Three chromium(III) complexes of general formula [Cr(ox)
2(pdaH)]
2− (where ox = C
2O
4
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)(H
2O)
2]
0 (P
1) and
cis-[Cr(ox)
2(H
2O)
2]
2− (P
2). The kinetics of these reactions were studied spectrophotometrically, within the 0.1–1.0 M HClO
4 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 P
1:P
2 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.