Rate constants and activation parameters for formation of the monocomplexes of Ni(II) ion with several mono-, bi-, and terdentate ligands in N,N-dimethylformamide were obtained by stopped-flow spectrophotometry. The gross features of substitution for all the ligands studied could be accommodated within the structure of an Id-type mechanism. 4-Phenylpyridine behaves most 'normally', and 1,10-phenanthroline stabilized most strongly outer-sphere complex formation with Ni(II). Comparison of these data with previously reported work by other authors for substitution at Ni(II) in acetonitrile with the same ligands indicates that in dimethyl-formamide pyridine-type ligands generally affect the stability of metal–ligand outer-sphere complexes less dramatically than in acetonitrile. Hammett correlation is observed for 1,10-phenanthroline and its 5- and 5,6-substituted derivatives. The slope of the Hammett correlation plot in dimethylformamide is in the order of −0.2, about half the value of −0.4 reported previously in acetonitrile by other authors. This indicates that the stability of the metal–ligand outer-sphere complex is affected more greatly by small differences in the electronic nature of the coordinating substituted 1,10-phenanthrolines in acetonitrile than it is in dimethylformamide.
Ligand substitution kinetics of nickel(II) ion in N,N-dimethylformamide
