SYNTHESIS AND CHARACTERIZATION OF THE COMPLEX OF 2-AMINO-5-ETHYLTHIO-1,3,4-THIADIAZOLE AND 2-PICOLINIC ACID WITH ZINC ION

JOURNAL OF FOOD SCIENCE VOLUME 3, ISSUE 10, november 2025 ISSN: 2181-385X 61 SYNTHESIS AND CHARACTERIZATION OF THE COMPLEX OF 2AMINO-5-ETHYLTHIO-1,3,4-THIADIAZOLE AND 2-PICOLINIC ACID WITH ZINC ION G.A. Khojabaevaa., A.A. Erejepovaa., R.R. Saburovab., B.S. Torambetova., Sh.A. Kadirovaa. aNational University of Uzbekistan named after Mirzo Ulugbek bKarakalpak State University named after Berdakh https://doi.org/10.5281/zenodo.17976964 Annotation: This article presents the synthesis of a Zn complex with 2-amino-5-ethylthio1,3,4-thiadiazole and picolinic acid, as well as the results of IR and XPS spectroscopy studies. IR spectral analysis indicated that the thiadiazole ligand coordinates in a monodentate manner, with coordination occurring through the nitrogen atom of the thiadiazole ring. In contrast, 2picolinic acid exhibits bidentate coordination, with coordination via both the nitrogen and oxygen (OH) atoms of the carboxyl group. X-ray Photoelectron Spectroscopy (XPS) confirmed the presence of a chlorine atom within the complex, and revealed that the elements are combined in the stoichiometric ratio of Metal:L:Pic = 1:2:2. Thermal effects and the products of thermolysis upon heating of the complex compound were investigated through thermal analysis. Key words: 2-amino-5-ethylthio-1,3,4-thiadiazole, 2-picolinic acid, complex compound, IR spectroscopy, stretching vibration, XPS spectroscopy, elemental analysis, thermal analysis. СИНТЕЗ И ХАРАКТЕРИСТИКА КОМПЛЕКСА 2-АМИНО-5EТИЛТИО-1,3,4-ТИАДИАЗОЛА И 2-ПИКОЛИНОВОЙ КИСЛОТI С ИОНОМ SИНКА АннотаsиY. В данной статье представлено получение комплекса sинка с 2-амино5-eтилтио-1,3,4-тиадиазолом и пиколиновой кислотой, а также результатi исследований методом ИКи РФEС-спектроскопии. Анализ ИК-спектров показал, что лиганад тиадиазола координируетсya монодентатно, при eтом координаsиya осуshествлyaетсya через атом азота тиадиазольного sикла. В отличие от него, 2пиколиноваya кислота проyaвлyaет бидентатнiй характер координаsии, взаимодействуya через атомi азота и кислорода (–ОН) карбоксильной группi. Рентгеновскаya фотоeлектроннаya спектроскопиya (XPS) подтвердила присутствие атома хлора в составе комплекса и показала, что eлементi находyaтсya в стехиометрическом соотношении Ме:L:Pic = 1:2:2. Термогравиметрический анализ позволил установит термические eффектi и продуктi термолиза при нагревании комплексного соединениY. Клyuчевiе слова: 2-амино-5-eтилтио-1,3,4-тиадиазол, 2-пиколиноваya кислота, комплексное соединение, ИК-спектроскопиya, валентнiе колебаниya, XPSспектроскопиya, eлементнiй анализ, термический анализ. JOURNAL OF FOOD SCIENCE VOLUME 3, ISSUE 10, november 2025 ISSN: 2181-385X 62 2-AMINO-5-ETILTIO-1,3,4-TIADIAZOL VA 2-PIKOLINIK KISLOTANING RUX IONI BILAN KOMPLEKS SINTEZI VA TAVSIFI Annotatsiya: Ushbu maqolada 2-amino-5-etiltio-1,3,4-tiadiazol va pikolin kislotasining Zn ioni bilan kompleksi sintez qilingani hamda IQva XPS-spektroskopiyasi yordamida o‘rganilgan natijalar keltirilgan. IQ spektrlarini tahlil qilish natijasida tiadiazol ligandi monodentat tarzda koordinatsiyalanishi va koordinatsiya tiadiazol halqasidagi azot atomi orqali amalga oshishi aniqlangan. Bunga farqli o‘laroq, 2-pikolin kislotasi bidentat koordinatsiya xususiyatini namoyon qilib, karboksil guruhidagi azot va kislorod (–OH) atomlari orqali bog‘lanadi. Rentgen fotoelektron spektroskopiyasi (XPS) kompleks tarkibida xlor atomining mavjudligini tasdiqladi hamda elementlar Me:L:Pic = 1:2:2 stexiometrik nisbatda birikkanini ko‘rsatdi. Termogravimetrik tahlil kompleks birikma qizdirilganda ro‘y beradigan termik jarayonlar va termoliz mahsulotlarini aniqlash imkonini berdi. Kalit soʻzlar: 2-amino-5-etiltio-1,3,4-tiadiazol, 2-pikolin kislotasi, kompleks birikma, IQspektroskopiya, valent tebranish, XPS-spektroskopiya, elementar tahlil, termik tahlil. Introduction. Coordination compounds play a vital role in modern inorganic and bioinorganic chemistry. They are considered the backbone of various chemical industries due to their wide application in different areas such as metal sensing, bioimaging, drug delivery, chemosensor, pharmacological and medicinal chemistry [1]. In recent years, metal complexes based on Schiff base ligands have provided diverse biological properties and excellent biological applications. Some of these are anti-microbial, anti-cancer, antipyretic, anti-inflammatory, soothing, anticonvulsant agents, antioxidant [3], [4], anti-diabetic [5], diuretic activities, analgesic, and