QUANTUM-CHEMICAL ANALYSIS OF SOME PHYSICO-CHEMICAL PROPERTIES OF SUCCINIC ACID, MONOETHANOLAMINE, DIETHANOLAMINE, TRIETHANOLAMINE AND THEIR COMPLEX COMPOUNDS

ABSTRACT

In this article, a quantum-chemical analysis of some physico-chemical properties of succinic acid, monoethanolamine, diethanolamine, triethanolamine and complex compounds that can be obtained based on them was carried out. Based on the results of quantum chemical analysis, the donor atoms in the molecules of succinic acid, monoethanolamine, diethanolamine, triethanolamine were determined and the atoms that could form a coordination bond were determined. The purpose of this is to carry out the synthesis of complex compounds on the basis of the theoretically obtained data and to study the physico-chemical properties of the synthesized complex compounds. It was determined that the complex compounds that can be formed as a result of the synthesis are coordinated with nitrogen and oxygen atoms in the ligands of succinic acid, monoethanolamine, diethanolamine, and triethanolamine.

АННОТАЦИЯ

В данной статье проведен квантово-химический анализ некоторых физико-химических свойств янтарной кислоты, моноэтаноламина, диэтаноламина, триэтаноламина и комплексных соединений, которые можно получить на их основе. По результатам квантово-химического анализа определены донорные атомы в молекулах янтарной кислоты, моноэтаноламина, диэтаноламина, триэтаноламина и определены атомы, способные образовывать координационную связь. Целью работы является проведение синтеза комплексных соединений на основе теоретически полученных данных и изучение физико-химических свойств синтезированных комплексных соединений. Установлено, что комплексные соединения, которые могут образовываться в результате синтеза, координируются с атомами азота и кислорода в лигандах янтарной кислоты, моноэтаноламина, диэтаноламина и триэтаноламина.

Keywords: succinic acid, monoethanolamine, diethanolamine, triethanolamine, electronic orbitals, electron densities and effective charges.

Ключевые слова: янтарная кислота, моноэтаноламин, диэтаноламин, триэтаноламин, электронные орбитали, электронные плотности и эффективные заряды.

Introduction. As a result of the high ability of ligands containing carbonyl group to form coordination compounds, various complex compounds were synthesized and their composition and properties were studied [1, p. 8; 2, p. 45; 3, p. 275]. If O- and N-containing ligands, including ethanolamines, are included in compounds with such properties, it is of theoretical and practical importance to study how they form a complex compound together. Because the reactivity of ethanolamines is high, it exhibits both amine and alcohol properties. They can synthesize complex compounds with mixed ligands as a result of different denaturation properties [4, p. 43; 5, p. 441; 6, p. 246].

The purpose of this research work is to carry out the synthesis of complex compounds based on theoretical data and to study the physicochemical properties of the synthesized complex compounds.

Methods. Succinic acid and ethanolaminesVarious physico-chemical properties were analyzed quantum-chemically using Gaussian 09 software package. Calculations were performed using the B3LYP method within the DFT theory. HyperChem, GausView programs were used to create and visualize model systems [7, p. 380].

Results and discussion. The system was optimized at the initial stage of theoretical research. At the next stage, basic calculations were carried out. In fig.1 the optimized electronic structure of the ligands and the Mulliken charge distribution are described.

Figure 1. Optimized electronic structure and distribution of Mulliken charges: monoethanolamine (a), diethanolamine (b), triethanolamine (c) and succinic acid (d)

Also, within the framework of quantum-chemical calculations, the free state of the ligand molecule (NOMO^[1]) and excited state (LUMO) electron orbitals were studied [8, p. 1094]. The results of the calculations are presented in fig.2.

Figure 2. MEA, DEA, TEA and succinic acid molecules state of electronic orbitals in free state and excited state and density of electron shells (DOS)

Calculations show that the energy difference between the free state (HOMO) and the excited state (LUMO). It is 4.199 eV in MEA, 5.236 eV in DEA, 4.159 eV in TEA and 5.199 eV in succinic acid.

The surface represented by the electrostatistical potential of the ligand molecules was calculated using DFT / B3LYP / 6–311 G (d, p) {C, H, N, O} / Lanl2DZ at 0.02 isovalue and 0.004 density values.

Figure 3. MEA (a), DEA (b), TEA (c) and succinic acid geometric structure, charge and MEP distribution of molecules of si (d)

The MEP (molecular electrostatic potential) plots in red and blue are the negative and positive electrostatic potentials, respectively. In the color scheme of the MEP graph, the red area indicates atoms with an unshared electron pair or a negative electrostatic potential; the intensity of the color is proportional to the absolute value of the potential energy. Positive electrostatic potentials are shown in the blue/yellow areas and characterize the polar hydrogen in the E–N bonds. The green areas cover the parts of the molecule with electrostatic potentials close to zero (C – C, C – N).

Fig.3 shows the geometrical structure of ligand molecules, charges and MEP distribution.

The results of calculations of ligand molecules are presented in table 1. Based on the values ​​of electron densities and effective charges in the donor and reactive active atoms of ligand molecules, it was found that the given results correspond to the data in the literature [9-12].

Table 1.

