Bis{N′-[3-(4-nitrophenyl)-1-phenylprop-2-en-1-ylidene]-N-phenylcarbamimidothioato}zinc(II): crystal structure, Hirshfeld surface analysis and computational study

The N2S2 donor set about the zinc atom in the title complex has a geometry approaching tetrahedral. A linear supramolecular chain featuring amine-N—H⋯O(nitro) hydrogen bonding is noted in the crystal.


Chemical context
Thiosemicarbazones constitute part of the versatile nitrogenand sulfur-donor ligands important in coordination chemistry because of their variable donor properties, structural diversity and pharmacological applications. These ligands usually act as monodentate or bidentate ligands and coordinate with transition and non-transition metal ions either in neutral or anionic form through thione/thiolate-sulfur and azomethine/ imine-nitrogen donor atoms (Lobana et al., 2009;Prajapati & Patel, 2019;Ş en Yü ksel, 2021). The pharmacological activities of metal complexes are usually enhanced compared to their parent free thiosemicarbazone ligands (Mathews & Kurup, 2021). The enhanced activities may be attributed to the redox potential and increased lipophilicity of the metal complexes (Rapheal et al., 2021). Transition-metal complexes derived from thiosemicarbazones exhibit widespread pharmacological activities inclusive of anti-tubercular (Khan et al., 2020), antimicrobial (Nibila et al., 2021), anti-bacterial (Prajapati & Patel, 2019), anti-malarial (Savir et al., 2020), anti-diabetic (Kumar et al., 2020), anti-viral (Rogolino et al., 2015) and anti- ISSN 2056-9890 cancer (Anjum et al., 2019;Balakrishnan et al., 2019). In this work, 4-phenyl-3-thiosemicarbazide was condensed with 4-nitrochalcone to form the thiosemicarbazone, which was then complexed with zinc(II) in a molar ratio of 2:1 to form the title compound, hereafter (I). In a continuation of on-going studies of metal complexes derived from thiosemicarbazones and their parent ligands (Tan, Ho et al., 2020;Tan, Kwong et al. 2020a,b), herein the synthesis, structure determination, Hirshfeld surface analysis and computational chemistry of (I) are described.

Structural commentary
The molecular structure of (I), Fig. 1, comprises a zinc atom S,N-coordinated by two thiosemicarbazone anions within an N 2 S 2 -donor set. From the data in Table 1, the key geometric parameters for both ligands bear a close similarity. However, the Zn-S1 and Zn-N1 bond lengths are shorter and longer, respectively, compared with the Zn-S2 and Zn-N5 bonds, each by ca 0.07 Å . The angles about the zinc atom range from an acute 86.77 (4) for the S1-Zn-N1 chelate angle, to a wide 131.16 (2) , for S1-Zn-S2, consistent with an approximate tetrahedral geometry. The mode of coordination of the thiosemicarbazone ligands leads to the formation of fivemembered chelate rings. These are nearly planar with r.m.s. deviations of 0.0459 and 0.0152 Å for the S1-and S2containing rings, respectively. However, the maximum deviation from the plane through the S1-chelate ring of À0.0613 (9) Å for the N1 atom suggests an alternate description of the conformation of the S1-ring might be valid. Another description might be an envelope conformation with the zinc atom lying 0.209 (3) Å out of the plane of the four remaining atoms (r.m.s. deviation = 0.0005 Å ). The dihedral angle between the mean plane through the rings is 73.28 (3) . There are three formal double bonds in each thiosemicarbazone anion. Owing to chelation, the configuration about the endocyclic imine bond is Z whereas that about the exocylic imine bond is E; the configuration of the ethylene bond is E.
Some major differences are noted in the conformations of the ligands. Thus, the sequence of dihedral angles formed 840 Tan et al. [Zn(C 22

Figure 1
The molecular structure of (I) showing the atom-labelling scheme and displacement ellipsoids at the 70% probability level.

