Redox chemistry of copper complexes of 6,7-dicyanodipyridoquinoxaline: A pulse radiolysis study

A series of copper (II) complexes having the general formula Cu(phen)n(dicnq)2−nCl2 (n = 0,1,2) (1,10-phenanthroline (phen) and/or 6,7-dicyanodipyridoquinoxaline (dicnq) were synthesized and characterized by optical, elemental analysis and IR. The reactions of oxidizing (OH) and reducing ( e aq - ) radicals with these complexes were studied by pulse radiolysis. Their absorption spectra have bands in the UV region (⩽350 nm) consisting of an intense π → π∗ transition due to the ligands (ε ∼ 105 dm3 mol−1 cm−1) and weak MLCT (dπ → π∗) band in the visible region and are non-luminescent. The OH radical reacts with all complexes at diffusion controlled rates and reacts by addition to the ligands and in the case OH adduct of Cu(dicnq)2Cl2, an intramolecular charge transfer followed deprotonation resulting in Cu(I) complex was noticed. The rates of reaction of e aq - with Cu(II) complexes are high (k ≈ 1010 dm3 mol−1 s−1) and the transient spectra show absorption maximum at 440 nm indicating reduction of Cu(II) to Cu(I).