Different weak interactions in the crystals of three isomeric (E)-N-methyl-N′-(nitrobenzylidene)-2-(thiophen-2-yl)acetohydrazides

Three isomeric methylated 2-(thiophen-2-yl)acetohydrazides show little consistency in the pattern of weak (C—H⋯O, C—H⋯π and π–π) interactions in their crystal structures.


Structural commentary
The molecular structure of (I) is shown in Fig. 1, which confirms that methylation has occurred at N2. The thiophene The molecular structure of (I), showing 50% displacement ellipsoids. Only the major orientation of the thiophene ring is shown.

Figure 3
The molecular structure of (III), showing 50% displacement ellipsoids. Only the major orientation of the thiophene ring is shown.

Supramolecular features
The packing in (I) can be decomposed into two different chains: in the first of these (Fig. 5), inversion dimers (about the point 0, 1 2 , 1 2 for the asymmetric molecule) linked by pairs of C10-H10aÁ Á ÁO3 hydrogen bonds (Table 1) generate R 2 2 (20) loops. These dimers are complemented by inversion-related pairs of C5-H5Á Á ÁCg1 (where Cg1 is the centroid of the thiophene ring) bonds; this second inversion dimer (about 1 2 , 1 2 , 1 2 ) is reinforced by an aromaticstacking interaction involving the C1-C6 benzene rings [centroid separation = 3.7118 (9) Å ; slippage = 1.27 Å ]. Together, the C-HÁ Á ÁO dimers and the C-HÁ Á Á +dimers alternate in [100] chains. In the second one-dimensional motif, the C8, C10-H10b and C12 bonds combine together to generate [001] chains ( Fig. 6) in which the carbonyl O1 atom accepts hydrogen bonds from two adjacent molecules to generate R 2 2 (9) loops. The cohesion of the chain is reinforced by a C-HÁ Á Á interaction from one thiophine ring to the next: the dihedral angle between two adjacent rings in the chain is 73.32 (4) . Taken  Fragment of a [100] hydrogen-bonded chain in the crystal of (I).

Figure 6
Fragment of an [001] hydrogen-bonded chain in the crystal of (I).

Figure 7
Inversion dimer in the crystal of (II) linked by a pair of C-HÁ Á ÁO hydrogen bonds. [Symmetry code: (i) 2 À x, 1 À y, 1 À z.] All H atoms not involved in hydrogen bonds have been omitted for clarity. Table 1 Hydrogen-bond geometry (Å , ) for (I).
Cg1 is the centroid of the thiophene ring. The packing in (II) features four C-HÁ Á ÁO interactions (Fig. 7, Table 2); the C13 bond ( Fig. 2) generates R 2 2 (28) loops and the C7 bond leads to C(7) chains propagating in [010]. The two C8 (methyl-group) bonds lead to (101) sheets. Taken together, these interactions lead to a three-dimensional network of molecules in the crystal. There are no C-HÁ Á Á or stacking interactions in (II).
Cg6 is the centroid of the C15-C20 ring.  Groom et al., 2016) for the common central -CH N-N(CH 3 )-C( O)-CH 2 -fragment of the title compounds revealed just three matches, viz. FOTMUX (Ramirez et al., 2009a), KULREP (Ramirez et al., 2009b) and OFEBIL (Cao et al., 2007). FOTMUX is an interesting binuclear copper complex but none of these materials have a close relationship to the isomeric compounds reported here.

Synthesis and crystallization
The appropriate derivative (Cardoso et al., 2014) of (1) (0.2 g, 1.0 equivalent) was suspended in acetone (5.0 ml) and potassium carbonate (4.0 equivalents) was added. The reaction mixture was stirred at room temperature for 30 min and methyl iodide (4.0 equivalents) was added. The reaction mixture was maintained at 313 K, until thin-layer chromatography indicated that the reaction was complete. The reaction mixture was rotary evaporated to leave a residue, which was dissolved in water (20.0 ml) and extracted with ethyl acetate (3 Â 10.0 ml). The organic phases were combined, dried with anhydrous MgSO 4 , filtered and then evaporated at reduced pressure. The crystals used for intensity data collection were recrystallized from ethanol solution.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 4. The H atoms were placed geometrically (C-H = 0.95-1.00 Å ) and refined as riding atoms. The constraint U iso (H) = 1.2U eq (carrier) or 1.5U eq (methyl) was applied in all cases. The methyl group was allowed to rotate, but not to tip, to best fit the electron density (AFIX 137 instruction). In each case, this group rotated from its initial orientation to minimize steric interaction with atom H7; the final orientation leads to a short C8-HÁ Á ÁO1 intramolecular contact but we do not regard this as a bond. The thiophene rings in (I)

Computing details
For all compounds, data collection: CrystalClear (Rigaku, 2012); cell refinement: CrystalClear (Rigaku, 2012); data reduction: CrystalClear (Rigaku, 2012); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: publCIF (Westrip, 2010).  Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

(II) (E)-N-Methyl-N′-(3-nitrobenzylidene)-2-(thiophen-2-yl)acetohydrazide
Crystal data where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.30 e Å −3 Δρ min = −0.28 e Å −3 Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

(III) (E)-N-Methyl-N′-(4-nitrobenzylidene)-2-(thiophen-2-yl)acetohydrazide
Crystal data where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.67 e Å −3 Δρ min = −0.61 e Å −3 Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.