Spectral, Thermal and Antibacterial Studies for Bivalent Metal Complexes of Oxalyl, Malonyl and Succinyl-bis-4-phenylthiosemicarbazide Ligands

Ragab R. Amin^1*, Ahmed A. M. El-Reedy², Tajedin Y. Alansi³, Yamany B. Yamany⁴

¹Basic Science Department, Faculty of Engineering, Nahda University, Beni-Suef, Egypt.
²Basic and Applied Science Department, Faculty of Oral and Dental Medicine, Nahda University, Beni-Suef, Egypt.
³Chemistry Department, Adama Science and Technology University, Adama, Ethiopia.
⁴Pharmaceutical Chemistry Department, Faculty of Pharmacy, Taif University, Taif, Saudia Arabia.

DOI: 10.4236/ojic.2016.62006                

Abstract

The thermogravimetry (TG) and derivative thermogravimetry (DTG) have been used to study the thermal decomposition of some oxalyl (H₄OxTSC), malonyl (H₄MaTSC) and succinyl-bis-4-phenyl- thiosemicarbazide (H₄SuTSC) ligands and their metal complexes using Horowitz-Metzger (HM) and Coats-Redfern methods. The kinetic thermodynamic parameters such as: E^*, ΔH^*, ΔS^*and ΔG^* are calculated from the DTG curves. The isolated complexes have the general composition [M₂(L) (H₂O)₆], where M=Cu(II), Zn(II), L=MaTSC and M=Co(II), Cu(II) or Sn(II) and L=Su TSC and [M₂(L) (H₂O)_n]·nH₂O where M=Cu(II), Co(II) or Sn(II), L=OxTS or Ma TSC. The tested compounds show a good activity against four strains of bacteria Gram negative Escherichia coli, Pseudomonas aeruginosa species and gram-positive Bacillus cereus and Staphylococcus aureus.

Keywords

Metal (II) Complexes, Bis-Thiosemicarbazide, Thermogravimetric, Antibacterial Studies

Received 16 November 2015; accepted 19 February 2016; published 22 February 2016

1. Introduction

Thiosemicarbazide and its derivatives have received considerable attention because of their pharamacological properties [1] . Thiosemicarbazide complexes show a broad spectrum of anticancer activity [2] [3] . Also, thiosemicarbazide derivatives are of current interest with respect to their uses as analytical reagents for separations of metal(II) ions [4] - [7] , analytical determination of metal ions [8] [9] , and clinical analysis [10] . Most of these compounds have antifungal [11] - [12] , antimicrobial [13] and antitumor activity [14] - [16] , as well as radio- pharmaceuticals applications [17] . Continuing our studies for the chemical and electrochemical synthesis of new metal complexes of ligands containing N, S and O atoms through the reaction of metal ions scarified from the anodic dissolution of metals [18] [19] . Our aim work in this paper to report novel complexes prepared from the reaction between bisthiosemicarbazi decompounds which have a good ability to form chelate complexes with transition metal [18] - [20] . We report here the thermal, spectral and biological evaluations of Co(II), Cu(II), Zn(II) and Sn(II) complexes for 1,1-oxalyl, malonyl and succinyl-bis-4-phenylthiosemicarbazide ligands. The modern spectroscopic investigations are used to elucidate the structure of the prepared materials. The thermal decomposition is also used to infer the structure of the metal complexes and to calculate the different thermodynamic activation parameters.

2. Experimental

2.1. The Organic Compounds

1) Preparation of 1,1-Oxalylhydrazide: 1,1-oxalyldihydrazine was prepared by adding oxalyl chloride (7 gm, 0.05 mol) to alcoholic solution of hydrazine hydrate (5 gm, 0.1 mole). The reaction mixture was exothermic and left to cool with stirring. A white crystal precipitate was formed and washed with ethanol diethyl ether and left to dry.

2) Preparation of 1,1-Oxalylbis (4-phenylthiosemicarbazide): It was prepared by adding phenylisothiocynate (2.8 gm, 0.02 mol) to an alcoholic solution of oxalic acid dihydrazide (1.18 gm, 0.01 mole). The reaction mixture was refluxed for 1 hour and left to cool with stirring. The resulting white crystals were collected and washed with ethanol and diethyl ether, respectively. The resulting solids were filtered hot, washed with hot dist. water, EtOH and dried by Et₂O and finally dried in vacuum over silica gel (Figure 1).

