Redetermination of 3-(ammoniomethyl)pyridinium dichloride

The crystal structure of the title compound, C6H10N2 2+·2Cl−, has been reported previously in the non-standard setting P21/a [Genet (1965 ▶). Bull. Soc. Fr. Miner. Crist. 88, 463–470], with an R value of 0.16. The current redetermination improves significantly the precision of the geometric parameters. In the crystal packing, cations and anions are linked by intermolecular N—H⋯Cl and C—H⋯Cl hydrogen bonds into a three-dimensional network.

The cation-layer interactions involve an ammonium group that hydrogen bonds to the perovskite layer (Long et al., 1997).
We report herein the crystal structure of the title compound, which was prepared by the reaction of pyridin-3-ylmethanamine and hydrochloric acid. Its crystal structure has been reported previously in the non standard setting P2 1 /a (Genet, 1965), with an R value of 0.16. The current redetermination improves significantly the precision of the geometric parameters.
The asymmetric unit of the title compound ( Fig. 1) consists of a two independent chloride anions and a 3-(ammoniomethyl)pyridinium dication. In the cation, the plane through the C2/C6/N2 atoms is tilted by 68.13 (14)° with respect to the pyridine ring. In the crystal packing (Fig. 2), intermolecular N-H···Cl and C-H···Cl hydrogen bonds (Table   1) connect neighbouring cations and anions into a three-dimensional network.
Colourless single crystals of the title compound suitable for X-ray analysis were obtained on slow evaporation of the solvent over a period of 48 h.

Refinement
Positional parameters of all the H atoms were calculated geometrically and were allowed to ride on their parent atoms, with C-H = 0.93-0.97 Å, N-H = 0.86-0.89 Å, and with U iso (H) = 1.2 U eq (C, N). Fig. 1. The molecular structure of the title compound, with displacement ellipsoids drawn at the 30% probability level. 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.