N′-[(1E)-(5-Nitrofuran-2-yl)methylidene]thiophene-2-carbohydrazide: crystal structure and Hirshfeld surface analysis

The title molecule is curved as seen in the dihedral angle [27.4 (2)°] between the outer rings. Supramolecular chains about a 41 screw axis are formed by amide-N—H⋯O(carbonyl) hydrogen bonding.

In the title carbohydrazide, C 10 H 7 N 3 O 4 S, the dihedral angle between the terminal five-membered rings is 27.4 (2) , with these lying to the same side of the plane through the central CN 2 C( O) atoms (r.m.s. deviation = 0.0403 Å ), leading to a curved molecule. The conformation about the C N imine bond [1.281 (5) Å ] is E, and the carbonyl O and amide H atoms are anti. In the crystal, N-HÁ Á ÁO hydrogen bonds lead to supramolecular chains, generated by a 4 1 screw-axis along the c direction. A three-dimensional architecture is consolidated by thienyl-C-HÁ Á ÁO(nitro) and furanyl-C-HÁ Á ÁO(nitro) interactions, as well asinteractions between the thienyl and furanyl rings [intercentroid distance = 3.515 (2) Å ]. These, and other, weak intermolecular interactions, e.g. nitro-N-OÁ Á Á(thienyl), have been investigated by Hirshfeld surface analysis, which confirms the dominance of the conventional N-HÁ Á ÁO hydrogen bonding to the overall molecular packing.

Structural commentary
In (I), Fig. 1, the conformation about the C6 N2 bond [1.281 (5) Å ] is E. A 5-nitrofuran-2-yl ring is connected at the C6 atom. The furanyl ring is almost planar [r.m.s deviation = 0.006 Å ] and the nitro group is almost co-planar with its attached ring as seen in the O3-N3-C10-O2 torsion angle of À1.7 (5) . The thienyl ring is also planar within experimental error [r.m.s. deviation = 0.005 Å ] and orientated so that the sulfur atom is syn to the carbonyl-O1 atom. Overall, the molecule is curved with the rings lying to the same side of the plane through the bridging CN 2 C( O) atoms, r.m.s. deviation = 0.0403 Å , with twists noted in both the S1-C1-C5-O1 and N2-C6-C7-O2 torsion angles of À9.8 (5) and 5.4 (6) , respectively; the dihedral angle between the fivemembered rings is 27.4 (2) .

Supramolecular features
The anti relationship between the carbonyl-O and amide-H atoms enables the formation of directional N-HÁ Á ÁO hydrogen bonds leading to supramolecular chains, generated by a 4 1 screw-axis propagating along the c-axis direction, Fig. 2a and Table 1. The chains are connected into a threedimensional architecture by thienyl-C-HÁ Á ÁO(nitro) and furanyl-C-HÁ Á ÁO(nitro) interactions, involving the same nitro-O4 atom, Table 1. In addition,interactions are formed between the two five-membered rings with the intercentroid distance being 3.515 (2) Å , and the angle of inclination is 3.9 (2) for symmetry operation: (i) 1 À y, 1 2 À x, À 1 4 + z. A view of the unit-cell contents is shown in Fig. 2b.

