Synthesis,Properties and Crystal Structures of Mononuclear Copper(II) Complexes with Bis(2-Pyridylmethyl)Amino Acids

Tetradentate Schiff-base carboxylate-containing ligands, bis(2-pyridylmethyl)amino-3-propionic acid (Hpmpa) and bis(2-pyridylmethyl)amino-4-butyric acid (Hpmba), react with CuCl₂ to give rise to the mononuclear complexes [Cu(Hpmpa)Cl]Cl · 2H₂O (1) and [Cu(Hpmba)Cl₂]· H₂O (2). These complexes have been characterized by X-ray crystallography, spectroscopic and cyclic voltammetry. Crystal structure of (1) shows that the copper(II) ion has a distorted square-pyramidal geometry with the three nitrogen atoms of the Hpmpa ligand and one chloride anion occupying the basal plane and an oxygen atom from the carboxylate group coordinating the axial position. In (2), the coordination environment around the copper(II) ion reveals a distorted square-pyramids with three nitrogen atoms of the Hpmba ligand and one chloride anion that comprise the basal plane, whereas the apical position is filled by the chloride anion. Cyclic voltammetry of the complexes gives two one-electron waves corresponding to Cu^II/Cu^III and Cu^III/Cu^I processes. The electronic spectra and redox potentials of the complexes are influenced significantly by the N-pendant carboxylate groups.