The synthesis and structural properties of a chloridobis{N-[(4-methoxyphenyl)imino]pyrrolidine-1-carboxamide}zinc(II) (acetonitrile)trichloridozincate coordination complex

The title compound was formed from the reaction of zinc(II) chloride and pyrrolidine-4-methoxyphenyl azoformamide ligands. The ligands associated in a bidentate manner and the recrystallized complex indicated that the central zinc(II) gave a chloride to a second zinc(II) chloride compound and associated with an acetonitrile solvent to give a acetonitriletrichloridozincate counter-ion.


Chemical context
Herein is presented pyrrolidinyl-4-methoxyphenylazoformamide, an arylazoformamide (AAF), acting as a ligand through its 1,3-heterodiene N N-C O motif to form a coordination complex with a zinc(II) metal atom.AAFs belong to the semicarbazone ligand family and there have been numerous reports and reviews of their use as ligands (Casas et al., 2000;Mir et al., 2024;Padhye ´& Kauffman, 1985).Semicarbazones and thiosemicarbazones have the capability to coordinate with late transition metals (e.g.Cu, Pd, Zn, and Ni) and these complexes have found applications due to their thermal stability, noteworthy biological properties, and high synthetic flexibility (Casas et al., 2000;Garg & Jain, 1988;Kasuga et al., 2003;Siji et al., 2010).Extending from the semicarbazones, numerous zinc(II) complexes have been reported to form with Schiff base ligands, exhibiting applications in catalysis and demonstrating antibacterial and anticancer properties (Kasuga et al., 2003;Pieczonka et al., 2014).AAFs, however, have been underexplored as ligands yet have been indicated as reagents for the Mitsunobu reaction (Hirose, et al., 2018).As ligands, AAFs differ from semicarbazones in the manner of the 1,3-heterodiene motif; where the semicarbazones form a five-membered coordination ring through a Schiff base of type R-C N-NH(R)-C O, the azoformamide uses the R-N N-C O to generate the fivemembered metal-chelate.For the coordination process described herein, two AAF ligands are coordinated by zinc(II) chloride, displacing a chloride that is then taken on by a separate acetonitrile-coordinated zinc(II) chloride, creating an acetonitrile zinc(II) trichloride anion and resulting in a 2:1 ratio of ligands to the metal atom in the formed cationic complex.The ligands remain neutral while the resultant zinc interaction is similar to the complexes formed with azothioformamide ligands when bound to copper(I) and silver(I) coordination complexes (Groner et al., 2019;Johnson et al., 2017;Pradhan et al., 2023).

Structural commentary
The X-ray crystal structure of the asymmetric unit of the title complex 1 and its packing structure are shown in Fig. 1.This complex crystallizes in the orthorhombic space group Pbca (61).In this structure, the Zn II ion coordinates two nitrogen atoms and two oxygen atoms of two pyrrolidine p-methoxy phenylazoformamide molecules along with one chlorine atom, providing a distorted trigonal-bipyramidal shape and rendering the complex positively charged.This positive charge is counterbalanced by the presence of [(CH 3 CN)ZnCl 3 ] as counter-ion.Notably, the bond length of Zn1 and the attached chlorine atom (Cl2) is 2.2202 (10) A ˚; Zn1 and the O1 atom of the azoformamide are measured at 2.002 (3) and 2.012 (3) in the two ligands whereas the Zn1-N1 bonds are 2.207 (3) and 2.211 (3) A ˚.

Supramolecular features, Hirshfeld surface analysis and 2D fingerprint plots
In the crystal, the positive complexes alternate with inverted [(CH 3 CN)ZnCl 3 ] counter-ions, as seen in Fig. 1b.
In order to visualize the intermolecular interactions, a Hirshfeld surface (HS) analysis was carried out using Crystal Explorer 17.5 (Spackman et al., 2021), which was also used to generate the associated two-dimensional fingerprint plots.Red and blue dots on the Hirshfeld surfaces (Fig. 2) indicate intermolecular contacts with distances shorter and longer than the van der Waals radii, respectively.

Synthesis and crystallization
The pyrrolidinyl-4-methoxyphenylazoformamide ligand was prepared in a two-step synthesis from commercially available Figure 1 (a) A view of the molecular structure of the title complex in its found asymmetric unit, with atom labeling.All displacement ellipsoids are drawn at the 50% probability level.(b) Crystal packing diagram of the title complex in ball-and-stick format.
4-methoxyphenylhydrazine•HCl and methyl chloroformate as shown in Fig. 4. The intermediate ester was isolated prior to forming the formamide similar to a recently reported synthesis of biologically active arylazothioformamides (Pradhan et al., 2023).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1.The hydrogen atoms were placed in calculated positions with C-H distances of 0.95 A ˚and refined as riding atoms with U iso (H) = 1.2U eq (C).Methyl H atoms were positioned geometrically and were allowed to ride on C atoms and rotate around the C-C bond, with C-H = 0.98 A ˚and U iso (H) = 1.5U eq (C).

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.

Figure 3
Figure 3 Two-dimensional fingerprint plots for the title compound showing (a) all interactions and delineated into (b) H� � �H (39.9%) and (c) H� � �Cl/ Cl� � �H (28.2%) contacts.The values d i (x-axis) and d e (y-axis) are the closest internal and external distances from given places on the Hirshfeld surface (in A ˚).

Figure 2 (
Figure 2 (a) Hirshfeld surface of the title compound mapped over d norm with Zn-Zn bond lengths in A ˚. (b) Arrangement of the compound in the crystal with interactions indicated.

Table 1
Experimental details.