The derived family compound hydrazones, thiosemicarbazones are more and more known in chemistry. Many compounds have been published by many research groups. In biological and medical fields, many activity tests have been done and results reported in the literature [2] - [6] . Semithiocarbazone are also used to synthesize metal complexes with transitions of lanthanides metals which generate a large diversity of the crystal structures [7] - [12] . These complexes have many physical properties such as magnetism [13] - [15] , fluorescence [5] [16] [17] or catalysis [18] - [20] . They are used as corrosion inhibitors [21] or as complexing agents for the removal of heavy metals from wastewater [22] . In the present work, we report the synthesis of two new Schiff-based thiosemicarbazone ligands C₃NH₄CONHNC(CH₃)C₆H₄OH H₄L²), their characterization by infrared and NMR spectroscopic methods and the resolution of their chemical structures by single-crystal X-ray diffraction. This synthetic organic compound is also submitted to antioxidant test to study the biologic activity.

All the chemical products and solvents are used without any purification. Thiocarbazide molecule, 2-hydroxacétophénone, cadmium dichloride dihydrated were acquired from Sigma Aldrich Chemicals and used without any further purification.

Infrared spectra were recorded on FTIR Spectrum Two of Perkin Elmer. ¹H, ¹³C{¹H} spectra were recorded on Bruker Avance 250 MHz spectrometer in DMSO-d6. Chemical shift (δ, ppm) are converted to the scale downfield from TMS as reference.

Elemental analyses were performed at the Institut de Chimie Moléculaire, Université de Bourgogne Franche-Comté, Dijon, France.

Single yellow block-shaped crystals of (E)-2-(1-(2-hydroxyphenyl) ethylidene) hydrazine-1-carbothiamide compound were used as supplied. A suitable crystal with dimensions 0.35 × 0.26 × 0.17 mm³ was selected and mounted on a MITIGEN holder oil on a XtaLAB Synergy, Dualflex, HyPix-Arc 100 diffractometer.

The antioxidant activity of H₄L² has been measured by using Akhtar et al. method [1] with some modifications. 3.8 ml of methanolic solution of DPPH (1,1-diphenyl-2-picrilhydrazyl) radicals as acceptor(40 mg/L) in 200 µL of H₄L² in different concentrations. The mixed solution is incubated in obscurity during thirty minutes and the value of absorbance is read at 517 nm in UV-Visible Lambda 365 de Perkin-Elmer spectrometer. The percent of inhibition has been calculated by using the mathematic equation.

CCDC 2332641 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via https://www.ccdc.cam.ac.uk/data_request/cif .

The data of elemental analysis: [%Calc: C = 51.65, H = 5.30, N = 20.08, S = 15.32: %Found: C = 51.47, H = 5.25, N = 19.96, S = 15.22] are corroborated with C₃NH₄CONHNC(CH₃)C₆H₄OH as formular.

Spectroscopic characterization results

The infrared spectrum ( Figure 1 ) reveals that the formation of H₄L² is characterized by the presence of phenolic υ(O-H), imine group υ(C=N) imine and υ(C=S) at 3280 cm⁻¹, 1587 cm⁻¹ 1235 cm⁻¹ et 733 cm⁻¹ respectively [25] . The absence of υ(S-H) in the IR spectrum at 2500 cm^-1 shows that a thione function is formed. NMR spectroscopic characterization reveals many informations. In the ¹H NMR, for example, the two signals as singular at 10.54 ppm and 7.92 ppm are corresponding of NH and OH protons of hydrazon and phenol groups respectively. The aromatic protons appear between 6.89 ppm and 7.52 ppm as multiplate. In the ¹³C NMR spectrum, appear three signals at 178.05 ppm, 148.26 ppm and 146.34 ppm which are attribute to carbon atoms of thione group (C=S), imine (C=N) group and phenolic C-O. The aromatic carbon atoms signals appear as multiplate between 132.1 ppm and 116.31 ppm [26] .

