PROPERTIES AND REACTIVITIES OF PENTADENTATE ETHYLENEDIAMINETETRAACETATE COMPLEXES OF RUTHENIUM(III) AND RUTHENIUM(II)

The reaction of the pentadentate edta complex of ruthenium(III) with various entering ligands L has been studiedas a function of pH, temperature, and L at 0.2 M ionic strength in aqueous solution. Over the pH range 0.8-8.5, the species Ruln(edta)H20 is the sole form reactive in the substitution processes. Both forward and reverse (k_x) rate constants [formula-omitted] have been determined, as well as activation parameters for the complexation (k) process (L, ki in M1 s1 (25C), k in s1 (25C), AHx in kcal mor1, AS, in cal deg1 mol1): acetonitrile, 30 7, 3.2 0.2, 8.3 0.5, -24 4; thiocyanate, 270 20, 0.5 0.1, 8.9 0.5, -18 3; pyridine, 6300 500, 0.061 0.002; isonicotinamide, 8300 600, 0.7 0.2, 6.6 0.5, -193; pyrazine, 20000 1000, 2.0 0.5, 5.7 0.5, -20 3. Forward rate constants for the analogous substitution reaction for Run(edta)H202 (25C, 0.2 M ionic strength) are as follows: thiocyanate, 2.7 0.2 M1 s1; acetonitrile, 13 1 M1 s1; isonicotinamide, 30 15 M1 s-1. The substitution reactions of Rum(edta)H20 proceed by an associative mechanism, while those of Run(edta)H202 appear to be dissociative in nature. Spectra and reduction potentials for the Ru(edta)L/2 complexes are reported. © 1979, American Chemical Society. All rights reserved.