The kinetics and mechanism of the substitution reactions of the aquapentacyanoruthenate(II) ion with naphthalene‐substituted ligands in aqueous medium

Abstract

AbstractThe kinetics and mechanism of substitution reaction of [Ru(CN)5H2O]3− anion with two naphthalene‐substituted ligands viz. Ln = nitroso‐R‐salt (NRS) and α‐nitroso‐β‐naphthol (αNβN) have been studied spectrophotometrically by monitoring an increase in absorbance at λmax = 525 nm corresponding to metal to ligand charge transfer (MLCT) transitions due to formation of substituted [Ru(CN)5L]n−3 as a function of pH, ionic strength, temperature, a wide range of ligands concentration, and [Ru(CN)5H2O3−] under pseudo‐first‐order conditions. The experimental observation suggests that [Ru(CN)5H2O]3− ion interacts with both ligands, which finally get converted into corresponding, [Ru(CN)5L]n−3 complexes as a final reaction product. The reaction is found to obey first‐order dependence each in [Ru(CN)5H2O3−] and [Ln]. The substituted products, viz. [Ru(CN)5L]n−3, in each case have strong MLCT transitions in visible region. The substitutional lability of [Ru(CN)5H2O]3− has been discussed in terms of electronic effect on the MOH2 bond interactions. The kinetic observation suggests that the complexation reaction of [Ru(CN)5H2O]3− with both the ligands, i.e., NRS and αNβN, follows an ion pair dissociative mechanism. The thermal activation parameters ΔH≠ and ΔS≠ have been calculated using Eyring's equation and provided in support for the proposed mechanistic scheme. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 43: 21–30, 2011