Thermal and Spectral Characterization of Cr(III), Co(II) and Cd(II) Metal Complexes Containing Bis-Imine Novel Schiff Base Ligand Towards Potential Biological Application
Md. Saddam Hossain1, Shudeepta Sarker1, A. S. M. Elias Shaheed1, Md. Mamun Hossain2, Abdul Alim-Al-Bari2, Md. Rabiul Karim1, C. M. Zakaria1, Md. Kudrat-E-Zahan1, *
1Department of Chemistry, University of Rajshahi, Rajshai, Bangladesh
2Department of Pharmacy, University of Rajshahi, Rajshai, Bangladesh
To cite this article:
Md. Saddam Hossain, Shudeepta Sarker, A. S. M. Elias Shaheed, Md. Mamun Hossain, Abdul Alim-Al-Bari, Md. Rabiul Karim, C. M. Zakaria, Md. Kudrat-E-Zahan. Thermal and Spectral Characterization of Cr(III), Co(II) and Cd(II) Metal Complexes Containing Bis-Imine Novel Schiff Base Ligand Towards Potential Biological Application. Chemical and Biomolecular Engineering. Vol. 2, No. 1, 2017, pp. 41-50. doi: 10.11648/j.cbe.20170201.16
Received: January 7, 2017; Accepted: January 21, 2017; Published: February 24, 2017
Abstract: Metal complexes of Cr(III), Co(II) and Cd(II) ions were synthesizedwith a ONS containing Schiff base ligand, 2-bis(2-oxoindolin-3-ylidene)hydrazinecarbothioamide which was derived from the condensation reaction of thiosemicarbazide and isatin. The ligand and complexes were isolated from the reaction in the solid form and characterized by IR, UV-Visible, Thermal analysis and some physical measurements. Spectroscopic evidence indicated that the Schiff base behaved as ONS coordinating hexadentate chelating agent. Magnetic susceptibility data coupled with electronic spectra suggested a distorted octahedral structure of the complexes. The overall reaction was monitored by TLC and UV-Visible spectral analysis. The Schiff base and their metal complexes have been shown moderate to strong microbial activity.
Keywords: Transition Metal Complex, IR, UV-Visible Spectra Analysis, Antibacterial Activity, Schiff Base, TGA and DTG
Schiff bases are condensation products of primary amines and carbonyl compounds. They were first discovered by a German chemist, Nobel Prize winner, Hugo Schiff. Structurally, Schiff base (also known as imine or azomethine) is an analogue of a ketone or aldehyde in which the carbonyl group (C=O) has been replaced by an imine or azomethine group. The versatility and flexibility of Isatin based Schiff base compounds having, acyl, aroyl and heteroacroyl Schiff bases have additional donor sites >C=O, >C=N-, etc. It has made the Schiff base to act as good complexing agents that form a variety of complexes with various transition and inner transition metals and has emphasized the attention of many researchers . Bis-Imines and their derivatives have outstanding characteristics that they can increase molecular conjugate system and enhance photoelectric property. Bis-Schiff base ligands and their coordination compounds having multifunctional groups play an important role in the areas of stereochemistry, structure of science, spectroscopy, magnetic fields . In recent years, sulfur containing ligands such as dithiocarbamates and thiosemicarbazones and their transition metal complexes have received more attention in the area of medicinal chemistry, due to their pharmacological properties, such as antiviral, antibacterial, antifungal, antiparasitic, and antitumor activities . In additon, due to their bonding modes, biological implications, structural diversity, and ion-sensing ability have received thiosemicarbazones as great interest in chemistry . Moreover, Schiff bases are regarded as privileged ligands . Schiff base complexes with different transition metals can act as catalysts for various reactions [6, 7]. The metal complexes of thiosemicarbazone dramatically increase the biological activities such as antibacterial, antifungal, anti HIV, and anti-inflammatory . Thiosemicarbazones and their metal complexes are also applicable in the field of material sciences such as nonlinear optical (NLO) , electrochemical sensing , and Langmuir film . Schiff bases derived from isatin exhibit many neurophysiological and neuropharmacological effects like antimicrobial, antiviral, anticonvulsant, anticancer, antimycobacterial, antimalarial, cysticidal, herbicidal and anti inflammatory activity [12–14]. They also exhibit anti-HIV, antiprotozoal and antihelminthic activities [15–17]. Recently, Cd(II), Ni(II), Co(II) and Zr(IV) metal complexes of bis-imine Schiff base ligand derived from diethylenetriamine and isatin was reported from our laboratory . In view of the interesting application of these type of Schiff base ligands and their metal complexes inspired us for the synthesis, characterization and biological activity studies of metal complexes with Schiff base ligands derived from isatin and thiosemicarbazide.
