Kinetics and Mechanism of Electron Exchange between Chromium(II) and Some Chromium(III)-Oxalate Complexes

Chromium(II) catalyzes the aquation of one oxalate group from Cr(C2O4)(3)(3-) and the trans-cis isomerization of Cr(H2O4)(2-)(H2O)(2)-. Both reactions obey the rate law - d[Cr(III)1 /dl m = k[Cr(II)][Cr(III)] for the chromium(11)-catalyzed path. The values of k in M-1 sec(-1) (enthalpies of activation follow in parentheses) at 250 and 1.2 M ionic strength are 0.129 (8.2) and 0.108 (11.9) for Cr(C2O4)(2)(8)- and trans-Cr(C2O4)2(H2O)2-, respectively. The results are discussed in terms of a chromium(II)-chromium(III) electron exchange utilizing two oxalate ligands as bridging groups. Evidence for such a mechanism is adduced from isotope tracer studies on the above reactions and the electron exchange between chromium(II) and cis-Cr(C2O4)(2)(H2O)(2)(-)