Kinetics and Mechanism of the Reductions of Oxalatotetraamminecobalt(III) by Iron(II), Vanadium(H), and Chromium(II)

The reduction of oxalatotetraamminecobalt(III) by iron(II), vanadium(II), or chromium(11) obeys the rate law -d In [Co(NH3)(4)CO4+] = k (M2+] M2+ where V2+ = Fe2+, V2+, or Cr2+. At [ClO4-] = 1.0 M and 25 degrees, k = (4.12 0.10) X 10(-4), 45.5 1.5, and (2 1) X 10' M-1 sec(-1) for iron, vanadium, and chromium, respectively. For the iron(II) reduction, Delta H +/- = 18.5 0.2 kcal mol(-1), and Delta S* = 12.1 +/- 0.8 eu. For the vanadium(II) reduction, Delta H+ = 12.3 +/- 0.5 kcal mol(-1) and AS* = 9.8 1.6 eu. Various mechanistic details of these and related reactions are discussed.