Analysis of the Hirshfeld surfaces
In order to acquire further information on the supramolecular association between molecules in the crystal of (I), the   Symmetry codes: (i) x; y À 1; z; (ii) Àx þ 3 2 ; y À 1 2 ; Àz þ 1 2 ; (iii) Àx þ 1; Ày þ 1; Àz þ 1. The bright-red spots on the Hirshfeld surface mapped over d norm in Fig. 4, i.e. near the amine-H7N, phenyl-H44 and nitro-O4 atoms correspond to the interactions leading to the linear chain; geometric data for the identified contacts in the Hirshfeld surface analysis are given in Table 3. Links between chains include phenyl-C37-HÁ Á ÁO3 (Fig. 4) View of the Hirshfeld surface mapped over d norm for (I), highlighting inter-chain C-HÁ Á ÁO and C-HÁ Á ÁC interactions.

Figure 4
Two views of the Hirshfeld surface mapped over d norm for (I) in the range À0.239 to +1.045 arbitrary units, highlighting N-HÁ Á ÁO and C-HÁ Á ÁO contact within red circles.

Figure 6
Two views of the Hirshfeld surface mapped over d norm for (I), highlighting weak interactions within red circles (see text).

Table 3
A summary of short interatomic contacts (Å ) for (I) a .

Contact
Percentage contribution

Contact
Percentage contribution

Figure 7
View of the Hirshfeld surface mapped over d norm for (I), highlighting CÁ Á ÁS short contacts.
The HÁ Á ÁS/SÁ Á ÁH contacts contribute 8.6% and appear as two blunt-symmetric wings at d e + d i $2.9 Å in Fig. 9(e). This feature reflects the long-range HÁ Á ÁS/SÁ Á ÁH contact evinced in the packing with a separation of 0.1 Å shorter than the sum of their van der Waals radii, Table 3. Although HÁ Á ÁN/NÁ Á ÁH contacts appear at d e + d i $2.6 Å in the fingerprint plot of Fig. 9(f), the contribution to the overall Hirshfeld surface is only 5.2%. The other 11 interatomic contacts have a negligible effect on the molecular packing as their accumulated contribution is below 11%, Table 4.

Figure 10
Perspective views of the energy frameworks calculated for (I) showing (a) electrostatic potential force, (b) dispersion force and (c) total energy, each plotted down the b axis. The radii of the cylinders are proportional to the relative magnitudes of the corresponding energies and were adjusted to the same scale factor of 50 with a cut-off value of 5 kJ mol À1 within 1 Â 1 Â 1 unit-cells.

Database survey
The  Table 6. From the data collated, there is an obvious homogeneity in the data to the point of common disparities in the Zn-S and Zn-N bond lengths formed by the two ligands in each complex. The range of tetrahedral angles are similar as are the dihedral angles formed between the chelate rings. A measurement of the distortion of a four-coordinate donor set from a regular geometry is quantified by the value of 4 (Yang et al., 2007). The value of 4 is 1.00 for an ideal tetrahedron and 0.00 for perfect square-planar geometry. The range of values for 4 listed in Table 6 vindicate the assignment of similar coordination geometries for (I)-(V), being distorted from a regular tetrahedron.

Synthesis and crystallization
Analytical grade reagents were used as procured and without further purification. 4-Phenyl-3-thiosemicarbazide (1.6723 g, 10 mmol) and 4-nitrochalcone (2.5325 g, 10 mmol) were dissolved separately in hot absolute ethanol (50 ml) and mixed while stirring. About five drops of concentrated hydrochloric acid were added to the mixture and the mixture was heated (348 K) while stirring for about 30 min. The yellow precipitate, (2E)-2-[3-(4-nitrophenyl)-1-phenylallylidene]-N-phenylhydrazine-1-carbothioamide, (VI), was filtered, washed with cold ethanol and dried in vacuo after which it was used without further purification. Compound (VI) (0.4047 g, 1 mmol) was dissolved in hot absolute ethanol (50 ml), which was added to a solution of Zn(CH 3 COO) 2 Á2H 2 O (0.1098 g, 0.5 mmol) in hot absolute ethanol (40 ml). The mixture was heated (348 K) and stirred for about 10 min, followed by stirring for about 1 h at room temperature. The white preci-pitate obtained was filtered, washed with cold ethanol and dried in vacuo. Single crystals were grown at room temperature by slow evaporation of (I) in a mixed solvent system containing methanol and acetonitrile (

Refinement
Crystal data, data collection and structure refinement details are summarized in

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.