KINETICS AND MECHANISM OF THE DISPLACEMENT OF AQUA-LIGANDS FROM CIS-DIAQUA-BIS(BIGUANIDE)CHROMIUM(III) BY PYRIDINE-2-ALDOXIME IN ETOH-H2O MIXTURES

Kinetic and mechanistic studies of the displacement of aqua ligands fr om cis-[Cr(BigH)2(H2O)2]3+ (BigH = H2NC(NH)CHC(NH)NH2) by pyridine-2-a ldoxime (LH) in EtOH-H2O mixtures, in the 30-45-degrees-C range, obey the following rate law over the 3.5 6.0 pH range, d[Cr(BigH)2(L)2+]/dt = k(a)K(E)[Cr(BigH)2(H2O)23+]T[LH]/1+K(E)[LH] where K(E) is the ion p air equilibrium constant and k(a) is the rate constant for the interch ange of the outer-sphere complex to inner-sphere complex. The anation rate constants are dependent upon pH but independent of ionic strength . Activation parameters (DELTAH(not-equal) and DELTAS(not-equal)) have been evaluated from Eyring plots and a mechanism (I(a)) involving out er-sphere association of reactants followed by associate interchange o f this outer-sphere complex into product is proposed.