Synthesis and characterization of some new [Co(NN) 2ACl] 2+ [(NN) = bidentate amine, A = monoamine] complexes and a study of the role of the inert ligand “A” in controlling the rate of aquation of [Co(NN) 2ACl] 2+ complexes

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A series of new complexes of type (a) cis-[Co(en)(tn)ACl]Y [en = 1,2-diminoethane, tn = 1,3-diamino propane, A = NH 3, MeNH 2, EtNH 2, n-BuNH 2, pyridine (py), β and γ-picoline (pic), imidazole (imz); Y = ZnCl 4 2− or 2ClO − 4] and (b) cis-[Co(tn) 2ACl]Y [A = py, β and γ-pic, 1-Me-imz and 1,2-dimethyl-imidazole (Me 2-imz)] have been prepared and characterized using UV-vis, 13C NMR and elemental analysis. The kinetics of the release of chloride ions from some complexes in the aqueous acidic phase has been studied at 40 and 50°C. Both types of complexes showed similar rate constant values [ k = 8.5 × 10 −5 to 1.77 × 10 −4 s −1 for type (a) and k = 6.85 × 10 −5 to 2.5 × 10 −4 s −1 for type (b)]. Indirect evidence for the existence of a distorted trigonal bipyramid (tbp) intermediate was obtained. The ability of the inert ligand “A” to control the rate of reaction by influencing the extent of distortion of square pyramid (sp) intermediate moiety (left after the removal of chloride) was demonstrated.