Transformation of a ditopic Schiff base nickel(II) nitrate complex into an unsymmetrical Schiff base complex by partial hydrolytic degradation: Structural and density functional theory studies

A new Schiff base complex [Ni(HL)(NO )](NO) (1) (HL = 3-[N,N-bis-2-(5-bromo-3-(morpholinomethyl) salicylideneamino) ethyl amine]) was synthesized from reaction of the ditopic ligand HL with Ni(NO) in anhydrous MeOH. Complex 1 is stable in the solid state, but prone to hydrolysis. Recrystallization of 1 from wet MeOH led to the isolation of a novel unsymmetrical complex [Ni(HL)(NO )](NO) (2) (HL = 2-[(2-(2-aminoethylamino) ethylimino) ethyl)-5-bromo-3-(morpholino methyl) salicylidene amine]). X-ray single-crystal analysis of complex 2 showed that complex 1 had undergone partial decomposition of one imine bond. In contrast, the Schiff base complex [Ni(HL)](NO) (3) (HL = N,N-bis(5-methyl-salicylidene) diethylenetriamine) was stable in wet methanol, and the single-crystal structure of 3 showed that the Ni(II) center was coordinated in an unsymmetrical square planar geometry. Density functional theory calculations were performed in order to obtain a geometry-optimized model of complex 1, in which the Ni(II) center was coordinated in a similar manner as that in complex 3. The thermodynamic parameters were calculated, in order to rationalize the difference in hydrolytic reactivity between complexes 1 and 3. © 2014 Springer International Publishing Switzerland.