Synthesis, Characterisation and Biological Activity of New Co, Ni, Zn and Cd Polymeric Complexes Derived from Dithiocarbamate Ligand

Synthesis of a new class of Schiff-base ligand with a tetrazole moiety to form polymeric metal complexes with Co II , Ni II , Zn II , and Cd II ions has been demonstrated. The ligand was synthesised by a multi-steps by treating 5-amino-2-chlorobenzonitrile and cyclohexane -1,3-dione, the 5,5'-(((1E,3E)- cyclohexane-1,3-diylidene)bis(azanylylidene))bis(2-chlorobenzonitrile) was obtained. The precursor (M) was prepared from the reaction 5,5'-(((1E,3E)-cyclohexane-1,3-diylidene)bis(azanylylidene))bis(2-chlorobenzonitrile) with NaN 3 to obtained (1E,3E)-N 1 ,N 3 -bis(4- chloro-3-(1H-tetrazol-5-yl)phenyl)cyclohexane-1,3-diimine (N). By reacting the precursor (M) with CS 2 /KOH, the required ligand was synthesised. Co (II), Ni (II), Zn (II), Cd (II) ions produce polymeric metal complexes with the formula [M(L)] n when they react with the ligand (L). These complexes were synthesised using the same methods. The geometrical structure of ligand and their polymeric complexes were determined using FTIR, 1 H, 13 C-NMR, electronic spectroscopy, ESMS, magnetic susceptibility, metal and chloride contents, micro elemental analysis and conductance. From the results ,we conclude that the L-complexes demonstrate the production of four-coordinate complexes with tetrahedral geometry for Co(II), Zn(II), and Cd(II), and square planer geometry for Ni (II). We examined the antibacterial activity of both ligand and complexes with two types of bacteria positive ( Bacillus stubtili and Staphylococcus aureus ) and negative ( Escherichia coli and Pseudomonas aeruginosa ) with concentration 10 -2 .


Introduction
Dithiocarbamates (DTCs) are a class of tiny chemical compounds that chelate metal ions extremely well 1 . There has been an abundance of studies and reviews on transition and non-transition metals, indicating that these compounds come in a wide variety of forms 2 . Dithiocarbamate's ligands are more sophisticated organic sulphur compounds. This may be because the CSS group has a low bite angle and is capable of reacting with the majority of metals in the periodic table. By adding a single pair of electrons, sulphur atoms can form complexes with metal atoms 3,4 . Stabilization of DTCs is possible in a wide variety of metal oxidation states, coordination geometries, and compounds. It encompasses a wide range of structural changes, from monomeric to polymeric molecular Abstract Synthesis of a new class of Schiff-base ligand with a tetrazole moiety to form polymeric metal complexes with Co II , Ni II , Zn II , and Cd II ions has been demonstrated. The ligand was synthesised by a multi-steps by treating 5-amino-2-chlorobenzonitrile and cyclohexane -1,3-dione, the 5,5'-(((1E,3E)cyclohexane-1,3-diylidene)bis(azanylylidene))bis(2-chlorobenzonitrile) was obtained. The precursor (M) was prepared from the reaction 5,5'-(((1E,3E)-cyclohexane-1,3diylidene)bis(azanylylidene))bis(2-chlorobenzonitrile) with NaN3 to obtained (1E,3E)-N 1 ,N 3 -bis(4chloro-3-(1H-tetrazol-5-yl)phenyl)cyclohexane-1,3-diimine (N). By reacting the precursor (M) with CS2/KOH, the required ligand was synthesised. Co (II), Ni (II), Zn (II), Cd (II) ions produce polymeric metal complexes with the formula [M(L)]n when they react with the ligand (L). These complexes were synthesised using the same methods. The geometrical structure of ligand and their polymeric complexes were determined using FTIR, 1 H, 13 C-NMR, electronic spectroscopy, ESMS, magnetic susceptibility, metal and chloride contents, micro elemental analysis and conductance. From the results ,we conclude that the L-complexes demonstrate the production of four-coordinate complexes with tetrahedral geometry for Co(II), Zn(II), and Cd(II), and square planer geometry for Ni (II). We examined the antibacterial activity of both ligand and complexes with two types of bacteria positive (Bacillus stubtili and Staphylococcus aureus ) and negative (Escherichia coli and Pseudomonas aeruginosa ) with concentration 10 -2 .
assemblies. Dithiocarbamates' structural structure is defined by their binding capabilities; their physical and chemical properties are described by their monodentate, bidentate chelating, and bidentate bridging variations 5,6 . Dithiocarbamate and dithiophosphinate complexes have a wide range of applications 7 . Dithiocarbamates are significant materials that have been extensively studied in coordination chemistry, medicine, and radiopharmaceutical chemistry, as well as sensing engineering and materials science, for their peculiarly explanatory 8 , biological 9 , and physicochemical 10 , properties, articulated biological activities 11 , and utility as models of metallo-enzyme dynamic sites 12 . DTCs have been shown to have significant biological activity, including antimicrobial activity 13 . When metal coordination is present, sulphur and nitrogen atoms play a critical role in defining the dynamic destinies of various metallobimolecules 14 . Thio macrocylic applications that have been proposed.
The subject of coordination chemistry is Schiff bases and their metal complexes 15 . Dithiocarbamates are a class of compounds that are widely employed because they exhibit a strong and selective affinity for a wide range of metal ions. As a result, over the last decade, self-assembly mediated by metal dithiocarbamate coordination has established itself as a feasible supramolecular approach for the construction of macrocycles, cages, catenanes, and nanoparticles. The bulk of applications are based on dithiocarbamate ligands' metal ion complexation capabilities, which have been demonstrated experimentally with transition metal ions. 16,17 .
Two sulphur donor atoms present in dithiocarbamate ligands efficiently form chelating compounds with all metal ions 18,19 . Due to the strength of their O-bond, dithiocarbamate molecules are capable of stabilising metal ions with a high oxidation state in metal complexes. While the sulphur atoms in dithiocarbamate ligands exhibit similar O-donor and N-back donation features, those ligands exhibit an unusual property in which an additional n-electron flows from nitrogen to sulphur via a planar delocalized orbital system 20,21 . The dithiocarbamate ligand can be coordinated to metals in three ways: bidenate, ansiobidnate, or monodenate 22 . Numerous metallic elements are essential for the biological system to function properly. Without the appropriate metal ion, a biological reaction catalysed by a particular metallo-enzyme would continue at a snail's pace 23 . We want to prepared new dithiocarbamate ligand, and react it with some metal complexes to prepare the polymeric complexes. Also, we want to characterisation the ligand and its metal complexes by spectral techniques and test the biological activity.

