Crystal structure of 4-formylpyridine semicarbazone hemihydrate

The molecule of the title compound C7H8N4O·0.5H2O, alternatively called (E)-1-(pyridin-4-ylmethylene)semicarbazide hemihydrate, is in the E conformation and is almost planar; the r.m.s. deviation of the positions of the atoms of the pyridine ring from the best-fit plane is 0.0039 Å. The C, N and O atoms of the rest of the molecule sits close on this plane with a largest deviation of 0.115 (4) Å for the O atom of the semicarbazone moiety. There is an intramolecular N—H⋯N hydrogen bond. In the crystal, molecules are linked into an infinite three-dimensional network by classical N—H⋯Os (s = semicarbazone) and Ow—H⋯N (w = water) hydrogen bonds.


S2. Database survey
An analysis of the geometry of the 4-formylpyridine semicarbazone molecule with Mogul (Bruno et al., 2004) showed all bond lengths, bond angles, dihedral angles and ring geometry as not unusual, with the largest |z-score| = 1.254 for the C6-C3-C2 angle.

S3. Synthesis and crystallization
Reagent grade chemicals were used in this work. The compound was prepared based on a similar reaction for the 2formylpyridine semicarbazone (Garbelini et al. 2009).
In an round bottom flask 2.4 g (21 mmol) of semicarbazide hydrochloride were dissolved in 20 mL of ethanol and 5 mL of water and mixed with 1.7 g (21 mmol) of sodium acetate and 15 mL of water. The mixture was kept under stirring and heating at 70°C until the complete dissolution. Then, 2.0 mL (21 mmol) of 4-formylpyridine was added and the resulting solution was cooled at -15 °C overnight. Colourless crystals were collected by filtration, washed with water and cold ethanol and dried under vacuum. The yield was 2.3 g (67%).

S4. Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1. Crystal data, data collection and structure refinement details are summarized in Table 1. Crystal data, data collection and structure refinement details are summarized in Table 1. The final structure was refined with SHELXL2014  with anisotropic displacement parameters for all non-hydrogen atoms; hydrogen atoms were refined isotropically as riding atoms at their theoretical ideal positions. Drawings were made with Crystal Impact Diamond 3.

Figure 1
View of the title molecule.Displacement ellipsoids are drawn at the 50% probability level.

Figure 2
The molecular packing viewed down the crystallograpic b axis, with the a axis pointed down, showing the three dimensional hydrogen bonding network.