Synthesis, spectral, electrochemical and magnetic properties of new phenoxo-bridged dicopper(II) complexes derived from unsymmetrical binucleating ligands with imino and amino side arms

Abstract

New unsymmetrical binuclear copper(II) complexes of the general formula [Cu 2L(X)]ClO 4, (X=OH, OAc) have been prepared by in situ complexation of the compound 3-[ N-methyl- N-(2-hydroxy-3,5-dichlorobenzyl)aminomethyl]-5-bromosalicylaldehyde ( mhdab) with various primary amines, copper(II) perchlorate and appropriate sodium salt. Positive ion FAB mass spectral studies of the complexes show the presence of a dicopper core in the complexes. Electronic spectra of the complexes show a broad band for the d–d transition in the region around 635–685 nm. A cyclic voltammetric study of the complexes shows two quasi-reversible reduction waves in the range E 1 pc=−0.52 to −0.86 V and E 2 pc=−1.02 to −1.16 V, and the reduction potentials are sensitive towards the chemical environment around the copper atoms. Cryomagnetic investigation of the complexes shows a moderately strong antiferromagnetic spin exchange interaction between the two copper(II) ions (−2 J 60–170 cm −1). ESR spectra of the complexes show a broad band at room temperature. The electrochemical and magnetic properties of the complexes are compared on the basis of the rigidity and conjugation of the ligands H 2L 1, H 2L 2 and H 2L 3.