COMPLEX COMPOUNDS OF 2-AMINO 1,3,4-THIADIAZOLE WITH 3d-METALS AND GLUTAR ACID

ABSTRACT

Article discusses the determination of Cu(II), Zn(II), Mn(II), Co(II), Cr(III), and Cd(II) metal salts with mixed ligands based on 2-amino-1,3,4-thiadiazole and glutaric acid. Synthesis of metal complex compounds with 2-amino-1,3,4-thiadiazole and succinic acid, study of the composition, structure and properties of the compounds obtained by the combined use of physio-chemical methods of research, synthesis of complex compounds and their composition, structure and to study its properties and to study the laws of complex formation.

АННОТАЦИЯ

В статье обсуждается определение солей металлов Cu(II), Zn(II), Mn(II), Co(II), Cr(III) и Cd(II) со смешанными лигандами на основе 2-амино-1,3,4-тиадиазола и глутаровой кислоты. Синтез комплексных соединений металлов с 2-амино-1,3,4-тиадиазолом и янтарной кислотой, изучение состава, структуры и свойств соединений, полученных комбинированным использованием физико-химических методов исследования, синтез комплексных соединений и их состава, структуры и изучение ее свойств, а также изучение законы образования комплексов.

Keywords: coordination compounds, ligands, metal-complex formers, IR spectrum, thermal analysis, endothermic and exothermic effects.

Ключевые слова: координационные соединения, лиганды, металлокомплексообразователи, ИК-спектр, термический анализ, эндотермические и экзотермические эффекты.

Introduction. Nowadays, research on synthesis, composition, structure and properties of complex compounds with heteroligands has become more globally widespread. It is important to determine the center of coordination, study the geometric structure, composition and properties of complex compounds with heteroligands. The study of coordination compounds of intermediate metals with nitrogen-containing heterocyclic ligands, including 2-amino-1,3,4-thiadizole, is one of the rapidly developing directions of modern coordination chemistry. 2-amino-1,3,4-thiadizole has a high coordination ability due to the presence of two nitrogen atoms in the molecule. The properties of the complexes of intermediate metals with these ligands are determined by various factors, including the nature of the metal, the presence and type of the substituent in the ligand, and the nature of the anion. Taking these factors into account makes it possible to synthesize complex compounds with different structures and physicochemical properties. Complex compounds synthesis of Zn (II), Cu (II), Ni (II), Co (II), Mn (II) and Cr (III) salts with 2-amino-1,3,4-thiadizole and glutaric acid and to study their composition, structure and properties, and to determine the laws of complex formation is the aim of this work [1-3].

Lab-experience part. Complex compounds were synthesized according to the method known [4]. According to it, 0.001 mol) 0.118 g of glutaric acid (Glu), (0.001 mol) 0.04 g of sodium hydroxide (0.001 mol), 0.101 g of 2-amino-1.3.4-thiadiazole (L) and copper(II) chloride 0.0855 g (0.0005 mol) were obtained. Glutaric acid (Glu) was dissolved in 5 ml of 96% ethanol, sodium hydroxide and cadmium (II) nitrate were dissolved in 5 ml of distilled water. First, sodium hydroxide was added to neutralize the glutaric acid. 2-amino-1.3.4-thiadiazole (L) was poured over it and mixed. The solution became colorless and clear. The mixture was removed for crystallization. After 3 days, small crystals formed, which were filtered and washed several times in ethanol. Yield = 65%. Liquid= 248 ^oC. Zn(II), Cu(II), Ni(II), Co(II), Mn(II) and Cr(III) chloride and nitrate salts with glutaric acid and 2-amino-1.3.4-thiadiazole with mixed ligand complex were synthesized in this way.

Result analysis. The composition, structure and properties of the synthesized complex compounds were analyzed using physico-chemical methods: elemental analysis, IR-spectroscopy, thermal analysis, electron diffuse reflection spectra. In the low-frequency range of the IR spectrum, absorption lines corresponding to metal-ligand bonds are visible. Determining these absorptions is of great importance, because M-L can be used to calculate the force constants of the bond. But in most cases it is difficult to find the absorption lines related to the M - L bond, in the region of 650-50 cm^-1 there are absorption lines related to deformational and vibrational vibrations of ligands. The use of other isotopes of the metal helps to determine the absorption lines belonging to the M-L bond.

Complex compounds with mixed ligands were synthesized with salts of Cu(II), Ni(II), Co(II), Zn(II) and Mn(II) in ethanol solution with glutaric acid and 2-amino-1.3.4-thiadiazole, the composition of L₁²:M:L₂² was determined for the synthesized complex compound. Symmetric and asymmetric valence bond vibrations of the =N-N= bond in the 2-amino-1.3.4-thiadiazole ring were determined in the low-frequency region at 1011-1038 cm^-1, ν(NH₂) at 3396 cm^-1 and the C=N- bond at 1615 cm^-1 region, absorption of characteristic valence vibrations of C-S-C bonds of medium intensity at 641-760 cm^-1 lines were recorded [5]. Also, the characteristic valence vibrations of the CH bond in the heteroring appeared in the high-frequency region at 2953-2984 cm^-1. Compared with the IR spectra of the mixed ligand complexes formed by 2-amino-1.3.4-thiadiazole (L1) and glutaric acid with Cu(II) salt, the symmetric valence vibrations of the C=N bond are 14-20 cm^-1, the =N-N= bond in the heterocyclic ring It was observed that the valence vibrations of 15-22 cm^-1 L1 shifted to the lower vibration region compared to the position of the L1 ligand in the IR spectrum [6].