2.1. Reagents and Chemicals
All the reagents used were of analar grade or chemically pure grade. All metal(II) salts were used as chloride and nitrate. The solvents such as ethanol, methanol, chloroform, diethyl ether, petroleum ether, DMSO (dimethyl sulfoxide), dichloromethane and acetontrile were purified by known procedure .
2.2. Physical Measurement
The melting point or the decomposition temperature of all the prepared ligand and metal complexes were observed in an electro thermal melting point apparatus model No. AZ6512. Vibrational spectra (IR) were recorded with SHIMADZU-8400, FTIR spectrophotometer, (Japan), in the range 4000-400 cm-1 with a KBr disc as reference. UV-Visible spectra of the complexes in DMF (0.0005 molar) were recorded in the region 200-800 nm on a THERMOELECTRON NICOLET evolution 300 UV-Visible spectrophotometer. The SHERWOOD SCIENTIFIC Magnetic Susceptibility Balance that following the Gouy method were used to measure the magnetic moment of the solid complexes. The electrical conductance measurements were made at room temperature in freshly prepared solution (10-3 M) in DMF using a WPACM35 conductivity meter and a dip-cell with a platinum electrode. The thermogravimetric analysis (TGA) was performed on Perkin Elmer Simultaneous Thermal Analyzer, STA-8000. The purity of the ligand and metal complexes were tested by Thin Layer Chromatography (TLC).
2.3. Preparation of Schiff Base [SB]
Isatin/indoline-2,3-dione (2.94 g, 20 mmol ) dissolved in absolute ethanol (30 mL) was added slowly to a constant stirring ethanolic solution of thiosemicarbazide (0.91 g, 10 mmol) containing 5 ml of conc. H2SO4. The reaction mixture was refluxed for 6h. On cooling, a solid orange product was formed which was filtered, washed with ethanol and diethyl ether and dried in vacuum over anhydrous CaCl2. The synthesized reaction of ligand and complexes were monitored by TLC using petroleum ether, ethyl acetate, toluene and methanol as solvent. The solid product obtained was found to be soluble in methanol, DMF and DMSO and insoluble in ethanol, acetone, diethyl ether, petroleum ether and isopropanol. The structure of Schiff base was shown in fig-1.
2.4. Preparation Procedure of Schiff Base [SB] Metal Complexes
The complexes have the general formula [M(SB)]; where M= Cr(III), Co(II), and Cd(II) ions and SB= Synthesized Schiff base ligand (Fig-1). Ethanolic solution (20 mL) of Cromimum(III) nitrate nona hydrate (0.400g, 1 mmol)/ Cobalt(II) chloride hexahydrate (0.2378 g, 1 mmol)/ Cadmimum(II) chloride mono hydrate (0.201 g, 1 mmol) was taken in a two necked round bottom flask and kept on magnetic stirring. A warm ethanolic solution (20 mL) of prepared Schiff base ligand (0.349 g, 1mmole) was added drop wise and stirred with heating for 4h. On cooling, precipitates were formed which were filtered, washed with ethanol, acetone, and diethyl ether and dried in vacuum desiccators over anhydrous CaCl2. The purity of each complexes were tested by TLC using petroleum ether, ethyl acetate, toluene and methanol as solvents. The complexes were soluble in DMSO and DMF. The structure of complex was shown in fig-2.
