Cs. Alexander et Rj. Balahura, PREPARATION, CHARACTERIZATION, AND CHROMIUM(II) REDUCTION OF AAMMINE(PHENANTHROLINE-2-CARBOXAMIDO-N)COBALT(III) PERCHLORATE, Inorganic chemistry, 33(7), 1994, pp. 1399-1405
The reduction of aammine(phenanthroline-2-carboxamido-N)cobalt(III) by
chromium(II) proceeds by formation of a binuclear intermediate follow
ed by intramolecular electron transfer. The observed rate constant can
be expressed as k(obs) = K(p)k(et)[Cr2+]/(1 + K(p)[Cr2+]), where K(p)
is the formation constant of the binuclear species and k(et) is the i
ntramolecular electron-transfer rate constant within the binuclear int
ermediate. At 25-degrees-C, I = 1.0 M (LiClO4), K(p) = 28 M-1, DELTAH-
degrees = 4.4 +/- 2 kcal mol-1, DELTAS-degrees = 22 +/-5 cal mol-1 deg
-1, k(et) = 140 s-1, DELTAH(double dagger) = 2.6 +/- 0.4 kcal mol-1, a
nd DELTAS(double dagger) = -40 +/- 6 cal mol-1 deg-1. Complete ligand
transfer is observed, and the initial chromium(III) product is a chela
te involving the carboxamido oxygen and one of the phenanthroline nitr
ogens. The subsequent reactions of this complex are also described.