US EPA

8537593 

Journal Article 

Cr2+ and V2+ reductions of the μ-amido-μ-formato-bis[tetra-ammine-cobalt(III)] and μ-amido-μ-acetato-bis[tetra-amminecobalt(III)] complexes 

Scott, KL; Sykes, AG 

1972 

1 

Journal of the Chemical Society. Dalton Transactions
ISSN: 1472-7773
EISSN: 1364-5447 

17 

1832-1837 

English 

10.1039/DT9720001832 

The first and only observable stage in the Cr2+ reduction of μ-amido-μ-formato-bis[tetra-amminecobalt(III)] perchlorate(I), in aqueous perchlorate media, obeys the rate law (i), where the Cr2+ reactant is present in large excess. -d ln [(CoIII)2]dt = kCr [Cr2+] + k1k2[Cr2+]/k-1 + k2[Cr2+] (i) With [Cr2+] > ca. 0.015M, so that k2[Cr2+] ≫ k-1, the right-hand side of (i) reduces to kcr[Cr2+] + k1. At 25 °C and μ = 1.0M (LiClO4), kcr = (1.68 ± 0.02) × 10-3 l mol-1 s-1 and k1 = (9.2 ± 0.8) × 10-6 s-1. For the μ-amido-μ-acetato-bis[tetra-amminecobalt(III)]complex, only the first term in (i) could be detected with certainty and at 25° and μ = 1.0M (LiClO4), kcr = (4.7 ± 0.5) × 10-4 l mol-1 s-1. Activation parameters have been obtained corresponding to kcr for both complexes and k1 for the μ-formato-complex (I). Reduction of the complexes with V2+ follows the rate law (ii). At 25° and μ = 1.0M (LiClO4), kv = (6.0 ± 0.3) × 10-2 l mol-1 s-1, for the -d ln [(CoIII)2]/dt = kv[V2+] (ii) μ-formato-complex (I) and (2.2 ± 0.1) × 10-2 l mol-1 s-1 for the μ-acetato-complex. The ratios kcr:kv are 0.028 and 0.021 respectively, suggesting that an outer-sphere mechanism is operative in each case. The effect of chloride ions on the Cr2+ reduction of the μ-formato-complex(I) has also been studied.