Synthesis, characterization and magnetic properties of dinuclear complexes of manganese(III) and manganese(II) with oxo and benzoate derivatives as bridging ligands

Abstract

Four new dinuclear Mn III complexes were synthesized: [{Mn(bipy)(H 2O)} 2(μ-O)(μ-2-ClC 6H 4COO) 2](NO 3) 2 ( 1), [{Mn(bipy)(H 2O)} 2(μ-O)(μ-3-ClC 6H 4COO) 2](NO 3) 2 ( 2), [{Mn(bipy)(H 2O)} 2(μ-O)(μ-4-ClC 6H 4COO) 2](NO 3) 2 ( 3) and [{Mn(bipy)(H 2O)} 2(μ-O)(μ-2-ClC 6H 4COO) 2](ClO 4) 2 ( 4), where bipy is 2,2′-bipyridyl and 2-, 3- and 4-ClC 6H 4COO are 2-, 3- and 4-chlorobenzoate. Magnetic susceptibility measurements were carried out on this series of complexes and the data were interpreted using the Heisenberg Hamiltonian − J 12 S 1 S 2 and led to small ferromagnetic coupling for 1 and 2 and small antiferromagnetic coupling for 3 and 4, respectively. By reaction of a solution of these complexes with H 2O 2 in the presence of ClO 4 − anion, three new dinuclear Mn II complexes, [{Mn(bipy) 2} 2(μ-2-ClC 6H 4COO) 2](ClO 4) 2 ( 5), [{Mn(bipy) 2} 2(μ-3-ClC 6H 4COO) 2](ClO 4) 2 ( 6) and [{Mn(bipy) 2} 2(μ-4-ClC 6H 4COO) 2](ClO 4) 2 ( 7), were obtained. Magnetic susceptibility data were interpreted with the same Hamiltonian, but for Mn II ions instead of Mn III. The experimental data indicate small antiferromagnetic coupling in all three coplexes. EPR spectra in powder samples and in frozen solutions agree with the formulae proposed.