Sodium 5-amino-1,3,4-thiadiazole-2-thiolate dihydrate

There are two 5-amino-1,3,4-thiadiazole-2(3H)-thiolate anions in the asymmetric unit of the title compound, Na+·C2H2N3S2 −·2H2O, which are almost perpendicular to each other [dihedral angle = 84.64 (6)°]. The two Na+ cations are in distorted fourfold coordinations by O atoms of the water molecules. The crystal structure is stabilized by N—H⋯S, O—H⋯N and O—H⋯S hydrogen bonds.

Interest in the study of 5-amino-1,3,4-thiadiazole-2(3H)-thione derivatives stems from their use as intermediates of pharmaceuticals (John et al., 1960;John, 1962). Nonetheless, there are few articles that describe this kind of crystal structure (Downie et al., 1972;Deng et al., 2005;Ma et al., 2007). As part of our studies of agrochemicals, the title compound 5-amino-2-thione-1,3,4-thiadiazole sodium dihydrate has been synthesized, and its crystal structure is reported in this article. The complex is located across an inversion centre, and is bridged by two symmetry equivalent water

S3. Refinement
All H atoms were initially located in a difference Fourier map. N-bound H atoms were located in a difference map and refined with an N-H distance restraint of 0.86 (1) Å. The water H atoms were refined using a riding model, with

Figure 1
The asymmetric unit of the title compound with the atomic labeling scheme. Displacement ellipsoids are drawn at the 40% probability level.

Figure 2
A partial packing diagram of title compound.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. 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 > 2σ(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 R-factors based on ALL data will be even larger.