SYNTHESIS AND RESEARCH OF A COMPLEX COMPOUND WITH A MIXED LIGAND BASED ON COBALT (II) CHLORIDE, AURINTRICARBONIC ACID, AND ACETAMIDE

ABSTRACT

Cobalt (II) chloride, a complex compound with a mixed ligand was synthesized based on aurintricarbonic acid and acetamide. To determine the composition of the obtained complex compound the elemental analysis was carried out. Quantum-chemical and thermal analysis methods were used to analyze the structure and properties of the complex unit. Based on the results obtained from modern physicochemical analysis methods, it was determined that the coordination number of the central atom in the complex compound is equal to 6.

АННОТАЦИЯ

Хлорид кобальта (II), комплексное соединение со смешанным лигандом, было синтезировано на основе ауринтрикарбоновой кислоты и ацетамида. Для определения состава полученного комплексного соединения был проведен элементный анализ. Для анализа структуры и свойств комплексного соединения были использованы методы квантово-химического и термического анализа. На основании результатов, полученных с помощью современных физико-химических методов анализа, было определено, что координационное число центрального атома в комплексном соединении равно 6.

Keywords: Cobalt (II) chloride, aurintricarbonic acid, acetamide, elemental analysis, quantum chemical analysis, thermal analysis

Ключевые слова: хлорид кобальта (II), ауринтрикарбоновая кислота, ацетамид, элементный анализ, квантово-химический анализ, термический анализ

Introduction. The study of coordination compounds explains their basic chemical properties, forms a complex, determines the nature of chemical bonds between ligands, uses modern physical research to determine the mechanisms of processes that go in the presence of coordination compounds, and changes in the reactivity of coordinated ligands. The obtained information is important for finding and synthesizing new chemical substances with predetermined properties, properties structures, and other important parameters. This is especially important for biologically active substances used in medicine. The enzyme that increases the activity in the organism is also a complex compound by its chemical nature. When smeared with metallic, it is treated by putting the leap into a state of the complex compound and getting out of the organism [1].

Literature review. Authors [2,3] in the works two ООССМе₃ groups were changed to 2-pyridonate anions or their corresponding analogs {Co₆(OH)₂(OOCCMe₃)₈(L)₂} (L= 2-pyridonate-, 6-methyl- 2-pyridonate -, 4– dimethyl–6 - pyrimidinonate and 3–methyl–2–quinoxalinate - anions) stability of structural analogs of hexanuclear cobalt(II) hydroxypivalates containing fragments was shown. Replacement of trimethylacetate anions with 2-pyridone ones gives rise to pyridone-carboxylate structures [(η¹-C₆H₇NO) M₆(µ₃-OH) (µ₃η²- C₆H₆NO)₃ (µ₂η²-C₆H₆NO) (µ₃-C₆H₆NO) (µ₃-ООССМе₃) (µ-ООССМе₃)₄] (η² ООССМе₃)] which have no structural analogs among carboxylate complexes in both cobalt and nickel.

It was found that 6-methyl-2-hydroxypyridonate anions are able to block the polynuclear metal base and prevent its degradation under the influence of abundant N-donor ligands. (HL)Ni₆(µ₃- ОН)(µ₃,η²-L)₃(µ,η²-L)(µ₃-L)(µ₃-ООССМе₃)(µ-ООССМе₃)₄(η²-ООССМе₃) during the thermolysis of the compounds, it was found that compounds with pyridonate and carboxylate anions Ni₆(µ₄- C₆H₆NO)₃(µ-OOC CMe₃)₄(η²µ₃-OOCCMe₃)₄(η²-OOCCMe₃)and oxo- and hydroxo- bridges formed under mild conditions are not retained [4,5].

The method of synthesis of polynuclear metall-complexes of second and third generation polydentate hyperbranched polyetherpolycarbonic acids was developed and metall-complexes containing Co(II) and Cu(II) atoms were synthesized. All hyperbranched metall-carboxylates of cobalt(II) and copper(II) have octahedral symmetry with monodentate and chelate-coordinated cobalt and bidentate-bridged and chelate-coordinated copper ions through the ionized carboxylate group oxygen atoms [6,7].

In [8], the composition and stability constants of polyetherpolycarboxylate hyperbranched polynuclear complexes of Co(II) in solution were found. An increase in stability was found when transitioning from cobalt and copper macrocomplexes with second-generation polyetherpolyacids containing propionate fragments to polyetherpolyacid macrocomplexes containing acrylate fragments. Chelate coordination of the central atom takes place in solutions for hyperbranched polyetherpolycarbonic acid complex forms of cobalt(II). In hyperbranched polyether polycarboxylates of copper(II), the effect of ‘carboxylate shift’ was observed with the increase in the concentration of metal ions, and the chelate coordination changed to bidentate-bridged coordination.

Based on the scientific data presented in the literature review, which is based on aurintricarbonic acid and urea of c​​obaltic salts the synthesis of coordination compounds, the composition, structure and physicochemical properties of the obtained compounds have not been sufficiently studied.

