4-Carboxypyridinium bromide

In the title compound, C6H6NO2 +·Br−, the hydroxy and carbonyl groups make torsion angles of 164.8 (4) and −17.6 (6)°, respectively, with the pyridinium ring. Intermolecular N—H⋯Br, O—H⋯Br and C—H⋯O hydrogen bonds contribute to the stability of the structure and link the molecules into chains along the b axis.

In the title compound, C 6 H 6 NO 2 + ÁBr À , the hydroxy and carbonyl groups make torsion angles of 164.8 (4) and À17.6 (6) , respectively, with the pyridinium ring. Intermolecular N-HÁ Á ÁBr, O-HÁ Á ÁBr and C-HÁ Á ÁO hydrogen bonds contribute to the stability of the structure and link the molecules into chains along the b axis.

4-Carboxypyridinium bromide Y. Wang
Comment Some materials have predominant dielectric-ferroelectric performance and they have much applications in many fields. The study of dielectric-ferroelectric materials has received much attention in recent years. PyHX(X=ICl 4 ,ClO 4 ,IO 4 ,ReO 4 etc) (Asaji et al.(2007); Wasicki et al.(1997)) are representative. As one part of our continuing studies on finding for dielectricferroelectric materials, we synthesized the title compound C 6 H 6 NO 2 + Brunexpected comparing to PyHX, but it has no phase-transition in dielectric-ferroelectric measurement during 93 K to 470 K (m.p. 483 K).
The asymmetric unit of the title compound contains one 4-Carboxypyridinium basic ion and one bromide negative ion (Fig 1). In contrast to the planar 3-carboxypyridinium chloride (Slouf, 2001), the carboxyl group in the title molecule is slightly rotated with torsion angles of 164.8 (4)° and -17.6 (6)°. In the planar 3-carboxypyridinium chloride structure, N-H···O hydrogen bonds form chains along the c axis, whereas in the title structure, 4-Carboxypyridinium basic ions and bromide ions are linked into chains along b through hydrogen bonds (Table 1, Fig 2). Crystallographic details of the title structure were examined with PLATON (Spek, 2009).

Experimental
Methyl benzoate 0.685 g (5 mmol) in ethanol (30 ml), and 1.01 g hydrobromic acid (40%, 5 mmol) was added. The mixed solution was filtrated and the crystals suitable for structure determination were grown by slow evaporation of the solution at room temperature for five days.

Refinement
Positional parameters of all the H atoms were calculated geometrically and were allowed to ride on the C atoms to which they are bonded,with C-H = 0.93 Å, N-H = 0.75-0.86 Å; with U iso (H) = 1.2U eq (C), with U iso (H) = 1.2-1.5U eq (N). Fig. 1. The molecular structure of the title compound, with the atomic numbering scheme. Displacement ellipsoids are drawn at the 30% probability level.

Figures
supplementary materials sup-2 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 Rfactors(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.