Synthesis , Characterization and Biological Evaluation of New Dithiocarbamate Ligand and Its Complexes with some Metal Ions

New bidentate dithiocarbamate ligand (NaL) namely [Sodium-2-(((3-methyl -4“(2,2,2-tri fluoro ethoxy) pyridin-2”-yl) methyl) sulfinyl)-1H-benzoimidazole -1-carbodithioate] was prepared. This free ligand was synthesized from the reaction of a (RS)-2-([3-methyl -4-(2,2,2-tri fluoroethoxy) pyridin-2-yl] methyl sulfinyl)-1H benzoimidazole, CS2 and NaOH in methanol as solvent. From reaction of dithiocarbamate salt (NaL) with metal ions (M); Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Pd(II)”, have obtained the DTC complexes at general molecular formula [M(L)2(H2O)2] and [Pd(L)2]. To characterize the ligand and its complexes, used different analyses methods such FTIR, UV-Vis, elemental microanalysis, atomic absoreption, magnetic susceptibility, conductance, melting points, 1 H13 CNMR spectroscopy, thermal analysis and mass spectrum. These studies indicated the formation of DTC complexes which their geometries about metal centers are octahedral; except Pd-complex is square planer. The bacterial activity evaluation against investigated bacterial species indicated that the metal complexes are more active than the free ligand when compared them.


Introduction
" Dithiocarbamates (DTC) are organic compounds, which played an important role in the development of chemistry, especially in coordination chemistry field".This is due to strongly chelating ability towards metal ions [1,2].The high ability of dithiocarbamates (DTC) to react with transition metals allowed them to be as useful ligands in both inorganic and bioinorganic chemistry.This is based on the sway of the anionic N-CS 2 ¯ moiety that has a variety of binding modes; mono, bi and bridging-dentate capable to form very stable complexes [3,4].Interestingly, DTCs can be stabilised at a different oxidation states of metals, the compounds form and coordination geometries that show great structural diversities which range from monomeric to polymeric molecular [5,6].The most common structural arrangements were the square planar and octahedral geometries [7].The great applications are contributed considerably in developing the dithiocarbamates and their complexes, where included; Biomedical applications [8], analytical chemistry applications [9], environmental applications [10], agriculture applications and in the industry [11].Also it investigates about the influence of dithiocarbamates against bacteria, fungi and microorganisms [12].In this paper we report about synthesis, characterisation and bacterial evaluation of new dithiocarbamate ligand and its metal complexes.

Instrumentations
1 H and 13 C-NMR were recorded using ultra shield 400 MHz Switzerland at Kharazmi University, Iran, conductivity measurements were carried out by Philips PW digital meters conductivity in DMSO at 10 -3 M, "FT-IR spectra were recorded as KBr discs in the range 4000-400 cm -1 using Shimadzu 8300s FT-IR spectrophotometer and as CsI discs in the range 400-200 cm -1" ."UV-Visiblespectra were recorded by Shimadzu UV-8300 vis160A ultraviolet spectrophotometer the range of (200-1100) nm at 10 -3 M in DMSO".Metal contents of the complexes were determined by flame atomic absorption using (Shimadzu at A.A 680 GBC 933 plus) atomic absorption spectrophotometer, magnetic susceptibility (μeff.B.M) were recorded by faraday method using balance magnetic susceptibility model (Sherwood Scientific).Melting point was determined by using (Stuart-melting point apparatus)."Determinations of (C, H, N and S) content for prepared compounds were carried out using Heraeus instrument (Vario EL)".Thermogravimetric analysis (TGA) was carried out using an STA PT-1000 Linseis company and mass spectrum by Shimadzu GC-Mass QPA-2013 spectrometer.

Synthesis of free ligand
A standard method was used in the synthesis of dithiocarbamte compounds [13], it was used with a slight modifications to prepare the free ligand Sodium 2-(3-methyl-4-(2,2,2trifluoroethoxy)pyridin-2-yl)methyl)sulfinyl)-1H-benzoimidazole-1-carbodithioate (NaL).Mixed equimolar amounts from reactors in following; (1 g, 2.70mmol) of (RS)-2-([3-methyl-4-(2,2,2-trifluoroethoxy)pyridin-2-yl] methylsulfinyl)-1H benzoimidazole was dissolved in 20ml of absolute methanol in a round bottom flask, then was added (0.10g, 2.70mmol) of sodium hydroxide dissolved in 2ml of double distilled water.The mixture was allowed to stir in a room temperature about 30 minutes and then was placed in ice bath.To this cold solution a pure carbon disulfide (0.163ml, 0.20g, 2.70mmol) was added drop-wise with constant stirring.The mixture was maintained at 0 °C for 4 h to result pale yellow solution then it was allowed at room temperature to evaporate, all of that was cleared in scheme (1).Sodium salt of dithiocarbamate was formed as a pale yellow powder, dried and recrystallized by methanol, washed several times by diethylether, decomposed at 201-203ºC.Yield:"66.67%and elemental microanalysis C.H.N. and S. were listed in Table( 1)".