3) Preparation of 1,1-Malonylbis-phenylthiosemicarbazide: 1,1-Malonyl bis-4-phenylthiosemicarbazide) was prepared by adding phenylisothiocynate (1.8 gm, 0.02 mol) to an alcoholic solution of malonic acid dihydrazide (1.32 gm » 0.01 mole). The reaction mixture was refluxed for 1 hour and left to cool with stirring. The resulting white crystals were collected and washed with ethanol and diethyl ether, respectively. The resulting solids were filtered hot, washed with hot dist. water, EtOH and dried by Et₂O and finally dried in vacuo over silica gel.

4) Preparation of 1,1-Succinylbis-4-phenylthiosemicarbazide: It was prepared by the same way [20] - [21] .

2.2. The In-Organic Compounds

The preparative results show that the direct electrochemical oxidation of the metals in the presence of a ligand solution is a one-step process and represents a convenient and simple route to a variety of transition metal complexes. The apparatus used in the electrochemical reaction consists of a tall-form 100 mL Pyrex beaker containing 50 mL of the appropriate amount of the organic ligand dissolved in acetone solution. The cathode is a platinum wire of approximately 1 mm diameter. In most cases, the metal (2 - 5 g ) was suspended and supported on a platinum wire. Measurements of the electrochemical efficiency, Ef, defined as moles of metal dissolved per Faraday of electricity, for the M/L system (where L = ligand used) gave E_f = 0.5 ± 0.05 mol・F⁻¹.

2.3. Synthesis of Metals Complexes

Electrolysis of cobalt metal into 60 ml of anhydrous acetone solution of 1,1-oxalaylbis (4-phenylthiosemi-car- bazide)ligand as an example, (1.2 gm, 5 mmol), 0.5 mg Et₄NClO₄ dissolved in two drops of water and 20 V current led to dissolution of 116 mg of Co during 120 min. (E_f = 0.5 mol・F^-1). Since, most of the products are insoluble in the reaction mixture, the collection procedure involved filtration, after which the solid was washed with diethyl ether. The resulting green powder was collected. By the same way Cu, Zn, and Sn complexes were isolated and all the data for carbon, hydrogen and nitrogen were gathered in Table 1.

3. Spectral, Analytical and Physical Measurements

3.1. IR, Raman and 1H-NMR Spectra

Infrared spectra for the three ligands and their metal complexes were recorded by Perkin Elmer FTIR 1605 using KBr pellets (Figures S1-S3). Also, Raman spectra for the ligands, Zinc(II) and Sn(II) metal complexes were recorded in the solid state on Thero Nicolet FT-Raman (USA) with a wavelength 1064 nm power according sample resolution was 8 cm⁻¹ at National Research Center, Cairo, Egypt (Figures S4-S6). The ¹H NMR spectra were recorded on an Varian Mercury VX-300 NMR spectrometer. ¹H-NMR spectra were run at 300 MHz and ¹³C-NMRspectra were run at 75.46 MHz in deuterated dimethylsulphoxide (DMSO-d₆).

3.2. Electronic and Mass Spectra

The electronic spectra for all the ligands and the metal complexes solutions were measured in UV/Vis range (190 - 1100) nm using Helios UV Spectrometer at Center Photo energy, Ain-Shams University. Mass spectra were recorded at SHIMADZU GC MS-QP 1000 EX Micro analytical Center, Cairo Universal, Giza and Al- Azher University, Egypt (Figures S7-S9).

3.3. Magnetic Molar Conductance Measurements

Magnetic measurements were carried out on a Sherwood scientific magnetic balance using Gouy method. Molar conductivities of freshly prepared 1.0 × 10⁻³ mol・L⁻¹ DMSO solutions were measured using Jenway 4010 conductivity meter.

3.4. Microanalytical and Magnetic Measurements

Carbon and hydrogen contents were determined using a Perkin-Elmer CHN 2400 analyser. Magnetic measurements were carried out on a Sherwood scientific magnetic balance using Gouy method.

Table 1. Significant IR spectral bands (cm⁻¹) of the ligand of 1,1-oxalyl-, malonyl, succinylbis-4-phenylthiosemicarbazide and their metal complexes.

3.5. Thermal Investigation

Thermogravimetric analysis (TGA and DTG) were carried out in dynamic nitrogen atmosphere (30 ml/min) with a heating rate of 10˚C/min using a SchimadzuTGA-50H thermal analyzer (Figures S10-S12).

3.6. Antibacterial Investigation

Bacterial cultures and growth conditions: Gram negative Escherichia coli, Pseudomonas aeruginosa species and gram-positive Bacillus cereus, Staphylococcus aureus species and fungal Aspergillus fumingatus, Candidaalbicans were used as test microorganisms. The surface of the medium was inoculated and covered with the tested organisms. The agar surface was allowed to dry from 3 to 5 minutes before applying disks. The disks were dipped into a beaker of the chemicals using sterile forceps and placed them in the previous medium. Cultures plates of bacteria were incubated for grown at 37˚C for 48 hours. Chloramphenicol was used as a standard antibacterial agent and Terbinafin was used as a standard antifungal agent.

