Kinetics of Aquation of the Tris(acetylacetonate) Complexes of Divalent Chromium, Cobalt, and Ruthenium. A Pulse Radiolytic Study1

The kinetics of aquation of Co(acac)3- and Cr(acac)3- were studied as a function of pH. The reactions leading to the loss of each of the three ligands in Co(acac)3- were well separated from each other while in the Cr(acac)3- complex the first step was too fast to follow with our experimental technique. The results are in agreement with a mechanism in which the bidentate-bound ligand is in equilibrium with the ligand bound only as a monodentate. These equilibrium constants are estimated. The ligand bound as monodentate is lost by an acid-catalyzed process, with an acid-independent contribution. The aquation reaction of Ru(acac)3- is too slow to be measured by the pulse radiolytic technique. Ru(acac)3H is a relatively strong acid. The results are compared to those obtained for the aquation reaction of Co(en)32+.