Equilibrium and kinetic study of pyridine binding to phthalocyaninatoiron(II) in dimethyl sulphoxide

Giovanna Pennesi, Claudio Ercolani, Paolo Ascenzi, Maurizio Brunori, Fabrizio Monacelli

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Abstract

The reaction between pyridine (py) and phthalocyaninatoiron(II), [Fe(pc)], in dimethyl sulphoxide (dmso) has been studied from the kinetic and the equilibrium viewpoints at 20 ± 0.5°C. In the presence of a large excess of pyridine the adduct [Fe(pc)(py)2] is formed via pseudo-first-order kinetics. The observed rate constants have the general form kobs. = k1f[py] + k1r, with k1f′ ≈ 1.5 × 104 dm3 mol-1 s-1 and k1f″ = 35.5 ± 0.7 dm3 mol-1 s-1 and k1r″ = 0.15 ± 0.02 s-1, for the binding and dissociation of the first and second py molecules, respectively. From the values of the equilibrium constant [K1]′ = (3.9 ± 0.1) × 105 dm3 mol-1] and of the second-order rate constant (k1f′) for the binding of the first py molecule, the dissociation rate constant has been estimated to be k1r′ ≈ 4 × 10-2 s-1. The value of the equilibrium constant for the binding of the second py (K1″ = 300 ± 28 dm3 mol-1), determined directly, is in good agreement with the corresponding value (240 ± 40 dm3 mol-1) obtained from the ratio k1f″/k1r″). The data obtained in the present study are discussed in the light of related previous studies.

Original languageEnglish
Pages (from-to)1107-1111
Number of pages5
JournalJournal of the Chemical Society, Dalton Transactions
Issue number6
DOIs
Publication statusPublished - 1985

ASJC Scopus subject areas

  • Chemistry(all)

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