Crystal structure of 3-(thiophen-2-yl)-5-p-tolyl-4,5-dihydro-1H-pyrazole-1-carbothioamide

In the title compound, the central pyrazole ring adopts a twisted conformation on the –CH—CH2– bond and its mean plane makes dihedral angles of 7.19 (12) and 71.13 (11)° with the attached thiophene and toluene rings, respectively. In the crystal, molecules are linked by N—H⋯S hydrogen bonds, forming chains propagating along [010].


Chemical context
Five-membered heterocyclic pyrazole analogues have been used extensively as building blocks in organic synthesis. They have been transformed efficiently into molecules of potential medicinal and pharmaceutical important. Pyrazole derivatives have known to exhibit diverse biological applications such as antidiabetic,anaesthetic, antimicrobial and antioxidant. In addition, they have also shown potential anticancer and antiamoebic activity and to be potent and selective inhibitors of tissue-nonspecific alkaline phosphatase (Sidique et al. 2009). Earlier we synthesized and -unsaturated compounds which served as useful intermediates for the synthesis of pyrazolines (Manjula et al., 2013) and thiazepines (Manjunath et al., 2014). As part of our ongoing research on pyrazole analogues, the title compound was synthesized and we report herein on its crystal structure. Studies of the biological activity of the title compound are underway and will be reported elsewhere.

Database survey
A search of the Cambridge Structural Database (Version 5.36, May 2015; Groom & Allen, 2014) revealed seven structures containing the 3-(thiophen-2-yl)-pyrazole unit. Amongst these are two thioamides; the phenyl derivative of the title compound, 5-phenyl-3-(2-thienyl)-2-pyrazoline-1-thioamide (HEFXEW; Işık et al., 2006), and 1-(N-ethylthiocarbamoyl)-3,5-bis(2-thienyl)-2-pyrazoline (YINFUX; Kö ysal et al., 2007). In these two compounds, the pyrazole rings have envelope conformations with the methine C atom as the flap, and the mean planes of the two rings are inclined to one another by 11.98 and 10.13 , respectively. This is in contrast to the situation in the title compound where the pyrazole ring has a twisted conformation on the -CH-CH 2 -bond and its mean plane is inclined to the thiophene ring by 7.19 (12) . In the crystal of the phenyl derivative (HEFXEW), molecules are also linked by N-HÁ Á ÁS hydrogen bonds, forming chains.

Synthesis and crystallization
A mixture of 3-(4-methylphenyl)-1-(thiophen-2-yl)prop-2-en-1-one (0.001 mol) and thiosemicarbazine hydrochloride (0.01 mol) and potassium hydroxide (0.02 mol) in ethyl alcohol (20 ml) was refluxed on a water bath for 6-8 h. The progress of the reaction was monitored by TLC. After completion of the reaction, the mixture was poured into icecold water and stirred. The solid that separated was filtered, and washed with ice-cold water. The product was recrystallized from ethyl alcohol to give the title compound as rectangular yellow crystals. Analysis calculated for View of the molecular structure of the title compound, showing the atom labelling. Displacement ellipsoids are drawn at the 50% probability level.

Figure 2
A view along the a axis of the crystal packing of the title compound. The hydrogen bonds and C-HÁ Á Á interactions are shown as dashed lines (see Table 1 for details). C-bound H atoms have been omitted for clarity. Table 1 Hydrogen-bond geometry (Å , ).
Cg3 is the centroid of the benzene ring C14-C19.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. H atoms were fixed geometrically and allowed to ride on their parent atoms: C-H = 0.93-0.98 Å with U iso (H) = 1.5U eq (C) for methyl H atoms and 1.2U eq (C) for other H atoms.    (12) Special details Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles Refinement. Refinement on F 2 for ALL reflections except those flagged by the user for potential systematic errors. Weighted R-factors wR and all goodnesses 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 observed criterion of F 2 > σ(F 2 ) is used only for calculating -R-factor-obs 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.