Decomposition kinetics of bis(biguanide)silver(III) cation in acid perchlorate media

Abstract

In acid perchlorate media, the title complex undergoes intramolecular redox decomposition generating ultimately Ag⁺ ion and oxidation products of the ligand. The reaction follows a simple first-order process, and the observed pseudo-first-order rate constant is given by k_obs=k₀+kK_a/[H⁺] where K_a is the deprotonation constant of the parent complex; pK_a is approximately 5.9 at 30°. The values of 10⁵ k₀(s^-1) and 10⁷ kK_a (Ms^-1) at 30°, I=1.0 M, are 9.3±0.1 and 11.8±1.3; corresponding ΔH ≠(kJ/mol), ΔS ≠(JK^-1 M^-1) values are 105±0.5, 23±1 and 79±8,-96±5, respectively. The results are compared with those for similar reaction of (ethylenebisbiguanide)silver(III) and effect of change in ligand structure on kinetic behaviours of these complexes is discussed.