4-Carbamoylpyridin-1-ium 2,2,2-trichloroacetate

In the asymmetric unit of the title salt, C6H7N2O+·C2Cl3O2 −, there are two crystallographic independent ion pairs. The amide groups of the 4-carbamoylpyridin-1-ium ions are slightly twisted out of the plane of the aromatic ring with C—C—C—N torsion angles of 8.8 (9)° and 4.6 (8)°. In the crystal, the 4-carbamoylpyridin-1-ium ion is N—H⋯O hydrogen bonded to the trichloroacetate ion via the pyridinium unit and amide group. Layers parallel to the ac plane are formed due to the N—H⋯O hydrogen bonding of the adjacent amide groups of 4-carbamoylpyridin-1-ium ions. Weak C—H⋯O interactions also occur.

In the asymmetric unit of the title salt, C 6 H 7 N 2 O + ÁC 2 Cl 3 O 2 À , there are two crystallographic independent ion pairs. The amide groups of the 4-carbamoylpyridin-1-ium ions are slightly twisted out of the plane of the aromatic ring with C-C-C-N torsion angles of 8.8 (9) and 4.6 (8) . In the crystal, the 4-carbamoylpyridin-1-ium ion is N-HÁ Á ÁO hydrogen bonded to the trichloroacetate ion via the pyridinium unit and amide group. Layers parallel to the ac plane are formed due to the N-HÁ Á ÁO hydrogen bonding of the adjacent amide groups of 4-carbamoylpyridin-1-ium ions. Weak C-HÁ Á ÁO interactions also occur.

Comment
Salts or co-crystals represent two possible ways to produce functional pharmaceutical materials. The salt or co-crystal formation is dependent on a pK a difference between the acid and the base (Karki et al., 2009;Friščić & Jones, 2010).
Here we present the structure obtained by contacting isonicotinamide and trichloroacetic acid in 1:1 molar ratio.
The asymmetric unit of (I) consists of two crystallographic independent 4-carbamoylpyridin-1-ium cations and two trichloroacetate anions (Fig. 1). The amide groups of 4-carbamoylpyridin-1-ium ions are only slightly twisted out of the plane of the aromatic ring with a C-C-C-N torsion angle of 8.8 (9)° and 4.6 (8)°, respectively. The 4carbamoylpyridin-1-ium ion is N-H···O hydrogen bonded to the trichloroacetate ion via the pyridinium unit and amide group (Fig. 2). Two-dimensional framework is formed due to the N-H···O hydrogen bonding of the adjacent amide groups of 4-carbamoylpyridin-1-ium ions. This layer formation is further stabilized by weak C-H···O interactions. In the structure of (I) typical amide-amide hydrogen-bonded homodimer is not present as is for example in the 4carbamoylpyridin-1-ium 3-carboxypicolinate (Das & Baruah, 2011).

Experimental
Crystals of the title compound were obtained by slow evaporation of a 1:1 mol. mixture of isonicotinamide and trichloroacetic acid in methanol at room temperature.

Refinement
The presence of atoms H1A and H3B bonded to N1 and N3, respectively was confirmed by the observation of peaks in those locations in an electron-density map. All H atoms were then added at calculated positions and refined using a riding model, with C-H = 0.93 Å and N-H = 0.86 Å, with U iso (H) = 1.2U eq (C) and 1.5U eq (N). To improve the refinement results, two reflection with too high value of δ(F 2 )/e.s.d. and with F o 2 < F c 2 were deleted from the refinement.
Displacement ellipsoid of O5 and O6 are large compared to the other atoms, however the treatment of O5 and O6 as disordered over two positions did not improve the model. The asymmetric unit of the title compound with displacement ellipsoids drawn at the 50% probability level.    (12) Special details Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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 > 2σ(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.