Synthesis, structural characterization and substituent effects of two copper(II) complexes with benzaldehyde ortho-oxime ligands

Two new Cu(II) complexes, [Cu(L-1)(2)] (1) and [Cu(L-2)(2)] (2) (HL1 = (E)-3-bromo-5-chloro-2-hydroxy benzaldehyde O-methyl oxime; HL2 = (E)-3-bromo-5-chloro-2-hydroxy benzaldehyde O-ethyl oxime), have been synthesized and characterized by physicochemical and spectroscopic methods. X-ray crystallographic analyses show that complexes 1 and 2 have similar structures, consisting of one Cu(II) atom and two L- units. In both complexes, the Cu(II) atom, lying on an inversion center, is four-coordinated in a trans-CuN2O2 square-planar geometry by two phenolate O and two oxime N atoms from two symmetry-related N,O-bidentate oxime ligands. Moreover, both complexes form an infinite three-dimensional supramolecular structure involving intermolecular C-H center dot center dot center dot Br hydrogen bonds and pi center dot center dot center dot pi stacking interactions between the metal chelate rings and aromatic rings. Substituent effects in the two complexes are discussed.