Electrochemistry of binary and mixed-ligand copper(II) complexes with pyrazine and dicyanamide bridging ligands in aqueous medium

Abstract

The binary copper(II) complexes, viz., [Cu(II) (pyz)_n(H₂O)_n] (<b>1</b>), and [Cu(II)(dca)_n(H₂O)_n] (<b>2</b>), and, mixed ligand complex, [Cu(II) (dca)_n(pyz)_n]. nH₂O (<b>3</b>), containing pyrazine (pyz) and dicyanamide (dca) bridging ligands (where n is number of ligand attached and it could be 1 to 6 ) are formed in aqueous medium. The electrochemical behavior of binary complexes in 1:1, 1:2 and 1:10 (Cu : pyz/dca) molar ratios and mixed ligand complex in 1: 1 :1 and 1:2:1 (Cu:dca:pyz) molar ratios have been carried out by cyclic voltammetry. The binary complex <b>1</b> undergoes a quasi-reversible single-electron redox process (Cu^2+/+), while the binary complex<b> 2</b> exhibits a totally irreversible reduction peak involving two electrons corresponding to Cu^2+/0 change. The reduction potential becomes positive with increasing concentration of pyz/or dca, clearly indicating that reduction becomes easier with increasing concentration of ligand in binary complexes. The mixed ligand complex <b>3</b> involving pyz and dca bridging ligands shows an irreversible reduction peak assigned to Cu^2+/0 electrode reactions. The UV-vis spectral properties of all the binary and mixed ligand complexes have been studied in aqueous medium.