Synthesis and structure of mono and mixed ligand coordination compounds of silver with 2-amino-1-metylbenzimizole

ABSTRACT

For the first time, conditions were developed for the synthesis of mono- and mixed ligands coordination compounds of silver containing 2-amino-1-methylbenzymidazole as the main ligand, and its ligand complex compounds in the mixture with diisopropyldithiophosphate acid, benzhydroxamic acid, diethyldithiocarbamates. The structure and coordination modes of ligand molecules in new mixed-ligand complexes have been established on the basis of a set of spectroscopic data and elemental analysis, and the features of thermal behavior have been revealed, which depend on the nature of complexing agents and ligands.

АННОТАЦИЯ

Впервые разработаны условия для синтеза моно- и смешаннолигандных комплексных соединений серебра, содержащих 2-амино-1-метилбензимидазол в качестве основного лиганда, и его лигандных комплексных соединений в смеси с диизопропилдитиофосфатной кислотой, бензгидроксамовой кислотой, диэтилдитиокарбаматами. Установлены строение и способы координации молекул лигандов в новых смешаннолигандных комплексах на основании совокупности спектроскопических данных и элементного анализа, выявлены особенности термического поведения, которые зависят от природы комплексообразователей и лигандов.

Keywords: silver, ligand, complex, 2-aminobenzimidazole, IR spectroscopy, element analysis, thermogravimetric analysis, quantum chemical calculation

Ключевые слова: серебро, лиганд, комплексное соединение, 2-аминобензимидазол, ИК-спектроскопия, элементный анализ, термогравиметрический анализ, квантово-химический расчет.

Introduction. The rapid development of coordination chemistry is directly related to the study of the role of metal complexes in vital processes. The study of the action mechanism of physiologically active substances on biological membranes, enzymes, etc. is one of the current issues [1-2]. Particular attention is paid to complexes containing heterocyclic compounds containing the nitrogen atom from different classes of biologically active coordination compounds as ligands. In this regard, metal complexes based on benzimidazole derivatives are promising, they play an important role in biological processes, as well as, used as pharmacological agents and effective plant protection products [3-5].

Although the coordination compounds of intermediate metals with aminobenzymidazole derivatives have been considered in many studies [6-9], at the beginning of our study there were no data on mixed ligand coordination compounds of silver containing benzimidazole derivatives. Mixed ligand complexes with 2-aminobenzymidazole as the main ligand and diisopropyldithiophosphate acid, benzohydroxamic acid, diethyldithiocarbamate as the additional ligands around the central atom have not been synthesized, and the reasons for the competitive coordination of the ligands have not been shown. Also coordination compounds of metals with R₂RS₂^- ions have interest for analytical chemistry, such complex compounds are used in industry as accelerators to vulcanization processes, as well as, additives to oils and motor fuels [10,11]. Mixed ligand complex compounds of metals with heterocyclic benzimidazole molecule and R₂RS₂^- ions, contained N coordination atoms, may exhibit specific biological activity. In this regard, the study of the structure and properties of biologically active complexes of silver  with benzimidazole is an urgent problem.

The aim of the work are to synthesize new coordination compounds of mono- and mixed ligands of silver ion with benzimidazole as the main ligand, to study their structure and properties by determination of relationships between composition, structure, properties.

Methods and materials. Chemically pure silver nitrate, benzhydroxamic acid (BGK), sodium diethyldithiocarbamate (DEDTK), potassium diisopropyldithiophosphate (DiPDTF), 96% ethanol were used. The N-heterocyclic ligand 1-amino-2-methylbenzymidazole (MAB)  was synthesized according to the methodology described in the literature [12]. FTIR, element analysis, powder X-ray diffraction (PXRD), differential-thermal analysis (DTA), scanning electron microscopy with energy-dispersion analysis (SEM-EDX) methods were used as research methods.

A LabX XRD-6100 diffractometer with CuKa radiation (Shimadzu, Japan) was used to determine the individuality of the synthesized complex compounds.

