Crystal structure of 2-[(2E)-2-methyl-3-phenylprop-2-en-1-ylidene]-N-phenylhydrazinecarboxamide

The title compound crystallizes with two independent molecules in the asymmetric unit. The semicarbazone moieties of which are essentially planar with the terminal phenyl rings twisted away from them. In the crystal, N—H⋯O hydrogen-bonding interactions link the two molecules into a centrosymmetric dimer, with adjacent dimers linked by weak C—H⋯O interactions to form a cage-like structure. These cage structures are interconnected by weak C—H⋯π interactions, forming supramolecular chains along the c-axis direction.


Chemical context
Semicarbazones are oxygen and nitrogen contributor ligands whose significance lies in their versatility of molecular sequence, which allows diverse geometries to be obtained. Semicarbazones exhibit amido-iminol tautomerism in solution due to the interaction of solvent molecules, but generally exist in the amido form in the solid state. The FT-IR and NMR spectra of semicarbazones indicate the existence of a keto form in the solid state that can be confirmed by single crystal X-ray diffraction analysis (Kurup et al., 2011;Sreekanth et al., 2004). Biological properties linked to antimicrobial (Siji et al., 2010) and antiparasitic (Soares et al., 2011) effects make semicarbazones important ligands in coordination chemistry. Compared to Gentamycin, a commonly used antibiotic, N 4 -phenylsemicarbazone derivatives exhibit moderate antibacterial activity at higher concentrations and also show DNA cleavage properties (Layana et al., 2016). Semicarbazones can function as brilliant ligands in a variety of metal ions (Kala et al., 2007) and co-ordinate to metal ions either in neutral (Siji et al., 2011) or in anionic forms (Reena et al., 2008). Structural studies of many semicarbazones and N 4 -phenylsemicarbazones have been reported and some of them adopt an E configuration with respect to the azomethine double bond along with both inter-and intramolecular hydrogen-bonding interactions (Reena et al., 2010;Layana et al., 2014Layana et al., , 2018. Semicarbazones form complexes with a variety of structural ISSN 2056-9890 features such as monomer, dimer and one-dimensional polymers (Kunnath et al., 2016). -Methyl-trans-cinnamaldehyde, a precursor for the synthesis of -methyl-trans-cinnamaldehyde-N 4 -phenylsemicarbazone, has significant antifungal activity and can self-couple and form complexes with some transition metals (Shreaz et al., 2011). The diverse structural features and substantial biological applications have prompted us to synthesize a new semicarbazone derived from -methyl-transcinnamaldehyde and N 4 -phenylsemicarbazide.

Structural commentary
The title compound crystallizes in the triclinic space group P1 symmetry with two independent molecules, I and II, in the asymmetric unit (Fig. 1). The semicarbazone units in I and II are essentially planar, with maximum deviations from the least-squares plane of 0.042 (1) Å for N2 in molecule I and 0.041 (1) Å for N4 in molecule II. The terminal phenyl rings in both two molecules are twisted away from the semicarbazone mean plane, making dihedral angles of 60.26 (8) and 28.76 (9) in molecule I and 31.07 (9) and 35.45 (8) in molecule II. Both molecules exist in an E configuration with respect to the C C and azomethine C N bonds. The azomethine C N and keto C O bond lengths [1.273 (2) and 1.2269 (17) Å , respectively] in molecule I are shorter than those for molecule II [1.2766 (19) Å and 1.2302 (18) Å respectively]. In contrast, the C N and C O bond lengths bond lengths reported for the two independent molecules of 2-benzoylpyridine semicarbazone are 1.294 (2) and 1.295 (2) Å and 1.2360 (19) and 1.2390 (19) Å respectively (de Lima et al., 2008).

Database survey
The structure of the title compound has not previously been reported (CSD version 5.39, update of August 2018; Groom et al., 2016). All geometric parameters in the title compound N-HÁ Á ÁO hydrogen bonds and weak C-HÁ Á ÁO intermolecular interactions (dashed lines) generating centrosymmetric dimers and a cage-like structure. Table 1 Hydrogen-bond geometry (Å , ).

Figure 1
ORTEP diagram showing the two molecules in the asymmetric unit, with atom labels and 50% probability displacement ellipsoids.

Synthesis and crystallization
Hot ethanolic solutions of N 4 -phenylsemicarbazide (0.1512 g, 1 mmol) and -methyl-trans-cinnamaldehyde (0.14 ml, 1 mmol) were mixed and refluxed for about 4 h. Colourless block-shaped crystals of the title compound (yield 83%) were separated by filtration, washed with ethanol and dried over P 4 O 10 in vacuo. Single crystals (m.p. 463AE2 K) were obtained by slow evaporation of a 1:1 mixture of ethyl acetate and ethanol.
Analysis The packing viewed along the b axis.

Figure 3
Weak C-HÁ Á Á intermolecular interactions (solid cones), linking the dimeric cage-like structures into a chain along the c axis.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. Reflections (111) and (001) were omitted due to bad agreement. All hydrogen atoms bound to carbon atoms were positioned geometrically with C-H distances of 0.93-0.96 Å and refined as riding, with U iso (H) = 1.2U eq (C) or 1.5U eq (C-methyl). The NH hydrogen atoms were located in a difference-Fourier map and refined with N-H restrained to 0.88AE0.01 Å .    ; program(s) used to refine structure: SHELXS97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012) and DIAMOND (Brandenburg, 2010); software used to prepare material for publication: publCIF (Westrip, 2010).