Formation and dissociation kinetics of the strontium(II) complex of cryptand C222 in binary dimethylsulfoxide-acetonitrile mixtures

Abstract

The dissociation and the formation rates of the Sr2+-C222 cryptate in different dimethylsulfoxide-acetonitrile mixtures have been studied spectrophotometrically using murexide as a metallochromic indicator. In all solvent mixtures used, the ratio of the rate constants for dissociation and formation of the cryptate was found to be in agreement with the formation constants obtained by an independent equilibrium spectrophotometric technique. The activation parameters Ea, ΔH‡ and ΔS‡ for the formation and dissociation of the cryptate were determined from the temperature dependence of the corresponding rate constants, and found to be strongly solvent dependent. There is a linear relationship between the logarithm of the formation constant as well as the activation parameters and the mol fraction of acetonitrile in the mixed solvent.