4. Results and Discussion

4.1. Infrared Spectra of H₄OxTSC (I) and Its Metal Complexes

The IR spectrum of compound I shows bands at 3306, 3196, and 3092 cm⁻¹ for the free-NH groups present in the ligand. The bands occurring at 1651, 1402, 1342, 902 and 831 cm⁻¹ are assigned to ν(C=O), thioamide I [β(NH) + ν(CN)], thioamide II [ν(CN) + β(NH)], ν(N-N) and ν(C=S), respectively [22] - [27] . The assignments of the infrared bands, Table 1, were performed by comparing the spectra of the complexes with the free ligands. The bands due to ν(C=S) and ν(C=N) groups appeared at 802 and 1533 cm⁻¹. On complexation, the bands of the thiosemicarbazide moiety respect to ν(C=S) and ν(C=N) are shifted towards higher wave numbers and notice that the very strong peak of ν(C=S) may be disappeared or decreasing in its intensity. The bands due to ν(C=S), ν(N?N) and ν(C=N) groups appeared at 835, 1101 and 1602 cm⁻¹ (Figure 1).

The IR spectra of Copper complex Ia compared with ligand H₄OxTS, indicates that bands due to ν(NH), ν(C=O) and ν(C=S) are absent, but new bands appear at ca. 1651 and 831 cm⁻¹ due to ν(N=C) and ν(C-S), respectively, suggesting removal of both the hydrazinic protons via enolisation and thi­oenolisation and bonding of the resulting enolic oxygen and thiolato sulfur takes place with Co(II), Cu(II), Zn(II) and Sn(II). Furthermore, the ligand bands due to thioamide I, thioamide II and ν(N-N) undergo a positive shift of in the range (20 - 41 cm⁻¹), (20 - 56 cm⁻¹) and (22 - 39 cm⁻¹) respectively. Some new appear bands in the range (755 - 777cm⁻¹) assigned to groups (C-S) vibrations. This is also confirmed by the appearance of bands in the range of 395 - 417 cm⁻¹, this has been assigned to the ν(M?N) [28] , and the appearance of bands in the range of 490 - 505 cm⁻¹, this has been assigned to the ν(M?O). A strong band found at 902 cm⁻¹ is due to the ν(N?N) group of the 1,1- oxalylbis(4-phenyl-thiosemicarbazide. Thus the ligand behaves as tridentate chelating agent coordinating through azomethine nitrogen, thiolate sulphur andenolic oxygen (Figure 2, Figure 3).

4.2. Raman Spectra

The Raman spectrum shows bands at 3201 cm⁻¹ for the NH groups present in H₄MaTS ligand. The bands occurring at 1635, 1405, 1355, 1088 and 824 cm⁻¹ are assigned to ν(C=O), thioamide I [β(NH) + ν(CN)], thioamide II [ν(CN) + β(NH)], ν(N-N) and ν(C=S), respectively [29] - [32] (Figure 4). An exhaustive comparison of the Raman spectra of the ligand and complexes gave information about the mode of bonding of the ligand in metal

Figure 1. 1,1-Oxalyl-bis(4-phenylthiosemicarbazide) H₄OxTSC (I).

Ph-NH-CS-NH-NH-CO-CO-NH-NH-CS-NH-Ph.

Figure 2. 1,1-Oxalaylbis(4-phenylthiosemicarbazide) bis-copper trihydrate (Ia).

Figure 3. 1,1-Oxalaylbis-4-phenylthiosemicarbazide distorted octahedral cobalt monoacetonedihydrate (Ib).

Figure 4. 1,1-Malonyl-bis(4-phenylthiosemicarbazide) H₄MaTSC (II). Ph-NH- CS-NH-NH-CO-CH₂-CO-NH-NH-CS-NH-Ph.

complexes. The Raman spectrum of complexes [Zn₂(MaTS)(H₂O)₆]) when compared with [H₄MaTS], indicates that bands due to ν(NH), ν(C=O) and ν(C=S) are absent, but new bands appear at ca. 1593 and 779 cm⁻¹ due to ν(N=C) and ν(C-S), respectively, suggesting removal of both the hydrazinic protons via enolisation and thi­oenolisation and bonding of the resulting enolic oxygen and thiolato sulfur takes place with Zn(II). Furthermore, the ligand bands due to thioamide I, thioamide II and ν(N-N) undergo a positive shift of (39 cm⁻¹), (40 cm⁻¹) and (2 cm⁻¹) respectively. Ramanbands of complexes are appear of bands at (779 cm⁻¹) assigned to groups (C-S) vibrations. It indicates that thione sulphur and also the enolic oxygen coordinates to the metal ion [33] - [35] . Thus, it may be concluded that the ligand behaves as hexadentate chelating agent coordinating through azomethine nitrogen and thiolate sulphur. The Raman spectrum of [H₄SuTS] shows bands at 3201, 3095 and 3063 cm⁻¹ for the two-NH groups present in the ligand. The bands occurring at 1650, 1405, 1355, 900 and 824 cm⁻¹ are assigned to ν(C=O), thioamide I [β(NH) + ν(CN)], thioamide II [ν(CN) + β(NH)], ν(N-N) and ν(C=S), respectively [33] - [35] . Raman spectral data of all the ligands and the metal complexes are summarized in Table 2.

