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) 5 H 2 O] 3− anion with two naphthalene‐substituted ligands viz. L n = 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) 5 L] n −3 as a function of pH, ionic strength, temperature, a wide range of ligands concentration, and [Ru(CN) 5 H 2 O 3− ] under pseudo‐first‐order conditions. The experimental observation suggests that [Ru(CN) 5 H 2 O] 3− ion interacts with both ligands, which finally get converted into corresponding, [Ru(CN) 5 L] n −3 complexes as a final reaction product. The reaction is found to obey first‐order dependence each in [Ru(CN) 5 H 2 O 3− ] and [L n ]. The substituted products, viz. [Ru(CN) 5 L] n −3 , in each case have strong MLCT transitions in visible region. The substitutional lability of [Ru(CN) 5 H 2 O] 3− has been discussed in terms of electronic effect on the M OH 2 bond interactions. The kinetic observation suggests that the complexation reaction of [Ru(CN) 5 H 2 O] 3− with both the ligands, i.e., NRS and αNβN, follows an ion pair dissociative mechanism. The thermal activation parameters Δ H ≠ and Δ S ≠ 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