Crystal structure of (E)-3-{[2-(2,4-dichlorobenzylidene)hydrazin-1-yl]carbonyl}pyridinium chloride trihydrate

In the title hydrated salt, C13H10Cl2N3O+·Cl−·3H2O, the organic cation exhibits a dihedral angle of 8.26 (14)° between the mean planes of the pyridinium and benzene rings, and dihedral angles of 8.70 (15) and 15.93 (5)° between the mean planes of the hydrazide group and the benzene and pyridinium rings, respectively. In the crystal, N—H⋯O, N—H⋯Cl, C—H⋯O, C—H⋯Cl, O—H⋯O, O—H⋯N and O—H⋯Cl hydrogen bonds link the complex cations, chloride anions and solvent water molecules into a three-dimensional network.

The asymmetric unit of the title compound, illustrated in Fig Table 1). One of the H atoms of the water molecule (O1W) forms bifurcated hydrogen bonds to the azomethine nitrogen and the carbonyl oxygen atoms of one neighbouring molecule and the same water molecule acts as a hydrogen bond acceptor towards another hydrazone molecule through N-H···O hydrogen bonds (Fig. 2). Further molecules are linked via a pair of C-H···O hydrogen bonds forming inversion dimers with an R 2 2 (10) ring motif (Fig. 3). The crystal structure is further stabilized by N-H···Cl, C-H···Cl and O-H···Cl hydrogen bonds.

S2. Synthesis and crystallization
2,4-dichlorobenzaldehyde (0.175 g, 0.001 mol) was added to an aqueous solution of nicotinicacid hydrazide (0.34 g, 0.001 mol), followed by 2 drops of concentrated HCl is added. After the addition was complete, the reaction mixture was stirred well at room temperature for 1 h. The colourless solid that formed was filtered, dried and washed with petroleum ether (40-60%). The crude solid obtained was dried and recrystallized from absolute alcohol. The recrystallized product was dried over vacuum. [m.pt: 411-413 K; yield:92%].

S3. Refinement
The H atoms of the solvent water were located in a difference map and refined freely. All Other H atoms were placed in  The molecular structure of the title compound, with the atom labelling. Displacement ellipsoids are drawn at the 50% probability level.

Figure 2
Crystal packing of the title compound viewed along the a axis. Hydrogen bonds are shown as dashed lines.

Figure 3
Part of the crystal packing of the title compound, showing the formation of R 2 2 (10) motif. The Cland the water molecules are omitted for the sake of clarity. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.28 e Å −3 Δρ min = −0.37 e Å −3 Special details 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.