DNA binding abilities, etc., [6-11]. They also show a significant role in biological systems, including human beings. For instance, hemoglobin, a carrier of oxygen transportation in the blood, is a metal complex of Fe (II) ions and is vital for human life. In addition, they have been utilized for treating various diseases associated with human beings due to their excellent anti-bacterial, anti-cancer, and anti-viral potential. The coordination compounds of different metal ions such as platinum (Pt), palladium (Pd), ruthenium (Ru), nickel (Ni), chromium (Cr), silver (Ag), and gold (Au) have been used as anti-cancer drugs. Moreover, the metal complex of chromium, gold, and copper ions exhibited excellent anti-bacterial activity. Derivatives of 1,3,4-thiadiazole are a relatively new class of compounds which demonstrate a broad array of biological activity, which makes these compounds of interest to a number of fields in medicinal chemistry and pharmacology worldwide [12-16]. Due to their high fungicidal potency against phytopathogenic fungi the 1,3,4-thiadiazole derivatives are considered JOURNAL OF FOOD SCIENCE VOLUME 3, ISSUE 10, november 2025 ISSN: 2181-385X 63 as potential pesticides [17]. Moreover, their significant antiproliferative activity against a number of cancer cell lines has been reported in parallel with the analgesic and antinociceptive properties [18]. Pyridine carboxylic acids are also known for their various biological applications, e.g. it is known that 2,4-pyridinedicarboxylic acid is capable of protecting certain enzymes from heat inactivation whereas 2,4-, 2,5and 2,6-pyridinedicarboxylic acids were found to inhibit or activate some metalloenzymes [19-20]. For this reason, the synthesis of metallocomplexes of 1,3,4-thiadiazole derivatives and the study of their properties are of great importance in the field of chemistry. Materials and methods. All chemicals used were analytical reagents and were commercially purchased from Sigma-Aldrich. Zn(ClO4)2, 2-amino-5-ethylthio-1,3,4-thiadiazole (L) and 2-picolinic acid (Pic) were used as received. Methanol used as solvent was distilled and dried. Synthesis of Zn[L2Pic2]ClO4. For the synthesis reaction, the molar ratio of Salt:L:Pic is 1:2:2 to a solution of 0.5 mmol of salt in methanol, and solutions of ligands in methanol are added in the sequence L(1) Pic(2). The reaction is refluxed for 8 hours. Then filtered, stored in a dry place for crystallization. The reaction yield is 65%. The structural formula of the complex compound is represented as follows: Results and Discussion. Comparison of the IR spectra of the free ligands demonstrates that significant shifts in frequencies can be indicative of the coordination sites involved in chelation or coordination. The IR spectra of L, Pic [21], and their complex are presented in Fig.1. The analysis of the infrared (IR) spectrum of L revealed significant changes in the absorption bands of the symmetric valence vibrations of the C=N bond within the ring, observed at 1572 cm⁻¹, which shifted to the higher frequency region at 1610 cm⁻¹, resulting in a substantial difference of approximately 38 cm⁻¹ compared to their position in the IR spectrum of the free L. For the valence vibrations of the =N-N= bond, this shift amounted to 14 cm⁻¹, while for the valence vibrations of the C-S bond, it was 18 cm⁻¹ [22]. In the infrared (IR) spectra of the JOURNAL OF FOOD SCIENCE VOLUME 3, ISSUE 10, november 2025 ISSN: 2181-385X 64 complex, a distinct band is observed in the short-wavelength region at 421 cm⁻¹, which is not present in the spectrum of the free ligand. This feature is ascribed to the valence vibrations of the M-N bonds [23]. In contrast, the vibrational frequencies of the C-H and N-H groups remain largely unaffected. In the IR spectra of Pic, a broad, intense absorption band around 3435 cm⁻¹ is attributed to the stretching vibration of hydroxyl groups from water molecules. The bands corresponding to the stretching vibration of the C−H and C=N bonds are situated at 3076 and 1641 cm-1, respectively. The band corresponding to the stretching vibration of the C=O group of the Pic is situated at 1712 cm-1 and disappears in the complex. According to the separation of the bands is indicative of the structure of a given carboxylate, the difference value of 258 cm-1 between the asymmetric (1605 cm-1) and symmetric (1347 cm-1) stretching vibration of the carboxylate group is in line with a bidentate bridging coordination mode of coordination. In addition, the O−H···N type of intermolecular hydrogen bonding of Pic can