4,4′-Bipyridine–3,3′-disulfanediylbis(1H-1,2,4-triazole-5-amine) (1/1)

In the title 1:1 adduct, C10H8N2·C4H6N8S2·, the components are connected through N—H⋯N hydrogen bonds, leading to a two-dimensional structure. The C—S—S—C torsion angle is −83.6 (1)°. The dihedral angle between pyridine rings is 1.86 (15)°.


Comment
The design and synthesis of novel inorganic-organic hybrid coordination complexes have attracted the attention of many chemists in recent years. So far, there are very few literature reports of structures containing 1H-1,2,4-triazole-5-amine-3thiolate (Rakova et al.2003;Hao et al., 2010;Aldoshin et al., 2003). We are interested in synthesizing new transition metal complexes containing 5-AMT. The title co-crystal was unexpectedly obtained in the course of synthesizing 5-AMT-Ni(II) complexes.
The molecular structure of the co-crystal is shown in Fig.1. The title compound is triclinic in the P-1 space group. C 4 H 6 N 8 S 2 .C 10 H 8 N 2 contains two 5-AMT units linked by an S-S disulfide bridge. The C-S-S-C torsion angle is 83.6 (1)°. This value is close to that of 81.9 (1)° determined for 5,5′-Dithiobis(1-phenyl-1H-tetrazole) (Brito et al., 2007).
The 4,4′-bipyridine molecule is connected to a C 4 H 6 N 8 S 2 molecule through N-H···N hydrogen bonds, which are similar to those in the co-crystal of C 10 H 8 N 2 .2C 2 H 3 N 3 S 2 (Deng et al., 2005). Further N-H···N hydrogen bonds between C 4 H 6 N 8 S 2 molecules leads to a two-dimensional network ( Fig.2 and Fig.3). There are face-to-face πi-πi stacking interactions between the 4,4′-bipyridine and triazole rings, the centroid-centroid distance is 3.630 Å.

Experimental
The title co-crystal has been prepared by adding 5-AMT(1.8 mmol), sodium hydroxide(1.2 mmol) and 4,4′-bipyridine(1.0 mmol) into a stirred mixture of CH 3 OH (7 mL) and H 2 O (5 mL) containing Ni(NO 3 ) 2 .6H 2 O (1.0 mmol). The mixture was refluxed for 5 h and then allowed to cool to ambient temperature. The filtrate was evaporated slowly at room temperature for 3 days to yield yellow crystalline products.

Refinement
Metal atom centers were located from the E-maps and other non-hydrogen atoms were located in successive difference Fourier syntheses. The final refinements were performed by full matrix least-squares methods with anisotropic thermal parameters for non-hydrogen atoms on F 2 .
The final refinements were performed by full martrix least-squares methods with anisotropic thermal parameters for non-hydrogen atoms on F 2 . All hydrogen atoms were located in the calculated sites and included in the final refinement in the riding model approximation with displacement parameters derived from the parent atoms to which they were bonded (U iso (H) = 1.2Ueq). C-H hydrogen atoms (aromatic) were included with distance set to 0.93Å and amide N-H hydrogen atoms were included with distance set to 0.86Å.

Figure 1
The molecular entities of the title compound, showing the atom-numbering scheme with displacement ellipsoids drawn at the 50% probability level.

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 > σ(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.