AN UNUSUAL, VERY RAPID, STOPPED-FLOW BASE HYDROLYSIS OF THE )[(PICDIEN)=1,9-BIS(2-PYRIDYL)-2,5,8-TRIAZANONANE]

The base hydrolysis of the complex alpha beta-anti-[Cr(Picdien)Cl](ClO 4)(2) has been studied in phosphate and gamma-collidine buffer solutio ns over the pH range 7.5-6.5, at 25 degrees C and mu = 0.100 mol(-1) d m(3). The calculated second-order rate constant, k(OH), was found to b e 1.05 +/- 0.07 x 10(4) mol(-1) dm(3) s(-1), the greatest reported, so far, for linear polydentate amine ligands. The activation parameters found are as follows:Delta H-not equal = 65 +/- 2 kJ mol(-1) and a Del ta S-not equal = 52 + 6 J K-1 mol(-1). The second-order rate constant obtained from a borax buffer solution over the pH range 8.5-10.4 by th e stopped-flow technique was found to be k(OH) = 1.32 +/- 0.03 x 10(4) mol(-1) dm(3) s(-1) at 25 degrees C, which is in good agreement with that obtained at lower pH values, confirming the linearity of the base hydrolysis over wide pH ranges. Copyright (C) 1996 Elsevier Science L td