Crystal structure of a second triclinic polymorph of 2-methylpyridinium picrate
The title molecular salt, C6H8N+·C6H2N3O7−(systematic name: 2-methylpyridinium 2,4,6-trinitrophenolate), crystallizes with two cations and two anions in the asymmetric unit. In the crystal, the cations are linked to the anionsviabifurcated N—H...(O,O) hydrogen bonds, generatingR12(6) graph-set motifs. Numerous C—H...O hydrogen bonds are observed between these cation–anion pairs, which result in a three-dimensional network. In addition, weak aromatic π–π stacking between the 2-methylpyridinium rings [inter-centroid distance = 3.8334 (19) Å] and very weak stacking [inter-centroid distance = 4.0281 (16) Å] between inversion-related pairs of picrate anions is observed. The title salt is a second triclinic polymorph of the structure (also withZ′ = 2) reported earlier [Anitaet al.(2006).Acta Cryst.C62, o567–o570; Chanet al.(2014).CrystEngComm,16, 4508–4538]. In the title compound, the cations and anions display a chequerboard arrangement when viewed down [100], whereas in the first polymorph, (010) layers of alternating cations and anions are apparent in a [100] view. It is interesting that the unit-cell lengths are almost identical for the two polymorphs, although the inter-axial angles are quite different.