Synthesis, X-ray crystal structure, and electrochemistry of copper(II) complexes of a new tridentate unsymmetrical Schiff base ligand and its hydrolytically rearranged isomer

A new unsymmetrical Schiff base ligand HL1, HBacabza, and its copper(II) complexes [Cu2L12(OAc)2] (1) and [Cu2L22(N3)2]·2H2O (2) with HBacabza = 3-(2-aminobenzylimino)-1-phenylbutan-1-one as HL1 and its hydrolytically rearranged isomer 3-(2-aminomethylphenyleneimino)-1-phenylbutan-1-one as HL2, have been synthesized and characterized by elemental analyses and spectroscopic methods. The rearrangement of HL1 to HL2 occurs in a hydrolysis-recondensation process in the reaction of HL1 with Cu(ClO4)2·6H2O and NaN3. The crystal structures of the ligand and its complexes have been determined by single crystal X-ray diffraction. The deprotonated Bacabza− coordinates to the metal center as a tridentate ligand. The acetate anion coordinates through one oxygen atom in complex 1 leading to a mono-atomic acetate oxygen-bridging dimeric copper(II) complex. Similarly, the azide anion coordinates through one nitrogen atom in complex 2 leading to a mono-atomic azide nitrogen-bridging dimeric copper(II) complex. The copper(II) ions adopt a distorted square pyramidal (4 + 1) coordination in these two complexes. The cyclic voltammetric studies of these complexes in N,N-dimethylformamide indicate that the reduction process corresponding to CuII/CuI is electrochemically irreversible in complex 1, presumably due to the structural changes during the course of redox reaction, and quasi-reversible in complex 2.