4.3. Electronic Spectra

The electronic spectrum of [Cu₂(OxTS)(H₂O)₆]・3H₂O, Ia, has bands characteristic for an octahedral geometry [35] . The spectrum shows (Table 3) two bands at 20,600 and 31,950 cm⁻¹ assigned to the ⁴T₁g ® ⁴A₂g (n₂) and ⁴T₁g ® ⁴T₁g (P) (n₃) transitions, respectively, in an octahedral structure. These bands were used to calculate the third spin-allowed band, ⁴T₁g ® ⁴T₁g [20] . The other ligand field parameters, B, b and the n₂/n₁ values were calculated to be 1060 cm⁻¹, 1.2 and 2.2, respectively, and are in good agreement with those reported for octahedral Co(II) complexes. The electronic spectrum of [Co(OxTS)(H₂O)₆]・6H₂O, Ib, shows shoulder bands at 32,260 and 20,600 cm⁻¹. The observed bands are due to ²B₁g ® ²Eg and ²B₁g ® ²A₁g transitions, on the basis of octahedral geometry is suggested [35] .

4.4. Magnetic Susceptibility

The observed values of magnetic moment for complexes are generally di­agnostic of the coordination geometry about the metal ion. Co(II) has the electronic configuration 3d^* and should exhibit a magnetic moment higher than that expected for two unpaired electrons in octahedral (1.5 - 3.3 BM). The magnetic moment observed for the Co(II) complexes lies in the value of 3.2 BM which is consistent with the octahedral stereochemistry of the complexes. Room-temperature magnetic moment of the Cu(II) complexes lies in the range of 1.5 BM, corresponding to one unpaired electron.

4.5. ¹H-NMR Spectra

The ¹H-NMR spectra of compounds Ic and IIc on comparing with that of the ligands indicates that the ligands acts as a hex dentate through the nitrogen atom of C=N oxygen atom of C=O and sulfur atom of C=S. ¹H-NMR spectrum of zinc (II) complex is in agreement with the suggested coordination through the C=N and C=S groups by the presence of the signals of (two from 2NH amine groups and two protons from 2NH amide groups).

Table 2. Significant Raman spectra bands (cm⁻¹) of 1,1-oxalyl, malonyl, succinyl-bis(4-phenylthiosemi- carbazide) and its metal complexes.

Table 3. The electronic spectral data of oxalyl, malonyl and succinyl-bis(4-phenylthiosemicarbazide) and its metal complexes.

(H₄OxTS) ¹H-NMRδ (ppm): 9.75(N5, 17H amide group), 1.95(N6, 18H amine group), 3.6(CN9, 21H aromatic), 6.6 - 7.5(CH-aromatic).

[Zn₂(OxTS)(ac)₂]・2H₂O¹H-NMRδ (ppm): 1.19(CH₃ acetone), 2.7(H₂O) (NH amide groups disappeared), (NH amine groups disappeared), 3.5(9,21CNH aromatic), 6.6-7.5(CH-aromatic shifted).

(H₄SuTS)¹H-NMRδ (ppm): 9.7(7,19NH amide group), 1.95(8, 20NH amine group),4(11, 23CNH aromatic), 2.5(3, 4CH₂) 6.6 - 7.75(CH-aromatic).

[Zn₂(SuTS)(ac)₂]2(H₂O)¹H-NMRδ (ppm): 1.1(H₂O), 1.2(CH₃ acetone) (NH amide groups disappeared), (NH amine groups disappeared), 2.5(CH₂), 4(CNH aromatic), 6.6 - 7.75(CH-aromatic shifted).

