Crystal structure and Hirshfeld surface analysis of 2,5-dibromoterephthalic acid ethylene glycol monosolvate

The crystal structure of the title molecular solvate features O—H⋯O hydrogen bonds, Br⋯O and π–π interactions. Hirshfeld surface analysis and fingerprint plots helped to identify the major contributors to the intermolecular interactions.


Chemical context
Terephthalic acid and its derivatives are important ligands in the construction of coordination frameworks with high dimensionalities and interesting topologies (Li et al., 1999;Seidel et al., 2011). They have also been shown to be versatile building blocks in crystal engineering to drive the selfassembly of functional supramolecular networks through intermolecular interactions such as hydrogen bonds, halogen bonds, and aromaticstacking interactions (Lemmerer, 2011;Karmakar et al., 2014;Meng et al., 2015).

Structural commentary
The structures of the molecular components in the title compound are shown in Fig. 1. The asymmetric unit contains one-half of a H 2 Br 2 tp molecule and one-half of an EG molecule. Both molecules are generated by application of inversion symmetry. The H 2 Br 2 tp molecule is not planar. Its ISSN 2056-9890 dibromobenzene ring system (r.m.s. deviation = 0.006 Å ) makes a dihedral angle of 18.62 (3) with the carboxylic group (r.m.s. deviation = 0.013 Å ). As a result of symmetry restrictions, the EG molecule adopts an anti-conformation with an O3-C5-C5 i -O3 i torsion angle of 180 [symmetry code: (i) 2 À x, Ày, 2 À z].

Supramolecular features
In the crystal, the H 2 Br 2 tp and EG molecules are linked by strong-to-medium O-HÁ Á ÁO hydrogen bonds between carboxylic acid and alcohol OH functions (Table 1) (Fig. 3). The combination of these intermolecular interactions results in the formation of a threedimensional supramolecular network.

Figure 1
The structures of the molecular components in the title compound with displacement ellipsoids drawn at the 50% probability level. The O-HÁ Á ÁO hydrogen bond is shown by a dashed line.

Synthesis and crystallization
H 2 Br 2 tp and EG were purchased from commercial sources and used as received. A solution of H 2 Br 2 tp (0.020 g) in 5 ml of EG was heated (333 K) to reflux for 15 min. The reaction solution was held for 2-3 h and colourless block-shaped crystals suitable for single-crystal X-ray diffraction analysis were obtained.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The carbon-bound H atoms were placed in geometrically calculated positions and refined as riding with C-H = 0.93 Å for aromatic and C-H = 0.97 Å for methylene hydrogen atoms with U iso (H) = 1.2U eq (C). The H atoms bound to O atoms were located from difference-Fourier maps but were refined with distance restraints of O-H = 0.82 AE 0.02 Å and U iso (H) = 1.5U eq (O).

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.