Synthesis, crystal structures and density functional theory study of dimeric copper(II) complexes of a tridentate Schiff-base ligand

Oxalate- or 4,4′-bipyridine-bridged dimeric copper(II) complexes, [Cu2L2(μ-ox)] (1) and [Cu2L2(μ-bipy)](BF4)2 (2) [where ox = oxalate, bipy = 4,4′-bipyridine, HL = N-(1H-pyrrol-2-ylmethylene)-2-pyridineethanamine, L− = HL−H+], have been synthesised and characterised by elemental analysis, IR, UV–Vis and single crystal X-ray diffraction. Crystal structure determinations carried out on 1 and 2 reveal that 1 is an oxalate-bridged centrosymmetrical square pyramidal dimeric copper(II) complex while 2 is a 4,4′-bipyridine-bridged non-centrosymmetric square planar dinuclear copper(II) complex. Comparison of the optimised geometries with the corresponding crystal structures suggests that the B3LYP/LANL2DZ level can reproduce the structures of 1 and 2 on the whole. The electronic spectra of 1 and 2 predicted by B3LYP/LANL2DZ method show some blue shifts compared with their experimental data. Thermal analysis carried out on 1 shows that there is only one exothermal peak at about 260 °C and the residue is presumably Cu2O4N6.

Two dicopper(II) complexes, an oxalate-bridged centrosymmetrical square pyramidal one [Cu2L2(μ-ox)] (1) and a 4,4′-bipyridine-bridged non-centrosymmetric square planar one {[Cu2L2(μ-bipy)](BF4)2}·1.5CH3CN (2·1.5CH3CN), were obtained by reacting N-(1H-pyrrol-2-ylmethylene)-2-pyridineethanamine (HL) with copper(II) tetrafluoroborate and oxalate (ox) or 4,4′-bipyridine (bipy) bridging ligand. Density functional theory calculations were performed to investigate the structures and spectral properties of 1 and 2.Figure optionsDownload as PowerPoint slide