KINETICS OF OXIDATION OF THIOSULFATE ION BY MIXED-VALENCE BIS(MU-OXO)DIMANGANESE COMPLEXES

摘要

The mixed-valence Mn-III,Mn-IV complexes, [Mn2O2(bipy)(4)](3+) (1) and [Mn2O2(phen)(4)](3+) (2) aquates rapidly but partially to [Mn2O2(bipy)(3)(H2O)(2)](3+) (1a) and [Mn2O2(phen)(3)(H2O)(2)](3+) (2a) in aqueous solutions containing excess bipy-Hbipy(+) (for 1) and phen-Hphen(+) (for 2) buffer in the range pH 4-5. In such media, the complexes suffer little auto-decomposition, core rearrangement and polynucleation, but are reduced by an extraneous reducing agent. For example, excess S2O32- reduces these complexes to Mn-II, and S4O62- is produced quantitatively. The aqua complexes 1a and 2a are kinetically more active than the corresponding parent complexes 1 and 2. Comparison with kinetic data for reactions of the complexes with NO2-, HSO3-, hydroquinone and ascorbic acid indicates a one-electron, outer-sphere rate determining step. Structural flexibility and ease of elongation of the metal-ligand bonds play important roles in controlling the kinetic lability. (C) 1997 Elsevier Science Ltd. [References: 70]