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Section 4. Chemistry
Kadirova Shaxnoza Abdukhalilovna, Doctor of Chemical Sciences, Professor of General and inorganic chemistry Department, National University of Uzbekistan named after Mirzo Ulugbek
Torambetov Batirbay Smetovich, PhD student of Department"General and inorganic chemistry"
of the faculty of Chemistry, National University of Uzbekistan named after Mirzo Ulugbek, Toshmurodov Turdibek Turdimurodovich, Junior researcher of laboratory "Organic sintesis" Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan Ziyaev Abdukhakim Anvarovich, Candidate inchemical science, senior researcher of laboratory "Organic sintesis" Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan
Azimova Durdona Abdullaevna, Master student of the Department of "General and inorganic chemistry" of Chemical faculty, National University of Uzbekistan named after Mirzo Ulugbek
E-mail:.......
SYNTHESIS AND INVESTIGATION OF COORDINATION COMPOUNDS OF ZINC AND COPPER NITRATES WITH 2-ETHYLTHIO-5-ACETAMIDO-1, 3, 4-THIADIAZOLE
Abstract. The coordination compounds of salt nitrates Zn(ll) and Cu(II) on the basis of ligand 2-ethylthio-5-acetamido-1, 3, 4-thiadiazole were synthesized. The synthesized compounds were investigated using the methods of elemental analysis, IR, ESI-mass spectroscopy and thermal analysis. As results, it was concluded that in the complex the ligand is coordinated to metals through the oxygen atoms of the carbonyl group and the nitrogen of the thiadiazole ring.
Keywords: 3d-metals, zinc, copper, 2-ethylthio-5-acetamido-1, 3, 4-thiadiazole, ligand, IR spectra, ESI-mass spectroscopy, structure, composition, thermal analysis.
A comprehensive study of complexation reac- mation of complex compounds in solution and their tions, the identity of the reaction mechanism, the for- isolation in solid form is of undoubted theoretical
active substances, given the phenomenon synergism seems to be very promising [7-8].
The purpose of the work is the synthesis and study of the coordination compounds of zinc and copper nitrates with 2-ethylthio-5-acetamido-1, 3, 4-thiadiazole.
The 2-ethylthio-5-acetamido-1, 3, 4-thiadiazole used as the ligand in the complex compounds (L, amorphous powder, with a gross formula C6H9N3OS2, mp. 194-196 °C, is well soluble in alcohols) was synthesized according to the method [9].
The synthesis of zinc nitrate complex with 2-eth-ylthio-5-acetamido-1, 3, 4-thiadiazole was performed by mixing hot 70% methanol solutions of the metal salt and ligand. The reaction mixture was boiled for 2 hours, filtered, left to crystallize for several days. After a time, small crystalline precipitate fell out, which was filtered, washed with methanol and dried in air. Expected yield of the product, determined T . and the nature of the solubility of the compounds obtained.
According to primary studies, it was determined that the complex was obtained in 70% yield, melted at 243 °C, the resulting complex is well soluble in water. According to the results of elemental analysis, it was identified that the following gross formula corresponds to the complex: ZnC12H22N8O10 (Table 1). The complex with copper nitrate was obtained in a similar way.
Table 1. - Yield, melting point and elemental analysis results of zinc (II) and copper (II) complexes based on 2-ethylthio-5-acetamido-1, 3, 4-thiadiazole
Compounds Yield,% T , melt/ oc Gross-Formula Found/Calculated,%
C H N O
[ZnL2(H,O),](NO,), 70 243 22,2/22,8 3.4/3.5 17.2/17.7 25.4/25.2
[CuL,(H,O),](NO,), 73 225 CUC12H22N8O10S4 22,8/22,3 3.5/3.7 17.8/17.3 25.4/27.1
Table 2. - The main absorption bands in the IR spectra of the ligand and complexes of zinc and copper nitrates based on it, cm-1
Types of vibrations v C=O s v NH S NH v C-N s v C-N v C=N s v -N=N- s v -N=N- v CH as 2 v CH2 vM^O vM^N
1 2 3 4 5 6 7 8
L 1698 3156 1457 1253 1304 1557 1008 1046 3048 2931
and practical interest. In addition, the theoretical and practical results of complex formation reactions with different classes of ligands make it possible to create new complexes, develop new methods for determining metals and obtain highly pure substances, as well as compounds with biologically activity properties.
Derivatives of thiadiazoles are of particular importance among heterocyclic compounds. From the literature [1-4] it is known that thiadiazole derivatives exhibit antibacterial, antimicrobial, herbicidal, and fungicidal properties. Interest in complexes of 3d-metals with biologically active heterocyclic ligands, in particular with thiadiazoles, is primarily due to the prospects of their use as biological preparations in medicine and agriculture [5-7]. The presence of several donor atoms in the thiadiazole molecule contributes to the formation of numerous coordination compounds with transition metal ions with mono- and bidentate coordination of ligands.
As the analysis ofliterature data shows, despite the fact that the history of the development of the chemistry of heterocyclic compounds has not been for a decade, the field of research of heterocyclic compounds based on thiadiazole derivatives as ligands of coordination compounds is insufficiently studied. Although the search among them is a special type ofbiologically
1 2 3 4 5 6 7 8
[ZnL2(H20)2](N03)2 1670 1440 1193 1224 1474 956 1054 550 425
[CuL2(H20)2](N03)2 1622 1486 1293 1486 964 1026 558 430
Figure 1. IR spectra of ligand (a) and complexes of Zn (II) nitrate (b) and Cu (II) (c) based on it
To determine the coordination centers in the ligand molecule, an IR spectroscopic study of the complexes was carried out [10].
