Bis(4,6-diaminopyrimidin-2-yl) disulfide dimethyl sufoxide disolvate

The title compound, C8H10N8S2·2C2H6SO, was obtained unintentionally during an attempt to prepare a thiolate derivative of trimethyltin. The complete disulfide molecule is generated by twofold rotation symmetry and the C—S—S—C torsion angle around the S—S bond is −85.70 (10)°. The molecules are connected via N—H⋯N hydrogen bonds into strongly corrugated layers parallel to (001), generating an R 2 2(8) motif. The solvent molecule, which exhibits minor disorder of its S atom [site occupancies = 0.9591 (18) and 0.0409 (18)], is linked to this layer via a pair of N—H⋯O interactions.

The title compound, C 8 H 10 N 8 S 2 Á2C 2 H 6 SO, was obtained unintentionally during an attempt to prepare a thiolate derivative of trimethyltin. The complete disulfide molecule is generated by twofold rotation symmetry and the C-S-S-C torsion angle around the S-S bond is À85.70 (10) . The molecules are connected via N-HÁ Á ÁN hydrogen bonds into strongly corrugated layers parallel to (001), generating an R 2 2 (8) motif. The solvent molecule, which exhibits minor disorder of its S atom [site occupancies = 0.9591 (18) and 0.0409 (18)], is linked to this layer via a pair of N-HÁ Á ÁO interactions.

Related literature
For information on the preferred conformations of organic disulfides, see: Są czewski et al. (2006).
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: HB2773).

Comment
The title compound, (I), is shown in Fig. 1. In the crystal it adopts a chiral conformation of C 2 symmetry with the torsion angle around the S-S bond of -85.70 (10)°. The S-S bond length of 2.0249 (7) Å is typical of disulfides in a screw conformation (Sączewski et al., 2006). In turn the torsion angle of -8.23 (13)° around the C-S bond shows that the disulfide S atoms are situated close to the pyrimidine plane.
The component molecules of (I) are connected via weak N-H···N interactions generating R 2 2 (8) hydrogen-bond motif into strongly corrugated layer parallel to (001) (Fig. 2, Table 1). The solvent molecules, which exhibit minor disorder of their S atoms, join to this layer via a pair of N-H···O interactions and thus all N-H donors are involved in hydrogen bonding.
Crystal packing in the title compound is shown in Fig. 3.
Experimental 1 mmol of 4,6-diaminopyrimidine-2-thiol was dissolved in 10 ml of DMSO at room temperature and was neutralized by the addition of 1 ml of 1 M solution of NaOH in methanol. Then, 5 ml of a methanolic solution containing 1 mmol of triorganotin chloride was added and the solution was stirred at room temperature for 1 h. Filtration removed minor solid byproducts and the solution was concentrated by rotary evaporation. After cooling and leaving the solution in the refrigerator for about one week, colourless prisms of (I) appeared.

Refinement
The S atom of the DMSO molecule is disordered over two positions in a 0.9591 (18):0.0409 (18) ratio. The minor component was refined isotropically.