Substitution reactions of trans-[Ru(NH3)4{P(OEt)3}(H2O)]2+ revisited. Mechanistic elucidation from a volume-profile analysis

Abstract

The complex-formation reactions of trans-[Ru(NH₃)₄{P(OEt)₃}(H₂O)]²⁺ with L = imidazole (Him), isonicotinamide (isn) and pyrazine (pyz) were studied in aqueous solution (I= 0.10 mol dm^–3, CF₃CO₂Na) as a function of entering ligand concentration and pressure up to 100 MPa, at 25.0 ± 0.1 °C. The volumes of activation for the complex-formation reactions were +4.2 ± 0.2 (pH 8.6), +1.9 ± 0.3 (pH 5.3) and +2.0 ± 0.3 cm³ mol^–1(pH 5.0), for L = Him, isn and pyz, respectively. In the case of isn and pyz as entering ligands the volumes of activation for the reverse aquation reactions were found to be +7.5 ± 0.4 and +10.4 ± 0.3 cm³ mol^–1, respectively. Based on the volume of activation data and the constructed volume profiles a dissociative interchange mechanism is proposed.