be seen at 2607 and 2152 cm-1 and it disappears in the complex which phenomenon confirms that the nitrogen atom is coordinated to the metal Zn(II) ion. Figure 1. IR spectra of L and Zn[L2Pic2]ClO4 complex It is widely recognized that X-ray Photoelectron Spectroscopy (XPS) is a valuable technique for determining the stoichiometry and oxidation states of the elements present in complex compounds. The XPS analysis reveals the presence of chlorine atoms on the surface of the complex, indicating the incorporation of a perchlorate anion within its structure Fig.2. Additionally, the elemental composition, expressed in terms of atomic fractions, yields a (M:L:Pic) ratio of 1:2:2. C:\Users\BRUKER\Documents\Bruker\OPUS_8.7.10\DATA\MEAS\L-2.0 L-2 Instrument type and / or accessory 1/17/2025 3241.96 3178.59 3133.83 3105.49 2973.60 2929.12 2867.77 2763.61 2650.18 1618.94 1599.63 1554.36 1522.64 1483.01 1444.11 1431.34 1415.60 1363.57 1321.05 1256.97 1130.53 1079.62 1050.03 1030.69 976.29 879.92 794.92 782.05 755.97 731.61 696.02 674.47 635.86 614.55 571.92 537.95 458.16 444.17 421.73 500100015002000250030003500 Wavenumber cm-1 40 50 60 70 80 Transmittance [%] Page 1/1 C:\Users\BRUKER\Documents\Bruker\OPUS_8.7.10\DATA\MEAS\M.0 M Instrument type and / or accessory 1/17/2025 3418.20 3382.02 3305.05 3251.70 3186.77 2970.71 2936.26 2873.65 1716.17 1610.98 1596.49 1572.71 1519.63 1440.75 1381.54 1345.03 1297.78 1263.88 1211.84 1178.91 1087.14 1065.85 1044.35 1018.50 975.25 856.16 828.87 781.26 750.78 692.92 639.17 620.71 553.33 509.27 462.73 437.28 413.14 500100015002000250030003500 Wavenumber cm-1 50 60 70 80 90 Transmittance [%] Page 1/1 JOURNAL OF FOOD SCIENCE VOLUME 3, ISSUE 10, november 2025 ISSN: 2181-385X 65 Figure 2. XPS analysis of Zn[L2Pic2]ClO4 complex The XPS results, including binding energies; height (CPS) which is a measure of the intensity of the photoelectron peak at a particular binding energy; peak area (P), which quantifies the number of photoelectrons emitted from a specific element or chemical state in the sample; atomic percent and the FWHM (Full Width at Half Maximum) parameters, are presented in Table 1. Table 1. Parameters of XPS analysis of Zn[L2Pic2]ClO4 complex Name Peak BE Height CPS FWHM eV Area (P) CPS.eV Area (N) Atomic % Zn2p3 1023,59 67267,28 5,51 386784,31 510,98 2,84 O1s 534,56 107600,76 5,47 603332,88 3507,43 19,49 C1s 287,82 108779,71 5,65 658902,42 9257,3 51,44 N1s 401,57 60196,78 5,42 328698,58 2973,87 16,52 S2p 166,77 44386,58 5,68 251906,83 1746,97 9,71 Cl2p 201,93 645,59 0,98 234,07 1,14 0,01 Thermogravimetric analysis of the ligand and the complex was conducted over a temperature range of 20°C to 1000°C. Thermal analysis encompasses the evaluation of molecular mass loss and thermo-effects associated with combustion, decomposition, oxidation, and reduction reactions, which occur during thermolysis, pyrolysis, and degradation processes under elevated temperature conditions. The thermogravimetric (TG) curve of the complex indicates an endothermic process at ~180°C, which corresponds to the melting temperature of the complex. The thermolysis process of this complex compound consists of four stages. During the second stage, between 190°C and 500°C, nearly 57% of the total mass is lost due to the decomposition of the organic components. JOURNAL OF FOOD SCIENCE VOLUME 3, ISSUE 10, november 2025 ISSN: 2181-385X 66 This stage is characterized by an exothermic effect. As a result of thermolysis, a metal chloride is formed as the final product, accounting for 20.63% of the mass (Fig.3). Figure 3. Thermal analysis of Zn[L2Pic2]ClO4 complex Conclusion. In conclusion, based on the IR spectrum analysis, it is observed that the thiadiazole ligand is coordinated in a monodentate manner, with coordination occurring through the nitrogen atom of the thiadiazole ring. In contrast, 2-picolinic acid exhibits bidentate coordination, with coordination via both the nitrogen and oxygen (OH) atoms of the carboxyl group. X-ray Photoelectron Spectroscopy (XPS) confirmed the presence of a chlorine atom within the complex, and revealed that the elements are combined in the stoichiometric ratio of Metal:L:Pic = 1:2:2. Thermal effects and the products of thermolysis upon heating of the complex compound were investigated through thermal analysis. REFERENCES 1. Karges J., Stokes R.W., Cohen S.M. (2021). Metal complexes for therapeutic applications. Trends in chemistry, 3(7), 523-534. 2. Fayyaz S., Shaikh M., Gasperini D., Nolan S. P., Smith A. D., Choudhary M. I. (2021). 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