Xray diffractometer characterization results

The organic ligand crystallizes in monoclinic space group P2₁/n. The crystal parameters are given in Table 1 and, length bonds and angles values in Table 2 . The asymmetric unit ( Figure 2 ) is consist of one 2-(1-(2-hydroxyphenyl)ethylidene)hydrazine-1-carbothiamidemolecule which adopt an E configuration in C2=N2 bond. This molecule contains one intramolecular NH---O hydrogen bond which comes from the hydrogen atom of OH group and the nitrogen atom of CN group. In this structure, sulfur S1 atom of thione group and nitrogen N2 atom of azomethine group are in trans conformation compared to N3-C1 [N2-N3-C1-S1 = 178.9(3)˚]. Then nitrogen atoms N1 and N2 are in Cis conformation compared to N3-C1 bond [N2-N3-C1-N1 = −8.06(15)˚]. The value of C1-S1 length bond [1.6980(11) Å] shows that H₄L² is in thione form in solid state [17] . This thione for mis confirmed by length bonds of N-C [N3-N2 = 1.3911(13) Å, N3-C1 = 1.3412(14) Å, N2-C2 = 1.2993(14)-N3 [1.374(4) Å] which values corroborated with N-C simple bonds [27] . The crystalline mesh ( Figure 3 ) is constituted of four organic molecules linked by NH···O intermolecular hydrogen bonds [N1-H(1A)···O2 = 2.9921(13)] and N1-H(1A)···O2 = 3.3577(10) [28] . These secondary interactions between molecules ensure the stability of crystallin network of H₄L² compound.

Symmetry codes: i) −x + 1/2, y − 1/2, −z + 1/2; ii) −x + 1/2, y + 1/2, −z + 1/2; iii) −x + 1, −y + 2, −z + 1.

Antioxidant properties are actually a chemical process that eliminates free radicals in the molecule. To trigger this process, hydrogen must be supplied to the free radicals when they are reduced to non-reactive species. This addition of hydrogen atom would remove the strange electronic characteristic responsible for radical reactivity. The hydrogen reactive using DPPH (1,1-diphenyl-2-picrilhydrazyl) radicals as acceptor, showed that a significant association could be found between the concentration of novel molecule and percentage of inhibition. The antioxydant activity of H₄L² has been evaluated by using DPPH radical method [1] . This method is used as well for biological or organic compounds as inorganic compounds. Figure 4 shows the evolution of antioxydant activity for H₄L² in solution for different concentrations compared to TROLOX solution. The inhibition of DPPH radical increases with the concentration of the organic ligand solution. The inhibition due to H₄L² varied from 5.18% - 25.90% which values are different from the inhibition due to the TROLOX (7.82% - 39.10%) between 100 to 500 µM solution. These results are corroborated with those which have published in the thiosemicarbazone derivative [29] Schiff base 2-(2-imino-1-methylimidazolidin-4-ylidene) hydrazinecarbothioamide.

Reactions between Thiosemicarbaldehyde and 2-hydroxy acetophenone, were studied, leading to the isolation as single-crystal of Thiosemicarbazone (E)-2-(1-(2-hydroxyphenyl)ethylidene)hydrazine-1-carbothiamide. Organic monomers are linked via secondary contacts leading to the formation of layer-like arrangements. The characterization of H₄L² was completed by the measurement of spectroscopic data. The antioxidant activity test gives interesting results. Inbiological activity vue, the results of the antioxydant test permeit to conclude that this organic ligand can be used to biological field.

The authors gratefully acknowledge the Cheikh Anta Diop University (Dakar, Senegal), the Centre National de la Recherche Scientifique (CNRS, France) and the University of Bourgogne Franche-Comté (Dijon, France). They also thank Mrs Fatoumata Aline Toure, Mrs Mame Bigue Gueye for infrared characteisation; Mr. Marcel Soustelle for elemental analyses.