4-Ethyl-3-(3-pyridyl)-1H-1,2,4-triazole-5(4H)-thione 0.095-hydrate

The title compound, C9H10N4S·0.095H2O, consists of discrete 4-ethyl-3-(3-pyridyl)-1H-1,2,4-triazole-5(4H)-thione molecules and a disordered molecule of water of hydration with partial occupancy, lying on a twofold rotation axis. The dihedral angle between the pyridine and triazole rings is 41.73 (8)°. In the crystal structure, molecules are hydrogen bonded via triazole NH groups and pyridyl N atoms, forming chains parallel to the a axis.


Related literature
The structure of (I) is composed of independent molecules of 4-ethyl-2,4-dihydro-5-(3-pyridyl)-3H-1,2,4-triazole-3thione ( Fig. 1) and a disordered water of hydration with partial occupancy lying on a two-fold rotation axis. The bond distances and bond angles in (I) agree well with the corresponding bond distances and angles reported in some compounds closely related to (I) (e.g., Dege et al., 2004Dege et al., , 2005Mazur et al., 2006;Dobosz et al., 2003;Demir, et al., 2006). The meanplanes formed by the pyridyl and triazole rings in (I) lie at 41.73 (8)° with respect to each other while the mean-plane of the ethyl group is inclined with the triazole ring at 80.39 (13)°.
The water of hydration is surrounded by four molecules of (I) with S1···O1 and N1···O1 separation of 3.074 (4) and 3.382 (9) Å, respectively (Fig. 2). The molecules of (I) are hydrogen bonded via N2-H2···N4 forming chains lying parallel to the a axis (details of hydrogen bonding geometry have been given in Table 1). The shortest distance between the centroids of pyridyl and triazole rings from two different molecules lying about inversion centers is 4.350 (3) Å.

Experimental
The title compound was prepared from the corresponding thiosemicarbazide by following the reported procedure (Ahmad et al., 2001). 4-Ethyl-1-(2-pyridoyl)thiosemicarbazide (12 mmol) was dissolved in an aqueous 4 N sodium hydroxide solution (65 ml). The solution was heated to reflux for 11.5 h, cooled and filtered. The filtrate was acidified to pH of 4-5, with 4 N hydrochloric acid. The solid product was filtered off, washed with water and recrystallized from aqueous ethanol (60%).
Crystals of (I) were grown by slow evaporation of the ethanol over 15 days at room temperature (yield 72%).

Refinement
Though all the H atoms could be distinguished in the difference Fourier map the H-atoms bonded to C-atoms were included at geometrically idealized positions and refined in riding-model approximation with the following constraints: pyridyl, methyl and methylene C-H distances were set to 0.95, 0.98 and 0.99 Å, respectively; in all these instances U iso (H) = 1.2 U eq (C).
H-atom bonded to N2 was taken from the difference map and was allowed to refine with U iso = 1.2 times U eq of N2. Towards the end of the refinement, a difference Fourier map revealed a peak that was included in the refinement as an O-atom the site occupancy factor of which refined to 0.095; its s.o.f. was fixed at that value during the final rounds of calculations. The H-atoms bonded to the O atom of the water molecule could not be located and were not included in the refinement but are included in the molecular formula. The atmospheric moisture was assumed to be the source of this partially occupied water of hydration. The final difference map was free of any chemically significant features. Fig. 1. ORTEP-3 (Farrugia, 1997) drawing of (I) with displacement ellipsoids plotted at 50% probability level.  as those based on F, and R-factors based on ALL data will be even larger.