Spin-orbit coupling and d2-d2 interactions in dinuclear bioctahedral metal clusters

The electronic structure and the metal-metal d(2)-d(2) interactions in dinuclear bioctahedral face-shared cluster complexes [M2X9](3)- (M = V, Nb, Ta, and X = Cl, Br, I) have been studied with OFT and topological methods QTAIM and ELF. The ground states of the complexes are shown to be spin-paired and nonmagnetic only in the approximation of spin-orbit interaction. The result correlates well with experimental data on magnetic susceptibility for solid-state complexes containing [Nb2X9](3)- and [Ta2X9](3-) anions as well as for [V2X9](3-) anions in low-temperature spin-paired modifications of Cs3V2Cl9 and Rb3V2Br9 complexes. The transition to the high-temperature spin-paramagnetic state of [V2X9](3-) anions is shown to be related to the bifurcation of d(2)-d(2) interaction at some critical distance D-CR(M-M) and to weakening of spin-orbit coupling in divanadium complexes. (C) 2013 Elsevier Ltd. All rights reserved.