Crystal structure of 5-[(4-carboxybenzyl)oxy]isophthalic acid

The title compound, 5-[(4-carboxybenzyl)oxy]isophthalic acid (CIA), is non-planar with the two benzene rings being almost perpendicular to one another, making a 87.78 (7)°. In the crystal, molecules are linked by three pairs of O—H⋯O hydrogen bonds, forming undulating sheets parallel to the bc plane and enclosing (8) ring motifs.


Chemical context
The design and synthesis of coordination polymers continues to attract interest due to their architectures as well as their potential applications (Erxleben, 2003). Recently, the rational design and synthesis of novel coordination polymers have attracted intense attention in the field of supramolecular chemistry and crystal engineering (Zhang et al., 2011). To date, large numbers of coordination architectures with interesting compositions and properties have been prepared using a wide variety of aromatic polycarboxylate-based ligands (Cambridge Structural Database; Groom et al., 2016). The title compound (CIA), a tricarboxylate ligand, has been shown to be a good candidate for the construction of coordination polymers (Ahmad et al., 2012a,b). Tricarboxylate ligands have been used in the synthesis of metal-organic framework complexes (MOFs)because of their photoelectric properties and for their potential nitrobenzene sensing (Hou et al., 2016). A Cd II MOF based on CIA has been structurally and functionally characterized, and was shown to be an highly selective CH 2 Cl 2 fluorescent sensor (Xia et al., 2015). A series of one-, two-and three-dimensional coordination polymers based on CIA have been structurally characterized and shown to display photoluminescence (Liu et al., 2012).
We have crystallized a reported polycarboxylate containing the ligand, 5-[(4-carboxybenzyl)oxy]isophthalic acid (CIA), which has the advantage of being flexible and has conformational freedom allowing it to conform to the coordination environment of transition metal ions. We report herein on the crystal structure of the title tricarboxylate ligand (CIA), synthesized by a reported procedure (Ahmad et al., 2012a,b).

Structural commentary
The molecular structure of the title compound (CIA) is illustrated in Fig. 1. The bond lengths and bond angles are normal and close to the values observed in related structures (Li & Ma 2011;He et al., 2014). The molecular shape of the title compound is bent around the central C9-O5 bond; the spacer ether group exhibits a C10-C9-O5-C1 torsion angle of À84.35 (19) . The benzene rings, C1-C6 and C10-C15, are roughly perpendicular to each another, with a dihedral angle of 87.78 (7) . The three O C-O bond angles of the carboxylic acid groups are 123.17 (17), 123.62 (17), 123.74 (17) Å , respectively, for O1 C7-O2, O3 C8-O4 and O6 C16-O7.

Supramolecular features
In the crystal, each molecule is linked to three others by three pairs of O-HÁ Á ÁO hydrogen bonds, forming undulating sheets parallel to the bc plane and enclosing R 2 2 (8) ring motifs (Table 1 and Fig. 2). The sheets are linked by C-HÁ Á ÁO hydrogen bonds and C-HÁ Á Á interactions, forming a threedimensional network (Table 1 and Fig. 3).

Synthesis and crystallization
The starting compound diethyl 5-(4-methoxycarbonylbenzyloxy)isophthalate (DMBI) was prepared by the following 1220 Faizi et al. The molecular structure of the title compound, with atom labelling. Displacement ellipsoids are drawn at the 40% probability level. Table 1 Hydrogen-bond geometry (Å , ).

Figure 2
A partial view of the O-HÁ Á ÁO hydrogen-bonding interactions between the donor and acceptor oxygen atoms of the carboxylic groups in the crystal of the title compound. The hydrogen bonds are shown as dashed lines (see Table 1 for details).
procedure: 5-hydroxyisophthalic acid diethyl ester (2 g, 8.4 mmol) and dry K 2 CO 3 (1.7g, 12.6 mmol) were mixed in dry acetonitrile (10 ml) and stirred for 30 min at 353 K. Then 4-bromomethyl benzoic acid methyl ester (1.9 g, 8.40 mmol) was added and the resulting solution was refluxed for 24 h. The solution was pored into ice-cold water and the solid precipitate obtained was filtered and dried in air (yield: 2.8 g, 86%). The title compound (CIA) was prepared as follows: DMBI (2 g, 5.17 mmol) was hydrolyzed by refluxing it with 6N NaOH solution (20 ml) for 24 h. After cooling to 278 K, the resulting solution was acidified with 6N HCl solution to obtain a white precipitate. This was collected by filtration, washed thoroughly with water, and dried in air. The solid powder was dissolved in dimethyl formamide and needle-like crystals were obtained by slow diffusion of diethyl ether into the solution, after 2-3 days (yield: 1.3 g, 80%).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The OH H atoms were located in a difference Fourier map and freely refined. The C-bound H atoms were positioned geometrically and refined using a riding model: C-H = 0.93-0.97 Å with U iso (H) = 1.2U eq (C).   Table 1 for details) . Fig 3 hard to make out, too many molecules shown program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenberg & Putz, 2006); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and PLATON (Spek, 2009).

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. 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 > 2sigma(F 2 ) is used only for calculating R-factors(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.