SUBSTITUTION-REACTIONS OF TRANS-[RU(NH3)(4)(P(OET)(3))(H2O)](2- MECHANISTIC ELUCIDATION FROM A VOLUME-PROFILE ANALYSIS() REVISITED )

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 degrees 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 cm(3) mol(-1) (pH 5.0), for L = Him. isn and pyz, res pectively. 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 cm(3) mol(-1), respectively. Based on the v olume of activation data and the constructed volume profiles a dissoci ative interchange mechanism is proposed.