3-Aminocarbonylpyridinium difluoroacetate at 123 K

In the crystal of the title compound, C6H7N2O+·C2HF2O2 −, the cation adopts a catemeric N—H⋯O hydrogen-bonded chain motif involving the carboxamide group, with two further N—H⋯O hydrogen bonds connecting the cations to adjacent difluoroacetate anions via the carboxamide and pyridinium N atoms. The carboxamide group of the nicotinamidium ion is twisted by 32.3 (6)° from the pyridine ring plane. A number of C—H⋯O and C—H⋯F interactions consolidate the packing.

In the crystal of the title compound, C 6 H 7 N 2 O + ÁC 2 HF 2 O 2 À , the cation adopts a catemeric N-HÁ Á ÁO hydrogen-bonded chain motif involving the carboxamide group, with two further N-HÁ Á ÁO hydrogen bonds connecting the cations to adjacent difluoroacetate anions via the carboxamide and pyridinium N atoms. The carboxamide group of the nicotinamidium ion is twisted by 32.3 (6) from the pyridine ring plane. A number of C-HÁ Á ÁO and C-HÁ Á ÁF interactions consolidate the packing.
The difluoroacetate (DFA -) salt reported here (Scheme 1) was discovered during a study of multicomponent crystal formation involving fluorinated solvents and a range of organic compounds. The ions in the NA + DFAsalt crystallize in space group P2 1 /c with one NA + cation and one DFAanion in the asymmetric unit (Fig.1). The internal C1-N1-C5 angle of the pyridinium ring in NA + DFAis 122.13 (9)°, in close agreement to the value reported in the NA + TFAsalt (122.5 (4)°) but represents a significant increase over the the non-ionized form of NA (117.59 (7)°, Miwa et al., 1999). In the DFAsalt, as in the TFAsalt and NA structures, the carboxamide group is not coplanar with the pyridinium ring with the angle between the planes of these groups being 32.30 (6)° [16.3 (8)° and 22.16 (4)° for NA + TFAand NA respectively].
The packing in NA + DFAconsists of hydrogen bonded chains of NA + ions extending parallel to the a-axis via contact N2-H2N···O1 between the anti-oriented H atom of the NH 2 group and the carbonyl O-atom, O1 (Fig. 2). Each cation forms an N-H···O hydrogen bond to O3 on a DFAion and this atom also accepts a second N-H···O hydrogen bond from a neighbouring cation in a parallel chain (Figure 3), that connect adjacent chains resulting in a two-dimensional sheet lying parallel to the ac plane. The remaining O-atom on the DFAion, O2, whilst not involved in any hydrogen bonds is involved in three C-H···O contacts to two DFAions and a cation. One further C-H···O contact is observed between O1 and C1-H1 on the pyridinium ring in a parallel chain of cations. C-H···F contacts are also observed (C3-H3···F1 and C4-H4···F2, see Table 2).

Experimental
The novel structure reported here was discovered during a study of multicomponent crystal formation in organic compounds using a range of fluorinated acids. Identification of the novel phase was initially made using multi-sample foil transmission X-ray powder diffraction analysis (Florence et al., 2003) and a suitable single-crystal for structure determination was obtained by isothermal evaporation at 278 K of a saturated solution of nicotinamide in DFAA.
supplementary materials sup-2 Refinement Aromatic H atoms bound to C were placed in idealized positions and in a riding mode, with C-H distance set to 0.95Å and U iso equal to 1.2 times U eq of the parent atom. All other H atoms were located by difference synthesis and then refined isotropically. Fig. 1. View of the title compound with the atom numbering scheme. Displacement ellipsoids for non-H atoms are drawn at the 50% probability level.

Special details
Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles Refinement. Refinement on F 2 for ALL reflections except those flagged by the user for potential systematic errors. Weighted Rfactors wR and all goodnesses 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 observed criterion of F 2 > σ(F 2 ) is used only for calculating -R-factor-obs 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.