84647-93-8Relevant articles and documents
Bis(2-(phenylazo)pyridine)copper(I) and -copper(II): Ligand π acidity and high formal potential of the copper(II)-copper(I) couple
Datta, Dipankar,Chakravorty, Animesh
, p. 1085 - 1090 (2008/10/08)
2-(Phenylazo)pyridine (L) yields cationic bisligand complexes with both copper(II) and copper(I). These are isolated as the perchlorates [CuL2] (ClO4)2 and [CuL2]ClO4. Grossly planar and tetrahedral structures are assigned to CuL22+ and CuL2+, respectively. The N=N stretch in CuL2+ shows a large shift to lower frequency (1375 cm-1) from the free-ligand value due to d(Cu)-π*(L) back-bonding. This effect is much less pronounced in CuL22+. The copper(I) complex shows two allowed transitions in the visible region tentatively assigned to t2 → π* (700 nm) and e → π* (560 nm) charge transfer. A broad ligand field band occurs in CuL22+ at 606 nm in MeCN. In the same solvent CuL2+ undergoes solvolytic equilibria, resulting in a decrease in extinction coefficient of the 700-nm band with dilution. The equilibrium constants for the reactions CuL2+ ?K1 CuL+ + L CuL+ ?K2 Cu+ + L are (298 K) K1 = 0.83 × 10-3 M-1 and K2 = 1.00 × 10-3 M-1. In methanol the couple CuL22+-CuL2+ has a formal potential, E°298, of 0.630 V at 298 K (voltammetry at platinum). The high potential is brought about by the strong d(Cu)-π*(L) bonding. Electrochemical studies in acetonitrile show that the solvolytic equilibria noted above are coupled with the electron-transfer step. The results can be rationalized by considering the observed response to be a weighted average of those due to the couples CuL22+-CuL2+ (E°298 = 0.735 V), CuL2+-CuL+, L (0.533 V), and CuL22+-Cu+, 2L (0.376 V).
