Crystal Structure and Cyclic Voltammetric Studies on the Metal Complexes of N-( Dimethylcarbamothioyl )-4-fluorobenzamide

We synthesized N-(dimethylcarbamothioyl)-4-fluorobenzamide compound and its copper(II) and nickel(II) complexes. The structures of compounds have been characterized by elemental analysis and spectral data (IR, H NMR). Furthermore, crystal and molecular structure of the synthesized complexes have been identified by using single crystal X-ray diffraction data. In the complexes formation the metal atom was coordinated via two sulfur atoms and two oxygen atoms. The single crystal structure of copper(II) and nickel(II) complex exhibits slightly distorted square planar geometry. The oxygen atoms are in a cis configuration. It appeared that the lengths of the thiocarbonyl and carbonyl bonds are longer than the average for C=S and C=O; meanwhile the C-N bonds in the complex ring appeared to be shorter than the average for C-N single bonds. These data show that C-O, C-S, and C-N bond lengths of the complexes suggest considerable electronic delocalization in the chelate ring. All bond lengths and angles obtained as a result of the analyses are found to be within experimental error limits. The obtained crystal analysis data shows that the structure of complex compounds is compatible with similar compounds in literature. Electrochemical behavior of complexes has been investigated by cyclic voltammetry technique in aprotic media. From the cyclic voltammetric investigation, both of the complexes have demonstrated electroactive properties.


Experimental
2.1.Chemicals.All chemicals used in present study such as 4-fluorobenzoyl chloride, potassium thiocyanate, dimethyl amine, hydrochloric acid, nickel acetate, copper acetate, sodium hydroxide, tetrabutylammonium hexafluorophosphate, dichloromethane, and ethanol were purchased from Merck.All solvents and chemicals were of reagent grade quality and used without further purification.2.2.Instrumentation.C, H, and N analyses were carried out on a Carlo Erba MOD 1106 instrument.FT-IR (KBr pellets) spectra were recorded on a Shimadzu 435 spectrophotometer between 4000 and 400 cm −1 . 1 H NMR spectra were recorded on a Bruker DPX 300 spectrometer, using CDCl 3 as solvent and TMS as internal standard.Single crystal X-ray diffraction data were collected on a Bruker AXS SMART APEX CCD diffractometer using monochromated MoK ( = 0.71073 Å) radiation.The structures were solved by direct and conventional Fourier methods [30].
Full-matrix least-squares refinement was based on  2 and hydrogen atoms derived from difference maps and refined at idealized positions riding at their parent C atoms [31].Cyclic voltammetry experiments were carried out using a CHI 660E electrochemical workstation.

Synthesis of the Ligand. N-(Dimethylcarbamothioyl)-4-
fluorobenzamide compound was synthesized according to literature [18,19].A solution of 4-fluorobenzoyl chloride (0.5 mol) in dry acetone (30 mL) was added dropwise to a solution of potassium thiocyanate (0.5 mol) in dry acetone (30 mL).The reaction mixture was heated under reflux for 1 h and then cooled to room temperature.The dimethyl amine (0.1 mol) was added dropwise by stirring to the solution of 4-fluorobenzoyl isothiocyanate (0.1 mol) in dry acetone (30 mL).The reaction mixture was heated under reflux for 1 h.Then, the mixture was poured into cold 0.1 M HCl acid solution.Then, the white precipitated solid compound was filtered.After that crystallization of the crude product by using a mixture of dichloromethane : ethanol (in 1 : 2 ratio by volume) gave N-(dimethylcarbamothioyl)-4fluorobenzamide as white crystals in 78% yield [18,19].

Synthesis of the Metal Complexes.
Complex compounds were prepared according to the method described in literature [18,19,29,32,33].A metal acetate solution in methanol was added dropwise to the ligand in a 1 : 2 molar ratio in methanol.Then, the pH was adjusted with 0.1 M NaOH or 0.1 M HCl for complex formation.The reaction mixture was stirred for 2 h at room temperature.The colored solid complexes were filtered and recrystallized from ethanol: dichloromethane (1 : 2, v : v) mixture [18,19].potassium thiocyanate in dry acetone.At the end of the reaction 4-fluorobenzoyl isothiocyanate appeared.In the second step, 4-fluorobenzoyl isothiocyanate reacted with dimethylamine in dry acetone solution to synthesize N-(dimethylcarbamothioyl)-4-fluorobenzamide [18,19].

