STUDIES ON THE KINETICS AND MECHANISM OF ANATION REACTIONS OF SOME 6-COORDINATE COMPLEXES OF CHROMIUM(III) IN AQUEOUS-SOLUTION

Rates of stepwise anation of cis-Cr(ox)(2)(H2O)(2)(-) with SCN-/N-3(-) , Cr(acac)(2)(H2O)(2)(+) with SCN- and Cr(atda) (H2O)(2) with SCN- hav e been investigated in weakly acidic aqueous solutions. Rate constants , k(I) and k(II) for the two steps in each system, are composite as k( x)=k(x)(0) + k(x)(X)[X(-)](x=I, II; X(-)=SCN-, N-3(-)). These rate con stants have been evaluated also as the corresponding Delta H double da gger and Delta S double dagger values. The results obtained and the pl ausible I, mechanism seem to suggest Cr-OOC bond dissociation (hence a strongly negative Delta S double dagger) generating the transition st ate in each system with outer-sphere association forming the precursor complex in the X(-) dependent paths.