To study the complex formation of metals with organic ligands by FTIR spectrometer IRTracer-100 (Shimadzu, Japan), spectra were recorded in the wavelength range of 400-4000 cm^-1 in KBr tablets.

Thermal analysis was performed by the STA 2500 Regulus DTA analyser,  Netzsch (Germany) at a speed of 9 °/min and a sample weight of up to 50 mg at T-1000, TG sensitivity.

Microstructure analysis was performed on a Zeiss EVO MA 10 electron microscope (Carl Zeiss, Germany) with an EDS energy dispersive analysis attachment.

The structures of the main ligand MAВ and the additional ligands is as follows:

Synthesis of mono- and mixed-ligand complex compounds

[Ag(МАВ)₂NO₃]. 0.294 g (0.002 mol) MAВ was dissolved in 10 ml of ethanol with following addition the  10 ml of aqueous solution of 0.170 g of AgNO₃. The next day the white precipitate was filtered under vacuum, washed with cold ethanol, and air-dried. Yield 87%.

[Ag(МАВ)₂(DiPDTF)]. 0.26 g (0.001 mol) of DiPDTF in 10 ml of ethanol was added at stirring to 0.170 g (0.001 mol) AgNO₃. The resulting white precipitate was filtered, washed in water and ethanol. Then dried precipitate dissolved in boiling alcohol, and 0.294 g (0.002 mol) of MAВ in 10 ml of ethanol was added dropwise while stirring. The next day, the precipitate formed at the bottom of the vessel was filtered and washed with water and alcohol, and dried at room temperature, recrystallized in boiling alcohol, and filtered again. White needle-shaped crystals were formed. Yield 88%

[Ag(МАВ)₂(BGK)]. 0.274 g (0.002 mol) of BGC in  ethanol solution was mixed with 0.170 g (0.001 mol) of AgNO₃. The reaction mixture was magnetic stirred at room temperature for one hour. A 0.294 g (0.002 mol) solution of MAВ in 10 ml of ethanol was then added dropwise while stirring. The mixture was heated in a water bath for one hour. After cooling, it was filtered and washed in water and alcohol. The dried white precipitate was re-filtered in boiling absolute alcohol. White needle-shaped crystals were formed. Yield 78%

[Ag(МАВ)₂(DEDTK)]. 0.170 g (0.001 mol) of AgNO₃ was mixed with 0.71 g (0.001 mol) of DEDTK in 10 ml of water. The reaction mixture was magnetic stirred at room temperature for one hour. A 0.294 g (0.002 mol) solution of MAВ in 10 ml of ethanol was then added dropwise while stirring. The mixture was heated in a water bath for one hour. After cooling, it was filtered and washed in water and alcohol. The dried cream-colored precipitate was re-crystallized in boiling absolute alcohol. Yield 85%.

The scheme of synthesis of  mono- and mixed-ligand silver complex compounds obtained as follows:

AgNO₃ + 2L¹ = [Ag(L¹)₂NO₃]

AgNO₃ + 2L¹ + nL² = [Ag(L¹)₂ L_n²] + NO₃^-

L¹ – MAB or FAB

L² – DiPDTF, BGK, DEDTK

The elemental analysis of the synthesized complex compounds is presented in Table 1.

Table 1.

Results of elemental analysis of synthesized silver complexes

All synthesized complex compounds are insoluble in water, low in alcohol, well soluble in benzene, acetone, ether, carbon tetrachloride, chloroform.

Results and Discussion. The scanning SEM-EDX is now widely used to determine of the nitrogen, sulfur and metal amounts in the prepared complex compounds (Figure 1). The silver peaks is clearly seen due to complex formation between the organic ligands and metal ions. The microstructure of the ligands was changed.

The elemental analysis of the obtained complexes was also confirmed by the results of X-ray fluorescence analysis (Fig. 2).

