Issue 2, 1990

Kinetics and mechanism of the hydrolysis of cis-β-carbonato(3,7-diazanonane-1,9-diamine)cobalt(III) and cis-β-carbonato(4,7-diazadecane-1,10-diamine)cobalt(III) cations in acidic aqueous solution

Abstract

The acid-catalysed hydrolyses of the complex cations cis-β-[CoL(CO3)]+[L = 3,7-diazanonane-1,9-diamine (L1) or 4,7-diazadecane-1,10-diamine (L2)] have been studied over the ranges 30.0 ⩽θ⩽ 40.0 °C and 1 ⩽ pH ⩽ 5 (for L2, 1 ⩽ pH ⩽ 2) at an ionic strength of 0.5 mol dm–3. The kinetic results exhibit a rate law of the form –d(ln [complex])/dt=k0+k1[H+] where the values of k0(25 °C), k1(25 °C), ΔH0, ΔS0, ΔH1, and ΔS1 are 1.0 × 10–4 s–1, 0.17 dm3 mol–1 s–1, 95 ± 15 kJ mol–1, –4 ± 4 J K–1 mol–1, 37 ± 2 kJ mol–1, and –137 ± 20 J K–1 mol–1 for the L1 complex and 3.9 × 10–5 s–1, 2.7 × 10–2 dm3 mol–1 s–1, 72 ± 10 kJ mol–1, –84 ± 25 J K–1 mol–1, 72 ± 4 kJ mol–1, and –34 ± 8 J K–1 mol–1 for the L2 complex. The acid-catalysed reactions are subject to a deuterium solvent isotope effect, consistent with a mechanism involving a rapid protonation equilibrium followed by slow ring opening of the carbonate ring. The diaqua product of the acid hydrolysis of the L2 complex undergoes cis-to-trans isomerization at rates comparable to the hydrolysis reaction under certain conditions. The values of kiso at 25 °C (I= 0.5 mol dm–3 HClO4) and corresponding activation parameters, ΔH and ΔS, are 1.1 ± 0.05 s–1, 115.8 ± 2.5 kJ mol–1, and 67 ± 21 J K–1 mol–1 respectively.

Article information

Article type
Paper

J. Chem. Soc., Dalton Trans., 1990, 599-603

Kinetics and mechanism of the hydrolysis of cis-β-carbonato(3,7-diazanonane-1,9-diamine)cobalt(III) and cis-β-carbonato(4,7-diazadecane-1,10-diamine)cobalt(III) cations in acidic aqueous solution

F. D. Baeta, S. A. Bajue and T. P. Dasgupta, J. Chem. Soc., Dalton Trans., 1990, 599 DOI: 10.1039/DT9900000599

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