Bis(4-aminobenzoic acid-κN)dichloridozinc(II)

Molecules of the title compound [ZnCl2(C7H7NO2)2], are located on a twofold rotation axis. Two 4-aminobenzoic acid moieties, and two chloride ligands are coordinated to a Zn atom in a tetrahedral fashion, forming an isolated molecule. Neighbouring molecules are linked through hydrogen-bonded carboxyl groups, as well as N—H⋯Cl hydrogen-bonding interactions between amine groups and the chloride ligands of neighbouring molecules, forming a three-dimensional network.

Molecules of the title compound [ZnCl 2 (C 7 H 7 NO 2 ) 2 ], are located on a twofold rotation axis. Two 4-aminobenzoic acid moieties, and two chloride ligands are coordinated to a Zn atom in a tetrahedral fashion, forming an isolated molecule. Neighbouring molecules are linked through hydrogen-bonded carboxyl groups, as well as N-HÁ Á ÁCl hydrogen-bonding interactions between amine groups and the chloride ligands of neighbouring molecules, forming a three-dimensional network.
Funding received for this work from the University of Pretoria is acknowledged.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: BT5408).

Comment
The crystal structure of dichloro-bis(4-aminobenzoic acid-N)-zinc(ii), I, was determined as part of an ongoing study of the coordination compounds formed between organic amines and metal halides. The related crystal structure of diiodo-bis(4aminobenzoic acid-N)-cadmium(ii) has been reported (Wang et al., 2002), but the crystal structures are not isostructural.
The asymmetric unit of I consists of one 4-aminobenzoic acid moiety coordinated to a ZnCl unit through the nitrogen atom, as shown in Fig. 1, with the Zn atom lying on a twofold rotation axis. The second half of the molecule is generated by the symmetry operator (-x, y, 1/2 -z), and the unit cell contains four dichloro-bis(4-aminobenzoic acid-N)-zinc(II) molecules.
The Zn atom is coordinated to two 4-aminobenzamide ligands, through the nitrogen atom, and to two chloro ligands, and displays a slightly distorted tetrahedral coordination geometry with the N-Zn-N angle equal to 114.99 (9)°, which is slightly larger than the ideal tetrahedral angle of 109.5° to reduce steric hinderance between the two bulky 4-aminobenzoic acid ligands. The N-Zn-Cl angles adopt values of 107.10 (5)° and 109.27 (5)°, while the Cl-Zn-Cl angle has a value of 109.00 (3)°. The 4-aminobenzoic acid ligands show a cis orientation relative to the Zn atom, and in each ligand the aromatic plane forms an angle of 2.7 (0.1)° relative to the carboxylic acid group plane, rendering the ligand non-planar.
The layered packing of the molecules parallel to the bc-plane is illustrated in Fig. 2. The aromatic rings pack in two layers, while the Cl-Zn-Cl moieties form a layer. Hydrogen bonding interactions between the carboxylic acid groups of neighbouring layers result in the formation of carboxylic acid dimers of graph set notation R 2 2 (8) (Bernstein et al., 1995) on both sides of the molecule, forming a zigzag, one-dimensional hydrogen bonded ribbon as shown in Fig. 3. Neighbouring one-dimensional ribbons are connected via N1-H1B···Cl1 (symmetry operator: -x + 1, y -1, -z + 3/2) hydrogen bonds to form the two-dimensional hydrogen bonded sheet illustrated in Fig. 3, with the intra-ribbon interactions described by the graph set notation R 2 2 (8). Additional N1-H1B···Cl1 (symmetry operator: -x + 1, -y, -z + 2) hydrogen bonds link neighbouring sheets to give a three-dimensional hydrogen bonded structure, with intra-sheet hydrogen bonds described by the graph set notation D 1 1 . Hydrogen bonding parameters are listed in Table 1.

Experimental
Dichloro-bis(4-aminobenzoic acid-N)-zinc(ii) was prepared by dissolving 4.34 g Zn(NO 3 ) 2 .6H 2 O (14.6 mmol, Sigma-Aldrich, 98%) and 1.00 g 4-aminobenzoic acid (7.29 mmol, Aldrich Chemistry, 99%) in a mixture of 50 ml distilled water and 50 ml e thanol (Merck, 99.5%). Dissolution was achieved by heating the solution in a beaker to approximately 60°C. Approximately 30 ml of the solution was transferred to a polytop vial, and one drop of HCl (Promark Chemicals, 32%) was added to the solution. Slow evaporation of the solvent mixture at room temperature gave yellow crystals of the title compound.
supplementary materials sup-2 Refinement All H atoms, except the carboxylic acid group hydrogen atom, were refined using a riding model, with C-H distances of 0.93 Å and N-H distances of 0.90 Å, and U iso (H) = 1.2U eq (C) or 1.2U eq (N). The carboxylic acid hydrogen atom was placed as observed on the difference Fourier map, and not further refined, with U iso (H)=1.2U eq (O).

Figures
Fig . 1. The asymmetric unit of I showing the atomic numbering scheme. Displacement ellipsoids are shown at the 50% probability level and H atoms are shown as small spheres of arbitrary radii.

Bis(4-aminobenzoic acid-κN)dichloridozinc(II)
Crystal data  Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.