Kinetic study of the reaction of meso-tetrakis (p-trimethylammoniumphenyl)porphinatodiaquorhodate(II) with chloride,bromide, iodide,hexacyanocobaltate(III) and thiocyanate ions in aqueous solution |
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| Authors: | J.G. Leipoldt H. Meyer |
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| Affiliation: | Department of Chemistry, University of the Orange Free State, Bloemfontein, Republic of South Africa |
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| Abstract: | The reaction of Cl?, Br?, I?, Co(CN)63? and NCS? with meso-tetrakis (p-trimethylammoniumphenyl)porphinatodiaquorhodate(III), [RhTAPP(H2O)2]5+, has been studied at 15, 25 and 35°C in 0.1 M [H+] with μ = 1.00 M (NaNO3). The value of the acidity constant, Kal, at 25°C is 4.39 × 10?9 M. The reactions are first order in anion concentration up to 0.9 M. The values of the stability constants, K1, and the second order rate constants, k1, for the reaction with Cl?, Br?, I?, Co(CN)63? and NCS? are respectively 0.23 M?1 and 2.5 × 10?3 M?1 s?1, 1.1 M?1 and 6.92 × 10?3 M?1 s?1, 40.0 M?1 and 17.0 × 10?3 M?1 s?1, 550 M?1 and 20.0 × 10?3 M?1 s?1, 3400 M?1 and 20.9 × 10?3 M?1 s?1. The porphine greatly labilizes the Rh(III). There has been about a 500-fold increase in the rate constant for substitution compared to that of [Rh(NH3)5H2O]3+. The substitution rates are however about the same as for [Rh(TPPS)(H2O)2]3?, indicating that the overall charge on the complex plays only a minor role. The kinetic results indicate that dissociative activation is occurring in these reactions. |
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| Keywords: | Author to whom correspondence should be addressed. |
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