Different packing motifs of isomeric (E)-N′-(halophenylmethylidene)-N-methyl-2-(thiophen-2-yl)acetohydrazides controlled by C—H⋯O interactions

The packing motifs in the isomeric title compounds feature inversion dimers or chains, mediated by C—H⋯O interactions, one of which is unusually short (H⋯O = 2.18 Å).


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

Figure 1
The molecular structure of (I), showing 50% probability displacement ellipsoids. Only the major orientation of the thiophene ring is shown.

Supramolecular features
The packing motifs in (I) and (II) feature inversion dimers linked by pairs of C-HÁ Á ÁO interactions ( Fig. 5; Tables 1 and   2), with the C-H grouping part of the thiophene ring: this generates an R 2 2 (14) loop. Weak C-HÁ Á Á interactions consolidate the structures, but there are no aromaticstacking interactions [minimum centroid-centroid separation = 4.86 Å for (I) and 4.85 Å for (II)].
The packing in (III) features two C-HÁ Á ÁO interactions (Table 3) arising from benzene and adjacent methine C-H groups, which link the molecules into [010] chains (Fig. 6), with adjacent molecules in the chain related by the 2 1 screw axis in the b direction. The C6 interaction is long, but deemed to be just significant, as it is consolidating the C7 bond. Individually, each C-HÁ Á ÁO bond generates a C(8) chain; collectively R 1 2 (6) loops arise. A very weak C-HÁ Á ÁCl bond is also observed. There are no C-HÁ Á Á contacts in (III) and we consider that the shortest ring-centroid separation of  Table 1 Hydrogen-bond geometry (Å , ) for (I).

Figure 4
The molecular structure of (IV), showing 50% probability displacement ellipsoids. Only the major orientation of the thiophene ring is shown.

Figure 5
An inversion dimer in the crystal of (I) linked by a pair of C-HÁ Á ÁO interactions. [Symmetry code: (i) Àx, Ày, 1 À z.] All H atoms except H13 have been omitted for clarity. 4.219 (5) Å is far too long to be regarded as a bonding interaction.
In the crystal of (IV), an unusually short C-HÁ Á ÁO interaction (Table 4) with HÁ Á ÁO = 2.18 Å leads to C(9) chains ( Fig. 7) propagating in the [301] direction. The acceptor O atom deviates from the plane of Cl1/C4/C5/H5 by 0.239 (6) Å . One reason for the short contact could be the presence of the adjacent electron-withdrawing Cl substituent, which will tend to 'activate' the H atom (Steiner, 1996). Two extremely weak C-HÁ Á ÁCl interactions and a C-HÁ Á Á contact occur, but there is nostacking (minimum centroid-centroid separation = 4.42 Å ) in the crystal of (IV).
Hirshfeld surface fingerprint plots for (I)-(IV) (supplementary Figs. 1-4) were calculated with CrystalExplorer17 (Turner et al., 2017) and percentage contact-surface contributions (McKinnon et al., 2007) are listed in Table 5. As might be expected, the percentage contact data for the isomeric (I) and (II) are very similar but it is interesting that the data for (III) and (IV) barely differ from those of the first two compounds, despite their different crystal structures: in every case HÁ Á ÁH contacts dominate the packing. This is quite different to the recently reported (E)-N 0 -(3-cyanorophenylmethylidene)-N-methyl-2-(thiophen-2-yl)acetohydrazide (V) and (E)-N 0 -(4-methoxyphenylmethylidene)-N-methyl-2-(thiophen-2-yl)acetohydrazide (VI) (Cardoso et al., 2017), where the percentage contributions of the different intermolecular contacts to the fingerprint plots differ by up to 20%.

Database survey
A survey of the Cambridge Structural Database (Groom et al., 2016) updated to June 2017 for the common central -CH N-N(CH 3 )-C( O)-CH 2 -fragment of the title compounds revealed seven matches, viz. ALAHEC (Cardoso et al., 2016b); FOTMUX (Ramírez et al., 2009a); KULREP (Ramírez et al., 2009b); OFEBIL (Cao et al., 2007), and EYUBAD, EYUBEH and EYUBIL; this latter trio of refcodes correspond to the three isomeric nitro compounds (Cardoso et al., 2016a) noted in the Chemical Context section above. To this list will soon be added the structures of (V) and (VI) noted above.

Synthesis and crystallization
The appropriate thienyl acetohydrazide derivative (Cardoso et al., 2014) (0.20 g, 1.0 equiv.) was suspended in acetone (5 ml) and potassium carbonate (4.0 equiv.) was added. The reaction mixture was stirred at room temperature for 30 min. and methyl iodide (4.0 equiv.) was added. The reaction mixture was maintained at 313 K, until thin-layer chromatography indicated the reaction was complete. The mixture was then rotary evaporated to leave a residue, which was dissolved in water (20 ml) and extracted with ethyl acetate (3 Â 10 ml). The organic fractions were combined, dried with anhydrous MgSO 4 , filtered and the solvent evaporated at reduced pressure. The crystals used for the intensity data collections were recrystallized from methanol solution.  [Symmetry codes: (i) 3 2 À x, y À 1 2 , 1 2 À z; (ii) x, y À 1, z.] All H atoms except H6 and H7 have been omitted for clarity.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 6. 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 N-methyl group was allowed to rotate, but not to tip, to best fit the electron density (AFIX 137 instruction in SHELXL; Sheldrick, 2015); in every case, this group rotated from its intial calculated orientation to minimize steric interaction with H7; the final optimized geometry leads to a short (HÁ Á ÁO $ 2.35 Å ) intramolecular C8-HÁ Á ÁO1 contact but we do not regard this as a bond.   (7), 20.3575 (14), 7.2721 (5) 9.4479 (7), 20.2175 (14), 7.2552 (5) 4.2194 (2), 13.0131 (9), 25.0758 (18) 6.7454 (5)  C11 bond for all compounds. The crystal of (III) used for data collection was small and data quality was poor. Iin the refinement, difference maps indicated significant unmodelled electron density in the vicinity of C4. This was modelled in terms of a minor impurity/disorder component with the Cl atom bonded to C4 rather than C3. Even after the disorder modelling, the residuals are high, but we deem the refinement to be acceptable in terms of its chemical information content. For all structures, 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 (Farrugia, 1997); software used to prepare material for publication: publCIF (Westrip, 2010).   (9) 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.

Hydrogen-bond geometry (Å, º)
Cg1 is the centroid of the thiophene ring, Cg2 is the centroid of the benzene ring.

(III)
Crystal data 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. ( where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.53 e Å −3 Δρ min = −0.40 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ.  (4)