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

Two new Cu(II) complexes, [Cu(L1)2] (1) and [Cu(L2)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···Br hydrogen bonds and π···π stacking interactions between the metal chelate rings and aromatic rings. Substituent effects in the two complexes are discussed.