Results and Discussion
Complexes were obtained with good yield by stirring the appropriate metal acetate with two equivalents of N-(dimethylcarbamothioyl)-4-fluorobenzamide for 2 hours in methanol [18,19].The reaction of complex is illustrated in Scheme 1. Ligand and its copper and nickel complex were characterized by different spectroscopic techniques including elemental analysis, IR, 1 H NMR spectroscopy, and single crystal X-ray diffraction study.
The FT-IR data of the prepared compounds are consistent with the proposed structures.In the FT-IR spectra of the ligand, the N-H stretching vibration is observed at ca 3200 cm −1 as an intense broad band.This absorption band disappears upon metal complex formation.The delocalization of the ] C=O stretching vibration causes a negative shift.The ] C=O stretching vibration can be observed in the ligand at 1695 cm −1 , and the ] CO stretching vibration of the corresponding Ni(II) and Cu(II) complexes appears at 1445 and 1493 cm −1 , respectively.This is in close agreement with other previously studied thiourea derivatives [18,19,29,[32][33][34][35].
The 1 H NMR spectra of all compounds are compatible with their expected structures.The 1 H NMR spectra of the ligands are consistent with their structures.In the 1 H NMR spectra, the N-H signal present in the ligand at  8.58 ppm disappears in the complexes.The aryl proton signals are shifted to lower field [18,19,29,[32][33][34][35].
3.2.Crystal Structure Analysis.Crystals of the synthesized compounds suitable for single crystal X-ray diffraction analysis were obtained by recrystallization from dichloromethane : methanol (1 : 2, v : v) mixture at room temperature.The ORTEP views of bis(N,N-dimethyl-N  -4-fluorobenzoylthioureato) nickel(II) (NiL 2 ) and bis(N,N-dimethyl-N  -4-fluorobenzoylthioureato) copper(II) (CuL 2 ) with atom numbering schemes are depicted in Figures 4 and 5, respectively.Further details concerning data collection and refinement are given in Table 1.Selected bond lengths and angles of NiL 2 and CuL 2 are listed in Table 2.The crystal structures (Figures 4 and 5) of the complexes confirm that the N-(dimethylcarbamothioyl)-4-fluorobenzamide ligand is a bidentate chelating ligand, coordinating with the copper or nickel atom through the thiocarbonyl and carbonyl groups [29,[32][33][34][35].Both structures are isotypic with very related geometric parameters.The planes of the dimethylamino groups as well as those of the p-fluorophenyl rings are almost parallel to the carbamothioyl moieties as shown from the torsion angles C-N-C-N and O-C-C-C with average 1.3(5) and 1.5(2) Å and 4.9(5) and 6.4(3) Å for NiL 2 and CuL 2 , respectively.The coordination around the metal centers deviates slightly from square planarity with S-M-S 85.26(6) ∘ and 88.62(2) ∘ and O-M-O 85.0(1) ∘ and 85.97(6) ∘ (Ni and Cu).

Journal of Chemistry
Ni(II) complex also exhibits an irreversible oxidation peak at +1.38 V that is considered to be ligand moiety.

Conclusions
In  [1, 4-7, 32, 34, 44, 45].Besides these, the crystal and molecular structure of synthesized complexes were analyzed by X-ray single crystal diffraction method.The comparative analysis was performed with literature data.The structure of these compounds is consistent with the structure of other benzoylthiourea derivatives.The bond lengths and angles also agree well with other thiourea derivatives.The electrochemical behaviors of copper(II) and nickel(II) complexes have been investigated in aprotic solvents by cyclic voltammetry.Cu(II) complex showed reversible behavior in potential range of 400 to −400 mV while Ni(II) complex showed quasi-reversible behavior in potential of 1600 to −400 mV.According to the obtained results, both Cu(II) and Ni(II) complexes have shown electroactive properties.

3. 1 .
Scheme 1: Synthesis reaction of the ligand and metal complexes.

3. 3 .
Electrochemistry.The electrochemical behaviors of copper(II) and nickel(II) complexes have been investigated in aprotic solvents by cyclic voltammetry.According to the obtained results, both Cu(II) and Ni(II) complexes have shown electroactive properties.Cyclic voltammogram of CuL 2 and NiL 2 in dichloromethane are shown in Figure 6.The results indicate that CuL 2 undergoes one-electron reversible redox waves in potential range of 400 to −400 mV.It can be seen from the cyclic voltammogram of Cu(II) complex in DCM at a scan rate of 0.1 V/s that a well-defined redox

Figure 4 :
Figure 4: Molecular structure of NiL 2 with anisotropic displacement ellipsoids drawn at 50% probability level.H-atoms omitted for clarity.

Figure 5 :
Figure 5: Molecular structure of CuL 2 with anisotropic displacement ellipsoids drawn at 50% probability level.H-atoms omitted for clarity.

Table 2 :
Bond lengths and angles for NiL 2 and CuL 2 complexes.