Synthesis, crystal structure and magnetic properties of new dinuclear Mn(III) compounds with 4-ClC6H4COO and 4-BrC6H4COO bridges

Four new dinuclear Mn(III) compounds have been synthesised: [{Mn(bpy)(H2O)}2(μ-4-ClC6H4COO)2(μ-O)}](ClO4)2 (1), [{Mn(EtOH)(phen)}2(μ-O)(μ-4-ClC6H4COO)2](ClO4)2 (2), [{Mn(bpy)(EtOH)}(μ-4-BrC6H4COO)2(μ-O){Mn(bpy)(ClO4)](ClO4) (3) and [{Mn(H2O)(phen)}2(μ-4-BrC6H4COO)2(μ-O)](ClO4)2 (4). The crystal structures of 2 and 3 are evidence for the tendency of the ethanol and the perchlorate to act as ligands. Due to the coordination of these groups, the environment of the manganese ions is elongated in the monodentate ligand direction, and this distortion is more important when this ligand is the perchlorate. The magnetic properties of the four compounds have been analysed: compounds 1, 3 and 4 show antiferromagnetic behaviour, with J = −6.33 cm−1 for 1, J = −6.76 cm−1 for 3 and J = −3.08 cm−1 for 4 (H = −JS1·S2), while compound 2 shows a very weak ferromagnetic coupling. For this compound, at low temperature the most important effect on the χMT data is the zero-field splitting of the ion, and the best fit was obtained with |DMn| = 2.38 cm−1 and |EMn| = 0.22 cm−1.