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

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 degrees C) = 1.4 x 10(3) kg mol(-1) s(-1) with Delta H* = 38.1 +/- 2.4 kJ mol(-1) and Delta S* = - 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 degrees than that of the Cu(bcp)(2)(+) complex, there was no significant difference between the structures of these 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. (C) 1998 Elsevier Science S.A. All rights reserved.