Where, M= Cr(III), Co(II), Cd(II) and X= Cl-, NO3- ions
3. Result and Discussion
3.1. Physical Properties
Some physical properties of the Schiff base ligand and its metal complexes such as melting point, color, magnetic moment etc are shown in table-1. The complexes are intensely colored, powdered solids, which decomposes above 300°C. Molar conductance values in DMSO (10-3M) showed low values (3-5 µS/cm) indicating  them to be non-electrolyte.
|Compound/Mol. formula||Color yield (%)||Melting point /°C||Conductivity /(µS/cm)|
3.2. Infrared Spectral Analysis
The observed IR-absorption bands 3419,3222 and 3142 cm-1due to aN-H, bN-H and cN-H respectively in the free Schiff base ligand as shown (fig-1). The strong band 1610 cm-1was assigned to ν(C=N) in the Schiff base ligand represented that free –NH2 group of thiosemicarbazide was converted to imine group. The band 1727 cm-1was assigned to ν(C=O) in Schiff base confirmed that carbonyl group of isatin was present in ligand. The strong band 1124cm-1 for ν(C=S) indicated C=S bond was present in the Schiff base ligand . During complexation the band 3222 cm-1 for bN-H shifted to lower absorption frequency evident that it was coordinated to metal atoms. The shifting of bands from 1727, 1610 and 1124 cm-1to lower absorption frequency suggested that C=O, C=N and C=S groups respectively was coordinated to central metal atoms. Also the appearance of new low absorption bands at (482-493), (532-604), (404-434) assigned toν(M-N), ν(M-O) and ν(M-S) respectively  confirmed that O,N and S atoms were coordinated to central metal atoms.
Where, [SB]= Schiff base ligand [C17H11N5O2S]
3.3. Magnetic Moment and UV-Visible Spectral Analysis
The spectral data of both Schiff base ligand 2-bis(2-oxoindolin-3-ylidene) hydrazine carbothioamide and their metal complexes were taken in DMF. The magnetic moment and UV-Visible spectral data was recorded in Table-3. At room temperature magnetic moment value of Cr(III) complex was found to 1.53 B. M representing one unpaired electron per Cr(III) ion. Electronic spectra of Cr(III) in DMF showed bands at 13,321–19,582 and 25,649–27,678 cm-1which may be assigned to 4A2g 4T2g(F) and 4A2g 4T2g(F) respectively . similarly, Co(II) complexes was found to 4.41 B. M indicativeof three unpaired electron per Co(II) ion attaining an octahedral environment, On the other hand Cd(II) complex showed zero magnetic moment that correspond to no unpaired electron per metal ion and showed absorption bands 430 nm that suggested octahedral geometry of the complexes. The electronic spectra of the Co(II) complex showed three bands observed at 15329 - 15496cm-1, 24318 - 24547 cm-1 and 2662 – 26853 cm-1 which may be assigned to 4A2g4T1g(F), 4A2g4T2g(F) and 4A2g4T1g(P) respectively .
