4-Hydroxy-1,2,6-trimethylpyridinium chloride monohydrate

In the crystal of the title hydrated molecular salt, C8H12NO+·Cl−·H2O, the water molecule makes two O—H⋯Cl hydrogen bonds, generating [010] zigzag chains of alternating water molecules and chloride ions. The cation is bonded to the chain by an O—H⋯O hydrogen bond and two weak C—H⋯Cl interactions. Weak aromatic π–π stacking [centroid–centroid separation = 3.5175 (15) Å] occurs between the chains.

In the crystal of the title hydrated molecular salt, C 8 H 12 NO + ÁCl À ÁH 2 O, the water molecule makes two O-HÁ Á ÁCl hydrogen bonds, generating [010] zigzag chains of alternating water molecules and chloride ions. The cation is bonded to the chain by an O-HÁ Á ÁO hydrogen bond and two weak C-HÁ Á ÁCl interactions. Weak aromaticstacking [centroid-centroid separation = 3.5175 (15) Å ] occurs between the chains.
The corresponding bond lengths and angles of the cation in (I) are comparable with those of related structures reported earlier (Seethalakshmi et al., 2006a(Seethalakshmi et al., ,b,c, 2007. In (I), water molecule acts as a donor for two different symmetry-related chloride anions and acts as an acceptor for the hydroxy group of the cation. As shown in Fig As shown in Fig. 5, an R 2 3 (8) loop is formed by the combination of O-H···O1W and O1W-H1W···Cl and C3-H3···Cl intermolecular interactions. As mentioned earlier, one of the methyl atoms C9 (via H9A) is participated in a weak intermolecular C-H···Cl interaction with chloride anion. Again, this interaction combines with C3-H3···Cl and two O1w-H···Cl interactions forming a ring which has a graph-set motif of R 2 4 (10). The R 2 3 (8) and R 2 4 (10) ring motifs are arranged alternately as a helical ribbon which run parallel to the b axis (Fig. 5). In the solid state, each chloride anion is tetra coordinated by two cations (via H3 and H9A) and two water molecules (via H1W and H2W). The tetra coordination angles in the range of 58.40-88.17°. There is a π···π stacking interaction also observed between two pyridinium rings related by center of inversion with centroid-to-centroid distance of 3.5175 (15) Å.

Experimental
The title salt was prepared by dissolving 1-methyl-2,6-dimethyl-4-hydroxypyridine (1.37 g) with HCl (0.92 ml) in distilled water (5 ml). The mixture was stirred at room temperature for 7 h and the clear solution was kept for evaporation at 60 °C after filtration. Finally crystalline powder was obtained and dissolved in distilled water. Colourless prisms were obtained following the slow evoporation technique.

Refinement
The positions of hydroxy H atom and H atoms of water molecule were determined from a difference Fourier map and refined freely along with their isotropic displacement parameters. In the final round of refinement, the O-H bond lengths of water molecule are restrained to 0.84 (2) Å. The methyl H atoms were constrained to an ideal geometry (C-H = 0.98 Å), with U iso (H) = 1.5U eq (C), but were allowed to rotate freely about the C-C and N-C bonds. The remaining H atoms were placed in geometrically idealized positions (C-H = 0.95 Å), with U iso (H) = 1.2U eq (C) and were constrained to ride on their parent atoms.

Special details
Experimental. The minimum and maximum absorption values stated above are those calculated in SHELXL97 from the given crystal dimensions. The ratio of minimum to maximum apparent transmission was determined experimentally as 0.597412. Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. 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 R-factors(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.