SYNTHESIS AND ANALYSIS OF THE COORDINATION COMPOUND OF Co(II) OXALATE WITH CALCIUM ACETATE

ABSTRACT

Calcium acetate of Co(II) oxalate the synthesis of the complex compound with factors affecting the synthesis of the resulting complex compound in room conditions were shown. The element composition of the synthesized complex was analyzed. The complex compound was studied using IR-spectroscopic and thermal analysis methods, and its chemical structure, coordination bond formation and thermal stability were determined. It was also proved that the complex compound is thermally and chemically stable.

АННОТАЦИЯ

Показан синтез комплексного соединения ацетата кальция с оксалатом Co (II) и факторы, влияющие на синтез полученного комплексного соединения в комнатных условиях. Проанализирован элементный состав синтезированного комплекса. Методами ИК-спектроскопии и термического анализа изучено комплексное соединение, определены его химическая структура, образование координационных связей и термическая устойчивость. Доказано, что комплексное соединение термически и химически стабильно.

Keywords: Cobalt(II) acetate, oxalic acid, calcium acetate, complex compound, infrared spectroscopy, differential scanning colorometry

Ключевые слова: Ацетат кобальта(II), щавелевая кислота, ацетат кальция, комплексное соединение, инфракрасная спектроскопия, дифференциальная сканирующая колорометрия.

Introduction. The study of coordination compounds allows to explain their main chemical properties, to form complexes, to determine the nature of chemical bonds between ligands, to determine the mechanisms of processes involving coordination compounds and changes in the reactivity of coordinated ligands using modern physical research. The information obtained is important for the targeted search and synthesis of new chemical substances with predetermined properties, composition and structure, as well as other important properties [1, 2]. This is particularly necessary for substances with biologically active properties that are used in medicine [3]. Enzymes that function in the human body are also complex chemical compounds [5]. When poisoned with metals, they are treated by changing them into complex compounds and eliminating them from the body [6].

The authors of [7] demonstrated the possibility of using heterometallic pivalate [Co₂Sm(Piv)₇(2,4-Lut)₂] as a SmCoO₃ precursor. In contrast to the previously discussed works, the authors determined the structure of the resulting complex. A comprehensive study (DSC and TGA with mass spectral analysis of gaseous products) of the thermolysis of the obtained compound in an inert atmosphere (dried Ar) and artificial air atmosphere was carried out. The solid product of thermolysis in air is a mixture of SmCoO₃ and Co₃O₄ (XRD), which is explained by the initial excess of Co atoms (compared to the 1:1 stoichiometry required to form pure SmCoO₃). A completely different character of decomposition was observed in an inert atmosphere. In this case, the volatile [Co₈(μ₄-O)₂(μ₂-OOCCMe₃)₆(μ₃-OOCCMe₃)₆] is removed before the final solid product is formed; thus, the Sm:Co ratio in the solid decomposition product is optimal for the formation of single-phase SmCoO₃.

As mentioned above, one of the main advantages of precursor methods for the preparation of complex oxides is the ability to control the ratio of heterometallic atoms at the synthesis stage of a given precursor complex. Thus, in [8], the use of 2,2′-bipyridyl (bpy) as a structure-forming ligand in the synthesis of heterometallic 3d-4f pivalate complexes [(bpy)CoLn(Piv)₅(H₂O)], [(bpy)NiLn(Piv)₅(H₂O)] and [(bpy)CuLn(Piv)₅(HPiv)] (Ln = Sm, Gd), i. e., the ratio of heterometallic atoms is optimal (to later obtain MLnO₃). The resulting compounds will be fully characterized. The synthesis methodology developed in [9] proved to be very convenient and versatile, allowing it to be applied to the pivalate synthesis of other lanthanides with other N-donor ligands (in particular 1,10-phenanthroline): [MLn(Piv)₅(fen)] (M=Co, Cu, Zn; Ln= Eu, Gd). A detailed study of the solid phase thermolysis of all the complexes under different conditions was carried out. A comparative analysis of the thermolysis of bihedral heterometallic complexes with a metal carboxylate framework {MLn(piv)₅} in oxidising environments was carried out, and the influence of the d-metal nature on the decomposition temperature of the metal framework of the same ligand complexes was shown. It was found that the introduction of the non-volatile N-donor ligand 1,10-phenanthroline into the complex leads to an increase in the starting temperature of the oxidative degradation of the metal carboxylate skeleton, but has almost no effect on the temperature at which the formation of solid thermolysis products ends. Solid-phase thermolysis in air leads to the formation of single-phase cobaltites (LnCoO₃) in Co-containing complexes, a mixture of phases in Cu-containing complexes (Ln₂CuO₄ and CuO), and mixtures of common ligand and NiO oxides in Ni complexes. The use of the [(bpy)CoSm(Piv)₅(H₂O)] complex has been shown to allow the preparation of ultrathin monophase SmCoO₃, the magnetic properties of which have been studied.