4.6. Mass Spectrum

The electronic impact mass spectrum of the ligand I shows a molecular ion (M+) peak at m/z = 243 amu corresponding to species C₉H₇N₃OS, which confirms the proposed formula. It also shows series of peaks at 70, 88, 111, 127 and 170 amu corresponding to var­ious fragments. The intensities of these peaks give the idea of the stabilities of the fragments. The electronic impact mass spectrum of the Ia complex 1,1-oxalayl-bis (phenylthiosemicarbazide) cobalt monoacetone dehydrate shows a molecular ion (M+) peak at m/z = 758 amu corresponding to species [C₂₂H₃₀Co₂N₆O₈S₂], which confirms the pro­posed formula. It also shows series of peaks at 39, 75, 90, 111, 127, 138, 169, 184, 201, 226, 243, 271 and 336 amu corresponding to various fragments.

5. Thermogravimetric Analysis

Thermogravimetric analysis curves (TGA and DTG) of I, Ia, Ib and Ic are discussed (Tables 4-6). Compound I was thermally decom­posed in mainly decomposition steps within the temperature range 25˚C - 700˚C. The first step (obs. = 42.5%, calc. = 42.4%) at 25˚C - 237˚C, may be attributed to the liberation of the 2(N₂H₂), 2(HCNS) and 1/2O₂ fragments. The second step at 237˚C - 337˚C (obs. = 30.2%, calc. = 30.4%), is accounted for the removal of 1/2O₂ and C₄H₄.

The complex Ia was thermally decom­posed in five successive decomposition steps within the temperature range 25˚C - 1000˚C. The first step (obs. = 6%, calc. = 6.6%) at 25˚C - 175˚C, may be attributed to the liberation of the 3 water molecules. The second step at 175˚C - 390˚C (obs. = 29.2%, calc. = 28.6%), is accounted for the removal of 2 acetone, 4 water and N₃H₃ fragment. The decomposition third step at 390˚C - 707˚C (obs. = 18.3%, calc = 18.9%) is accounted for the removal of (C₄N₃S₂) fragment. The fourth step at 707˚C - 990˚C (obs. = 22.8%, calc = 22.8%) is accounted for the removal of (C₉H₇) fragment. The rest of the ligand molecule was removed and fifth the decomposition of the Co(II)/L complex molecule ended with a final 2CoO and residual carbon 3/2C₂ fragment (obs. = 23.7%, calc = 22.9%).

The TG curve of Ib complex indi­cates that the mass change begins at 25˚C and continuous up to 1000˚C. The first and second mass loss corresponds to the lib­eration of the 12 water molecules and two (HCN) fragment (obs. = 34.4%, calc = 33.9%) at 25˚C - 342˚C. The third step occurs in the range 342˚C - 475˚C and corresponds to the loss of (CN₄S) (obs. = 12.8%, calc = 12.6%). The fourth and fifth decomposition step are final decomposition organic ligand to the C₁₃H₈, 1/2S₂, O₂ fragments and Cu₂ metal residual atoms (obs. = 52.8%, calc = 53.4%).

Ic complex was thermally decom­posed in mainly five decomposition steps within the temperature range 25˚C - 700˚C. The first decomposition step (obs. = 20.64%, calc = 20.64%) at 25˚C - 245˚C, may be attributed to the liberation of two water and two acetone molecules. The second step at 245˚C - 386˚C (obs. = 23.4%, calc = 23.6%) is accounted for the removal of the 2(HCN), 2N₂ and S₂ fragments. The third step found within the temperature 386˚C - 700˚C (obs. = 19.7%, calc = 19.96%). The rest of the ligand molecule was removed and fourth the decomposition of theligand molecule ended with a final residue of (C₈H₄), (ZnO) and zinc metal (obs. = 36.3%, calc = 35.7%).

Ligand II was thermally decomposed in mainly decomposition steps within the temperature range successive

Table 4. The thermal data of 1,1-oxalylbis(4-phenylthiosemicarbazide) and its metal complexes.

Table 5. The thermal data of 1,1-malonayl-bis(4-phenyl thiosemicarbazide) and its metal complexes.

Table 6. The thermal data of 1,1-succinyl-bis(4-phenylthiosemi carbazide) and its metal complexes.

decomposition steps at 25˚C - 700˚C. The first decomposition step (obs. = 39.14%, calc. = 39%) at 25˚C - 245˚C, may be attributed to the liberation of 2(HNCO), 2H₂S and 2(NH) fragments. The second decomposition step at 245˚C - 345˚C (obs. = 32.8%, calc. = 32.5%), is accounted for the removal of 2(HCN) and (C₂H₂). The decomposition of the ligand molecule ended with a final (C₁₇H₂) residue (obs. = 28%, calc = 28.3%).