Interpretation of the IR spectrum of the Zn(ll) nitrate complex (Table 2) showed that the absorption bands of symmetric stretching vibrations of the C=O bond undergo significant changes at 1698 cm-1 and shift to the low frequency region and manifest themselves at 1670 cm-1. The absorption band of symmetric stretching vibrations of the C=N group from 1557 cm-1 to 1474 cm-1 also changes, shifting to the low-frequency region by ~ 83 cm-1 compared to the position in the IR spectrum of the free ligand. From that it can be deduced that, when coordinating to the complexing ion, two heteroatoms are involved in the ligand molecule - the N4 atoms of the heterocycle and the oxygen of the carbonyl group of the acetylamine substituent. In the IR spectrum of the complex, in contrast to the spectrum of the free ligand, in the low-frequency region at 550 cm-1 and
425 cm-1, new bands appear, attributed, according to [5], to vibrations of the M-O and M-N bonds.
The spectrum of the complex also showed (v(O-H) 3376 cm-1, deformation vibrations at 1614 cm-1, pendulum vibrations at 704 cm-1) new bands corresponding to the absorption bands of the coordinated water molecule.
To determine the relative molecular mass and quantitative study of the complexes, the samples were analyzed by HPLC-mass spectrometry.
ESI mass spectrometry (electrospray) was used to obtain mass spectra of substances using a 6420 Triple Quad LC / MS mass spectrometer (Agilent Technologies, USA). The mass spectra of the sample was recorded with positive ionization. The intensity of the fragmenter is 10.0 V, the gas flow rate of the desiccant is 12 Z/min, the gas temperature is 300 °C, the gas pressure on the needle of the sprayer is 20 psi, the evaporator temperature is 300 °C, and the voltage on the capillary is 4000V.
Figure 2. Mass spectrum of the complex of Zn (II) nitrate based on the ligand 2-ethylthio-5-acetamido-1, 3, 4-thiadiazole, taken under the conditions of ionization by spraying in an electric field, the solvent is acetonitrile
In the ESI-MS spectra of the Zn(NO3)2 and L [ZnL(H2O)2]+ (Fig. 2). In the spectrum there is no complex, four types of complex ions are observed: sharpness peak of the molecular ion M+*, however, [ZnLNO3]+, [ZnL2(HO)2]+ [ZnLHO]+ and there is a peakwith m/z = 537. The most intense in the
spectrum are the peak Zn2+ (m/z = 64) and HL+ (m/z = = 203.9). As a result of the fragmentation ofM+*, peaks appear with m/z = 537.1, m/z = 507, which showed that there are two ligand molecules around the zinc ion — a nitrate anion and water molecules. The nature of ESI-MS fragmentation for the [ZnL2(H20)2]+ complex (m/z = 507) indicates a loss of -H20, which
" [ZnL2(H2O)]+ 489 m/z (<1%)
H2O
[ZnL2(H2O)2]+-
507 m/z (<1%)
corresponds to an unstable ion with m/z = 489 (Fig. 3) with a low intensity. At the next stage, the loss of one ligand molecule from the complex resulted in a more stable ion with m/z = 307. Then we observed a loss of the second ligand molecule, which causes the formation of an ion consisting oftwo water molecules and zinc with m/z = 101 (Fig. 3).
(NO3) [ZnL2(NO3)+2H]+ 537 m/z (3%)
"H2O+,
L
[ZnL(H2O)2+3H]+ 307 m/z (5%)
L
[Zn(H2O)2]+ 101 m/z (30%)
2H2O
Zn2+
101 m/z (100%)
Figure 3. Fragmentation of complex [ZnL2(H2O)2]+
The results of the spectral data obtained for the synthesized complexes show that the studied ligand is coordinated to the central atom by the nitrogen atoms N4 of the heterocycle and the oxygen of the carbonyl group. According to the results of spectral analysis, it was found that the water molecule is also coordinated in the inner sphere, and the nitrate ac-idoligand is extra-sphere, and the coordination polyhedron probably has an octahedral configuration.
To determine thermal stability and mass loss with increasing temperature, the method of thermal analysis was applied.
Thermo-analytical studies of the samples were performed on a Netzsch Simultaneous Analyzer STA 409 PG (Germany) instrument, with a K-type thermocouple (Low RG Silver) and aluminum crucibles. All measurements were carried out in an inert nitrogen atmosphere with a nitrogen flow rate of 50 ml/min. The temperature range of measurements was 20-400 °C, the heating rate was 5 K/min. The amount of sample per measurement is 3 mg. The measuring system was calibrated with a standard set of substances KN03, In, Bi, Sn, Zn.
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Figure 4. Thermal analysis of the complex [ZnL2(H2O)2](NO3)2
Thermocatalytic studies were conducted in the terval, two areas of weight loss with an endother-temperature range from 20 to 400 °C. In this in- mic process are observed on the TG curve: the
first is from 110 °C to 170 °C -6.77% (DSC peak T =144.2 °C, which corresponds to the removal
max '
of two water molecules from the internal sphere of the complex, the second section 240-270 °C (DSC peak Tmax=242.7 °C) corresponds to the melting and decomposition of nitrate anions with the release of NO2 and O2. The enthalpy of these two processes is -243.9 and -210.8 J/g/, respectively.
Based on the conducted studies, it can be concluded that the synthesized coordination compounds of zinc and copper nitrates have an octahedral structure, where two molecules of the heterocyclic ligand
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are coordinated by the bidentate, the fifth and sixth places in the coordination polyhedron are water molecules. According to the results of physico-chemical studies of the synthesized complexes, we can offer the following structure:
