DOI: https://doi.org/10.20535/kpi-sn.2019.3.175733

EFFECT OF pH CHANGE ON THE STABILITY OF HETEROMETALIC COMPLEX COMPOUNDS OF NICKEL (II)–COBALT (III) WITH MONOETHANOLAMINE IN ALCOHOL SOLUTIONS

Irina S. Kuzevanova, Artur O. Zulfigarov, Vadim A. Potaskalov, Alexander A. Andriiko, Natalia E. Vlasenko

Abstract


Background. The application of the cobalt (III) nickel (II) heterometalic complex with monoethanolamine, which is used as a precursor for the preparation of electrocatalytic materials on inert carriers, remain insufficiently studied. Of particular importance is the control of the pH range of the reaction medium, which can significantly affect the composition and structure of the active centers after deposition and pyrolytic decomposition.

Objective. The purpose of the paper is the experimental determination of the pH range in which the composition of 2Co–Ni complex compounds with monoethanolamine will remain unchanged and study of the transformations that occur with complex compounds depending on the change in pH value.

Methods. Synthesis of {Ni[CoEtm3]2}(NO3)2 and studies of its durability by methods of potentiometric titration with chloride acid (C = 0.1 M) and sodium hydroxide (C = 0.1 M). Studying the structural transformations of the obtained complex compound and its decomposition products in alcohol solutions using electronic absorption spectra.

Results. The study of the stability of alcoholic solutions of the intracomplex cobalt (III) compound with monoethanolamine and the heterometallic compound 2Co–Ni with monoethanolamine in alkaline and acidic media made it possible to establish the limits of the pH range in which the synthesis of the synthesized complex compounds does not occur. For the results of the analysis of the obtained absorption spectra and redox titration, it can be argued that there is no change in the coordination environment of metals (Co (III), Ni (II)) in the range of 7 to 8 pH. With an increase in the pH of the medium above 8, the complex compounds are destroyed with the formation of Co2+ and Ni2+ salts. In the case of lowering the pH below 7, the above complex compounds are converted to chloroacidic amines. The corresponding transformations that occur with CoEtm3 and {Ni[CoEtm3]2}(NO3)2 under the influence of acid and alkali in alcohol solutions are described by the proposed decomposition schemes.

Conclusions. The obtained results indicate the need to control the pH of the reaction medium with the promising development of technology for producing catalytic materials using the {Ni[CoEtm3]2}(NO3)2 heteronuclear complex as precursors and clearly set the pH limits in the range from 7 to 8 units.


Keywords


Monoethanolamine; Cobalt (III); Nickel (II); Potentiometric titration; Electronic absorption spectra

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