Mixed chromium(III) complexes with pyridinedicarboxylato and oxalato ligands: kinetic studies in HClO4 solutions

Abstract

Three chromium(III) complexes of general formula [Cr(ox)2(pdaH)]2− (where ox = C2O4 2− and pdaH− is N,O-bonded 2,3-, 2,4- or 2,5-pyridinedicarboxylic acid anion) were obtained and characterized in solution. Acid-catalysed aquation of [Cr(ox)2(pdaH)]2− gave two products: [Cr(ox)(pdaH)(H2O)2]0 (P1) and cis-[Cr(ox)2(H2O)2]2− (P2). The kinetics of these reactions were studied spectrophotometrically, within the 0.1–1.0 M HClO4 range, and the pseudo-first-order rate constants for the oxalato (k obs1) and pdaH− (k obs2) ligands dissociation were calculated based on the determined pseudo-first-order rate constants (k obs) and P1:P2 molar ratio. The dependencies of the pseudo-first-order rate constants on [H+] are as follows: k obs1 = b 1[H+] and k obs2 = b 2[H+], where b 1 and b 2 are the second-order rate constants for the oxalato and pdaH− ligands dissociation, respectively. Kinetic parameters were determined and the mechanism of the pdaH− ligand dissociation is proposed.