Synthesis of [Ni(L) 2 (H 2 O) 2 ] complex
" A general method was used to achieve dithiocarbamate complexes [14,15]"."Asolution of (0.101g, 0.425mmol) NiCl 2 .6H 2 O in 10ml ethanol was added drop wise to a round bottom flask, volume (100) ml, which contains a solution of (0.4g, 0.850mmol) of the dithiocarbamate ligand salt (NaL), dissolved in 10ml of ethanol.The reaction mixture was stirred and heated under reflux for 4 h, then was left to evaporate at room temperatures".The resulted solid washed with distilled water then by diethyl ether, dried at room temperature to give a pale green solid, m.p= 271 ºC.Yield: 0.242g (57.81%),Scheme (2) showed that.

Mass Spectrum of the ligand (NaL)"
" The electrospray (+) mass spectrum of NaL is exhibited successive fragments related to ligand s'tructure"."Theparent ion peak for the ligand is observed at m/z = 467.6 which corresponds to M + (15%) for C 17 H 13 N 3 NaO 2 S 3 F 3 ; requires = 467.4.The other peak fragments are shown in Figure (5)."

The IR Spectra for the DTC Complexes
The FTIR spectrum of [Co(L) 2 (H 2 O) 2 ], Figure (6),"exhibits bands related to the ligand with the appropriate shift due to complex formation"."The spectrum displays band at 1629 cm - 1 , which is related to ν(C=N) moiety, when the band at 1587 cm -1 was assigned to ν ar (C=C) modes of aromatic system"."Also the spectrum was displayed band at 1469 cm - 1 , which is related to ν(N-CS 2 ) mode, compared with that detected in the free ligand at 1446 cm -1" ."Thecomplex exhibited two bands, which are attributed to the asymmetric ν(CS 2 ) at1055 cm -1 and symmetric ν(CS 2 ) at 942 cm -1 stretching"."Thesebands are characteristic for an anisobidentate chelating mode of the ligand to the metal ions [27,28]"."Atlower frequency (far FTIR) complex [Co(L) 2 (H 2 O) 2 ], exhibited two bands at 393cm -1 and 375cm -1 that are assigned to the ν(M-S) vibrational mode and supporting the anisobidentate chelation mode of the ligand [27]"."Theν ar (C-H) stretching of the aromatic ring which occurs slightly above 3000 cm -1 is observed at 3068 cm -1 , when the ν(C-H) stretching for the aliphatic group is detected at 2939 cm -1" [19].Also the IR spectrum exhibited broad band at 3471cm -1 and new' band at 816cm -1 that may be attributed to υ(OH) and δ(OH) respectively which refer to coordinated H 2 O molecule (aqua) with Co-complex in molecular formula [29]."TheFTIR spectra for and [Pd(L) 2 ] complexes, Figures (7) show similar trend to that of the [Co(L) 2 (H 2 O) 2 ] complex and same reasoning could be used to interpret the spectrum, all the results are summarized in table (2)." The Electronic Spectra and Magnetic Studies for the DTC Complexes The electronic spectrum of Co II -complex, exhibits five peaks, The first and second peaks at (279 nm=35842 cm -1 ) and (353 nm= 28328cm -1 ) were assigned to the ligand field (L.F), while the third peak at(401 nm=24937 cm -1 ) is due to charge transfer transition.The peaks at visible region (d-d) at (565 nm=17699 cm -1 ), (724 nm=13812 cm -1 ) due to the d-d electronic transition typ ( 4 T 1 g (F) → 4 T 1 g (P) ) and ( 4 T 1 g (F) → 4 A 2 g (F) ) respectively, transitions confirming an octahedral structure around Co(II) central metal ion [30]."Themagnetic susceptibility measurement for the solid Co(II) complex is (4.86)B.M. also is indicative of three unpaired electron per Co(II) ion suggesting consistency with its octahedral environment [31]."The electronic spectrum of Ni-complex showed peaks in the (281nm=35587 cm -1 ) and (352 nm= 28409cm -1 ) were assigned to the ligand field.And another peak in the (390nm=25641 cm -1 ) due to charge transfer transition.And the peaks at visible region at (837 nm=11947 cm -1 ) and (937nm=10672 cm -1 ) due to the d-d electronic transition.These peaks are assigned to ( 3 A 2 g→ 3 T 1 g (P) ) and ( 3 A 2 g→ 3 T 2 g (F) ) respectively, transitions confirming an octahedral structure around Ni (II) ion complex [32]."Themagnetic susceptibility measurement for the solid Ni(II) complex is (2,9) B.M. also is indicative of two unpaired electrons per Ni (II) ion suggesting consistency with its octahedral geometry [31]."The electronic spectrum of Cu-complex showed two peaks in the range (274 nm=36496 cm -1 ) and (352nm=28409 cm -1 ) are assigned to the ligand field.And another peak in the range (371 nm=26954 cm -1 ) is due to charge transfer transition.The peak at visible region at (722 nm=13850cm -1 ) is due to the d-d electronic transition type."Thispeak is assigned to ( 2 Eg→ 2 T 2 g) transition confirming a distorted octahedral structure around Cu(II) ion complex [33]."Themagnetic susceptibility measurement of Cu(II) complex is (1.89)B.M., which suggests the presence of one unpaired electron with its octahedral environment [31]."The electronic spectral of Zn II -and Cd II -complexes.In each case the spectrum showed three intense peaks in the U.V region at (274nm=36496cm -1 , 368nm=27173cm -1 ) and (277nm=36101cm -1 , 347nm=28818cm -1 ) for Zn II and Cd II -complexes respectively, assigned to the ligand field.While the peaks at (406nm=24630cm -1 ) and at (401nm=24937cm -1 ) are assigned to the charge transfer transitions.Finally the metal ion of these complexes belongs to d 10 system and these metals do not show d-d transition.These complexes are diamagnetic as expected and it showed octahedral geometries [34,35].The electronic spectrum of Pd-complex, Figure (8) showed two peaks in the range (302 nm=33112 cm -1 ) and (345nm=28989cm -1 ) are assigned to the ligand field.And another peak in the range (380 nm=26315 cm -1 ) due to charge transfer transition.The peaks at visible region at (719 nm=13908cm -1 ) and (804 nm=12437cm -1 ) due to the d-d electronic transition type.These peaks are assigned to ( 1 A 1 g→ 1 B 1 g) and ( 1 A 1 g→ 1 E 1 g) respectively, transitions confirming a square planer structure around Pd(II) ion complex, This complex is diamagnetic [36].Electronic spectral data and magnetic susceptibility for these complexes are summarised in table (3) 2 .6H 2 O, NiCl 2 .6H 2 O, CuCl 2 .2H 2 O, ZnCl 2 , CuCl 2 .2H 2 O and PdCl 2 ), (RS)-2-([3-methyl -4-(2,2,2-tri fluoroethoxy) pyridin-2-yl] methyl sulfinyl)-1H benzoimidazole, Carbon disulfide, DMSO, Ethanol and Methanol.

