4-Bromobenzoyl 4-bromobenzoate monohydrate

In the title compound, C14H8Br2O3·H2O, the organic and water molecules both have crystallographically imposed C s symmetry. The dihedral angle between the aromatic rings is 45.76 (11)°. In the crystal structure, intermolecular C—H⋯O and O—H⋯O hydrogen bonds link the molecules into chains parallel to the a axis. No π–π stacking interactions are observed in the crystal structure.

In the title compound, C 14 H 8 Br 2 O 3 ÁH 2 O, the organic and water molecules both have crystallographically imposed C s symmetry. The dihedral angle between the aromatic rings is 45.76 (11) . In the crystal structure, intermolecular C-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonds link the molecules into chains parallel to the a axis. Nostacking interactions are observed in the crystal structure.

Comment
Chelate ligands have found widespread use in coordination chemistry due to the enhanced thermodynamic stability of resultant coordination compounds in relation to coordination compounds exclusively applying comparable monodentate ligands (Gade 1998). Combining different sets of donor atoms in one chelate ligand molecule, a probe for testing and accomodating metal centers of different Lewis acidities is at hand. In our efforts to synthesize a chelate ligand featuring a set of oxygen, sulfur and nitrogen as possible donor atoms, a crystalline reaction product was obtained whose crystal structure analysis revealed the unintentional synthesis of the hydrated anhydride of para-bromobenzoic acid. The crystal structure of the anhydrous anhydride is apparent in the literature (McCammon & Trotter, 1964;Duesler et al., 1981).
The asymmetric unit comprises half of the organic molecule and half of the molecule of crystal water. The least-squares planes defined by the atoms of both aromatic moieties intersect at an angle of 45.76 (11)° (Fig. 1). In the crystal structure, intermolecular C-H···O and O--H···O hydrogen bonds can be observed (Table 1). The carbonylic O atoms of the anhydride serve as twofold acceptors for the hydrogen bonds originating from the water molecule as well as the H atom of an adjacent molecule bonded to the C atom in ortho position to the carboxylic acid functionality. A description of the C-H···O hydrogen bonds in terms of graph-set analysis (Etter et al., 1990;Bernstein et al., 1995) necessitates a R 2 2 (14) descriptor on the unitary level. In total, the moieties of the crystal structure are connected to chains parallel to the crystallographic a axis (Fig. 2). No π-π stacking interaction is observed. The packing of the compound in the crystal structure is shown in Fig. 3.

Experimental
The compound was prepared upon reacting 4-bromobenzyl chloride (2.5 mmol) with potassium thiocyanate (2.5 mmol) and dipyridin-2-ylamine (2.5 mmol) in refluxing acetone (15 ml) for two hours. Crystals suitable for the X-ray diffraction study were obtained upon free evaporation of the reaction mixture.

Refinement
Carbon-bound H atoms were placed in calculated positions (C-H = 0.95 Å) and were included in the refinement in the riding model approximation, with U iso (H) set to 1.2U eq (C). The H atom of the water molecule was located on a difference Fourier map and refined using a DFIX instruction (d O-H set to 0.85 Å), with U iso (H) set to 1.5U eq (O). Fig. 1. The molecular structure of the title compound, with anisotropic displacement ellipsoids drawn at 50% probability level. Symmetry code: (i) x, -y + 1/2, z.    (14)