The valence vibrations of the C-S-C group remained unchanged at 641-760. Here, it can be concluded that the heterocyclic ligand binds to the central atom through a donor-acceptor bond, participating in coordination with unpaired electron pairs of the nitrogen atom in the thiadiazol ring. In the composition of the complex compound, the metal atom is binuclear, 3 nitrogen atoms of the ring near the amino group of the L¹ molecule are connected to the metal through a donor-acceptor bond, and glutaric acid is connected to the metal atom through an ionic bond with the oxygen atoms of the carbonyl group. Table 1 present the results of the IR-spectrum of complex compounds synthesized on the basis of mixed ligands. Vibration spectra of 2-amino-1,3,4-thiadiazole and its complexes with metals were studied by several authors [6].

However, due to their complexity, the interpretation of these spectra causes certain difficulties. From the analysis of literature data, 2-amino-1,3,4-thiadiazole is bidentate in complex compounds with various metals, where it is connected to the central atom of the metal complex with a sulfur atom and a nitrogen atom in the amino group [7]. Absorption areas at 1531, 1483 and 1316 cm^-1 in the IR spectrum of 2-amino-1,3,4-thiadiazole are explained by valence vibrations of C-N bonds [8]. In the spectra of compounds corresponding to these oscillations, fields appear in other circles: the high-frequency components move from the low-frequency circle to the opposite, high-frequency circles. This shows that the values of C=N bonds in these compounds are not equal. The main interest was the appearance of intense lines in the 813-889 cm^-1 region of the valence vibrations of C-S bonds in the IR-spectra. In the literature, these lines are characteristic of the CS valence vibration. When comparing the IR absorption spectra of 2-amino-1,3,4-thiadiazole and its complex compounds, the frequency range of the NH bond valence vibration is compared with that of uncoordinated ligands.

Table 1.

Basic vibrational frequencies of IR spectra (cm-1)

It was studied that the coordination number of the central atom is equal to 6 by forming an ionic bond with the oxygen atom of the carboxyl group of glutaric acid. Based on quantum-chemical calculations, it was supposed to participate in coordination through the oxygen atom in the glutaric acid molecule and through the sulfur in the 2-amino-1,3,4-thiadiazole molecule and the nitrogen atom in the amino group, indeed, the reaction of these atoms was confirmed by the presence of valence vibrations of M←N, M←O bonds at frequencies of 439-477, 525-576 cm^-1 in the IR spectrum of the complexes [9].

Electronic Spectrum of diffusion regression of the powder complex was studied to determine the nature of the ligand and electronic transitions of the synthesized complex compounds, as well as the degree of oxidation of Cu (II), Cr (II) and Mn (II) ions, as well as the spatial structure of the complex compounds. The coupling between the d-d electron transition, which gives the color of the complex ion, and Dq (the energy of splitting the ion into states in the octahedral field) is determined by the ²D term in the ground state from the d-configuration with an octahedral structure. In the octahedral field, this term splits into ²T_2g and ²E_2g states. In the octahedral space, d¹ and d⁶, d⁴ and d⁹ configuration ions are divided into terms the same. In the tetrahedral field, d⁴ and d⁹-configuration ions decompose into lower T_2g and higher E_g terms, while (d¹ and d⁶)-configuration ions decompose into low-energy E_g and higher-energy T_2g terms [10-11].

For complexes of Cu(II) with an octahedral structure (d⁹-configuration), three electronic transitions can be observed according to the Orgel diagram:

³A_2g →  ³T_2g , ³A_2g→ ³T_1g(F),   va ³A_2g→ ³T_1g(P),

In fact, the electronic spectra of the octahedral complex compound containing all [Cu(L)₂∙(Glu)₂∙2H₂O] showed three absorption lines with intense lines at 13900, 17280 and 27570 cm^-1. Figure 2 shows the Electronic Spectrum of diffusion regression lines of complex compounds.

Figure 1. [Cu(L)₂∙(Glu)₂∙2H₂O]

Table 2.

Results of main transition lines (cm^-1)

In octahedral complexes of Co(III) with low-spin (t_2g)6 electronic configuration, electrons can transfer from one singlet A₁g term to other singlet 1T_1g 1T_2g terms:

1A₁g → 1T₁g and A₁g → 1T₂g

Since complexes with a tetrahedral structure do not have a center of symmetry, they may not obey the Laporte selection rule. As a result, the speed of d-d transitions in tetrahedral complexes is much higher than in octahedral complexes.

For the high-spin complex, only one 3T_2g→ 3E_g, electron transition is observed. For a high-spin complex ion, there is only one absorption band at 12000 cm^-1 in the electron spectrum. The blue color of the complex comes from this absorption. According to the diagram for low-spin complexes, two electron transitions 1A₁g→1T ₁g and 1A₁g→1T₂g should be expected. In fact, two absorption bands are observed in the electronic spectra of low-spin complexes.

It was found that 2-amino-1,3,4-thiadiazole-metallo-glutaric acid L:M:L is combined in the ratio 2:1:2 in the synthesized complex compounds. The nitrogen atom in the 2-amino-1,3,4-thiadiazole molecule is donor-acceptor bonded with metal ions, and the oxygen atom of the glutaric acid molecule is bonded through an ionic bond. It was analyzed that the synthesized complex compounds depend on the nature of the metal.

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