Synthesis and Characterization of New Bidentate Schiff Base Ligand Type (NO) Donor Atoms Derived from Isatin and 3-Amino Benzoic Acid and Its Complexes with Co(II), Cu(II), Cd(II) and Hg(II) Ions

New bidentate Schiff base ligand (L) namely [(Z)-3-(2-oxoindolin-3ylildeneamino)benzoic acid] type (NO) was prepared via condensation of isatin and 3-amino benzoic acid in ethanol as a solvent in existence of drops of (glac. CH3COOH). The new ligand (L) was characterized base on elemental microanalysis, FT-IR, UV-Vis, 1 H-NMR spectra along with melting point. Ligand complexes in general formula [M(L)2Cl2]. H2O, where: M II = Co, Cu, Cd, and Hg; L= C15H10 N2O3 were synthesized and identified by FT-IR, UV-Vis, 1 H-NMR (for Cd complex only) spectra, atomic absorption, chloride content along with molar conductivity and magnetic susceptibility. It was found that the ligand behaves as bidentate on complexation via (N) atom of imine group and (O) atom of carbonyl group of five member ring. The electronic spectral data and μeff values (Co, Cu) of the complexes exhibited octahedral geometry around Co II , Cu II , Cd II , Hg II metal ions. The results of antibacterial activity showed that only Hg(II) complex has high activity (35 mm) for staphylococcus aureas.


Introduction
1H-indol-2,3-dione (Isatin) is an important substrate, where it can be used for preparing of a wide variety of heterocyclic compounds, such as indoles and a raw material for drug synthesis.Isatin, due to its cis α-dicarbonyl moiety, is a good substrate for complexes formation, either alone or deprotonated, isatin was found in mammalian tissues [1].A wide numbers of Schiff bases and their complexes have been studied for significant class of ligand in coordination chemistry [2].The structure and bonding of Schiff bases complexes assist understanding the complexes.Most of the biological systems possess metal ions in unsymmetrical environments.These structures can be modified through condensation with aldehyde and ketones [3][4][5].Isatin derivatives are reported to show many biological activities like antibacterial, antifungal, antiviral, anti-allergic and anti-inflammatory activities [6][7][8][9][10].The complexes of Schiff bases of pyrazoline derivative have a diversity of applications in biological, analytical, pharmacological areas, and clinical [11].In this paper we synthesized new Schiff base from reacted isatin and 3-aminobenzoic acid and its complexes with Co(II), Cu(II), Cd(II) and Hg(II).

Experimental Chemicals
Regent grade isatin, 3-aminobenzoic acid were obtained from Fluka and used as received while metal salt (Cobalt chloride hexahydrate, Cupper chloride dihydrate, Cadmium chloride monohydrate and Mercury dichloride.

Instruments
The IR spectra for prepared compounds were recorded as KBr discs using a FT-IR tests can Shimadzu (FT-IR) 8300 series spectrophotometer in range (4000 -400 cm -1 ).Electronic spectra were measured in region (200 -1000 nm) for 10 -3 M solution in DMSO at 25 ˚C using Shimadzu 160 A spectrophotometer with 1.000 ≠ 0.001 cm matched quartz cell.Elemental micro analysis were performed on a (C.H. N) analyzer from (Elemental micro analyses, Euro vector, model EA 3000 origin). 1 H-NMR spectra of prepared ligand (L) and cadmium complex were recorder in DMSO-d 6 using model: NMR Ready Pro 60 MHz, Origin: Canada and reported in ppm (S).Electrical conductivity measurements of the complexes were recorded at 25 ˚C for 10 -3 M solution of the sample in DMSO using Eutech 150 conductivity meter.Magnetic susceptibility measurement were obtained by balance magnetic susceptibility model MSB -MKI.Metal contents of all complexes were determined by atomic absorption technique by using Shimadzu (AA 680 G).TG were obtained using apparatus type STA PT -1000 L 1 NSEIS as the temperature range of 30 -600 CO, the measurement obtained in central laboratory.In addition melting points were obtained using (Stuart Melting Point Apparatus) type Dig melt (MSRS).

Synthesis Co(ll), Cu(ll), Cd(ll) and Hg(ll) complexes
(1 mmole) of metal chloride salt in (20 ml) of (C 2 H 5 OH) was mixed with (2 mmole) of new ligand (L) in (20 ml) of warm ethanol in round bottom flask, the pH of reaction mixture is regulated to (7.2).Resulting reaction mixture is refluxed (1-2) hrs on water bath.The solid complex precipitated was filtered off, washed with ethanol and dried under vacuum to give metal complex, scheme (2).

