, initially formulated as [L₂V^III(OH)₂V^IIIL₂]⁴⁺[L = 1,10-phenanthroline(phen) or 2,2′-bipyridine(bipy)] have been investigated. The complexes were isolated as the sulphate or mixed hexafluorophosphate–chloride salts. Electronic spectra and magnetic and e.s.r. measurements show that the complexes are novel examples of binuclear mixed-valence species, containing vanadium in the oxidation states II and III bridged, probably, by a hydroxo-group. Characteristic visible bands of high intensity were observed at 16 000 and 19 000 cm^–1 and arise because of intervalence electron transfer. Vanadium 2p_3/2 and 3p binding energies, obtained from X-ray photoelectron spectra, are characteristic of oxidation states of III and below. Individual bands due to more than one oxidation state of vanadium could not be detected with certainty, though some broadening was observed.