Crystal structure and Hirshfeld surface analysis of a zinc xanthate complex containing the 2,2′-bipyridine ligand

The ZnII ion lies on a crystallographic twofold axis and has distorted tetrahedral coordination geometry. Two weak C—H⋯S intramolecular hydrogen bonds exist between the bipyridyl and thiol groups. In the crystal, molecules are linked by weak C—H⋯O and C—H⋯S hydrogen bonds, forming a three-dimensional supramolecular architecture.


Chemical context
Xanthates (dithiocarbonates, ROCS 2 À ) have attracted the attention of scientific groups of researchers due to their diverse applications. Metal xanthates have been used as singlesource precursors to metal sulfide materials (Kociok-Kö hn et al., 2015). It was reported that metal xanthates have cytotoxic activity on human cancer cells (Efrima et al., 2003;Friebolin et al., 2005). Cellulose xanthate have been used for the column separation of alcohols by chromatographic methods (Friebolin et al., 2004). Zinc(II) xanthate complexes have a tetrahedral geometry, while zinc(II) xanthate complexes with neutral bidentate nitrogen donor ligands are either strongly distorted octahedral or tetrahedral. In our previous work, Zn II 2-methoxyethylxanthate with N,N,N 0 ,N 0 -tetramethylethylenediamine was synthesized, structurally characterized and studied by density functional theory (Qadir et al., 2019). The complex showed a tetrahedral environment around metal center and the HOMO-LUMO band gap was 3.9 eV. Aromatic heterocyclic nitrogen donor ligands have been used by researchers to prepare mixed-ligand complexes of transition metals with supramoleculer architectures. In this work, the synthesis and crystal structure of a zinc(II) 2-methoxyethyl xanthate involving 2,2 0 -bipyridine is reported. Hirshfeld surface analysis was used to further investigate the intermolecular interactions.

Structural commentary
The title complex ( Fig. 1) comprises one Zn II ion, one 2,2 0bipyridine ligand and two 2-methoxyethyl xanthate ligands. The Zn II ion is coordinated to two N atoms of the 2,2 0 -bipyridine ligand and two S atoms from two 2-methoxyethyl xanthate ligands in a distorted tetrahedral environment and lies on a crystallographic twofold rotation axis. The Zn-N and Zn-S bond lengths are 2.083 (5) and 2.295 (2) Å , respectively, whereas the bond angles around the central Zn II ion are in the range 78.7 (3)-126.64 (10) ( Table 1). The bond lengths and angles of the ZnN 2 S 2 coordination units correspond to those in the structures of mixed-ligand Zn II coordination compounds (see; Database Survey). The C-O bond lengths range from 1.346 (8) to 1.453 (8) Å although all of the C-O bonds show single-bond character. In the {S 2 C} part of the xanthate ligands, the C1-S1 distance is 1.727 (7) Å , which is typical of a single bond whereas the C1-S2 distance of 1.652 (7) Å is typical of a carbon-to-sulfur double bond. The C-N and C-C bond lengths in 2,2 0 -bipyridine are normal for 2-substituted pyridine derivatives (Strotmeyer et al., 2003;Iskenderov et al., 2009;Golenya et al., 2012).

Supramolecular features
The crystal packing of the title compound ( Fig. 2) features intermolecular C8-H8Á Á ÁO5 ii hydrogen bonds (Table 2), which connect the molecules into supramolecular chains propagating along the a-axis direction. Weak intramolecular C-HÁ Á ÁS hydrogen bonds are also observed.

Hirshfeld surface analysis
The Hirshfeld surface analysis and the associated twodimensional fingerprint plots were performed with Crystal-Explorer17.5 (Turner et al., 2017). The Hirshfeld surface of the title complex is shown in Fig. 3a and 3b. The intermolecular interactions are represented using different colours, red indicating distances closer than the sum of the van der Waals radii, white indicating distances near the van der Waals radii separation, and blue indicating distances longer than the van der Waals radii (McKinnon et al., 2007). The weak C-HÁ Á ÁO and C-HÁ Á ÁS hydrogen bonding in the crystal of the title complex are represented as red spots on d norm . Selected twodimensional fingerprint plots are shown in Fig. 4 for all contacts as well as those delineated into HÁ Á ÁH, SÁ Á ÁH/HÁ Á ÁS and CÁ Á ÁH/HÁ Á ÁC contacts, whose percentage contribution is also given. HÁ Á ÁH intermolecular contacts make the highest percentage contribution (36.3%), a result of the prevalence of hydrogen from the organic ligands. The SÁ Á ÁH/HÁ Á ÁS and OÁ Á ÁH/HÁ Á ÁO intermolecular contacts are due to the attractive C-HÁ Á ÁS and C-HÁ Á ÁO hydrogen-bonding interactions and make percentage contributions of 24.7 and 14.4%, respectively, indicating these to be the dominant stabilizing interactions in this crystal. In addition, CÁ Á ÁH/HÁ Á ÁC contacts contribute 15.1% to the Hirshfeld surface. The small percentage contributions from the other different interatomic contacts to the Hirshfeld surfaces are as follows: NÁ Á ÁH/HÁ Á ÁN  Table 1 Selected geometric parameters (Å , ).

Figure 1
The molecular structure of the title complex, with the atom labelling. Displacement ellipsoids are drawn at the 50% probability level. Symmetry code: (i) 1 À x, y, 1 2 À z.
The structure with refcode IGUGUO has a distorted trigonalbipyramidal coordination environment.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. The C-bound H atoms were positioned geometrically and refined using a riding model, with C-H = 0.95, 0.98 and 0.99 Å with U iso (H) = 1.5U eq (C) for methyl H atoms and 1.2U eq (C) otherwise. The crystal was a weak diffractor (I/ at 0.81 resolution was 5.1) and refined as a two-component twin with HKLF 4 data (twin law À1 0 0 0 À 1 0 0 0 À 1) but this had little effect. The anisotropy of N1 was restrained with ISOR 0.01 0.02 in SHELXL (Sheldrick, 2015).

(2,2′-Bipyridine-κ 2 N,N′)bis(2-methoxyethyl xanthato-κS)zinc(II)
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. Refinement. Refined as a 2-component inversion twin.