Chromium(III)-lutidinato complexes of general formula [Cr(lutH)
n
(H
2O)
6−2n
]
3−n (where lutH
− is N,O-bonded lutidinic acid anion) were obtained and characterized in solution. Acid-catalysed aquation of [Cr(lutH)
3]
0 leads to only one ligand dissociation, whereas base hydrolysis produces chromates(III) as a result of subsequent ligand liberation
steps. The kinetics of the first ligand dissociation were studied spectrophotometrically, within the 0.1–1.0 M HClO
4 and 0.4–1.0 M NaOH range. In acidic media, two reaction stages, the chelate-ring opening and the ligand dissociation, were
characterized. The dependencies of pseudo-first-order rate constants on [H
+] are as follows:
k
obs1 =
k
1 +
k
−1/
K
1[H
+] and
k
obs2 =
k
2
K
2[H
+]/(1 +
K
2[H
+]), where
k
1 and
k
2 are the rate constants for the chelate-ring opening and the ligand dissociation, respectively,
k
−1 is the rate constant for the chelate-ring closure, and
K
1 and
K
2 are the protonation constants of the pyridine nitrogen atom and coordinated 2-carboxylate group in the one-end bonded intermediate,
respectively. In alkaline media, the rate constant for the first ligand dissociation depends on [OH
−]:
k
obs1 =
k
OH(1) +
k
O[OH
−], where
k
OH(1) and
k
O are rate constants of the first ligand liberation from the hydroxo- and oxo-forms of the intermediate, respectively, and
K
2 is an equilibrium constant between these two protolytic forms. Kinetic parameters were determined and a mechanism for the
first ligand dissociation is proposed. The kinetics of the ligand liberation from [Cr(lut)(OH)
4]
3− were also studied and the values of the pseudo-first-order rate constants are [OH
−] independent.