Abstract
Inner complex compound of cobalt(III) with diaminoethanol, [Co(DetmHdetm)], and polynuclear complex compound 2Co-Ni with diaminoethanol, [Ni(CoDetmHdetm)2](NO3)2, were synthesized. Stabilities of the obtained compounds were investigated in non-aqueous (dimethylformamide) solutions at different values of pH (from acid to alkaline). Methods of potentiometric titration and electron absorption spectra were used to determine the range of pH values where the compounds do not decompose. As a result of these studies, we found that at the upper value of pH=7, the coordination surrounding of the metals (Co(III), Ni(II)) does not change. When the pH value becomes lower than 7 (with adding HCl acide), the inner complex of Co(III) begins to decompose. The ligand H2detm is replaced by Cland partial protonization of diethanolamine occurs. Also, transformation of N,Ncis isomer of inner complex compound of cobalt(III) to N,N-trans isomer takes place, thus reducing the symmetry of the complex. As for the polynuclear complex compound 2Co-Ni, when pH value becomes lower than 7, molecules of solvent begin to react with the products of partially destroyed complex. As a result, new complex compound is formed with the increase of coordination number of nickel(II) from 4 to 6. However, in alkaline solutions where pH values are up to 10, the heterometal complex compound of 2Co-Ni remains stable. Only partial hydrolysis of the solvent occurs in these conditions. The schemes of transformations of [Co(DetmHdetm)] and [Ni(CoDetmHdetm)2](NO3)2 occuring in non-aqueous (dimethylformamide) solutions at different values of pH (from acid to alkaline) are presented in the paper. The results of this study can be used for the preparation of precursor solution for the technology of catalytic materials production. Evidently, the range of pH from 7 to 10 must be maintained in order to avoid the contamination of the final products by the decomposed wastes of complexes and solvent.
Highlights
The article is devoted to preparation of polynuclear complex compounds of cobalt (III) with aminoalcohol ligands and further studies of their structure as well as electrocatalytic properties in the reactions of intercalation /deintercalation of lithium in carbon materials and reactions of discharge-ionization of hydrogen on carbon nanotubes
The 3d metal compounds which to allow catalyzing main part of chemical technology processes continue investigating to develop more effective composition and maximum universal methods of causing [9, 10, 11]. It was shown [12] that the products of pyrolitic destruction of polynuclear complex compounds of cobalt(III)-nickel(II) with aminoalcohol ligands grafted onto the surface of carbon materials are catalytically active relatively to some electrolytic reactions such as reduction of oxygen, intercalation of lithium into graphite and dischargeionization of hydrogen
The structure of coordination compound 2Co-Ni was investigated which allowed to predict the composition of active catalytic centers on the surface after the pyrolitic decomposition [14].The non-aqueous solutions of the polynuclear complexes are used as precursors for grafting the complexes on the surface of catalytic materials before the thermal treatment
Summary
The article is devoted to preparation of polynuclear complex compounds of cobalt (III) with aminoalcohol ligands and further studies of their structure as well as electrocatalytic properties in the reactions of intercalation /deintercalation of lithium in carbon materials and reactions of discharge-ionization of hydrogen on carbon nanotubes. The stability of coordination compounds of Co(III) with aminoethanol ligands wasnt investigated for depending of the range of pH environment This parameter is very important, because it straightly influence on the structure of catalytic materials. The 3d metal compounds which to allow catalyzing main part of chemical technology processes continue investigating to develop more effective composition and maximum universal methods of causing [9, 10, 11] It was shown [12] that the products of pyrolitic destruction of polynuclear complex compounds of cobalt(III)-nickel(II) with aminoalcohol ligands grafted onto the surface of carbon materials are catalytically active relatively to some electrolytic reactions such as reduction of oxygen, intercalation of lithium into graphite and dischargeionization of hydrogen. The structure transformations in the solutions were studied by electron absorption spectra method (EAS) using VIS spectrometer UNICO2100
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