Synthesis, crystal structure and Hirshfeld surface analysis of bromidotetrakis[5-(prop-2-en-1-ylsulfanyl)-1,3,4-thiadiazol-2-amine-κN 3]copper(II) bromide

The molecular and crystal structure of the bromidotetrakis[5-(prop-2-en-1-ylsulfanyl)-1,3,4-thiadiazol-2-amine-κN 3]copper(II) bromide complex was studied and Hirshfeld surfaces and fingerprint plots were generated to investigate the various intermolecular interactions.

The strong complexing capability of thiadiazole derivatives is associated with the existence of numerous sulfur and nitrogen atoms and the distinctiveness of its structure, specifically, the presence of unshared electron pairs and donor characteristics.They generate complexes with elements whose ions possess partially vacant d-orbitals or occupied d-orbitals and a low positive charge, exhibiting various polyhedral structures.In this context, investigating the complex-forming properties of thiadiazole derivatives is pertinent in delineating the characteristics of the molecular and electronic structure of the original ligands and the stereochemistry of the coordination polyhedron (Hassan et al., 2018).This study focuses on the synthesis, examination of the structure, and characteristics of the [Cu(L)4Br]Br complex, where L is 2-amino-5-allylthio-1,3,4-thiadiazole (AAT), employing single-crystal X-ray diffraction (SC-XRD).

Structural commentary
The crystals of [Cu(AAT) 4 Br]Br possess an ionic-molecular structure.The complex crystallizes in the fourfold tetragonal system, space group P4/n, and the asymmetric unit comprises one molecule of 2-amino-5-allylthio-1,3,4-thiadiazole (AAT), one Cu 2+ ion with a multiplicity of 0.25, and Br À ions in two positions with multiplicities of 0.25 each.The Br À ions occupy special positions on fourfold axes, and this symmetry transformation generates the formula unit.In [Cu(AAT) 4 Br]Br, the copper atom exhibits a square-pyramidal geometry and its coordination sphere includes four nitrogen atoms (N2) from the heterocyclic ligands and a bromine anion at the top of the pyramid.These nitrogen atoms lie in one plane.The planar AAT molecules are nearly perpendicular to this plane, exhibiting a slight twist of the Br1CuN2 planes.All the amino groups are in a syn arrangement.One of the Br À ions is integrated into the inner coordination sphere, while the second Br-ion resides in the outer sphere (Fig. 1).As a result, the inner coordination sphere of the complex takes the shape of a tetragonal pyramid, where the basal positions are filled by nitrogen atoms from the 2-amino-5-allylthio-1,3,4-thiadiazole ligands, and the apical position is occupied by the Br À ion.
The Cu-Br bond length in the compound measures 2.7474 (7) A ˚, closely resembling the Cu-Br distance in the [CuL 4 Br 2 ](H 2 O) 2 molecule, which is 2.9383 A ˚ (Berezin et al., 2018).Apparently, the binding of the Br À ion into the inner coordination sphere induces a distortion of the CuN 4 plane.The effect of this distortion is to the reduce N-Cu-N coordination angles [88.446 (18) and 161.04 (11) � ], in contrast to the angles of 90 and 180 � expected in an ideal square-planar structure.The sum of bond angles at the Cu atom is 353.8 � .The Cu atom deviates from the (N2) 4 plane toward Br À by 0.333 A ˚.The length of the Cu-N coordination bonds is 2.0206 (17) A ˚, similar to those bonds in analogous complexes.For instance, in nitrato-tetrakis(2-amino-5-ethyl-1,3,4-thiadiazole)copper(II) nitrate, the average Cu-N bond length is 2.003 A ˚ (Kadirova et al., 2008), aligning with the sum of the covalent radii of Cu and N.

Supramolecular features
In the crystal structure of [Cu(AAT) 4 Br]Br, in addition to the aforementioned intramolecular hydrogen bonds, there exist intermolecular hydrogen bonds.The second bromide ion, positioned in the outer sphere, forms a hydrogen bond with the second (not participating in the intramolecular hydrogen bond) hydrogen atom of the amino group N3H2 (Table 1).The outer-sphere Br2 ion also resides on the fourfold axis, resulting in the generation of a layer in the crystal perpendicular to the fourfold axis due to this symmetry transformation.As a result, in the crystal packing, the cationic coordination complexes form columns along the [001] crystallographic axis (Fig. 2).
The bromine anions of the outer sphere of the complex are located between the columns due to the formation of the N3-H3B� � �Br2 intermolecular hydrogen bonds with the amino groups of the ligand (Table 1).
The interaction energies of the secondary interactions system within the structure were calculated using the HF method (HF/3-21G) in CrystalExplorer17 (Spackman et al., 2021).Although these calculations may not yield precise values for an ionic interaction, they effectively highlight the direction of strong interactions.The result shows the total energy (E tot ), which is the sum of the Coulombic (E ele ), polar (E pol ), dispersion (E dis ) and repulsive (E rep ) contributions.The four energy components were scaled in the total energy (E tot = 1.019E ele + 0651E pol + 0901E dis + 0.811E rep ).The interaction energies were investigated for a 3.8 A ˚cluster around the reference molecule.The calculation reveals two stronger interactions within the neighbouring molecules.The strongest interaction total energy (E tot ) is À 112.5 kJ mol À 1 (�-27 kcal mol À 1 ), with the polar (À 30.1 kJ mol À 1 ), disper-sion (À 123.3 kJ mol À 1 ), Coulombic (À 58.5 kJ mol À 1 ) and repulsive (96.0 kJ mol À 1 ) energies (with green colour) (Fig. 3).

Hirshfeld surface analysis
To further investigate the intermolecular interactions present in the title compound, a Hirshfeld surface analysis was performed, and the two-dimensional (2D) fingerprint plots were generated with CrystalExplorer17 (Spackman et al., 2021).Fig. 4 shows the three-dimensional (3D) Hirshfeld surfaces of the complex with d norm (normalized contact

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

Figure 2
Figure 2 Packing of [Cu(AAT) 4 Br]Br complex molecules in the crystal structure in projections along the (a) b and (b) c crystallographic axis.Hydrogen bonds are indicated by blue dashed lines.

Figure 3
Figure 3Interaction energy calculations within the structure were performed using the HF method (HF/3-21 G) (CrystalExplorer17;Spackman et al., 2021.The thickness of the tube represents the value of the energy.The distribution of the interactions according to type shows strong interactions along the crystallographic a-axis direction (the largest values are represented here).The total energy framework (in blue) and its two main components, dispersion (in green) and Coulombic energy (in red), are shown for a cluster around a reference molecule also exhibit stronger interactions along the crystallographic a-axis direction.

Figure 4
Figure 4 Views of the three-dimensional Hirshfeld surface of the complex [Cu(AAT) 4 Br] + cation plotted over d norm in views along the (a) [110] and (b) [001] directions.

Table 2
Experimental details.