Dinuclear copper(II) complexes containing oxamate and blocking ligands : crystal structure, magnetic properties and DFT calculations.

Abstract

Three dinuclear copper(II) complexes containing oxamate-based ligands with the chemical formula [Cu(opba)Cu(dap)(H2O)]H2O (1), [Cu(opba)Cu(dap-OH)(H2O)]1.5H2O (2), and [Cu(opba)Cu(en)(H2O)]·4H2O (3) in which opba = o-phenylenebis(oxamato), dap = 1,3- diaminopropane, dap-OH = 2-hydroxy-1,3-diaminopropane and en = ethylenediamine have been synthesized and their crystal structures have been determined by single-crystal X-ray diffraction. The molecular structures of 1-3 consist of neutral dicopper(II) complexes obtained by the "complex as ligand" strategy, in which each [Cu(opba]2‒ fragment acts as a bidentate ligand towards the copper(II) ion bonded to the amine capping ligands (dap, dap OH and en) and the two other carbonyl groups are uncoordinated. Variable-temperature magnetic susceptibility measurements of 1-3 in the temperature range of 4-300 K reveal a strong antiferromagnetic coupling between the metal centers through the oxamate bridge with J = −183.5 cm−1 (1); J = −195.8cm−1 (2), and J = −195.6 cm−1 (3). The fit of the variable-temperature magnetic susceptibility data of 3 revealed that coupling CuIICuII···CuIICuII between the dinuclear entities is very weak. In all cases, the Hamiltonian used was H = −JS1·S2. DFT calculations based on the broken-symmetry formalism were used to provide further insight and an explanation for the reported behavior.