A ferromagnetic interaction between Cu2+ centers through a [CrO4](2-) bridge: Crystal structures and magnetic properties of [{Cu(acpa)}(2)(mu-MO(4))] (M=Cr,Mo) (Hacpa=N-(1-acetyl-2-propyridene)(2-pyridylmethyl)amine)

The reaction of [Cu(acpa)](+) with [MO(4)](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(II) complexes with metalate bridges, [{Cu(acpa)}(2)(mu-CrO4)]. 4CH(3)OH . 4H(2)O (1) and [{Cu(acpa)}(2)(mu-MoO4)]. 4H(2)O (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(II) ions are bridged by the [MO(4)](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 [MO(4)](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(II) 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. Crystal data: 1, monoclinic, space group P2(1)/m, a = 8.349(2) Angstrom, b = 17.616(3) Angstrom, c = 10.473 Angstrom, beta = 107.40(2)degrees, Z = 2; 2, monoclinic, space group P2(1)/m, a = 8.486(2) Angstrom, b = 18.043(3) Angstrom, c = 9.753(2) Angstrom, beta = 95.82(2)degrees, Z = 2.