US EPA

7749011 

Journal Article 

Electron transfer kinetics of cobaloxime complexes 

Wang, KF; Jordan, RB 

1996 

Yes 

Canadian Journal of Chemistry
ISSN: 0008-4042
EISSN: 1480-3291 

National Research Council of Canada 

OTTAWA 

74 

5 

658-665 

English 

10.1139/v96-071 

WOS:A1996UP79100005 

The rates of oxidation of CoII(dmgBF2)2(OH2)2 by CoIII(NH3)5X2+ (X = Br-, Cl-, and N3-) have been studied at 25°C in 0.10 M LiClO4. The rate constants are 50 ± 9, 2.6 ± 0.2, and 5.9 ± 1.0 M-1 s-1 for X = Br-, Cl-, and N3-, respectively, in 0.01 M acetate buffer at pH 4.7. The relative rates are consistent with the inner-sphere bridging mechanism established earlier by Adin and Espenson for the analogous reactions of CoII(dmgH)2(OH2)2. The rate constants with CoII(dmgBF2)2(OH2)2 typically are ∼103 times smaller and this is attributed largely to the smaller driving force for the CoII(dmgBF2)2(OH2)2 complex. The outersphere oxidations of cobalt(II) sepulchrate by CoIII(dmgH)2(OH2)2+ (pH 4.76-7.35, acetate, MES, and PIPES buffers) and CoIII(dmgBF2)2(OH2)2 + (pH 3.3-7.42, chloroacetate, acetate, MES, and PIPES buffers) have been studied. The pH dependence gives the following rate constants (M-1 s-1) for the species indicated: (1.55 ± 0.09) × 105 (CoIII(dmgBF2)2(OH2) 2+); (5.5 ± 0.3) × 103 (CoIII(dmgH)2(OH2)2+); (3.1 ± 0.5) × 102 (CoIII(dmgH)2(OH2)(OH)); (2.5 ± 0.3) × 102 (CoIII(dmgBF2)2(OH2)(OH)). The known reduction potentials for cobalt(III) sepulchrate and the diaqua complexes, and the self-exchange rate for cobalt(II/III) sepulchrate, are used to estimate the self-exchange rate constants for the dioximate complexes. Comparisons to other reactions with cobalt sepulchrate indicates best estimates of the self-exchange rate constants are ∼2.4 × 10-2M-1 s-1 for CoII/III(dmgH)2(OH2)2 and ∼5.7 × 10-3 M-1 s-1 for CoII/III(dmgBF2)2(OH2)2. 

electron transfer; cobaloxime; inner sphere; outer sphere; self-exchange