Binuclear Divalent Complexes of Cobalt , Nickel and Copper with N 2 S Ligand Derived from 1 , 3 , 4-Thiadiazole-2 , 5-dithiolate Dipotassium Synthesized via Click Chemistry

A new ligand containing a N2S donor set of atoms has been prepared using Click Chemistry from the reaction of 1,3,4-thiadiazole-2,5-dithiol dipotassium salt with propargyl bromide followed by the addition of the product formed from the reaction of sodium azide and octyl iodide, using Cu(I) as catalyst. The ligand was characterized using FT-IR, UV-Vis, H, C NMR spectroscopes and C, H, N elemental analysis. The corresponding Co(II), Ni(II) and Cu(II) complexes were characterized by FT-IR, UV-Vis spectroscopes as well as conductivity and magnetic susceptibility measurements. These measurements suggest that the geometry around the Co is tetrahedral, while around the Ni and Cu it is distorted octahedral. The solubility’s of the ligand and its complexes were measured in different solvents.


Introduction
Five membered aromatic systems containing three hetero atoms at symmetrical positions have been studied due to their interesting physiological properties (Hussain, Sharma, & Amir, 2008), as well as their involvement in the life processes (Salimon et al., 2010).More than 90% of new drugs contain heterocyclic compounds indicating the importance of this class of compound to biological and medicinal chemistry (Dua et al., 2011).Aromatic heterocyclic ligands and their metal complexes play key roles as catalysts, anti-HIV, anti-microbial and β-lactamase inhibitors in biological reactions (Suijkerbuijk et al., 2007;Oliva et al., 2010).In addition, this type of compounds has other applications like anticorrosive agents, photographic materials, agrochemicals and dyes (Kumar et al., 2009).Sharpless and Meldal (2002) improved the regioselectivity of the reactions forming heterocyclic molecules by using Cu(I)-catalyzed reactions of organic azides and terminal alkynes (Click Chemistry).The origin of the Cu(I) catalyst can be a Cu(I) salt (e.g.CuI), or generated by oxidation of a Cu(0) complex or reduction of a Cu(II) complex (Martinelli, 2008).
1,3,4-Thiadiazole can act as a ligand and its complexes have a wide variety applications especially as antifungal and antibacterial agents (Samee & Vajragupta, 2011;Kumar, 2010).The Co complexes have been interesting in our life, being a simple example of these compounds B 12 Vitamin a cobalt complex.An simple of these cobalt compounds is B 12 Vitamin which that use as tablets and injections for treatment the verve damage in human body (Chang, 2010).Copper is found in all living organisms and it is important for the function of several enzymes and proteins involved in energy metabolism.Control of the number and type of coordinating atoms is the key for achieving metal complexes that mimics the coordination sphere and reactivity of metal-containing enzymes (Yorimitsu & Oshima, 2006;Cristina et al., 2009;Creaven et al., 2006).Nickel compounds have been interesting for many reasons, in biological systems, nickel forms complexes with adenosine triphosphate, amino acids, peptides, proteins and deoxyribonucleic acid (Reddy et al., 2012;Air Quality Guidelines, 2000).Nickel complexes with sulfur coordination spheres have attracted considerable interest as model compounds for the active centers of nickel sulfur enzymes (Sellman, 2000).Also several nickel compounds have been interested in energy field (Kopera, 2004), Ni(II) can be used as a counter ion in preparation of epoxides (Gash, 2004).
In this study we have synthesized and characterized a heterocyclic ligand containing both a 1,3,4-thiadiazole ring,

Preparation of Nickel(II) Complex
Nickel chloride 6H 2 O (0.0188 g, 0.1117 mmol) was dissolved in MeOH (5mL), then added to a solution of the ligand (0.03 g, 0.0558 mmol) dissolved in MeOH (5 mL).The mixture was refluxed for 2 h.producing a yellow-green precipitate which was removed by filtration.The solid was washed with Et 2 O (5 mL) and cold MeOH (5 mL) then recrystallized from acetonitrile.

Preparation of Copper(II) Complex
Copper chloride 2H 2 O (0.0178 g, 0.1117 mmol) was dissolved in MeOH (5 mL), then added to a solution of ligand (0.03 g, 0.0558 mmol) dissolved in MeOH (5 mL).The mixture was refluxed for 2 h producing a green-yellow precipitate.The solid was removed by filtration then , washed with Et 2 O (5 mL) and cold MeOH (5 mL).The complex was recrystallized from acetonitrile.

Results and Discussion
The ligand was prepared from two precursors: compound 1 (synthesized from the reaction of the sodium azide with octyl iodide) and compound 2 (obtained from the reaction of propargyl bromide with 1,3,4-thiadiazole-2,5-dithiol dipotassium salt), using Click Chemistry catalyzed by Cu(I).This ligand reacts with Co(II),Ni(II) and Cu(II) salts to produce binuclear complexes.The solubility of all compounds was determined in different solvents Table 1.

Elemental Analysis
The C, H, N elemental analysis of 2,5-bis[1-octyl-1H-1,2,3-triazol-4-yl) methylthio]-1,3,4-thiadiazole is in good agreement with the theoretical values.Table 2 shows the theoretical and calculated percentage of C, H, N and S elements.The theoretical data was calculated using the Chem Office, CS ChemDraw Ultra program by drawing the molecules and use the analyze structure.

F
Figure 2. IR spe

Figure
Figure 1.I spec

Figure
Figure 9. UV-V Cobalt chloride.6H 2 O (0.0188 g, 0.1117 mmol) was dissolved in MeOH (5 mL), then added to a solution of the ligand (0.03 g, 0.0558 mmol) dissolved in MeOH.The solution was refluxed for 2 h. to produce a blue precipitate.The solid was removed by filtration, washed with Et 2 O (5 mL) and cold MeOH (5 mL).The solid was recrystallized from acetonitrile.
Scheme 4. Preparation of Cobalt(II) complex

Table 1 .
Solubility of ligand and complexes

Table 2 .
Melting point and C.H.N elemental analysis of ligand Calculated values shown in parentheses.