Materials and Methods
Aldrich reagents were used exactly as they were received. Prior to use in the preparation, solvents were dried according to normal procedures. All three tests CHNS were carried out on a Heraeus (Vario-EL) instrument. The spectra of I.R. discs used as KBr discs were measured between 4000 and 400 cm -1 using a Shimadzu-8400.S F.T.I.R. spectrophotometer. At a temperature of 25°C, the ultraviolet spectra of 0.001 M solutions of complexes in (CH3)2SO were investigated using Shimadzu ultra-violet (1800) spectroscopy. 1 H and 13 C-NMR spectroscopy, the spectra were collected using a Jeol 300-MHz spectrometer in a DMSO-d6 solution, with tetra-methylsilan (TMS) serving as an internal standard for 1 H-NMR. (ES) mass spectrometry was used to achieve the spectra of ligand and complexes. Stuart's melting point electro-thermal uncorrected melting points were generated using SMP/40 capilary melting point equipment. A Shimadzu was used to determine the metals. 680-G.-(A.A..) 680-G. Chloride content in complexes were determined using the potentiometric titration method with a 686-Titrp processor and 665Dosimat-Metrohim Swiss. A PW 9526 differential conductivity metre was used to determine the conductivity of DMSO solutions, and a magnetic susceptibility balance was utilised to measure the magnetic moments at ambient temperature.

Synthesis of Complexes
A solution of L (1 mmol) in ethanol (20 mL) was stirred for 3 minutes, and then followed by a dropwise addition of metal chloride a solution of metal chloride (1 mmol) in (10mL) which (MCl2 = CoCl2.6H2O, NiCl2.6H2O, ZnCl2 and CdCl2.2H2O). The reaction mixture was heated at reflux for 2 hours under N2 atmosphere, and a solid was formed. The solid product was washed with hot ethanol and dried at room temperature, which achieved Co II , Ni II , Zn II. , and Cd II. as solid polymeric complexes. After that, the solid product was washed in hot ethanol, and dried under vacuum. As shown in Scheme 2, this method produced non-electrolyte complexes with the broad formulas [M(L)] n (where M = Co II , Ni II ., Zn II. , and Cd II. ).

Synthesis
The recently found tetrazole Schiff base ligand L was synthesised in large quantities by reacting cyclohexane-1, 3-dione with 5-amino-2chlorobenzonitrile Scheme 1. The ligands were synthesised in three phases, with methanol serving as the reaction medium. On the other hand, precursor (N) is a neutral precursor. The ligand (L) is a type of electrolyte that can accommodate a single metal ion. The ligand was characterised using  Table 1, FT-IR Table 2, UV-Vis.

