Bis(1,3,4-thiadiazol-2-yl) disulfide

The title compound, C4H2N4S4, lies about a twofold rotation axis situated at the mid-point of the central S—S bond. Each of two thiadiazole rings is essentially planar, with an rms deviation for the unique thiadiazole ring plane of 0.0019 (7) Å. C—H⋯N hydrogen bonds link adjacent molecules, forming zigzag chains along the c axis. In addition, these chains are connected by intermolecular S⋯S interactions [S⋯S = 3.5153 (11) Å] , forming corrugated sheets, and further fabricate a three-dimensional supramolecular structure by intermolecular N⋯S contacts [S⋯N = 3.1941 (17) Å].

The title compound, C 4 H 2 N 4 S 4 , lies about a twofold rotation axis situated at the mid-point of the central S-S bond. Each of two thiadiazole rings is essentially planar, with an rms deviation for the unique thiadiazole ring plane of 0.0019 (7) Å . C-HÁ Á ÁN hydrogen bonds link adjacent molecules, forming zigzag chains along the c axis. In addition, these chains are connected by intermolecular SÁ Á ÁS interactions [SÁ Á ÁS = 3.5153 (11) Å ] , forming corrugated sheets, and further fabricate a three-dimensional supramolecular structure by intermolecular NÁ Á ÁS contacts [SÁ Á ÁN = 3.1941 (17) Å ].
This work was supported by the Natural Science Foundation of China (grant No. 20872058).
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: SJ2643).  (Coyanis et al., 2002, Wang & Cao, 2005. Ligands involving thiadiazole group have also shown interesting coordination chemistry with transition metal ions (Huang et al., 2004;Zheng et al., 2005).

Structure Reports Online
Exploring the applications of thiadiazole derivatives as ligands for metal complexation, we report here the synthesis and structure of bis(1,3,4-thiadiazolyl)5,5'-disulfide (I), a new and potentially multi-functional ligand (Fig. 1).
The title compound,C 4 H 2 N 4 S 4 , lies about a twofold rotation axis situated at the mid-point of the central S-S bond. Each of the thiadiazole rings is essentially planar, with an rms deviation for the unique thiadiazole ring plane of 0.0019 (7)Å. The dihedral angle and centroid-centroid distance between the two thiadaizole rings are 86.64 (44)° and 5.25 (14) Å, respectively.

Experimental
The title compound was prepared by adding hydrogen peroxide (30%, 10.4 mL) drop-wise to a solution of 2-mercapto-1,3,4-thiadiazole (0.2 mol) in ethanol (30 mL) and water (20 mL) at room temperature. The mixture was then refluxed for 6 h. The reaction mixture was taken up in hexane (100 mL), washed with water and brine, and dried with Na 2 SO 4 .
The solvent was removed under reduced pressure, and the crude product was recrystallised from ethanol to give the title compound as colourless solid in 85% yield. Colorless block-like single crystals were obtained by slow evaporation from ethanol at room temperature.

Refinement
The H atoms were positioned geometrically and treated as riding with d(C-H) = 0.93Å, U iso =1.2U eq (C) Figures   Fig. 1. View of (I) with the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level.  Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and Rfactors based on ALL data will be even larger.