Hirshfeld surface analysis
Crystal Explorer 3.1 (Wolff et al., 2012) was used to generate Hirshfeld surfaces mapped over d norm , d e , shape-index, curvedness and electrostatic potential. The latter were calculated using TONTO (Spackman et al., 2008;Jayatilaka et al., 2005) integrated into Crystal Explorer, wherein the experimental structure was used as the input geometry. In addition, the electrostatic potentials were mapped on Hirshfeld surfaces using the STO-3G basis set at Hartree-Fock level of theory over a range AE0. The molecular structure of (I), showing displacement ellipsoids at the 70% probability level.   Symmetry codes: (i) Ày þ 1 2 ; x; z À 1 4 ; (ii) x þ 1 2 ; y À 1 2 ; z À 1 the Hirshfeld surface to the nearest atom inside and outside, respectively, enable the analysis of intermolecular interactions through the mapping of d norm . The combination of d e and d i in the form of a two-dimensional fingerprint plot (McKinnon et al., 2004) provides a useful summary of intermolecular contacts in the crystal. Two views of Hirshfeld surfaces calculated for (I), mapped over d norm in the À0.1 to 1.2 Å range are shown in Fig. 3. The bright-red spots near the amino-N-H and carbonyl-O atoms, labelled as '1' in Fig. 3, indicate their roles as respective donor and acceptor sites in the dominant N-HÁ Á ÁO hydrogen bonding in the crystal. These also appear as blue and red regions, respectively, corresponding to positive and negative electrostatic potentials, respectively, on the Hirshfeld surface mapped over electrostatic potential in Fig. 4. The light-red spots labelled as '2' and '3' in Fig. 3, and light-blue and lightred regions in Fig. 4, represent the intermolecular thienyl-C-HÁ Á ÁO(nitro) and furanyl-C-HÁ Á ÁO(nitro) interactions involving the nitro-O4 atom as described above in Supramolecular features. The immediate environment about the molecule within d norm mapped Hirshfeld surface mediated by the above interactions is illustrated in Fig. 5.

Figure 4
A view of the Hirshfeld surface mapped over electrostatic potential for (I). The red and blue regions represent negative and positive electrostatic potentials, respectively.

Figure 5
A view of Hirshfeld surface mapped over d norm for showing intermolecular interactions about a reference molecule of (I).

Table 2
Summary of short interatomic contacts (Å ) in the crystal of the title compound.
The overall two-dimensional fingerprint plot is shown in Fig. 6a and those delineated into OÁ Á ÁH/HÁ Á ÁO, HÁ Á ÁH, NÁ Á ÁH/HÁ Á ÁN, CÁ Á ÁH/HÁ Á ÁC, CÁ Á ÁC, CÁ Á ÁO/OÁ Á ÁC and SÁ Á ÁH/ HÁ Á ÁS contacts (McKinnon et al., 2007) are illustrated in Fig. 6b-h, respectively; their relative contributions to the overall Hirshfeld surface are summarized in Table 3. In the fingerprint plot delineated into OÁ Á ÁH/HÁ Á ÁO contacts, which make the greatest contribution to the Hirshfeld surface, i.e. 36.4%, arises from the N-HÁ Á ÁO hydrogen bond and is viewed as a pair of spikes with tips at d e + d i $2.1 Å in Fig. 6b. The C-HÁ Á ÁO interactions, which are masked by the above interactions, appear as the groups of green points appearing in pairs in the plot. However, a forceps-like distribution of points in the fingerprint plot delineated into CÁ Á ÁO/OÁ Á ÁC contacts, In the fingerprint plot corresponding to HÁ Á ÁH contacts, which make the next most significant contribution to the surface, Fig. 6c, the points are scattered in the plot at (d e , d i ) distances greater than their van der Waals separations with the comparatively low contribution, i.e. 13.6%, due to the relatively low hydrogen-atom content in the molecule. The absence of characteristic wings in the fingerprint plot delineated into CÁ Á ÁH/HÁ Á ÁC and the low contri-