*= Decompose
Where M denotes cobalt, nickel, zinc, and cadmium. Scheme 2. The general chemical structure of polymeric complexes After heating, the complex formation was solid compounds, inert to air and soluble in DMF and DMSO, but not soluble in other solvents. Insolubility may refer to the polymeric character 26 . Additionally, because of L essential structural influence, polymeric complex chain assemblies can be formed 27 . As a result, the sulphur atom in the dithiocarbamate segment is required for the vacant position on the unsaturated metal centre to be filled, resulting in ladder-like structures. The complexes' anticipated geometries were obtained by analysing their spectra and other analytical data. The analytical results corroborated the formulas provided Table 1, FT-IR peaks Table 2, UV-Vis spectra are presented Table 3.

FT-IR and NMR Spectra
The FT-IR of precursor (N) and free ligand revealed strong peaks for the functional groups v(N-     The ligand's 1 H and 13 C-NMR spectra indicated signals corresponding to the both proton, and carbon, nuclei (see experimental section). 1 H-NMR spectrum of L Fig. 6, contained a peak between 1.83 and 2.05 ppm, corresponding to two methylen group protons (C4-H, m, CH2, 2H). Between 2.94 and 3.08 ppm, a signal is assigned to (C3,5-H, CH2, 4H, t), whereas the chemical shift between 3.61 and 3.61 ppm is attributed to (C1-H, CH2, s, 2H). The chemical shift of 7.28 ppm indicates that two protons have been assigned to the (C8-H, d, CHaro., 2H). The chemical shift of 7.52 ppm indicates that two protons have been assigned to the (C12-H, d, CHaro., 2H), whereas the signal at 7.86 ppm indicates that two protons have been assigned to the (C9-H, d, CHaro., 2H). Due to its connection to the chloro atom, this peak was moved downfield in compared to the (C8-H) peak (electron withdrawing group). By eliminating the N-H group, the dithiocarbamate group is generated. 13 C NMR showed chemical shifts at 19.991 (C4) and 31.121 (C4) Fig. 7. (C3,5). at 119.706 and 126.562, the chemical shift may be assigned to (C8, 12). The resonances at 137.457 and 137.486 ppm, can be attributed to (C9,10). The chemical shift at 144.332, may be attributed to (C11). The resonance at 162.868ppm may be assigned to (C13). While it is possible to ascribe the chemical signal at 169.988ppm to (C2,6). The signal with a strong chemical shift at 188.749ppm could be assigned to CS2 group.

Electronic Spectra, Magnetic Moments and Conductivity Measurements
L's electronic spectrum, Fig. 13 ,revealed a peak at 289 nm attributable to *. The electronic spectra of the L polymeric complexes demonstrated a hypsochromic shift of the bands associated with the intra-ligand * transition and charge transfer (C.T) peak. The tetrahedral structure is consistent with the spectrum of the Co(II) complex 33,34 Fig. 14. The eff value of magnetic moment indicates a tetrahedral structure with a high spin number. Due to the diamagnetic nature of the Ni (II) complex, a square planar form surrounding the Ni atom has been proposed 35 Fig. 15. When compared to the projected values, the polymeric compounds demonstrated low magnetic moment values at room temperature. This could be a result of metal-metal interactions mediated by dithiocarbamate. Additionally, the assembly of polymeric structures may result in considerable electron delocalization between structures 36 . In the spectra of Zn(II) and Cd(II) complexes, bands associated with intraligand n* and * have been found 37 Figs. 16 and 17. The diamagnetic compounds, as expected, have a d 10 system, implying a tetrahedral structure. L complexes are non-electrolytes based on their molar conductivities 38 , see Table  3.  Individual tests using DMSO alone found no activity against any bacterial species. The effect of the preparation compounds on bacterial species is described in Table 4, which displays the size of inhibition zones measured against the development of various bacterial strains by mm. According to the findings, the ligands had no antibacterial activity against Escherichia coli and Escherichia coli.
As a result, the formation of complexes boosts antibacterial activity when compared to free ligands. The chelation idea may be able to explain why complex activity has risen so much. Chelation decreases the polarity of the metal, allowing it to share some of its positive charge with the donor group and allowing for -electron delocalization across the ring. The cadmium complex is approximately twice as effective against bacteria. This may be explained by the Cd atom's toxicity, as well as its molecular weight and electronic configuration (d 10 system) in comparison to other metal ions. 39

Conclusion
The synthesis coordination chemistry of novel tetrazole Schiff-base ligands capable of polymerizing with Co II , Ni II , Zn II and Cd II ions. Polymeric complexes were formed when the tetrazole ligand was combined with metal chloride. Many measurments are used to the ligand and its complexes. These techniques indicated the development of polymeric complexes with tetrahedral geometries surrounding metal centers for Co (II) , Zn (II). and Cd (II). , and square planar surrounding metal centers for Ni (II). complexes. The low magnetic values and solubility of these chemicals indicate their polymeric nature. Also, the effects of L and its complexes on gram-positive and gram-negative bacteria were tested.