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

The 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 λ_max = 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)₅H₂O^3?] 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)₅H₂O^3?] 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