Figure 7
Two views of Hirshfeld surface mapped with shape-index property for (I).
The pairs of red and blue regions identified with arrows indicatestacking interactions.  bution to the Hirshfeld surface, Fig. 6e and Table 3, clearly indicate the absence of C-HÁ Á Á interactions in the crystal. However, a pair of thin edges with their ends at d e + d i $2.9 Å belong to short interatomic CÁ Á ÁH contacts,  Fig. 6f. The presence ofstacking interactions between the symmetryrelated thienyl and furanyl rings is also indicated by the appearance of red and blue triangle pairs on the Hirshfeld surface mapped with the shape-index property identified with arrows in the images of Fig. 7, and in the flat region on the Hirshfeld surface mapped over curvedness in Fig. 8. Finally, although the SÁ Á ÁH/HÁ Á ÁS contacts in the structure of (I) make a 8.9% contribution to the surface, and also show a nearly symmetrical distribution of points in the corresponding fingerprint plot, Fig. 6h, they do not have a significant influence on the molecular packing as they are separated at distances greater than the sum of their van der Waals radii. The final analysis based on the Hirshfeld surfaces is an evaluation of enrichment ratios (ER) (Jelsch et al., 2014); a list of the ER values is given in Table 4. The low content of hydrogen in the molecular structure of (I) yields a very low ER, 0.72, indicating no propensity to form intermolecular HÁ Á ÁH contacts. The ER value of 1.55 from OÁ Á ÁH/HÁ Á ÁO contacts is in the expected 1.2-1.6 range and confirm their involvement in the N-HÁ Á ÁO and C-HÁ Á ÁO interactions. The presence of intermolecular C-HÁ Á ÁO interactions is also confirmed through the ER value near to unity i.e. 0.99, corresponding to the CÁ Á ÁO/OÁ Á ÁC contacts. The high propensity to formstacking interactions between the thienyl and furanyl rings is reflected from the high enrichment ratio 2.66 for CÁ Á ÁC contacts. The ER value of 1.26 resulting from 6.75% of the surface occupied by nitrogen atoms and a 7.5% contribution to the Hirshfeld surface from NÁ Á ÁH/HÁ Á ÁN contacts is due to the presence of short NÁ Á ÁH contacts in the structure, Table 2. The ER values < 1 related to other contacts and low % contribution to the surface indicate their low significance in the crystal. The relative dispositions of the heteroatoms in the two structures are the same but, the twist in (II) is significantly less as seen in the dihedral angle of 10.2 (6) between the fivemembered rings. This is highlighted in the overlay diagram in Fig. 9. The molecular structure of the all thienyl analogue of (I) has been described recently (Cardoso et al., 2016b). There are two almost identical, near planar molecules in the asymmetric unit and each adopts the conformation indicated in Scheme 2, which might be described as having the thienyl-S atoms syn. The intramolecular SÁ Á ÁS separations of 3.770 (4) and 3.879 (4) Å , are beyond the sum of their van der Waals radii. The conformational differences found for the thienyl molecules is consistent with our NMR studies that indicate multiple conformations exist in solution for these compounds.

Figure 9
Overlay diagram of molecules of (I) (red image) and (II) (blue). The molecules have been overlapped so that the five-membered rings are coincident.

Figure 8
A view of Hirshfeld surface mapped over curvedness for (I). The flat regions highlight the involvement of rings instacking interactions.

Synthesis and crystallization
The title compound was prepared following a procedure outlined in Fig. 10. Yellow rods of (I) were grown by slow evaporation of a methanol solution held at room temperature.

Refinement details
Crystal data, data collection and structure refinement details are summarized in Table 5. The C-bound H atoms were geometrically placed (C-H = 0.95 Å ) and refined as riding with U iso (H) = 1.2U eq (C). The N-bound H atom was located from a difference map and refined with (N-H = 0.88AE0.01 Å ), and with U iso (H) = 1.2U eq (C). The slightly elongated displacement ellipsoid for the C2 atom in the thienyl ring is likely due to unresolved disorder in the ring where the second, co-planar orientation related by 180 to that modelled is present. However, this was not modelled as the maximum residual electron density peak was only 0.46 e Å À3 , 0.61 Å from the C2 atom. It is also noted that the relevant S-C and C-C bond lengths show the expected values. Preparation of the title compound. Reagents: i = SO 2 Cl 2 , MeOH; ii = N 2 H 2 ÁH 2 O, EtOH; iii = 5-nitrofurancarbaldehyde, EtOH.  program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012), QMol (Gans & Shalloway, 2001) and DIAMOND (Brandenburg, 2006); software used to prepare material for publication: publCIF (Westrip, 2010).

N′-[(1E)-(5-Nitrofuran-2-yl)methylidene]thiophene-2-carbohydrazide
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.