|Complexes||µeff (B.M)||λ max (cm-1)||Assignment|
|[C17H11 CrN5O2S]||1.53||13,321–19,582|| |
|[C17H11 CoN5O2S]||4.3||15329 – 15496|| |
|24318 – 24547|| |
|2662 – 26853|| |
3.4. Thermogr Avimetric Analysis
TGA was carried out for solid Cr(III), Co(II) and Cd(II) metal complexes under N2 flow. The heating rate was suitably controlled at 30°C min-1 and the weight loss was measured from the ambient temperature up to 800°C. The TGA and DTG curve of Cr(III) complex was shown in fig-7, the curve indicated that the complex was decomposed into 3 or 4 main steps. Where, the 1St step involves the removal of one molecule of water (calculated 4.29%, experimental 4.12% weight) at temperature range 52-180°C [23, 24]. The part of ligand –NH-CS- was decomposed between temperature range 190-263°C (calculated 10.26%, experimental 10.01% weight). The major fragmentation was occurred at temperature range 273-454°C that suggested the decomposition of ligand part –C8H5N2O from the complex (calculated 72.31%, experimental 65.49% weight) at 3rdsteps of decomposition [25-26]. In the last step at above 630°C temperature the complex was completely decomposed and removed as Cr/CrO (calculated 12.96%, experimental 10.34% weight). From the TGA and DTG curve of [C17H11 CoN5O2S] complex (fig-8) indicated that the complex was stable up to 2800C and decomposition was taken place into three main steps. In 1st step of decomposition the part of ligand –C3HN3S- (calculated 27.27%, experimental 26.39% weight) between 278-297°C were decomposed. At temperature range 405-650°C the rest part of ligand –C7H5NO- (calculated 58.47%, Experimental 51.95% weight) was removed. At above 700°C temperature the complex was decomposed completely and removed as Co/CoO . The [C17H11 CdN5O2S] complex was stable up to 290°C temperature as shown in (fig-9). The TGA and DTG curve of [C17H11 CdN5O2S] complex shown that the complex was decomposed into three main steps, where the major fragmentation was taken place between temperature range 300-700°C which involved the decomposition of ligand. At above 765°C temperature the complex was completely decomposed and removed as Cd/CdO. All the possible degradation pathways is shown in Fig-10.
|Complexes||Steps||Temperature Range/ °C||DTG Peak/ °C||TG mass loss% calc./found||Assignments|
3.5. Antibacterial Activity
The prime objective of performing the antibacterial screening is to determine the susceptibility of the pathogenic microorganism. The tested compound which, in turn is used to selection of the compound as a therapeutic agent. The free Schiff base ligand and their metal complexes were screened for their antibacterial activity against strains the Bacillus cereus ATCC25923, Escherichia coli ATCC 25922, Shigellasonnei, Shigellaboydii, Enterobacter, Salmonella typhinium of 4500. The compounds were tested at a concentration of 50 µg/ 0.01 mL in DMSO solution using the paper disc diffusion method [27-34]. The susceptibility zones were measured in diameter (mm) and the result were listed in table-5. The susceptibility zones were the clear zones around the discs killing the bacteria. All the Schiff base and metal complexes were individually exhibited varying degrees of inhibitory effects on the growth of tested bacterial species.
|Tested Bacteria||Diameter of zone inhibition(mm) of tested compounds||Kanamycin (30µg/disc)|
Where, [SB]= Schiff base ligand[C17H11N5O2S]
In this paper we have explored the synthesis and coordination chemistry of Cr(III), Co(II) and Cd(II) complexes with new Schiff base ligand 2-bis(2-oxoindolin-3-ylidene) hydrazinecarbothioamide was derived from the condensation reaction of thiosemicarbazide and isatin. The physicochemical analysis indicated the formation of six coordinated metal complexes. IR spectral analysis indicated that N, O and S atoms were coordinated to central metal atom. Magnetic moment, UV-Visible and Thermogravimetic analysis confirmed the Proposed structure of Metal complexes. TGA analysis indicated that all the complexes are thermally stable up to 200°C and Cd(II) complex were more stable. Biological activity revealed that the ligand and its metal complexes have antibacterial activity as compared to the standard antibiotic (Kanamycin). The metal complexes had more antibacterial activity than its free Schiff base ligand.
The authors are thanks full to the Science and Technology Ministry of Bangladesh for their financial support. We also thanks to the Chairman, Department of Chemistry, University of Rajshahi, Rajshahi-6205, Bangladesh for the laboratory Facilities.