COMPLEXATION IN THE SYSTEM ZINC (II)-CHROME (III)-NICKEL (II)-GLYCINE-WATER

Abstract

The relevance of studying complexation in the system under consideration is associated with the development of the role of heteronuclearcompounds in the processes of electrochemical production of alloys. According to the known concepts, in heteronuclear compounds, the more electronegative atom makes a greater contribution to the bonding orbital, and the orbital of the less electronegative atom, to the antibonding one. This contributes to the convergence of the reduction potentials of metal ions present in such a compound and the production of an electrochemical alloy. In addition, it is known that an increase in the effective radius of complex ions, which is characteristic of heteronuclear compounds, decreases the activation energy of their electrochemical reduction. The aim of this work is to obtain data on complexation in the system Zn (II)-Cr (III)-Ni (II)-glycine-water, composition and stability of heteronuclear compounds. The establishment of the composition of the complexes formed in the system under study was preceded by the acquisition of data on the complexation of each of the indicated elements in individual solutions. It was previously established that in the Zn(II)-Cr (III)-glycine-water system in the pH range 1.0-3.5, heteronuclear forms [CrZn(HGly)4Gly4]+ and [CrZn(HGly)2Gly6]− prevail, at pH 2.2 - 4.0, the share of [CrZnGly8]3− accumulation increases. To establish the composition of the resulting complexes, we used pH metric titration and the method of nuclear magnetic relaxation (NMR) of protons in combination with mathematical processing of the results (CPESSP program). The formation of heteronuclear complexes [CrNiZn(HGly)4Gly4]3+, [CrNiZn(HGly)2Gly6]+ was established, their formation constants and the fraction of accumulation (HGly - glycine) were calculated. The results of the work were used in the development of electrolytes for the process of electrochemical alloying of zinc coatings simultaneously with chromium and nickel.