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 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 Cu^IICu^II⋯Cu^IICu^II coupling 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.