Research methodology. The starting materials required for the synthesis of the complex compound were made in the following ways i.e. to obtain aurintricarbonic acid, solutions of aluminon and barium hydroxide were mixed in appropriate masses in a 2:3 mol ratio, and the mixture was heated to 80 ⁰C. In this, the dark red solution of aluminon changed to pale red and ammonia gas was released. A 0,1 molar solution of H₂SO₄ was added dropwise to the obtained solution in proportion to the mass of barium aurintricarbonate. The BaSO₄ salt precipitated and the precipitate in the solution was filtered off [9,10].

(C₆H₃)₃(OH)₂O(COONH₄)₃ + Ba(OH)₂ =  ((C₆H₃)₃(OH)₂O(COO)₃)₂Ba₃ + NH₃↑ + H₂O

((C₆H₃)₃(OH)₂O(COO)₃)₂Ba₃ + H₂SO₄ = (C₆H₃)₃(OH)₂O(COOH)₃ + BaSO₄↓

Hydrogen peroxide was added to the CoCl₂ solution to obtain cobalt (III) hydroxide.

CoCl₂ + H₂O₂ = Co(OH)₃ ↓+ H₂O + O₂↑

The resulting yellow-pink solution of aurintricarbonic acid was poured over the precipitate of cobalt (III) hydroxide and the reaction was carried out in a water bath at 50 ⁰C until the precipitate was completely dissolved.

(C₆H₃)₃(OH)₂O(COOH)₃ + Co(OH)₃ = (C₆H₃)₃(OH)₂O(COO)₃Co + 3H₂O

Acetamide solution was added to the resulting solution in a 1:1 mol ratio. The mixture was stirred on a magnetic stirrer for 1.5 h at 60 ⁰C at 800 rpm. A dark red solution was obtained and left at room temperature for 5 days. As a result, complex crystals were formed.

Analysis and results. Elemental analysis of synthesized compounds and microstructure was determined using an Aztec Energy Advanced X-Act (Oxford) instruments brand scanning electron microscope SEM EVO MA 10 (Zeiss) energy dispersive X-ray spectrometer (Table 1)[11].

Table 1.

Results of elemental analysis of the complex compound [(C₆H₃)₃(OH)₂O(COO)₃Co∙NH₂COCH₃∙H₂O]

Based on the data obtained by SEM-EDA, it can be concluded that the coordination of metal ions with ligands leads to changes in the microstructure of ligands, in particular, it is recorded by many metal peaks, which is confirmed by EDA [12].

[(C₆H₃)₃(OH)₂O(COO)₃Co∙NH₂COCH₃∙H₂O]  in determining the spatial structure and coordination number of the central atom in the coordination compound, optimization was carried out in the non-empirical 3-21G B3LYP approximation in the Gaussian 9.0 program. Cobalt of the possible coordination structure aurintricarboxylic (acid-?-уточнить у автора нужно ли слово «кислота» здесь) carbamide. Four variants with coordination numbers 4 and 6 in a 1:1 ratio and coordination numbers 6 and 8 in a 1:2 ratio were considered. The stability of complex compounds was determined based on the minimum heat of formation [13].

Figure 1. Bond lengths (a), electrostatic potential fields (b), charge distribution (c) and HOMO-LUMO fields (d) of the complex compound molecule

As a result, the heat of formation of a complex compound with a coordination number of 4 in a 1:1 ratio is -488.96 kcal/mol, and a heat of formation of a complex compound equal to 6 is -557.13 kcal/mol, the coordination number of the central atom obtained in a 1:2 ratio is 6 the heat of formation of the complex compound was found to be –139.25 kcal/mol, and the heat of formation of the compound with coordination number equal to 8 was 119.53 kcal/mol. Thus, we can see the stability of the compound with the coordination number of cobalt equal to 6 in the complex compound obtained in a mutual ratio of 1:1 (Fig. 1).

According to the obtained DTA results, three endothermic effects at 137, 265, 364 ⁰C and three exothermic effects at 343, 554, 682 ⁰C were determined. The first identified endoeffect corresponds to a molecule of water escaping from the inner sphere of a complex compound. The lost mass is in the range of 130-140 ⁰C and is 2.33% of the initial mass. The second endothermic effect corresponds to the carbon dioxide released from acetamide, and the third endothermic effect corresponds to the carbon dioxide molecule released from aurintricarbonate. An increase in temperature leads to the escape of all gas molecules and the formation of metal oxide as the final products of decomposition. The total mass loss for the complex compound corresponds to 130-690 ⁰C and is 72.44% (Fig. 2).

Figure 2. Derivatogram of complex compound [(C₆H₃)₃(OH)₂O(COO)₃Co∙NH₂COCH₃∙H₂O]

Conclusion. A coordination compound with a mixed ligand was synthesized based on cobalt (III) aurintricarbonate and acetamide. Optimum conditions of synthesis and energy parameters of possible complex compounds were studied as a result of quantum-chemical analysis. Compounds were studied based on minimum values ​​of formation energies. The synthesized complex compound was subjected to elemental analysis. As a result, it was determined that it is in an octahedral structure with a coordination number of 6. The presence of one molecule of water in the inner sphere was proved by thermal analysis.

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