Crystal structure of 5-amino-4H-1,2,4-triazol-1-ium pyrazine-2-carboxyl­ate: an unexpected salt arising from the deca­rboxylation of both precursors

Both the 3-amino-2H,4H-1,2,4-triazolium cation and the pyrazine-2-carboxyl­ate anion in the title salt, C(2)H(5)N(4) (+)·C(5)H(3)N(2)O(2) (−), were formed by an unexpected deca­rboxylation reaction, from 5-amino-1H-1,2,4-triazole-3-carb­oxy­lic acid and pyrazine-2,3-di­carb­oxy­lic acid, respectively. The dihedral angle between the pyrazine ring (r.m.s. deviation = 0.008 Å) and the carboxyl­ate group in the anion is 3.7 (3)°. The extended structure of the salt contains a supra­molecular zigzag tape in which cations and anions are engaged in strong and highly directional N—H⋯N,O hydrogen bonds, forming R (2) (2)(8) and R (2) (2)(9) graph-set motifs. The packing between the tapes is mediated by π–π stacking inter­actions between the triazole and pyrazine rings.