4-(Ammoniomethyl)pyridinium dichloride

The title compound, C6H10N2 2+·2Cl−, contains a network of 4-(ammoniomethyl)pyridinium cations and chloride anions which are interconnected by N—H⋯Cl hydrogen bonds. The crystal packing is also influenced by intermolecular π–π stacking interactions between identical antiparallel organic cations with a face-to-face distance of ca 3.52 Å.

The title compound, C 6 H 10 N 2 2+ Á2Cl À , contains a network of 4-(ammoniomethyl)pyridinium cations and chloride anions which are interconnected by N-HÁ Á ÁCl hydrogen bonds. The crystal packing is also influenced by intermolecularstacking interactions between identical antiparallel organic cations with a face-to-face distance of ca 3.52 Å .

Experimental
Data collection: CAD-4 EXPRESS (Straver, 1992); cell refinement: CAD-4 EXPRESS; data reduction: RC93 (Watkin et al., 1994); program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: CRYSTALS (Betteridge et al., 2003); molecular graphics: CAMERON (Watkin et al., 1996); software used to prepare material for publication: CRYSTALS. The coordination chemistry of anions was the starting point for the development of new compounds having many practical and potential applications in various fields, such as supramolecular chemistry (Schmidtchen and Berger, 1997) and biochemical processes (Pajewski et al., 2004). Moreover, halide anions have been successfully used to assemble double-helical motifs of various molecules containing aromatic groups, with π-stacking interactions within the helices (Sessler et al., 2003).

Structure Reports Online
These anions can be useful for such applications because of the high flexibility of their coordination (Ilioudis et al., 2000).
Here, a new member of this family, the title compound (C 6 H 10 Cl 2 N 2 ), is presented, which has been obtained during our studies of the preparation of new organic hydrochloride compounds. As shown in Fig. 1, to ensure charge balance the organic species is doubly protonated at N1 and N2. Thus, the structure consists essentially of an 4-(ammoniomethyl)pyridinium cations and two Clanions, associated in a hydrogen-bonded network. The Clanions and the antiparallel pair of organic cations associate each other via hydrogen-bonding interactions to construct a convoluted hydrogen-bonded chain network which runs along the [111] direction at b = 1 / 2 (Fig. 3). This chain is made up by a four-membered donor-acceptor ring, involving two Cl atoms, fused along the N-H···Cl hydrogen bond (Fig. 2). These intermolecular hydrogen bonds generate edge-fussed [R 2 4 (8) and R 2 4 (20)] motifs (Bernstein et al., 1995). When viewed in perspective, the molecules chains have a marked zigzag structure and somewhat resembles a helix. As can be seen in Fig.2, the neighbouring pyridinyl rings run parallel in opposite directions and stack each other by turns in a face-to-face mode. The nearest centroid-centroid distance is 3.52 Å, less than 3.8 Å, a usually acceptad maximum value for π-π interactions (Jin et al., 2005). An examination of the organic moiety geometrical features shows that the atoms building the pyridinyl ring have a good coplanarity and they form a conjugated plane with average deviation of 0.005 Å). The mean value of C-C and N-C bond lengths are 1.381 (2) and 1.332 (2) Å) which are between that of a single bond and a double bond and agree with those in the literature (Oueslati et al., 2006). However, it is worth noticing that the C-N-C angles of pyridine are very sensitive to protonation (Krygowski et al., 2005). A pyridinium cation always possesses an expanded angle of C-N-C in comparison with the parent pyridine.
The C1-N1-C5 angle [122.3 (2) °] is consistent with the type of pyridinium cation. In fact, the protonation of the nitrogen atom N1 decreases its electronegativity; hence the corresponding C-N-C angles becomes larger.

Experimental
An aqueous 1M HCl solution and 4-(amminomethyl)pyridine in a 2:1 molar ratio were mixed and dissolved in sufficient ethanol. Crystals of (I) grew as the ethanol evaporated at 293 K over the course of a few days.

Refinement
The refinement was carried out with Iσ(I)>3 and a sinθ/λ>0.01 to get rid of the reflections in the vicinity of the beamstop. The refinement was thus carried out using 1609 reflections (out of the 1995 independent ones). The R value reported corresponds to the recomputed value with a 2σ cutoff (SHELX like).

supplementary materials sup-2
The H atoms were all located in a difference map, but those attached to carbon atoms were repositioned geometrically. The H atoms were initially refined with soft restraints on the bond lengths and angles to regularize their geometry (C-H in the range 0.93-0.98, N-H in the range 0.86-0.89 and O-H = 0.82 Å) and U iso (H) (in the range 1.2-1.5 times U eq of the parent atom), after which the positions were refined with riding constraints. Fig. 1. A view of (I), showing 40% probability displacement ellipsoids and arbitrary spheres for the H atoms.