а                                                                                    б

Figure 1. Microstructure of [Ag (MAВ)₂(DiPDTF)] complex compound (a) and SEM-EDX data (b)

Figure 2. EDX result of the [Ag (MAВ)₂(DiPDTF)]

XRD of the synthesized complexes shows that samples do not contain impurities of the original products (Fig. 3). The presence of many XRD intense peaks indicates the complex crystalline structure of the complexes. It was found that XRD patterns, plane d-spacing and line intensity of metal complexes differed from the corresponding ligands. This indicates that the synthesized complex compounds have a separate individual crystal lattice.

Figure 3. XRD of the [Ag(MAB)₂(DEDTK)] complex compound

The FTIR spectra of mono- and mixed-ligand complex compounds of silver and MAB were obtained and analyzed to determine the properties of the ligands coordination centers to the central atom. For comparison, the IR spectra of the MAB, DiPDTF, Dtz, DEDTK organic ligands were analyzed. The FTIR spectra of complex compounds are shown in Figures 4-5.

Symmetrical (ν_s) and asymmetric (ν_as) valence vibrations of the νNH₂ group are observed in the IR spectrum of the primary MAB ligand in the 3452–3200 cm^-1 region. The deformation vibrations of δNH₂ give insignificant intensity in the range of 1615-1655 cm^-1 for the exo-amino group, and endo-amino group shows bands in the range of 1546 cm^-1. The wide band in  the 3087-3034 cm^-1 region belongs to the valence vibrations of the νСH group, and bands in the 1595-1540 cm^-1 range belong to the νС=N groups of the heteroaromatic system [13].

The FTIR spectra of the DiPDTF ligand and its complex compounds are presented in the works [14-17]. The FTIR spectra of the DiPDTF ligand have a number of intense vibration lines. It can include the vibration bands of the P-O-R and P-O groups. The bands in the range 2960–2869 cm^-1 refer to asymmetric and symmetrical vibration of the СН₃-group. The asymmetric and symmetrical deformation vibrations of the dCH₃ group include bands in the region of 1470-1347 cm^-1. The vibrations of the Р-О-R group correspond to the bands in the area of ​​1178-1106, 1025-975, 940-810 cm^-1. The valence vibrations of the nР-О group include lines at 790–740 cm^-1. The presence of asymmetric lines with a maximum of 684–640 cm^-1 is related to the P=S group vibrations. The lines in the area of 590–500 cm^-1 belong to the P-S- vibrations. The P-S-bonds are equivalent, and the negative charge is distributed between the sulfur atoms. During the transition from ligands to complexes, a low-frequency shift of thenP=S and nP-S- lines is observed, it proves the formation of a metal-sulfur covalent bond. IR-spectroscopic study data of mixed ligand silver complexes show the bond formation between MAB and DiPDTF molecules. In this case, the shift of the vibrations lines of the С=N, N-Н and Р=S, P-S- R=S groups, as well as, the expansion and disintegration of the it’s spectral signals. In the FTIR spectrum of [Ag(MAB)₂(DiPDTF)] mixed ligand complexes, it was observed that the vibration frequency (680 cm^-1) of the nР=S group shifted to a lower frequency of 35 cm^-1 than same nР=S frequency of the original DiPDTF molecule. The changes in the nР-S- region, shift of the the nР-S- group bands to a higher frequency of 23 cm^-1 were observed. This confirms that this group is involved in coordination. New lines appear in the spectrum of the [Ag(MAB)₂(DiPDTF)] mixed-ligand silver complex at 3452-3309 cm^-1 (δNH), 1650-1660 cm^-1 (νС=N), 1546 cm^-1 (νС=N), it proves that silver binds DiPDTF heterocyclic and molecules.

Based on the FTIR spectrum of a mixed ligand complex silver compound with MAВ and BGK, the effect of benzohydroxamic acid (C₆H₅-C(O)NHOH) containing amine group in the acidic hydroxamate fragment can be determined. characteristic frequencies of valence vibrations of the С=О and NН groups of the BGK molecule were  observed in the FTIR spectrum [18]. During the complex formation process, the characteristic frequencies of C=O shifted to the lower frequency field, indicating the formation of a complex between the metal and the BGK. The shift of the C=O frequencies in the metal complexes is very large (27 cm^-1), which indicates the formation of a strong complex compound.