The complex IIa was thermally decom­posed in five steps within the temperature range 25˚C - 1000˚C. The first step (obs. = 5.2%, calc. = 4.94%) at 25˚C - 188˚C, may be attributed to the liberation of the two H₂O molecules. The second step at 188˚C - 448˚C (obs. = 33.1%, calc. = 33.5%), is accounted for the removal of 6H₂O, 2N₂, 2(HCN), and C₂H₂ fragments. The decomposition third step at 448˚C - 760˚C (obs. = 23.4%, calc = 22.9%) is accounted for the removal of S₂and O₂ molecules. The fourth step found at 760˚C - 885˚C (obs. = 21.8%, calc = 22.5%) is accounted for the removal of CH₄ and C₁₂H₄ fragments.

The TG curve of IIb complex indicates that the mass change begins at 25˚C and continuous up to 1000˚C. The first and second mass loss corresponds to the liberation of the 6 H₂O molecules (obs. = 16.4%, calc = 15.4%) at 25˚C - 245˚C. The third step occurs in the range 245˚C - 475˚C and corresponds to the loss of N₂, 2(HCN), N₂H₂, and O₂ (obs. = 20.6%, calc = 20.5%). The fourth step at 475˚C - 765˚C (obs. = 42.4%, calc = 42.5%) is accounted for the removal of (C₁₃H₈, S₂) fragments. The fifth steps are final decomposition organic ligand to the C₂ and Cu₂ residual (obs. = 20.6%, calc = 21.5%).

The complex IIc was thermally decom­posed in mainly four steps within the temperature range 25˚C - 700˚C. The first decomposition step (obs. = 15.5%, calc = 15.3%) at 25˚C - 224˚C, may be attributed to the liberation of 6 H₂O. The second step at 224˚C - 338˚C (obs. = 26.5%, calc = 26.9%) is accounted for the removal of 2N₂, S₂, 1/2O₂ and 2(HCN) fragment. The decomposition third step found within the temperature 338˚C - 643˚C (obs. = 18.6%, calc = 18.2%) is accounted for the removal of 1/2O₂, CH₄ and C₂H₂ fragments. The rest of the ligand molecule was removed and fourth the decomposition of the ligand molecule ended with a final residue metal of Zn₂ and C₁₂H₄ fragment (obs. = 39.4%, calc = 39.5%).

Ligand III was thermally decom­posed in mainly decomposition steps within the tem­perature range successive decomposition steps within the temperature range 25˚C - 700˚C (Figure 5). The first decomposition step (obs. = 36%, calc. = 35.8%) within the temperature range 25˚C - 234˚C, may be attributed to the liberation of the 2(HCN), 2N₂ and S₂ fragments. The second decomposition steps found within the temperature range 234˚C - 334˚C (obs. = 32.1%, calc. = 32.3%), which is reasonably accounted by the removal of O₂ and C₄H₆. The decomposition of the ligand molecule ended with a final C₁₂H₁₀ residue (obs. = 31.86%, calc = 31.7%).

The complex IIIa was thermally decom­posed in four successive decomposition steps within the temperature range 25˚C - 1000˚C. The first decomposition step (obs. = 31.9%, calc. = 32%) within the temperature range 25˚C - 332˚C, may be attributed to the liberation of the 6water molecules, 2(HCN) and N₂H₂ fragments. The second decomposition steps found within the temperature range 332˚C - 550˚C (obs. = 16.9%, calc. = 16.8%), which is reasonably accounted by the removal S₂, O₂ and C₂H₂ fragments. The rest of the ligand molecule was removed and fourth the decomposition of the Co(II)/L complex molecule ended with a final 3/2C₂ and Co₂ metal is cobalt residue (obs. = 26.6%, calc = 26.8%).

The TG curve of complex IIIb indicates that the mass change begins at 25˚C and continuous up to 1000˚C. The first mass loss corresponds to the liberation of the 12 water molecules (obs. = 17.8%, calc = 17.8%) within the temperature range 25˚C - 465˚C, (Figure 6). The second decomposition steps found within the temperature range 465˚C - 700˚C (obs. = 15%, calc. = 14.8%), which is reasonably accounted by the removal of 2(HCN), 2N₂ and 2(CH₂) fragments. The decomposition fourth and fifth decomposition step are final decomposition organic ligand to the found within the temperature 910˚C-more than 1000˚C (obs. = 33.3%, calc = 32.6%) which is reasonably accounted for by the removal of carbon and 4(CuO), all the thermal diagrams in Figure S12.

