5-Amino-1H-pyrazol-2-ium hydrogen succinate

In the cation of the title salt, C3H6N3 +·C4H5O4 −, the protonated pyrazolium ring is planar (r.m.s. deviation = 0.012 Å). An intramolecular C—H⋯O hydrogen bond occurs in the anion. In the crystal, N—H⋯O hydrogen bonds and a weak C—H⋯O interaction between the cations and anions form two sets of R 2 2(8) graph-set ring motifs. Intermolecular O—H⋯O hydrogen bonds between these lead to a criss-cross pattern along the b axis. In addition to the classical hydrogen bonds, a weak C—H⋯π(pyrazolium) interaction is observed and contributes to crystal packing. All of these interactions link the molecules into a two-dimensional supramolecular framework parallel to (10-1).

In the cation of the title salt, C 3 H 6 N 3 + ÁC 4 H 5 O 4 À , the protonated pyrazolium ring is planar (r.m.s. deviation = 0.012 Å ). An intramolecular C-HÁ Á ÁO hydrogen bond occurs in the anion. In the crystal, N-HÁ Á ÁO hydrogen bonds and a weak C-HÁ Á ÁO interaction between the cations and anions form two sets of R 2 2 (8) graph-set ring motifs. Intermolecular O-HÁ Á ÁO hydrogen bonds between these lead to a criss-cross pattern along the b axis. In addition to the classical hydrogen bonds, a weak C-HÁ Á Á(pyrazolium) interaction is observed and contributes to crystal packing. All of these interactions link the molecules into a two-dimensional supramolecular framework parallel to (101).
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.

Synthesis and crystallization
A mixture of commercially available 3-aminopyrazole (0.5 g, 6.02 mmol) and succinic acid (0.71 g, 6.02 mmol) were dissolved in 5 ml of hot dimethylsulfoxide. The reaction mixture was stirred for 15 mins at 323 K. The resulting solution was allowed to cool slowly at room temperature upon which X-ray quality crystals of the title salt were obtained after few days; M.pt: 368-373 K.

Refinement
The N-bound H2A and H3A atoms were located by a difference map and refined isotropically. All of the remaining H atoms were placed in their calculated positions and then refined using the riding model with atom-H lengths of 0.93Å (CH); 0.97Å (CH 2 ); 0.82Å (OH) or 0.86Å (NH). Isotropic displacement parameters for these atoms were set to 1.2 (CH, CH 2 , NH) or 1.5 (OH) x U eq of the parent atom.
The title salt, (I), crystallizes with one independent monocation (A) and a monoanion (B) in the asymmetric unit (Fig.   1). In the cation the protonated pyrazolium ring is planar. In the crystal, N-H···O hydrogen bonds involving two hydrogen atoms on the amino group (H1AA, H1AB), a N2A-H2A···O3B intermolecular hydrogen bond and a weak C2A-H2AA···O1B intermolecular interaction between cations and anions form two sets of R 2 2 (8) graph set ring motifs (Fig. 2). Intermolecular O-H···O hydrogen bonds between the anions leads to a criss-cross pattern along the b axis. In addition to the classical hydrogen bonds, a weak C-H···Cg(pyrazolium) intermolecular interaction is observed and contributes to crystal packing. All of these interactions directly link the molecules into a 2D supramolecular framework along (1 0 -1).
Dashed lines indicate a C3A-H3AA···O1B intermolecular hydrogen bond linking the cation and anion within the asymmetric unit.   Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq O1B 0.43675 (7