Structural study and electron exchange kinetics of the bis (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline) copper(II)/(I) couple in acetonitrile

Abstract

Kinetic studies of the electron exchange reaction between Cu(bcp) 2 2+ and Cu(bcp) 2 ' were carried out in acetonitrile (bcp = 2.9-dimethyl-4,7-diphenyl-1,10-phenanthroline). The electron self-exchange rate constant was k ex (25°C = 1.4×10 3 kg mol −1 s −1 with ΔH ∗ = 38.1±2.4 kJ mol −1 and ΔS ∗ = −57±8 J mol −1 K −1 (ionic strength 0.1 mol kg −1 (tetraethylammonium tetrafluoroborate)). A small dependence of the rate constant on the ionic strength was observed. Electron spin resonance study of the Cu(II) species revealed that the Cu-N distances and the dihedral angles between the two NCuN planes in Cu(bcp) 2 2+ and Cu(dmp) 2 2+ complexes (dmp = 2.9-dimethyl-1.10-phenanthroline) are identical in solution. Although the comparison of the crystal structures suggests that the dihedral angle in the Cu(dmp) 2 ' complex is closer to 90° than that of the Cu(bcp) 2 + complex, there was no significant difference between the structures of those complex ions in solution. The electron self-exchange rate constants for the Cu(bcp) 2 2+/+ and the Cu(dmp) 2 2+/+ couples were similar to each other, despite the difference in radii of these ions.