Structural characterization of two benzene-1,2-diamine complexes of zinc chloride: a molecular compound and a co-crystal salt

The structures of two zinc complexes containing bidentate benzene-1,2-diamine ligands are reported. (Benzene-1,2-diamine-κ2 N,N′)dichloroidozinc displays a distorted tetrahedral geometry. The 1:1 co-crystal salt trans-diaquabis(4,5-dimethylbenzene-1,2-diamine- κ2 N,N′)zinc chloride 4,5-dimethylbenzene-1,2-diamine exhibits a tetragonally distorted octahedral zinc coordination sphere.


Structural commentary
As seen in Fig. 1, compound (I) exhibits a distorted tetrahedral coordination sphere for the metal cation. Tables 1 and 2 give relevant geometric parameters found in the coordination sphere. The diamine ligand and the Zn atom sit on a mirror plane and, hence, are rigorously planar as a result of the symmetry constraint. The Zn-N bond lengths observed at the two temperatures are the same within the calculated s.u.s. The Zn-Cl bond lengths differ within the s.u.s, with the 200 K structure being 0.0030 (5) Å longer. The bond lengths observed at both temperatures fall within the s.u. of the average value [2.221 (19) Å ] of similar complexes but the Cl-Zn-Cl bond angles are smaller than the average of the values [115 (1) ] reported for similar Zn II dichlorides in a tetrahedral environment (Shi et al., 2010;You, 2005;Lee et al., 2007).

Figure 4
A view of the parallel sheets found in (I

Supramolecular features
As seen in Figs. 3 and 4 and Tables 4 and 5, N1-H1Á Á ÁCl hydrogen bonds between adjacent molecules result in strips of molecules of (I) along [100]. The strips form planes parallel to (101). Additional N2-H2Á Á ÁCl bonds join the strips to form the three-dimensional network.

Synthesis and crystallization
Compound (I) was prepared by mixing a solution of 100. mg (0.734 mmol) zinc chloride dissolved in approximately 5 mL ethanol with a solution of 238 mg (2.20 mmol) benzene-1,2diamine dissolved in approximately 5 mL ethanol. The mixture became cloudy with a fine white precipitate. After the addition of 4 drops of 6 M HCl, the mixture was gently heated, filtered and allowed to slowly evaporate. After two days, 0.0273 g (0.117 mmol, 15% yield) of clear, colorless crystals were isolated, which were used for data collection. The diffraction pattern showed signs of degradation as the temperature was lowered to 200 K from 300 K and so data sets were collected at both temperatures.
Compound (II) was prepared by combining solutions of 100 mg (0.734 mmole) zinc chloride in a few mL of ethanol and 300 mg (2.20 mmol) 4,5-dimethylbenzene-1,2-diamine in a few mL of ethanol. After the addition of 4 drops of 6 M HCl, the mixture was gently heated and filtered. The filtrate was divided into three portions and each allowed to slowly evaporate. After several days, a small number of clear, colorless crystals in the shape of hexagonal plates were isolated, one of which was used for data collection. research communications Table 6 Hydrogen-bond geometry (Å , ) for (II).

Refinement details
Crystal data, data collection and structure refinement details are summarized in Table 7. For compound (I), data sets were collected at 300 K (Ia) and 200 K (Ib). The diffraction pattern showed clear degradation at the lower temperature. Examination of the crystal subjected to the cold stream showed fractures that were not previously present. As seen in Table 7, the cell constant s.u.s, R values and S values are lower for the 300 K data set. For both (I) and (II), all hydrogen atoms were located in difference Fourier maps. For (I), all hydrogen atoms bonded to the nitrogen atoms were refined freely, including isotropic displacement parameters. For (Ia), the hydrogen atoms bonded to the benzene carbon atoms were refined using a riding model with C-H = 0.93 Å and U iso (H) = 1.2U eq (C), whereas these hydrogen atoms were refined with C-H = 0.95 Å and U iso (H) = 1.2U eq (C) for (Ib).
For (II), the amine hydrogen atoms of the non-coordinating 4,5-dimethylbenzene-1,2-diamine were refined freely, including the isotropic displacement parameters. For the hydrogen atoms of the coordinating amines, the atomic coordinates were refined freely with U iso (H) = 1.2U eq (N). The hydrogen atoms of the water ligands were refined freely, including the isotropic displacement parameters. The methyl hydrogen atoms were refined with C-H = 0.98 Å 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. Refinement. Refined as a 2-component inversion twin.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Zn1 0.12910 ( where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.31 e Å −3 Δρ min = −0.22 e Å −3 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.

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Acta Cryst. (2016). E72, 1037-1042 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.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )