Influence of counter anions on structural, spectroscopic and electrochemical behaviours of copper(II) complexes of dipyrido[3,2-f: 2′,3′-h]-quinoxaline (dpq)

A set of three copper(II) complexes, [Cu(II)dpq)(2)Cl-2] (1), [{Cu-II(dpq)(2)(SCN)}{(Cu-II(dpq)(SCN)(3)}] (2) and [Cu-II(dpq)(2)(N-3)](ClO4) (3), derived from the ligand dipyrido[3,2-f: 2',3'-h]-quinoxaline (dpq) have been reported. The molecular and the crystal structures of all the complexes have been determined by Xray crystallography. The structural results confirm that depending on the selected anions, a great variety of geometries are observed with copper(II). The light blue compound 1 has a distorted octahedral geometry with a [CuN4Cl2) core. Compound 2 consists of a cationic part, {Cu-II(dpq)(2)(SCN)}(+), and an anionic part, [Cu-II(dpq)(SCN)(3)}(-). In both the cationic and anionic part, the geometry around the copper(II) ion is distorted square pyramidal. In compound 3, one azide anion is coordinated to the metal centre providing a distorted square pyramidal geometry. The quinoxaline ring in 1 and 2 is involved in intermolecular pi-pi interactions leading to the generation of a sinusoidal chain in 1 and a zigzag chain in 2. The electronic absorption spectra and the redox behaviour of all the complexes have been studied in dimethyl sulfoxide. (C) 2008 Elsevier Ltd. All rights reserved.