4-Carbamoylpyridin-1-ium 2,2,2-trichloroacetate–isonicotinamide (1/1)

In the crystal structure of the title 1:1 co-crystal, C6H7N2O+·C2Cl3O2 −·C6H6N2O, the amide groups of the 4-carbamoylpyridin-1-ium ion and the isonicotinamide molecule are twisted out of the plane of the aromatic ring with C—C—C—N torsion angles of 21.5 (4) and −33.5 (4)°, respectively. The 4-carbamoylpyridin-1-ium and isonicotinamide amide groups form R 2 2(8) hydrogen-bonded dimers via N—H⋯O=C interactions. The two remaining amide H atoms (i) link dimers via the cation to an isonicotinamide and (ii) from the isonicotinamide to a trichloroacetate anion. The pyridinium H atom also forms an N—H⋯O hydrogen bond with the trichloroacetate anion. Due to the extended hydrogen bonding, including C—H⋯O and C—H⋯Cl interactions, all components in the structure aggregate into a three-dimensional supramolecular framework.

(8) hydrogen-bonded dimers via N-HÁ Á ÁO C interactions. The two remaining amide H atoms (i) link dimers via the cation to an isonicotinamide and (ii) from the isonicotinamide to a trichloroacetate anion. The pyridinium H atom also forms an N-HÁ Á ÁO hydrogen bond with the trichloroacetate anion. Due to the extended hydrogen bonding, including C-HÁ Á ÁO and C-HÁ Á ÁCl interactions, all components in the structure aggregate into a three-dimensional supramolecular framework.

Franc Perdih Comment
Co-crystals have attracted much attention in recent years owing to their contributions to crystal engineering and pharmaceutical chemistry. They were found to be useful in improving the stability, solubility, dissolution rate and mechanical properties (Karki et al., 2009;Friščić & Jones, 2010). Here we present the structure obtained by reacting isonicotinamide and trichloroacetic acid in 2:1 molar ratio.
Similar twisting was observed for example in isonicotinamide-2-naphthoic acid (1/1) (Madeley et al., 2011). Aromatic rings of 4-carbamoylpyridin-1-ium ion and isonicotinamide molecule are not coplanar, but are inclined by 35.05 (12)°. In the crystal, all the components of the structure are associated via the extended system of hydrogen bonds (N-H···O and N-H···N) and weak C-H···O and C-H···Cl interactions into extended three-dimensional supramolecular framework (Figs. 2, 3). The 4-carbamoylpyridin-1-ium ion is hydrogen bonded via N-H···O hydrogen bonding of the pyridinium unit to the trichloroacetate ion. The amide groups from 4-carbamoylpyridin-1-ium and isonicotinamide form a dimer via N-H···O hydrogen bonding, that is a typical supramolecular hydrogen-bonded synthon observed for amide-amide homodimers. Furthermore, the amide group of the cation is hydrogen bonded to the pyridine unit of isonicotinamide and the amide group of the isonicotinamide is hydrogen bonded to the trichloroacetate ion.

Experimental
Crystals of the title compound were obtained by slow evaporation of a 2:1 mol. mixture of isonicotinamide and trichloroacetic acid in methanol at room temperature.

Refinement
All H atoms were initially located in a difference Fourier maps. H atoms attached to N atoms were refined isotropically with U iso (H) = 1.5U eq (N). Other H atoms were treated as riding atoms in geometrically idealized positions, with C-H = 0.93 Å, and with U iso (H) = 1.2U eq (C).

Computing details
Data collection: CrysAlis PRO (Agilent, 2011); cell refinement: CrysAlis PRO (Agilent, 2011); data reduction: CrysAlis PRO (Agilent, 2011); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997) and DIAMOND (Brandenburg, 1999); software used to prepare material for publication: WinGX (Farrugia, 1999) and publCIF (Westrip, 2010  The asymmetric unit of the title compound with displacement ellipsoids drawn at the 50% probability level. i -x, -y + 1, z + 3/2; ii x -1/2, -y + 3/2, z + 1; iv x + 1/2, -y + 3/2, z; v x -1/2, -y + 3/2, z -1.  Crystal packing of the title compound. For the sake of clarity, hydrogen bonding is not presented.  (6) 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.