Kinetics and mechanism of the base hydrolysis of thecis-chlorobis(ethylenediamme)(benzimidazole)cobalt(III) cation |
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| Authors: | Robert W. Hay Paul R. Norman |
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| Affiliation: | (1) Chemistry Department, University of Stirling, FK9 4LA Stirling, Scotland |
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| Abstract: | Summary The hydrolysis ofcis-[CoCl(en)2(bzmH)]2+ (en=ethylenediamine, bzmH=benzimidazole) has been studied over the pH range 8.31–11.58 at I=0.1 mol dm–3 and 25°. Potentiometric titration of aqueous solutions of the [Co(en)2(bzmH)OH2]3+ complex obtained by silver(I) catalysed aquation of the chloro-complex give pK1=5.81 and pK2 = 8.84 for Equilibria (1) and (2) at 25° and I=0.1 mol dm–3. Spectrophotometric titration of the hydroxy complex also gives a value of pK2=8.88 for the ionisation of the coordinated benzimidazole. The kinetic data can be interpreted in terms of base hydrolysis ofcis-[CoCl(en)2(bzmH)]2+ (kOH=220 dm3 mol–1s–1) andcis-[CoCl(en)2(bzm)]+ (kOH=14.9 dm3 mol–1s–1). Comparisons with the corresponding imidazole and pyridine complexes are made. |
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