3-Cyanoanilinium hydrogen oxalate hemihydrate

In the title hydrated molecular salt, C7H7N2 +·C2HO4 −·0.5H2O, contains a 3-cyanoanilinium cation, a hydrogen oxalate anion and half a water molecule in an asymmetric unit. The dihedral angle between the CO2(H) and CO2 planes of the hydrogen oxalate ion is 7.96 (1)°. In the crystal, the components are linked by N—H⋯O and O—H⋯O hydrogen bonds, forming a layer lying parallel to the ac plane.

In the title hydrated molecular salt, C 7 H 7 N 2 + ÁC 2 HO 4 À Á0.5H 2 O, contains a 3-cyanoanilinium cation, a hydrogen oxalate anion and half a water molecule in an asymmetric unit. The dihedral angle between the CO 2 (H) and CO 2 planes of the hydrogen oxalate ion is 7.96 (1) . In the crystal, the components are linked by N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonds, forming a layer lying parallel to the ac plane.

Comment
Salts of amide attracted more attention as phase transition dielectric materials for its application in micro-electronics, memory storage (Chen et al., 2000;Liu, et al. 1999;Zhao, et al. 2003). With the purpose of obtaining phase transition crystals of 3-aminobenzonitrile salts, its interaction with various acids has been studied and we have elaborated a serie of new materials with this organic molecule (Dai & Chen 2011;Xu, et al. 2011;Zheng 2011). In this paper, we describe the crystal structure of the title compound.
The asymmetric unit is composed of a 3-cyanoanilinium cation, a carboxyformate anion, and a half molecule of water ( Fig. 1). The geometric parameters of the title compound agree well with reported similar structure (Dai & Chen 2011).
The cation is almost planar (r.m.s. deviation 0.0062 Å, benzene ring as the best plane).
The cations are surrounded by the anions and water molecules via hydrogen bonds which play an important role in stabilizing the crystal structure. In the crystal structure, all the amino H atoms are involved in N-H···O hydrogen bonds with carboxyformate anion and water molecule with the distances of 2.797 (2) Å, 2.778 (2) Å and 2.788 (2) Å, respectively. In addition, the H atoms of water molecule and carboxyformate anion are involved in the O-H···O Hbonding interactions. In the crystal structure, those H-bonds link the ionic units into a two-dimensional sheets parallel to the ac plane (Table 1 and Fig. 2).

Experimental
The commercial 3-aminobenzonitrile (3 mmol, 324 mg) and oxalic acid (3 mmol, 270 mg) were dissolved in 50 ml water/MeOH solution (1:1 v/v). The solvent was slowly evaporated in air affording colourless block-shaped crystals of the title compound suitable for X-ray analysis.

Refinement
The H atoms were included in the refinement at geometrically idealized positions and treated in riding mode with O-H = 0.82 Å, N-H = 0.89 Å and C-H = 0.93 Å, with U iso (H) = 1.2U e q(C) or 1.5U e q(O/N); a rotating-group model was used for the -NH 3 group.

Computing details
Data collection: CrystalClear (Rigaku, 2005); cell refinement: CrystalClear (Rigaku, 2005); data reduction: CrystalClear (Rigaku, 2005); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure:   where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.28 e Å −3 Δρ min = −0.24 e Å −3 Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. 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 R-factors(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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq O1W 0.5000 0.3943 (