Figure 4. FTIR of the [Ag(MAB)₂(DiPDTF)] complex compound

Figure 5. FTIR of the [Ag(MAB)₂(BGK)] complex compound

Differential thermal analysis was performed to determine the thermal stability and composition of the obtained complex compounds (Figure 6). For example, the derivatogram of the [Ag(MAB)₂(DiPDTF)] complex consists from 3 curves. Analysis of the differential thermogravimetric analysis curve (DTGA) (curve 2) shows two intensive decomposition temperature ranges. The decomposition temperature of [Ag(MAB)₂(DiPDTF)] is 163.45 ^oC. First decomposition range corresponds to a 164-307 ^oC, and second decomposition range corresponds to 425-940 ^oC. The most intensive decomposition process takes place in the first decomposition interval. During this interval, the 56.3% of the sample was decomposed. The main mass loss occurs in the range of 150-930 ^oC with 90.2% of the mass loss.

Figure 6. DTA of the [Ag(MAB)₂(DiPDTF)] complex compound

The decomposition temperature of the [Ag(MAB)₂(BGK)] complex compound is 158.41 ^oC. First decomposition range corresponds to 152-317 ^oC with an intensive decomposition process, and second decomposition range have temperature of 325-994 ^oC with 84.6% mass loss. The DTA data is given in Table 2 below. The results show that the total mass loss takes place in the range of 89-995 ^oC.

Table 2.

DTA results of [Ag(MAB)₂(BGK)]

The DTA of the [Ag(MAB)₂(DEDTK)] complex compound shows similar trend. The initial decomposition temperature of [Ag(MAB)₂(DEDTK)] is 149.40 ^oC. First decomposition range is 150-512 ^oC, and second decomposition range is 544-715 ^oC. The basic mass loss occurs in the range of 154-745 ^oC resulting to full thermolysis, the silver oxide remains as a residue.

Conclusion. For the first time, mono-and mixed coordination compounds of silver (I) with MAB and DiPDTF, BGK, DEDTK were synthesized. The composition and structure of the synthesized complex compounds were studied by element, SEM-EDX, thermal analysis and FTIR-spectroscopic method. The synthesized complex compounds have silver ion binds MAB by monodentate mode via endocyclic nitrogen atom of the heterocycle, and the secondary ligands (DiPDTF, BGK, DEDTK) coordinated by bidentate mode forming tetrahedral coordination compounds.

References:

1. Haas, K.L. and Franz, K.J., 2009. Application of metal coordination chemistry to explore and manipulate cell biology. Chemical reviews, 109(10), pp.4921-4960.
2. Maldonado, N. and Amo-Ochoa, P., 2021. The role of coordination compounds in virus research. Different approaches and trends. Dalton Transactions, 50(7), pp.2310-2323.
3. Raducka, A., Czylkowska, A., Gobis, K., Czarnecka, K., Szymański, P. and Świątkowski, M., 2021. Characterization of Metal-Bound Benzimidazole Derivatives, Effects on Tumor Cells of Lung Cancer. Materials, 14(11), p.2958.
4. Wang, X., Ling, N., Che, Q.T., Zhang, Y.W., Yang, H.X., Ruan, Y. and Zhao, T.T., 2019. Synthesis, structure and biological properties of benzimidazole-based Cu (II)/Zn (II) complexes. Inorganic Chemistry Communications, 105, pp.97-101.
5. Hernández-Romero, D., Rosete-Luna, S., López-Monteon, A., Chávez-Piña, A., Pérez-Hernández, N., Marroquín-Flores, J., Cruz-Navarro, A., Pesado-Gómez, G., Morales-Morales, D. and Colorado-Peralta, R., 2021. First-row transition metal compounds containing benzimidazole ligands: An overview of their anticancer and antitumor activity. Coordination Chemistry Reviews, 439, p.213930.
6. Lopez-Sandoval, H., Londono-Lemos, M.E., Garza-Velasco, R., Poblano-Meléndez, I., Granada-Macías, P., Gracia-Mora, I. and Barba-Behrens, N., 2008. Synthesis, structure and biological activities of cobalt (II) and zinc (II) coordination compounds with 2-benzimidazole derivatives. Journal of Inorganic Biochemistry, 102(5-6), pp.1267-1276.
7. Maurya, R.C., Sharma, P. and Sutradhar, D., 2003. Metal Thiocyanato Complexes: Synthesis, Magnetic, and Spectral Studies of Some Mixed‐Ligand Thiocyanato Complexes of Nickel (II) Involving Benzothiazole and Benzimidazole Derivatives. Synthesis and reactivity in inorganic and metal-organic chemistry, 33(3), pp.387-401.
8. Téllez, F., López-Sandoval, H., Castillo-Blum, S.E. and Barba-Behrens, N., 2008. Coordination behavior of benzimidazole, 2-substituted benzimidazoles and benzothiazoles, towards transition metal ions. ChemInform, 39(40), p.i.
9. Korolenko, S.E., Malinina, E.A., Avdeeva, V.V., Churakov, A.V., Nefedov, S.E., Kubasov, A.S., Burlov, A.S., Divaeva, L.N., Zhizhin, K.Y. and Kuznetsov, N.T., 2021. Zinc (II) and cadmium (II) complexes with the decahydro-closo-decaborate anion and phenyl-containing benzimidazole derivatives with linker NN or CN group. Polyhedron, 194, p.114902.
10. Mukhortov I.V., Pochkailo K.A., Doikin A.A., Levanov I.G. Relationship between the structure and tribological characteristics of zinc dialkyldithiophosphates // Mashinostroenie. -2016. -T.16. -No 4. -C. 67-74.
11. Berkani S., Dassenoy F., Minfray C. Model Formation of ZDDP Tri-bofilm from a Mixture of Zinc Metaphosphate and Goethite // Tribology Inter-national. -2014. -V. 79. -P. 197–203.
12. Pozharsky A.F., Anisimova V.A., Tsupak E.B. Practical work on the chemistry of heterocycles. - Rostov University, 1988. -158p
13. Daminova Sh.Sh., Kadirova Z.Ch., Sharipov Kh.T. IR spectroscopic study of transition metals with impregnated sorbents based on Porolas // Uzbekistan chem. journal. -2016. -N6. -P.3-9.
14. Daminova S.S., Kadirova Z. C., Sharipov K. T., Talipov S. A., Hojamberdiev M. Alkyl substituents of P, S, N-containing organic ligands influencing the uptake of Au3+ and Pt2+ ions over a hydrophobic hypercrosslinked polymeric sorbent. Polyhedron, 2020, 184, 114568.
15. Daminova Sh.Sh., Sharipov Kh.T., Pardaeva N. IR-spectroscopic study of Pd (II), Pt (II, IV) and Rh (III) compounds with phosphorus thioacids // XIX International Chernyaev Conference on Chemistry, Analytics and platinum metal technology. 2010. -S. 95-96.
16. Daminova Sh.Sh., Turaev Kh.Kh., Alimnazarov B.Kh., Abdurakhmonov Sh. IR spectroscopic study of the structure of metal complexes with phosphorus dithioacids // XXIV International Chugaev Conf. on coordination chemistry. Abstracts of the report. St. Petersburg, June 15-19, 2009 -S.55-56.
17. Babaeva G., Ruzieva B.Yu., Daminova Sh.Sh., Kadirova Z.Ch., Turaev X.X. Synthesis in IK-spectroscopic study of mixed complexes of dialkilditiofasfatov Ag (I) // VI - Republican scientific-practical conference on "Actual problems of analytical chemistry", dedicated to the 90th anniversary of A.G. Ganiev. April 16-18, 2020, Termez. –S. 193-194
18. Holmén B. A., Tejedor-Tejedor M. I., Casey W. H. Hydroxamate complexes in solution and at the goethite-water interface: A cylindrical internal reflection Fourier transform infrared spectroscopy study //Langmuir. – 1997. – Т. 13. – №. 8. – С. 2197-2206.