6. Kinetic Studies

1,1-Oxalyl, 1,1-malonyl and 1,1-succinyl-bis-4-phenyl-thiosemicarbazide and all the metal Co(II), Cu(II), Zn(II) and Sn(II) complexes thermodynamic activation parameters of decomposition processes of the samples, namely activation energy, E^*, enthalpy, ΔH^∗, entropy, ΔS^*, and Gibbs free energy change of the decomposition, ΔG^*, were evaluated graphically (Figures S13-S27) by employing the Coats-Redfern and Horowitz-Metzger relations [34] - [36] . All the thermodynamic parameters for the rest of materials, malonyl and Succinyl complexes were also calculated,. All the data for Kinetic thermal studies were summarized in Tables 7-9. The high values of the activation energy illustrated to the thermal stability of the complexes. The activation energies of decomposition

Figure 5. 1,1-Succinyl-bis(4-phenylthiosemicarbazide) (III). Ph-NH-CS-NH- NH-CO-CH₂-CH₂-CO-NH-NH-CS-NH-Ph.

Figure 6. 1,1-Succinyl bis-4-phenylthiosemicarbazide) Tris-copper trihydrate (IIIb).

were in the range 55 - 450 kJ・mol^?1. The high values of the activation energy illustrated to the thermal stability of the complexes. ΔG is positive for reaction for which ΔH is positive and ΔS is negative. The reaction for which ΔG is positive and ΔS is negative considered as unfavorable or non spontaneous reactions. Reactions are classified as either exothermic (ΔH < 0) or endothermic (ΔH > 0) on the basis of whether they give off or absorb heat. Reactions can also be classified as exergonic (ΔG < 0) or endergonic (ΔG > 0) on the basis of whether the free energy of the system decreases or increases during the reaction. The thermodynamic data obtained with the two methods are in harmony with each other. The activation energy of all 1,1-oxalyl-bis (4-phenyl) thiosemicarbazide and its Co²⁺, Cu²⁺, Zn²⁺ and Sn²⁺ complexes is expected to increase in relation with decrease in their radii (Tunali and Ozkar 1993). The smaller size of the ions permits a closer approach of the ligand (H₄OxTSC). Hence, the E value in the first stage for the Zn²⁺ complex is higher than that for the other Sn²⁺, Cu²⁺ and Co²⁺ complex. The correlation coefficients of the Arrhenius plots of the thermal decomposition steps were found to

lie in the range 0.9925 to 0.9995 showing a good fit with linear function. It is clear that the thermal decomposition process of all complexes is non-spontaneous, i.e., the thermal stability of the complexes. The activation energy of Ligand II and its Co²⁺, Cu²⁺, Zn²⁺ and Sn²⁺ complexes is expected to increase in relation with decrease in their radii. The high values of the activation energy illustrated to the thermal stability of the complexes. The data were calculated and are summarized in Table 8. The smaller size of the ions permits a closer approach of the ligand (H₄MaTSC). Hence, the E value in the first stage for the Zn²⁺ complex is higher than that for the other Sn²⁺, Cu²⁺ and Co²⁺ complex. The activation energies of III and its metal complexes are summarized in Table 9. The high values of the activation energy illustrated to the thermal stability of the complexes. It is clear that the

Table 7. Kinetic parameters using the Coats-Redfern (CR) and Horowitz-Metzger (HM) operated for (H₄OxTS) and its complexes.

Table 8. Kinetic parameters using the Coats-Redfern (CR) and Horowitz-Metzger (HM) operated for: (H₄MaTS) and its Co(II), Cu(II), Zn(II) and Sn(II) complexes.

Table 9. Kinetic parameters using the Coats-Redfern (CR) and Horowitz-Metzger (HM) operated for 1,1-succinyl-bis (phenylthiosemicarbazide) and its Co(II), Cu(II), Zn(II) and Sn(II) complexes.

thermal decomposition process of compounds I, II, III and Co²⁺, Cu²⁺, Zn²⁺, Sn²⁺ metal complexes are non-spontaneous, i.e., the materials are thermally stable.

7. Antimicrobial Activity

Three compounds were tested in vitro for their antibacterial activities against four strains of bacteria Gram negative Escherichia coli, Pseudomonas aeruginosa species and gram-positive Bacillus cereus and Staphylococcus aureus. The bacteria were maintained on nutrient agar media. The minimal inhibitory concentration of some of the tested compounds was measured by a threefold serial dilution method. The screening results indicate that not all the compounds exhibited antibacterial activities. In this study, the tested compounds oxalyl, malonyl, and succinyl bis-4-phenylthiosemicarbazide were active against both Bacillus cereus, Staphylococcus aureus which are Gram-positive bacteria as well as Escherichia coli and Pseudomons aeruginose which are Gram-negative bacteria. However, the antibacterial activity was very pronounced against the Gram-negative bacteria and could be classified in the order of very good activity.

