Issue 0, 1968

The kinetics of some outer-sphere reactions of europium(II) with cobalt(III) ammine complexes

Abstract

The kinetics of the reactions of europium(II) with hexa-amminecobalt(III), aquopenta-amminecobalt(III), and µ-amido-deca-amminedicobalt(III) have been studied in aqueous perchloric acid solutions of ionic strength µ 0·40M(using LiClO4) at 20–50°. All three reactions are independent of hydrogen-ion concentration over the range [H+]= 0·03 to 0·36M, which is consistent with the reactions proceeding by an outer-sphere mechanism. In each case the kinetics conform to a rate equation of the form: Rate =kobs[Eu2+][Complex]. At 25° rate constants and activation parameters are: kobs= 1·7 × 10–3 I. mole–1 sec.–1, ΔH= 8·8 ± 0·5 kcal. mole–1, and ΔS=–42 ± 1·6 e.u. for Co(NH3)63+; kobs= 7·4 × 10–2 I. mole–1 sec.–1, ΔH= 9·3 ± 0·5 kcal. mole–1, and ΔS=–32·5 ± 1·6 e.u. for Co(NH3)5(H2O)3+; and kobs= 5·8 × 10–2 I. mole–1 sec.–1, ΔH= 9·6 ± 0·5 kcal. mole–1, and ΔS=–32 ± 1·6 e.u. for (NH3)5Co·NH2·Co(NH3)55+.

The rate constant for the reaction of chromium(II) with (NH3)5Co·NH2·Co(NH3)55+ at 25° and µ 0·40M is 3·07 × 10–3 I. mole–1 sec.–1. Rate constants and activation parameters for the reactions of Eu2+, V2+, and Cr2+ with Co(NH3)63+, Co(NH3)5(H2O)3+, and (NH3)5Co·NH2·Co(NH3)55+ are compared.

Article information

Article type
Paper

J. Chem. Soc. A, 1968, 2836-2839

The kinetics of some outer-sphere reactions of europium(II) with cobalt(III) ammine complexes

J. Doyle and A. G. Sykes, J. Chem. Soc. A, 1968, 2836 DOI: 10.1039/J19680002836

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