2,2′-Dithiodianiline: a redetermination at 100 K

Structural studies of the title compound [systematic name: 2,2′-(disulfanediyl)dianiline], C12H12N2S2, were previously performed at room temperature [Gomes de Mesquita (1967 ▶). Acta Cryst. 23, 671; Lee & Bryant (1970 ▶). Acta Cryst. B26, 1729; Ribar et al. (1975 ▶). Bull. Yugoslav. Crystallogr. Centre, A10, 68]. The results of the current redetermination allow a clarification of the nature of the intra- and intermolecular N—H⋯S hydrogen bonding described in the literature for this compound. On cooling to 100 K, the unit cell contracts most in the c axis, and it changes rather less in the directions involving the strongly hydrogen-bonded chains, which are the a and b axes. In the crystal structure, N—H⋯N hydrogen bonds link neighbouring molecules into two-dimensional frameworks parallel to the ab plane. An additional intermolecular N—H⋯S hydrogen bond has also been established, based on freely refined H-atom positions. Intermolecular C—H⋯π interactions further stabilize the crystal structure.

Structural studies of the title compound [systematic name: 2,2 0 -(disulfanediyl)dianiline], C 12 H 12 N 2 S 2 , were previously performed at room temperature [Gomes de Mesquita (1967). Acta Cryst. 23, 671; Lee & Bryant (1970). Acta Cryst. B26, 1729; Ribar et al. (1975). Bull. Yugoslav. Crystallogr. Centre, A10, 68]. The results of the current redetermination allow a clarification of the nature of the intra-and intermolecular N-HÁ Á ÁS hydrogen bonding described in the literature for this compound. On cooling to 100 K, the unit cell contracts most in the c axis, and it changes rather less in the directions involving the strongly hydrogen-bonded chains, which are the a and b axes. In the crystal structure, N-HÁ Á ÁN hydrogen bonds link neighbouring molecules into twodimensional frameworks parallel to the ab plane. An additional intermolecular N-HÁ Á ÁS hydrogen bond has also been established, based on freely refined H-atom positions. Intermolecular C-HÁ Á Á interactions further stabilize the crystal structure.
A search of the November 2008 release of the Cambridge Structural Database (Allen, 2002) reveals that the room temperature crystal structures of the title compound ( Fig. 1) were first reported with R = 0.057 for 369 reflections (Gomes de Mesquita, 1967), then followed with R = 0.086 for 1313 reflections (Lee & Bryant, 1970) and R = 0.042 (Ribar et al., 1975).
The current redetermination at 100 K increases significantly the precision of the structural and geometrical parameters and provides a lower R value (R = 0.048 based on 2750 independent observed reflections).
Comparison with the previously reported unit cell parameters (Ribar et al., 1975) reveals that on cooling to 100 K, a expands by 0.41 %, whereas b and c contract by 1.15 and 1.74 %, respectively. This can be explained by the fact that along the c axis, the molecules are interconnected by weak C-H···π interactions only whereas along the a and b axes, the molecules are interconnected by the stronger hydrogen bonds (Figs 2 & 3, Table 1). The previously reported structure (Lee & Bryant, 1970) suggests two intramolecular N-H···S hydrogen bonds, but the current work observes no such intramolecular hydrogen bonds with bond angle larger than 120°. The bond lengths are comparable to but more precise than the previously reported structures (Lee & Bryant, 1970;Ribar et al., 1975).

Experimental
The title compound is obtained by exposing 2-aminobenzenethiol to sunlight in an open beaker for two days. The reagent 2-aminobenzenethiol undergoes self aerial oxidation to furnish the crystals. The crude product obtained through the photochemical condition was washed with ethanol and dried. Single crystals suitable for X-ray analysis were obtained from ethanol by slow evaporation.

Refinement
All the H atoms were located from difference Fourier map [range of C-H = 0.93 (3) -1.00 (3) Å, and see Table 1 for N-H distances] and allowed to refine freely. Fig. 1. The molecular structure of the title compound, showing 50% probability displacement ellipsoids for non-H atoms and the atom-numbering scheme.

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cyrosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1)K.
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 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 R-factors based on ALL data will be even larger.