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

Three dinuclear copper(ii) complexes containing oxamate-based ligands with the chemical formula [Cu(opba)Cu(dap)(H2O)]center dot H2O (1), [Cu(opba)Cu(dap-OH)(H2O)]center dot 1.5H(2)O (2), and [Cu(opba)Cu(en)(H2O)]center dot 4H(2)O (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 a 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 = -195.8 cm(-1) (2), and J = -195.6 cm(-1) (3). The fit of the variable-temperature magnetic susceptibility data of 3 revealed that (CuCuMIDLINE)-Cu-II-M-II HORIZONTAL (ELLIPSISCuCuII)-Cu-II coupling between the dinuclear entities is very weak. In all cases, the Hamiltonian used was H = -JS(1)center dot S-2. DFT calculations based on the broken-symmetry formalism were used to provide further insight and an explanation for the reported behavior.