4-(2-Carboxyvinyl)pyridinium iodide

In the crystal structure of the title salt, C8H8NO2 +·I−, the cations and anions are linked by bifurcated N—H⋯(O,I) hydrogen bonds. A near-linear O—H⋯I hydrogen bond also exists between the cation and anion, resulting in a two-dimensional network. In the cation, the carboxyl group is twisted with respect to the pyridine ring at a dihedral angle of 15.34 (17)°.

In the crystal structure of the title salt, C 8 H 8 NO 2 + ÁI À , the cations and anions are linked by bifurcated N-HÁ Á Á(O,I) hydrogen bonds. A near-linear O-HÁ Á ÁI hydrogen bond also exists between the cation and anion, resulting in a twodimensional network. In the cation, the carboxyl group is twisted with respect to the pyridine ring at a dihedral angle of 15.34 (17) .
The conformation of the cation is stabilized by an intramolecular N-H···I and C-H···O hydrogen bond (Table 1). In the crystal structure ( Fig. 2), molecules are connected by intermolecular N-H···O, O-H···I and C-H···O hydrogen bonds into chains running parallel to the b axis (Table 1).
The dielectric constant of the title compound as a function of temperature indicates that the permittivity is basically temperature-independent, suggesting that this compound should be not a real ferroelectrics or there may be no distinct phase transition occurred within the measured temperature range.

Experimental
In a dry, N 2 -filled three-necked flask fitted with stirrer, 4-pyridinecarboxaldehyde (1.07 g, 10 mmol) and malonic acid (2.50 g, 24 mmol) were dissolved in pyridine (4 ml) and piperidine (0.1 ml) and this solution was refluxed for 4.5 h and the mixture was then worked up. To the suspension was then added ethylether (5 ml), and the white precipitate was filtered and washed with ethylether (3.5 ml) to give (E)-3-(4-pyridyl)acrylic acid. (E)-3-(4-pyridyl)acrylic acid (0.5 g, 3 mmol) and hydriodic acid (0.43 g, 3 mmol) were dissolved in ethanol (10 ml). After slow evaporation of the solution over a period of 3 days, orange prismatic crystals of the title compound suitable for X-ray diffraction analysis were isolated.

Refinement
All H atoms were placed at calculated positions with C-H = 0.93, N-H = 0.86 and O-H = 0.82 Å, and refined in riding mode with U iso (H) = 1.5U eq (O) and 1.2U eq (C,N). Fig. 1. A partial packing diagram of the title compound, with the displacement ellipsoids were drawn at the 30% probability level.