Magnetic Interactions Between Copper(?) Centers Through [MO₄]²- (M = Cr(VI) and Mo(VI)) Bridges

Abstract

The reaction of [Cu(acpa)]⁺ with [MO₄]²- (Hacpa = N-(1-acetyl-2- propyridene)(2-pyridylmethyl)amine and M= Cr and Mo) in water-methanol or water-acetonitrile solution affords dinuclear copper(?) complexes with metalate bridges, [{Cu(acpa)}2(μ-CrO₄)].4CH₃OH. 4H₂O (1) and [{Cu(acpa)}₂(μ- MoO₄)].4H₂O (2), respectively. The crystal structures and the magnetic properties have been studied. Complexes 1 and 2 are isomorphous and the structures are made up of discrete dimers in which two copper(?) ions are bridged by the [MO₄]^2- anion. The coordination geometry about the copper(II) ions is square planar with a N₂O chelate group from acpa and an oxygen atom from [MO₄]^2-. Magnetic susceptibility measurements for 1 revealed that a ferromagnetic interaction between copper(II) ions is propagated through the [CrO₄]^2- bridge and the coupling constant (2J) was evaluated to be 14.6(1) cm⁻¹ (H = −2JS ₁.S ₂). In 2, two copper(?) ions bridged by [MoO₄]^2- anion are antiferromagnetically coupled with the 2J value of −5.1(4) cm⁻¹. The ferromagnetic interaction in 1 is explained by means of the orbital topology of frontier orbitals.