3,5-Diamino-1-phenyl-1,2,4-triazolium bromide

The title salt, C8H10N5 +·Br−, crystallizes with two independent structural units in the asymmetric unit. The two independent cations have different conformations, the triazole and phenyl rings forming dihedral angles of 32.57 (6) and 52.27 (7)°. In both cations, the amino groups are planar (the sum of the angles at the N atom of each amino group is 360°) and conjugated with the triazole ring. Intermolecular N—H⋯N and N—H⋯Br hydrogen bonds consolidate the crystal packing.

The title salt, C 8 H 10 N 5 + ÁBr À , crystallizes with two independent structural units in the asymmetric unit. The two independent cations have different conformations, the triazole and phenyl rings forming dihedral angles of 32.57 (6) and 52.27 (7) . In both cations, the amino groups are planar (the sum of the angles at the N atom of each amino group is 360 ) and conjugated with the triazole ring. Intermolecular N-HÁ Á ÁN and N-HÁ Á ÁBr hydrogen bonds consolidate the crystal packing.
In the crystal the identical and parallel cations of type A or B form stacks along the b axis of the monoclinic cell (  (Table 1). The nearest chains in the plane perpendicular to b axis are connected with each other by continuous net of hydrogen bonds N3-H3A···N2' i and N3'-H3'A···N2 ii , forming parallel molecular layers with identity period equal to the unit-cell parameter b (Fig. 6). The layers are connected with one another by hydrogen bonds N5-H5A···Br1 iii and N5'-H5'A···Br1 iv . In the parallel layers one-type cations are turned from each other by 180°, i.e. they are space related by inversion centre with coordinates [0, 0, 0]. Thereby, the C 8 H 10 N 5 + cations and bromide anions form a three-dimensional framework in the crystal.
In conclusion, the present study and previously reported theoretical (Anders et al., 1997) and experimental (Chernyshev et al., 2008) results indicate that the structures attributed to the products of quaternization of 1-substituted 3,5-diamino-1,2,4-triazoles (Steck et al., 1958), apparently, are erroneous and need correction by means of modern analytical methods.
Also it would be interesting to investigate the structure of salts of another 1-substituted 3-amino-1,2,4-triazoles with a view to evaluate the role of C3-NH 2 group in the delocalization of positive charge in 3-amino-1,2,4-triazolium cations.
A mixture of 1-phenyl-1H-1,2,4-triazole-3,5-diamine hydrobromide (0.73 g, 2.85 mmol), 2,4-pentanedion (0.371 g, 3.71 mmol) and ethanol (5 ml) was refluxed for 15 min and then cooled to room temperature. Starting 1-phenyl-1H-1,2,4-triazole-3,5-diamine hydrobromide used for the preparation of TPB was obtained by addition of equimolar amount of 48% hydrobromic acid to an ethanol solution of 3,5-diamino-1-phenyl-1,2,4-triazole. The latter compound was synthesized by known method (Steck et al., 1958).    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 Rfactors(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.