Mer-[Cr(pic)(3)](0) and [Cr(ox)(2)(pic)](2-) undergo successive base hydrolysis to give chromates(III). Dissociation of the first ligand, pic from [Cr(pic)(3)](0) and ox from [Cr(ox)(2)(pic)](2-), proceeds in two stages, namely initial chelate-ring opening followed by slower liberation of the monodentate ligand. Kinetics of both the stages were studied spectrophotometrically in 0.2-0.9 M NaOH solution, under pseudo-first-order conditions. The calculated values of k(obs) were independent of [OH-]. A mechanism is proposed, where the formation of intermediates in the hydroxo form prevents the monodentate ligand from undergoing chelate-ring closure. Evidence for the formation of an intermediate with O-bonded picolinate is given. The effects of pH and the complex composition on the reactivity are discussed.
