VOLUMES OF ACTIVATION FOR SUBSTITUTION-REACTIONS OF TRIS(1,10-PHENANTHROLINE)IRON(II) AND TRIS(2,2'-BIPYRIDYL)IRON(II) COMPLEXES WITH HYDROXIDE AND CYANIDE IONS FROM HIGH-PRESSURE SOLUTION KINETICS

The effect of high pressure on the rates of substitution of Fe(phen)32+ and Fe(bpy)32+ (phen = 1,10-phenanthroline; bpy = 2,2'-bipyridyl) with hydroxide and cyanide ion has been evaluated. All reaction rates are significantly retarded upon the application of pressure. The hydroxide-dependent component of the rate expression exhibits volumes of activation (AΔV‡) of + 19.7 ± 0.3 and +21.5 ± 0.4 cm3 mol-1 for substitution of Fe(phen)32+ and Fe(bpy)32+, respectively. The cyanide-dependent term exhibits ΔV‡ of + 19.8 ± 1.0 and +20.9 ± 1.6 cm3 mol-1 for substitution of Fe(phen)32+ and Fe(bpy)32+, respectively. A rate-determining dissociative interchange mechanism is most consistent with the observation that ΔV‡ for substitution of each complex is positive, pressure-independent, and independent of nucleophile. © 1979, American Chemical Society. All rights reserved.