Copper(II) complexes of new tetradentate NSNO pyridylthioazophenol ligands: synthesis, spectral characterization and crystal structure

Abstract

Abstract Copper(II) complexes of a series of new tetradentate NSNO ligands were synthesized and characterized spectroscopically. The ligands were also characterized by elemental analyses, IR, 1H NMR, FAB-MS and UV–Vis spectroscopy. The solid-state structures of two complexes 2a and 4a were established by X-ray crystallography. The geometry about the copper ion of the complexes is dependent on the counter anion of the copper salt used. The five-coordinated copper ion is distorted square pyramidal when SCN− or Cl− ligate with the copper(II) ion, occupying the equatorial position, whereas the geometry about the four-coordinated copper ion is square planar when the counter anion is perchlorate. The electronic spectra of 2 and 3 in methanol show that the distortion of square pyramidal towards trigonal bipyramidal geometry about the copper ion of the complexes in solution is dependent on the presence of the electron withdrawing group. All the complexes exhibit a band for S(σ) → Cu(II) charge transfer (LMCT) in the range of 380–394 nm. The EPR spectra of complexes 2 and 3 are consistent with the fact that the unpaired electron is predominantly in the d x 2 - y 2 orbital as gII > gI. The redox behavior of all the complexes in methanol was studied by CV using TBAP as the supporting electrolyte.