Antimicrobial study of biological activity
Antimicrobial activities of the ligand and the complexes have been carried out against the pathogenic bacteria like Escherichia coli and staphylococcus aureus using nutrient agar medium by disc diffusion method.The test solution was prepared in DMSO and soaked in filter paper of 5 mm diameter and 1 mm thickness.The discs were placed on the already seeded plates and incubated 37 ˚C for 24 hrs.The diameter (mm) of the inhibition zone around each disc was measured after 24 hrs.Streptomycin was used as standard [13].

Results and discussion
New ligand (L) and its complexes [Co(II), Cu(II), Cd(II) and Hg(II)] have been synthesized and identified by spectral measurements and elemental analytical data.They are stable in air.The elemental micro analysis results for the ligand and their metal complexes are in a good agreement with the calculated values.Table (1) shows the stoichometry of the metal (II) complexes and the molar conductance of 10 -3 M of the complexes in DMSO solvent 25 ˚C measured.

IR spectra
The IR spectrum of the free ligand (L) shows strong band at 3384 cm -1 refers to ѵ(O-H) stretching corresponding to carboxylic group, Table (2).The stretching frequency of carbonyl ѵ(C=O) group at 1732 cm -1 in spectrum of ligand shifted to lower frequency in spectra of all complexes, Figure (3).This shifting indicated the coordination between (O) atom of carbonyl group and metal ion [16].The band at 1689 cm -1 in spectrum of free ligand attributed to ѵ(C=N) of imine group which was shifted to lower frequency region suggesting that this group was involved in coordination via (N) atom of imine group was involved in coordination [17,18].Similarly a band ѵ(N-H) stretching frequency at 3205 cm -1 in ligand remains unaffected in complex, Figure (4) providing evidence for its non-coordination.A band at 3448 cm -1 , 3363 cm -1 , 3338 cm -1 , 3240 cm -1 in Cd(II), Co(II), Cu(II) [19] metal complexes refers to overlap band of hydrated water molecules and v(O-H) of carboxyl group.The appearance of new band in the spectra of Cd(II), Co(II), Cu(II) and Hg(II) metal complexes at range (567, 677, 606, 594) cm -1 due to and (487, 577, 471, 484) cm -1 due to ѵ(M-N) [20] and ѵ(M-O) [21] respectively.
The spectrum of Cu(II) complex gave absorption peak at 300 nm, 406 nm due to ligand field.The μ eff value (1.72) B.M was a good evidence for octahedral formula.The peak at 700 nm was caused by electronic transition [25] 2 E g → 2 T 2g .The (d-d) electronic transition of Co(II) and Cu(II) complexes were a good agreement with octahedral geometry around these ions [26].The electronic spectra of Cd(II) and Hg(II) complexes show two absorption peaks at (299 nm and 295 nm) and at (416 nm) due to intra-ligand this indicates no (d-d) electronic transition happened (d 10 -system) in visible region.These complexes are diamagnetic as expected, that is a good result for Cd(II) and Hg(II) octahedral geometry around this ions [27].

Chloride content
The chloride content measurement for all complexes, Table (1) gave approximated values for theoretical values.

Antibacterial activity
Antibacterial activity of ligand and Co, Cu, Cd and Hg complexes against one strain of gram (+ ve) bacteria (Staphylococcus aureus) and gram (-ve) bacteria (Escherichia coli) were recorded.The results indicate only Hg(II) complex have a high activity (35 mm) for staphylococcus aureus.This can be attributed to an Hg(II) complex solution which have ability to solvate the fit layer of bacteria cell and destroy it, Figure (7), Table (4).The difference in the calculation in observe of the residue weight may be related to the sublimation up on thermal decomposition [28].

Conclusion
In this research, we have reported the synthesis of new Schiff base ligand achieved from the reaction of isatin and 3-aminobenzoic acid and then prepared its complexes with [Co(II), Cu(II), Cd(II) and Hg(II)].The structure of the ligand and its prepared complexes were confirmed via FT-IR, U.V-Visible, 1 H-NMR, elemental micro analysis, thermal analysis and chloride content.The ligand behaves as bidentate ligand with metal ions through its (N) atom of azomethine group and (O) atom of carbonyl group of five member ring, forming octahedral geometry around [Co(II), Cu(II), Cd(II) and Hg(II)].