3-(1H-Imidazol-1-yl)propanaminium 2-carboxy-4,6-dinitrophenolate

In the title salt, C6H12N3 +·C7H3N2O7 −, the imidazole ring is planar, with a maximum deviation of 0.0013 (14) Å for the N attached to the propanaminium group. In the anion, a single intramolecular O—H⋯O hydrogen bond is observed. The mean planes of the nitro groups in the anion are twisted from the benzene ring mean plane making dihedral angles of 24.7 (9) and 3.9 (6)°. In the crystal, the ammonium H atoms form N—H⋯N and N—H⋯O hydrogen bonds, resulting in an infinite chain along [111]. In addition to the classical hydrogen bonds, weak C—H⋯O and π–π [centroid–centroid distance = 3.7124 (9) Å] interactions are also observed, which lead to the formation a three-dimensional supramolecular structure that links the chains into layers along the bc plane.

In the title salt, C 6 H 12 N 3 + ÁC 7 H 3 N 2 O 7 À , the imidazole ring is planar, with a maximum deviation of 0.0013 (14) Å for the N attached to the propanaminium group. In the anion, a single intramolecular O-HÁ Á ÁO hydrogen bond is observed. The mean planes of the nitro groups in the anion are twisted from the benzene ring mean plane making dihedral angles of 24.7 (9) and 3.9 (6) . In the crystal, the ammonium H atoms form N-HÁ Á ÁN and N-HÁ Á ÁO hydrogen bonds, resulting in an infinite chain along [111]. In addition to the classical hydrogen bonds, weak C-HÁ Á ÁO and -[centroid-centroid distance = 3.7124 (9) Å ] interactions are also observed, which lead to the formation a three-dimensional supramolecular structure that links the chains into layers along the bc plane.
TSY thanks the University of Mysore for research facilities and is also grateful to the Principal, Maharani's Science College for Women, Mysore, for giving permission to undertake research. JPJ acknowledges the NSF-MRI program (grant No. CHE-1039027) for funds to purchase the X-ray diffractometer.
Supporting information for this paper is available from the IUCr electronic archives (Reference: FJ2659).

Comment
Imidazole rings appear frequently in biologically active compounds, both natural and man-made (ten Have et al., 1997).
The mean planes of the nitro groups in the anion are twisted from the phenyl ring mean plane with maximun angles of 24.7 (9)° and 3.9 (6)°, respectively. The hydrogen atoms on the terminal N atom of the cation form N-H···N and N-H···O intermolecular hydrogen bonds resulting in an infinite 1D chain along [1 1 1]. In the crystal, in addition to the classical hydrogen bonds, weak C-H···O (Table 1) and Cg1-Cg2 π-π intermolecular interactions are observed with an intercentroid distance of 3.7125 (9)Å (symmetry operation -x,1-y,-z; Cg1 and Cg2 are the centroids of the C1B-C6B and N1A/C1A/N2A/C3A/C2A rings) which contribute to crystal packing stability (Fig. 2).

Refinement
All of the H atoms were placed in their calculated positions and then refined using the riding model with Atom-H lengths of 0.95Å (CH); 0.99Å (CH 2 ); 0.84Å (OH) or 0.91Å (NH 3 ) . Isotropic displacement parameters for these atoms were set to 1.2 (CH, CH 2 , NH 3 ) or 1.5 (OH) times U eq of the parent atom. Idealised ammonium and tetrahedral OH were refined as rotating groups.