8. Conclusion

The activation energies of decomposition of 1,1-oxalyl, 1,1-malonyl and 1,1-succinyl-bis-4-phenyl-thiosemi- carbazide and all the metal complexes are calculated. The data are summarized in Tables 7-9. The high values of the activation energy are illustrated to the thermal stability of the complexes. It is clear that the thermal decomposition process of all 1,1-oxalyl-bis-4-phenylthiosemicarbazide (H₄OxTSC) and its complexes is thermally stable. The activation energy of Ligand II and its Co²⁺, Cu²⁺, Zn²⁺ and Sn²⁺ complexes are expected to increase in relation with decrease in their radii. The high values of the activation energy are illustrated to the thermal stability of the complexes. The data are calculated and are summarized in Table 7, Table 8. The smaller size of the ions permits a closer approach of the ligand (H₄MaTSC). Hence, the E value in the first stage for the Zn²⁺ complex is higher than that for the other Sn²⁺, Cu²⁺ and Co²⁺ complex. The activation energies of III and its metal complexes are summarized in Table 9. The high values of the activation energy are illustrated to the thermal stability of the complexes. It is clear that the thermal decomposition process of compounds I, II, III and Co²⁺, Cu²⁺, Zn²⁺, Sn²⁺ metal complexes are non-spontaneous, i.e., the materials are thermally stable. The tested compound I, II and III show a good activity against four strains of bacteria Gram negative Escherichia coli, Pseudomonas aeruginosa species and Gram-positive Bacillus cereus and Staphylococcus aureus.

Appendix

Figure S1. IR spectra for 1, 1-Malonyl bis-4phenyl thiosemicarbazide and its metal complexes.

Figure S2. IR spectra for 1,1-Oxalyl bis-4phenyl thiosemicarbazide and its metal complexes.

Figure S3. IR spectra for 1, 1-Succinyl bis-4phenyl thiosemicarbazide and its metal complexes.

Figure S4. Raman spectra for 1, 1-Malonylbis-4phenyl thiosemicarbazide and Zinc-metal complex.

Figure S5. Raman spectra for 1, 1-Oxalaylbis-4phenylthiosemicarbazide, Zinc and Tin-metal complexes.

Figure S6. Raman spectra for 1, 1-Oxalaylbis-4phenylthiosemicarbazide, Zinc and Tin-metal complexes.

Figure S7. Ultraviolet and Visible spectra diagram of 1,1-Malonyl-bis (4- phenyl thiosemicarbazide) and its metal complexes.

Figure S8. Ultraviolet and Visible spectra diagram of 1,1-Oxalyl-bis (4- phenyl thiosemicarbazide) and its metal complexes.

Figure S9. Ultraviolet and Visible spectra diagram of 1,1-Succinyl-bis(4- phenyl thiosemicarbazide) and its metal complexes.

Figure S10.TGA and DTGA diagram of 1,1-oxalyl-bis(4- phenyl thiosemicarbazide), H₄OxTSC and its metal complexes.

Figure S11.TGA and DTGA diagram of 1,1-malonayl-bis(4-phenyl thiosemicarbazide), H₄MaTSC and its metal complexes.

Figure S12.TGA and DTGA diagram of 1,1-succinyl-bis(4- phenyl thiosemicarbazide), H₄SuTSC and its metal complexes.

Figure S13. Kinetic data curves of: 1,1-Oxalyl-bis(4-phenyl thiosemicarbazide).

Figure S14. Kinetic data curves of: [Co₂OxTS (ac)₂(H₂O)₄]・3H₂O complex.

Figure S15. Kinetic data curves of [Cu₂OxTS(H₂O)₆]・6H₂O complex.

Figure S16. Kinetic data curves of: [Zn₂OxTS(ac)₂]・2H₂O complex.

Figure S17.Kinetic data curves of [Sn₂OxTS(H₂O)₂] complex.

Figure S18. Kinetic data curves of 1,1-Malonayl-bis(4-phenyl thiosemicarbazide).

Figure S19. Kinetic data curves of [Co₂MaTS(H₂O)₆]・2H₂O complex.

Figure S20.Kinetic data curves of: [Cu₂MaTS( H₂O)₆] complex.

Figure S21.Kinetic data curves of [Zn₂MaTS(H₂O)₆] complex.

Figure S22. Kinetic data curves of [Sn₂MaTS(H₂O)₆]・2H₂O complex.

Figure S23. Kinetic data curves of 1,1-Succinyl-bis(4-phenyl thiosemicarbazide).

Figure S24. Kinetic data curves of [Co₂SuTS(H₂O)₆] complex.

Figure S25. Kinetic data curves of [Cu₂SuTS( H₂O)₆] complex.

Figure S26. Kinetic data curves of [Zn₂SuTS(ac)₂]・2H₂O complex.

Figure S27. Kinetic data curves of [Sn₂SuTS(H₂O)₆] complex.

NOTES

^*Corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

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