EPR study of the magnetic states of a mixed-valence VIV4VV2 alkoxypolyoxovanadium cluster

Abstract

The EPR studies of the hexanuclear vanadium cluster in a [VIV4VV2O7(OCH3)12] single crystal are reported. The spectrum of the mixed valence clusters consists of a single lorentzian line and additional signals in the magnetic field range ∼240–440 mT and is observed in the 4.2–300 K temperature range. At about 190 K, on cooling, an abrupt change of the spectrum due to the structural phase transition, followed by a strong hysteresis, is discovered. Temperature dependence of the EPR spectra indicates an electron transfer between VIV and VV. Obtained results are discussed in the framework of the Heisenberg–Anderson–Zener Hamiltonian approach. The possibilities of other approaches is also considered.