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, [Cu(2)L(2)(mu-ox)] ( 1) and [Cu(2)L(2)(mu-bipy)] (BF(4))(2) (2) [ where ox = oxalate, bipy = 4,4'-bipyridine, HL = N-(1H-pyrrol-2-ylmethylene)-2-pyridine-ethanamine, 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 degrees C and the residue is presumably Cu(2)O(4)N(6). (C) 2009 Elsevier B. V. All rights reserved.