The complexation of Nil' with 2-aminomethylbenzimidazole (L) has been investigated at 20-40 "C, / = 0.30 mol dm-3. Both monoprotonated and unprotonated ligands bind the metal ion to form [NiL],', and the rate and activation parameters for the formation and acid-catalysed dissociation of this chelate are calculated. In the presence of salicylaldehyde (Hsal), a mixed-ligand complex, [NiL(sal)] +, is also formed as an intermediate which further condenses to the Schiff-base complex, [NiL']' [HL' =

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... -(benzimidazol-2-ylmethyl)salicylideneimine]. The kinetics of the fast ternary complex formation and its slow intramolecular transformation to the Schiff base complex have been investigated at 25 "C. The presence of L in the co-ordination sphere of Ni2+ enhances the dissociation of [NiL(sal)] + to [NiLI2+ and sal-with respect to [Ni(sal)] +, as evidenced by the stability constants of [NiL(sal)]+ and [Ni(sal)]+. Calculations based on the values of ASo for the ionisation of H,L2+ and the formation of [NiLI2+