Cobalt-Imidazole Complexes: Effect of Anion Nature on Thermochemical Properties.

A solvent-free method was proposed for the synthesis of hexaimidazolecobalt(II) nitrate and perchlorate complexes-[Co(C3H4N2)6](NO3)2 and [Co(C3H4N2)6](ClO4)2-by adding cobalt salts to melted imidazole. The composition, charge state of the metal, and the structure of the resulting complexes were confirmed by elemental analysis, XPS, IR spectroscopy, and XRD. The study of the thermochemical properties of the synthesized complexes showed that [Co(C3H4N2)6](NO3)2 and [Co(C3H4N2)6](ClO4)2 are thermally stable up to 150 and 170 °C, respectively. When the critical temperature of thermal decomposition is reached, oxidative two-stage gasification is observed. In this case, the organic component of the [Co(C3H4N2)6](NO3)2 complex undergoes almost complete gasification to form Co3O4 with a slight admixture of CoO, which makes it attractive as a component of gas-generation compositions, like airbags.

CO2 Methanation: Solvent-Free Synthesis of Nickel-Containing Catalysts from Complexes with Ethylenediamine.

CO2 methanation was studied in the presence of nickel catalysts obtained by the solid-state combustion method. Complexes with a varying number of ethylenediamine molecules in the coordination sphere of nickel were chosen as the precursors of the active component of the catalysts. Their synthesis was carried out without the use of solvents, which made it possible to avoid the stages of their separation from the solution and the utilization of waste liquids. The composition and structure of the synthesized complexes were confirmed by elemental analysis, IR spectroscopy, powder XRD and XPS methods. It was determined that their thermal decomposition in the combustion wave proceeds in multiple stages with the formation of NiO and Ni(OH)2, which are reduced to Ni0. Higher ethylenediamine content in the complex leads to a higher content of metal in the solid products of combustion. However, different ratios of oxidized and reduced forms of nickel do not affect the initial activation temperature of nickel catalysts in the presence of CO2. It was noted that, after activation, the sample obtained from [Ni(C2H8N2)2](NO3)2 exhibited the highest activity in CO2 methanation. Thus, this complex is a promising precursor for CO2 methanation catalysts, and its synthesis requires only a small amount of ethylenediamine.

The Use of Hybrid Genetic Algorithm in the Kinetic Analysis of Thermal Decomposition of [Ni(C2H8N2)3](ClO4)2 with Overlapping Stages.

This work describes the mathematical modeling of the thermal decomposition of the complex compound [Ni(En)3](ClO4)2 (En = C2H8N2 = ethylenediamine) in an inert atmosphere under non-isothermal conditions. This process is characterized by several simultaneous and intense stages: elimination of ethylenediamine from the nickel coordination sphere, decomposition of perchlorate anions, and explosive-like oxidation of free or bound ethylenediamine. These stages overlap and merge into a one step on the differential thermogravimetric curve. Typically, this curve is modeled as a one-stage process during kinetic analysis. In this paper, for the first time, the data from the dynamic mass-spectral thermal analysis and thermogravimetric analysis were modeled using the hybrid genetic algorithm, and the results were compared. A two-stage scheme of [Ni(En)3](ClO4)2 thermolysis was proposed and the kinetic parameters for each stage were obtained. It was shown that the decomposition of [Ni(En)3](ClO4)2 begins with the elimination of one molecule of ethylenediamine (stage A), then the perchlorate anions quickly decompose with the evolution of oxygen (stage B). We believe that the resulting ClO4-x- (x = 1-3), as stronger oxidizing agents, instantly start an explosive-like exothermic process of ethylenediamine oxidation (stage B).