Tris(ethane-1,2-diamine-κ2 N,N′)zinc(II) tetrachloridozincate(II)

The crystal structure of the title compound is consolidated by N—H⋯Cl and C—H⋯Cl hydrogen bonding interactions.


Structure description
Ethylenediamine (en) is a common chelating ligand that is widely used in transition-metal complexes. It cannot only chelate metal cations by two nitrogen atoms, but also offers hydrogen atoms to form N-HÁ Á ÁX hydrogen bonds. Metal complexes containing an ethylenediamine (-NCH 2 CH 2 N) backbone have attracted significant interest as potential anticancer agents because of their rich redox chemistry and relative ease of manipulation (Mihajlović et al., 2012;Beaumont et al., 1976). Metal-containing compounds offer many advantages over conventional carbon-based compounds, their ability to coordinate ligands in a three-dimensional configuration allowing the functionalization of groups that can be tailored to defined molecular targets (Fricker, 2007;Meggers, 2009).
Metals such as zinc act as a key structural component in many proteins and enzymes, including transcription factors, cellular signalling proteins and DNA repair enzymes (Prasad, 1995;Prasad & Kucuk, 2002). Zinc deficiency during pregnancy may produce serious defects and foetal loss (Hernick & Fierke, 2005). Zinc also possesses antiviral, antibacterial and wound-healing properties with zinc complexes also being used in the treatment of gastrointestinal disorders, acne and infertility (Cunnane, 1988). Against this background, the X-ray structural characterization of the title compound has been carried out in order to determine the molecular conformation, binding modes and hydrogenbonding interactions.
data reports Fig. 1 shows the molecular entities of the title complex, [Zn(C 2 H 8 N 2 ) 3 ][ZnCl 4 ], which comprises an ZnCl 4 2À anion and a [Zn(en) 3 ] 2+ complex cation. The Zn II atom of the tetrachloridozincate(II) anion is in an almost regular Cl 4 tetrahedral environment, with Zn-Cl bond lengths in the range 2.255 (1)-2.272 (9) Å . The zinc cation displays a distorted octahedral coordination geometry defined by six N atoms from three ethylenediamine ligands, with Zn-N distances in the range of 2.173 (3)-2.219 (3) Å . The N-Zn-N angles of the en ligands are about 80 . They are noticeably smaller than the ideal octahedral angle of 90 . The five-membered chelate rings are non-planar, with N-C-C-N torsion angles of À57.5 (4), À55.4 (4) and À55.9 (5) . All of the three en ligands assume a synclinal conformation about the C-C bond.
In the crystal structure, adjacent ions are connected via intermolecular hydrogen bonds. The N-HÁ Á ÁCl hydrogenbonding interactions between the N atoms of the ethylenediamine ligands and Cl atoms of the tetrachloridozincate anion connect the molecules, together with the weak C-HÁ Á ÁCl intramolecular interactions, generating a three-dimensional network (Fig. 2, Table 1).

Synthesis and crystallization
Zinc chloride (1.36 g, 2 mol) was dissolved in 25 ml of EtOH/ H 2 O (1:4 v/v) mixture. To this solution, ethylenediamine (1.0 ml, 3 mol) in 25 ml of an HCl/EtOH (2:3 v/v) mixture was added dropwise. The mixture was stirred and heated to 338 K for 2 h and allowed to stand at room temperature until colourless crystals separated (3-4 weeks). Crystals suitable for single-crystal XRD were collected after recrystallization using acidified water.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The crystal packing of title complex, viewed approximately down the a axis, with hydrogen bonds (Table 1) shown as dashed lines. Table 1 Hydrogen-bond geometry (Å , ).

Figure 1
View of the molecular structure of the title complex, showing the atom labelling. Displacement ellipsoids are drawn at the 30% probability level.
of Chemistry, Pondicherry University, for the single-crystal XRD instrumentation facility.