Crystal structures of crotonaldehyde semicarbazone and crotonaldehyde thiosemicarbazone from X-ray powder diffraction data

Crotonaldehyde semicarbazone and crotonaldehyde thiosemicarbazone show the same E conformation around the imine C=N bond. Each molecule has an intramolecular N—H⋯N hydrogen bond, which generates an S(5) ring. Intermolecular N—H⋯O hydrogen bonds in the semicarbazone link the molecules into layers parallel to the bc plane, while weak intermolecular N—H⋯S hydrogen bonds in the thiosemicarbazone link the molecules into chains propagating in [110].


Chemical context
The chemistry of semicarbazones and thiosemicarbazones is especially interesting due to their special role in biological applications such as anti-proliferative, anti-tumoral, anticonvulsant, anti-trypanosomal, herbicidal and biocidal activities (Beraldo et al., 2002;Kasuga et al., 2003;Teixeira et al., 2003;Beraldo & Gambino, 2004;Mikhaleva et al., 2008;de Oliveira et al., 2008;Alomar et al., 2012;Gan et al., 2014). They are also important intermediates in organic synthesis, mainly for obtaining heterocyclic rings, such as thiazolidones, oxadiazoles, pyrazolidones, and thiadiazoles (Greenbaum et al., 2004;Kü çü kgü zel et al., 2006). Semicarbazones and thiosemicarbazones have received considerable attention in view of their simplicity of preparation, various complexing abilities and coordination behavior that can be used in analytical applications (Garg & Jain, 1988;Casas et al., 2000). They are of interest from a supramolecular point of view since they can be functionalized to give different supramolecular arrays.

Supramolecular features
As a result of the presence of potential hydrogen-donor sites in molecules (I) and (II), supramolecular hydrogen-bonding interactions are observed in both compounds (Tables 1 and 2). In the crystal of (I), molecules are linked by pairs of N-HÁ Á ÁO hydrogen bonds, forming inversion dimers with R 2 2 (8) ring motifs (Fig. 2a). The resulting dimers are connected through N-HÁ Á ÁO hydrogen bonds, forming layers parallel to bc plane. In the crystal of (II), molecules are linked by weak N-HÁ Á ÁS hydrogen bonds, forming chains propagating in [110] (Fig. 2b).

Synthesis and crystallization
All reactions and manipulations were carried out in air with reagent grade solvents. The IR spectra were recorded on a Jasco FT-IR 300E instrument. 1 H and 13 C{ 1 H} NMR spectra were recorded on a Bruker Bio spin 400 spectrometer. Microanalysis was performed using EURO EA. Powder X-ray diffraction data were collected with Stoe Transmission diffractometer (Stadi P).

Table 2
Hydrogen-bond geometry (Å , ) for (II).  For the synthesis of (II), crotonaldehyde (0.5 g, 7.1 mmol) was added to thiosemicarbazide (CH 5 N 3 S; 0.65 g, 7.1 mmol) in 5 ml water and the mixture was stirred at room temperature for 24 h. The product was separated by filtration and recrystallized from absolute ethanol to produce the product (II) (white powder; m.p. 435-436 K) in 72.5% yield.

Refinement details
Crystal data, data collection and structure refinement details are summarized in Table 3. Compounds (I) and (II) crystal-lized in the form of a very fine white powder. Since no single crystals of sufficient size and quality could be obtained, the crystal structures of both compounds were determined from X-ray powder diffraction patterns. The powder samples of (I) and (II) were lightly ground in a mortar, loaded into two Mylar foils and fixed onto the sample holder with a mask of suitable internal diameter (8.0 mm). The powder X-ray diffraction data were collected at room temperature with a STOE transmission STADI-P diffractometer using monochromatic Cu K a1 radiation (= 1.54060 Å ) selected with an incident beam curved-crystal germanium Ge(111) monochromator with a linear position-sensitive detector (PSD). The patterns were scanned over the angular range 5.0-80.0 (2). For pattern indexing, the extraction of the peak positions was carried out with the program WinPLOTR (Roisnel & Rodríguez-Carvajal, 2000). Pattern indexing was performed with the program DICVOL4.0 (Boultif & Louë r, 2004). The first 20 lines of the powder pattern were indexed completely on the basis of a monoclinic cell for (I) and a triclinic cell for (II). The figures of merit (de Wolff et al., 1968;Smith & Snyder, 1979) are sufficiently acceptable to support the   (Farrugia, 2012), Mercury (Macrae et al., 2006) and publCIF (Westrip, 2010). (Rodríguez-Carvajal, 2001). The number of molecules per unit cell was estimated to be Z = 4 for (I) and Z = 2 for (II). The initial crystal structures for (I) and (II) were determined by direct methods using the program EXPO2014 (Altomare et al., 2013). The models found by this program were introduced into the program GSAS (Larson & Von Dreele, 2004) implemented in EXPGUI (Toby, 2001) for Rietveld refinement. During the Rietveld refinements, the background was refined using a shifted Chebyshev polynomial with 20 coefficients. The effect of asymmetry of low-order peaks was corrected using a pseudo-Voigt description of the peak shape (Thompson et al., 1987), which allows for angle-dependent asymmetry with axial divergence (Finger et al., 1994) and microstrain broadening, as described by Stephens (1999). The two asymmetry parameters of this function, S/L and D/L, were both fixed at 0.022 during this refinement. Intensities were corrected from absorption effects with a function for a plate sample in transmission geometry with a Ád value of 0.15 for (I) and 0.72 for (II) ( is the absorption coefficient and d is the sample thickness).
These Ád values were determined experimentally. Before the final refinement, all H atoms were introduced in geometrically calculated positions. The coordinates of these H atoms were refined with strict restraints on bond lengths and angles until a suitable geometry was obtained, after that they were fixed in the final stage of the refinement. No soft restraints were imposed for (I), while for (II) the CH 3 -CH bond was clearly stretched (close to 1.6 Å ), therefore a single soft restraint was carried out to obtain a normal value (1.49 Å ). The final refinement cycles were performed using isotropic atomic displacement parameters for the C, N and O atoms, an anisotropic atomic displacement parameter for S atom in (II) and a fixed global isotropic atomic displacement parameter for the H atoms. The preferred orientation was modelled with 12 coefficients using a spherical harmonics correction (Von Dreele, 1997) of intensities in the final refinement. The use of the preferred orientation correction leads to a better molecular geometry with better agreement factors. The final Rietveld plots of the X-ray diffraction patterns for both (I) and (II) are given in Fig. 3.  (Larson & Von Dreele, 2004); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012), Mercury (Macrae et al., 2006); software used to prepare material for publication: publCIF (Westrip, 2010).