1 H
, " 13 C-NMR spectra for the ligand (NaL)" " The 1 H-NMR spectrum for the ligand NaL in Figure (3) showed the following characteristic chemical shift (DMSO-d 6 as a solvent)": The spectrum showed the singlet signal at =8.35 ppm is assigned to proton for C 14 .The singlet chemical shifts at =7.57ppm and 7.55 ppm are assigned to protons for C 7 and C 4 respectively.The signal at chemical shift =7.54 ppm is assigned to the proton for C 15 .The multiple chemical shifts at =7.10 ppm and 7.09 ppm refers to the protons of the C 6 and C 5 respectively.A signal at δ= 4.54 ppm attributed to the two protons for C 19 of methylene group, While a multiple signal at δ= 4.36 ppm attributed to the two protons for C 11 of another methylene group.The chemical shift at δ=2.51 is assigned to DMSO solvent.The chemical shift at δ=2.19 is assigned to the three protons for C 18 of methyl group.The NMR spectral data of ligand was reported in literatures [24,25].The 13 C-NMR spectrum of a ligand NaL, Figure (4) in DMSO-d 6 solvent showed that the chemical shift at = 192.3 ppm attributed to carbon atom C 10 for S=C-S of dithiocarbamate group [4].The carbon atoms C 16 and C 12 resonated with the chemical shifts at δ= 161.2, 160.1 ppm respectively.The carbon atom C 14 resonated with the chemical shift at δ =152.4 ppm.The carbon atoms C 2 , C 9 and C 8 resonated with the chemical shifts at δ = 148.0,144.7 and 127.9 ppm respectively.The carbon atoms C 5 and C 6 resonated with the chemical shift at δ = 125.1 ppm.The carbon atom C 20 of C-F 3 group resonated with the chemical shift at δ =122.4 ppm.Also the carbon atoms C 4 and C 7 resonated with the chemical shifts at δ=121.9, 119.5 ppm respectively.While the carbon atoms C 17 , C 15 resonated with the chemical shifts at δ= 117.0, 106.7 ppm respectively.The carbon atom C 19 for C-O resonated with the chemical shift at δ= 73.8 ppm, While the carbon atom C 11 for C-S=O resonated with the chemical shift at δ= 60.1 ppm.The chemical shift at δ=40.06 ppm attributed to DMSO solvent.Finally the chemical shift at δ =10.5 ppm attributed to the carbon atom C 18 of methyl group.The 13 C-NMR spectral data of ligand was reported in literatures [9,26].