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

Abstract 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 )](ClO 4 ) ( 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 X-ray 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 [CuN 4 Cl 2 ] 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 π–π 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.