Parameters of ligands obtained from quantum chemical calculations

For MEA, the highest negative charge in the molecule according to the value of the charges on the donor atoms was determined on the nitrogen atom (-0.667).

For the DEA ligand, the highest negative charges in the molecule based on the value of the charges on the donor atoms were determined on the nitrogen and oxygen atoms (-0.588 and -0.558 eV, respectively).

For the TEA ligand, in terms of the value of the charges on the donor atoms, the atom with the highest potential for donation was the oxygen atom of the hydroxyl group (-0.556 eV), but also the nitrogen atoms (-0.533 eV).

In order to determine the stability of complexes that can be formed based on the results obtained from the quantum-chemical analysis of ligands, their structure, effective negative charges on atoms, interatomic distances and formation energies were optimized using the DFT/B3LYP/Lanl2DZ {M = Co, Ni, Cu} method.

The results of calculations show that the formation energies for [Co(Suc)(MEA)], [Ni(Suc)(DEA)₂] and [Cu(Suc)(TEA)₂] complexes are -281.45, -486.18 and -763.43 (Hartree) respectively.

When studying the distribution of Mulliken effective charges in ligands and complexes, redistribution of charges in ligands is observed during complex formation. In the [Co(Suc)(MEA)] complex ion, it can be seen that the nitrogen atom bound to the ligand metal is shifted relative to that of the free ligand (-0.301 (ligand), -0.175 (complex)) [13; p. 12]. In the complex ion [Ni(Suc)(DEA)₂], it was observed that the nitrogen atom bound to the ligand metal shifted relative to that of the free ligand ((N) -0.283 (ligand), -0.228 (complex)), and the charges of other heteroatoms in the ligands also changed significantly [14; p. 47]. The distribution of Mulliken effective charges of complexes is shown in fig.4.

In order to predict reaction centers of electrophilic and nucleophilic processes, electrostatic surface potentials were obtained for optimization in B3LYP/6-311G(d, p)/Lanl2DZ geometry. Different values ​​of the electrostatic potential on the surface are depicted in different colors, where the potential increases in the following order: red<yellow<yellow<green<blue. Negative, redmolecular electrostatic potential (MEP) domains are associated with nucleophilic reactivity, and positive (blue) domains are associated with electrophilic reactivity.

In the molecules, negative (red) areas were detected over oxygen and partially nitrogen atoms, and positive (blue) areas around hydrogen atoms. Thus, it is predictable that the electrophilic ligand will be attacked more by oxygen and nitrogen. According to the calculation data (fig.4), the MEP map shows that negative potentials are located around oxygen and nitrogen atoms, positive potentials are around hydrogen atoms, and in complexes, the potentials decrease and this means that the electron field of donor atoms is centered in the center of complex molecules.

Figure 4. [Co(Suc)(MEA)], [Ni(Suc)(DEA)₂] and [Cu(Suc)(TEA)₂] MEP areas and bond lengths in complexes

The green area covers the parts of the molecule with electrostatic potentials close to zero (C–C, C–N).

Figure 5. [Co(Suc)(MEA)] (a), [Ni(Suc)(DEA)₂] (b) and [Cu(Suc)(TEA)₂] (c) distribution of charges of atoms in the compositional complexes

In the complex formed by copper succinate with triethanolamine, two molecules of TEA are placed symmetrically to each other. The reason for this is that the size of the molecule is large and it tries to place the molecules as far as possible to eliminate the mutual steric effect [15; p. 36].

If we consider the charge distribution in the upper occupied and lower vacant molecular orbitals of the synthesized compound, we can see that the main charge distribution is located around the coordination node.

a)                                                                 b)

c)

Figure 6. [Co(Suc)(MEA)] (a), [Ni(Suc)(DEA)₂] (b) and [Cu(Suc)(TEA)₂] distribution of charges in HOMO and LUMO in the complexes

The calculation of the intrinsic reaction coordination (IRC) pathway consists of two internal loops, called the outer and inner loops. The outer loop is performed by IRC points, and the inner loop is performed by steps to optimize the geometry of the molecule for a given IRC point. The geometry of the first IRC point transition state starts in one of two possible descent directions, called the saddle point. Each subsequent IRC point represents the optimized geometry of the previous point. At the beginning of each step, a turning point in the direction opposite to this gradient is determined. When working in complex compound weight coordinates, this direction corresponds to the acceleration of the corresponding atom. The endpoint of this internal reaction coordinate corresponds to the point of minimum energy equidistant from the inflection point from top to bottom.

Figure 9. Intrinsic reaction coordination of the [Co(Suc)(MEA)] complex

Figure 10. Intrinsic reaction coordination of the [Cu(Suc)(TEA)₂] complex

Figure 11. Intrinsic reaction coordination of the [Ni(Suc)(DEA)₂] complex

Conclusions. Based on the obtained quantum-chemical analysis, it was determined that the donor atoms in the ligands in the complex compounds of cobalt, nickel and copper (II) succinates with ethanolamines are nitrogen in the amino group and oxygen in the carbonyl group. From the quantum-chemically calculated internal reaction coordinates of complex compounds, it can be seen that the internal energy of the substance formed as a result of the reaction tends to the minimum, and the reaction rate increases.

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