2-(1H-Pyrazol-3-yl)pyridinium chloride monohydrate

The title organic salt, C8H8N3 +·Cl−·H2O, exhibits a rich hydrogen-bonding network involving all constituent species. The water molecules are engaged in strong O—H⋯Cl interactions with the chloride anions, two neighboring protonated 2-(1H-pyrazol-3-yl)pyridinium species interact via N—H⋯N bonds with two pyrazole rings. Further, a short and highly directional C—H⋯O interaction is observed connecting the pyridinium ring to the water molecule of crystallization. Weak C—H⋯Cl and N—H⋯Cl interactions contribute to the stabilization of the crystal structure.

The title organic salt, C 8 H 8 N 3 + ÁCl À ÁH 2 O, exhibits a rich hydrogen-bonding network involving all constituent species. The water molecules are engaged in strong O-HÁ Á ÁCl interactions with the chloride anions, two neighboring protonated 2-(1H-pyrazol-3-yl)pyridinium species interact via N-HÁ Á ÁN bonds with two pyrazole rings. Further, a short and highly directional C-HÁ Á ÁO interaction is observed connecting the pyridinium ring to the water molecule of crystallization. Weak C-HÁ Á ÁCl and N-HÁ Á ÁCl interactions contribute to the stabilization of the crystal structure.
Our research group has been particularly interested in the use of this molecule and its derivatives. For example, we have reported the crystal structures of both the molybdenum complex cis-[Mo(CO) 4 L] (Coelho et al., 2006) and the organic (Coelho et al., 2007). We have recently isolated single crystals of (I) as a secondary (minor) phase (see Experimental). Following our on-going interest in the structural details of organic crystals (Paz & Klinowski, 2003;Paz et al., 2002), here we report the supramolecular structure at 150 K of the monohydrate form of the title salt: C 8 H 8 N 3 The asymmetric unit of the title compound, (I), is composed of a cationic C 8 H 8 N 3 + moiety (protonated at the pyridine ring), one chloride anion and one water molecule of crystallization (Fig. 1). The two aromatic rings of 2-(3pyrazolyl)pyridinium can be considered as coplanar (the average planes containing the rings are tilted by only ca 1°).
The existence of several chemical groups capable of hydrogen bonding either as donors or acceptors leads to the formation of a complex supramolecular network. Water molecules and chloride anions are involved in strong (d D···A ranging between ca 3.11 and 3.21 Å) and highly directional [<(DHA) angles above 170° -see Table 1] O-H···Cl hydrogen bonding interactions forming a R 2 2 (8) graph set motif as depicted in Fig. 2a (Bernstein et al., 1995). It is important to emphasize that the water molecule itself acts as the acceptor in an unusual C-H···O water interaction. Indeed, even though this interaction is not considered as classic (Nangia & Desiraju, 1998), in the structure of (I) the d D···A distance is considered short [2.7203 (16) Å] and the <(DHA) angle is 156°. Thus, these geometric parameters allow us to infer that this interaction seems to play an important role in the supramolecular organization of (I). In addition, the close proximity of the pyrazolyl rings belonging to two adjacent 2-(3-pyrazolyl)pyridinium moieties promote the formation of two N-H···N interactions describing a R 2 2 (6) motif (Fig. 2a). The alternation between the two aforementioned graph set motifs and the single C-H···O water interaction leads to the formation of a supramolecular tape (solely based on strong interactions) running parallel to the [011] vector of the unit cell (Fig. 3).
supplementary materials sup-2 The crystal packing of (I) is further promoted by the existence of a number of weak C-H···Cl and one N-H···Cl hydrogen bonding interactions as shown in Fig. 2b (Table 1), which establish connections between adjacent supramolecular tapes (not shown).

Experimental
Crystals of (I) were isolated as a secondary product while reacting in dichloromethane MoO 2 Cl 2 with 2-(3pyrazolyl)pyridine.

Refinement
Hydrogen atoms bound to carbon and nitrogen were located at their idealized positions and were included in the final structural model in riding model approximation with C-H = 0.95 Å and N-H = 0.88 Å, and with U(H) set to 1.2U eq (C, N).
H atoms associated with the water molecule of crystallization were directly located from difference Fourier maps and included in the structure with the O-H and H···H distances restrained to 0.95 (1) and 1.55 (1) Å, respectively, with U(H) set to 1.5U eq (O).
The final difference Fourier map synthesis showed the highest peak (1.26 eÅ -3 ) located at 0.25 Å from the C5 atom. Fig. 1. Asymmetric unit of (I) with all non-hydrogen atoms represented as thermal displacement ellipsoids drawn at the 80% probability level and hydrogen atoms as small spheres with arbitrary radii. The labeling scheme is provided for all non-hydrogen atoms.  Table 1 for geometric details of the highlighted hydrogen bonding interactions.    (2)