Research methodology. Calcium acetate and cobalt (II) oxalate salts of the ‘pure for analysis’ brand were used for the synthesis of complex compounds.

The following method was used to synthesize Co(II) oxalate acetate calcium complex compound: an aqueous solution of Co oxalate (0.001 mol) and an aqueous solution of Ca acetate (0.002 mol) were mixed with a magnetic stirrer at a speed of 800 revolutions at a temperature of 40⁰C for 1 hour. At first, the solution turned dark red, then pink, and was left at room temperature for 15 days. As a result, Co(II) oxalate acetate Ca complex was formed [10].

Analysis and results. Elemental analysis of synthesized compounds andmicrostructure was determined using an Aztec Energy Advanced X-Act (Oxford) instrument brand scanning electron microscope SEM-EVO-MA 10 (Zeiss) energy dispersive X-ray spectrometer. Determining the amount of elements in substances using a scanning electron microscope (SEM) is widely used in solving specific scientific and technological problems due to the high information content and reliability of the obtained research results for the analysis of materials [11].

Table 1.

The results of the elemental analysis of the complex compound formed by Co(II) oxalate with calcium acetate

In order to determine the coordination centers and coordination paths of the synthesized compounds, the synthesized compounds were analyzed by IR-spectroscopic method (Fig. 1).

As a result of the analysis of the coordination compound formed by Co (II) oxalate with Ca acetate, comparing it with the IR spectrum of the original substances, it was found that changes occurred in the IR spectrum of the new substance. The main changes were observed in the Co-O bond, and there were also changes in the asymmetric and symmetric acetate group vibrations.

In cobalt oxalate, the vibration frequency of the Co-O bond is observed at 476 cm^-1, after coordination, the vibration frequency increases and moves to 493 cm^-1. In calcium acetate, the vibrational frequency of 638 cm^-1, which is typical for the Ca-O bond, shifts to the 671 cm^-1region in the complex compound.

Asymmetric and symmetric vibrations of the acetate anion n_s(COO-)=1447 cm^-1 and n_as(COO-)=1531 cm^-1 was observed. Changes in the vibration fields are observed when moving to the coordinated state, n_s(COO-)=1368 cm^-1, changed to n_as(COO-)=1556 cm^-1. This corresponds to bidentate-bridged coordination and indicates that the acetate anion forms a bridged bond with the central atom. Another evidence proving the presence of the acetate group in the synthesized compounds is the presence of deformational and valence vibrations of the methyl group in the absorption region at 1031 cm^-1 in the IR spectrum of the synthesized compound (Table 1).

Figure 1. IR-spectrum of the compound [(CoC₂O₄)₂∙Ca(CH₃COO)₂]

Table 2.

Characteristic frequencies of absorption in IR spectra of coordination compound

The thermal stability of the synthesized complex compound was analyzed based on the results of derivatographic analysis of various exothermic and endothermic heat effects observed with mass change as a result of destruction.

In the derivatogram of [(CoC₂O₄)₂∙Ca(CH₃COO)₂] complex, three endothermic effects were observed at temperatures of 136, 155, 220^oC and two exothermic effects at temperatures of 185, 285^oC. At a temperature of 136^oC, the first endoeffect complex begins to decompose. The exoeffect at 185⁰C is due to the combustion of thermolysis products, and at 220^oC the decomposition of acetic and oxalic acid residues is completed. The exothermic observation at 285^oC can be explained by the burning of thermolysis products of metal and ligands and the formation of the last product - metal oxide. The total mass reduction in the temperature range of 30-400^oC was 62.2% (Fig. 2).

Figure 2. Derivatogram of [(CoC₂O₄)₂∙Ca(CH₃COO)₂]

Conclusion. As a result of elemental analysis, it was determined that in the composition of Co(II) oxalate acetate calcium complex compound, the initial substances are in a ratio of 1:2. It was proved that the coordination compound formed as a result of IR-spectroscopic analysis is a polynuclear heterometallic complex compound. In this case, the coordination bond is realized through bidentate-bridged coordination of acetate groups.The synthesized coordination compound decomposes at a relatively low temperature. In this case, the maximum mass loss is not more than half of the sample mass, and no mass change is observed after 400^oC. Based on this, it can be concluded that the ligands are connected directly by the coordination bond and are located in the inner sphere, and this weak bond breaking occurs at a relatively low temperature.

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