5-Fluoroisophthalic acid

In the crystal structure of the title compound, C8H5FO4, the complete molecule is generated by crystallographic twofold symmetry with two C atoms and the F atom lying on the axis. The molecule is almost planar with the carboxyl group twisted with respect to the mean plane of the benzene ring by a dihedral angle of 2.01 (1)°. In the crystal, intermolecular O—H⋯O hydrogen bonds and C—H⋯F interactions connect the molecules into a two-dimensional supramolecular array.

In the crystal structure of the title compound, C 8 H 5 FO 4 , the complete molecule is generated by crystallographic twofold symmetry with two C atoms and the F atom lying on the axis. The molecule is almost planar with the carboxyl group twisted with respect to the mean plane of the benzene ring by a dihedral angle of 2.01 (1) . In the crystal, intermolecular O-HÁ Á ÁO hydrogen bonds and C-HÁ Á ÁF interactions connect the molecules into a two-dimensional supramolecular array.

Comment
As an analogue of isophthalic acid (Bhogala et al. 2005;Derissen, 1974), 5-fluoroisophthalic acid has been seldom used in the crystal engineering of organic or inorganic-organic systems (Zhang et al. 2010). The fluorinated group may participate in hydrogen-bonding and may also induce luminescence properties. Herein we report the crystal structure of the title compound, C 8 H 5 FO 4 , to further investigate the supramolecular interactions involving the fluorine atom. The structure of the title compound, is shown below. The molecule presents C 2 symmetry with the fundamental unit lying on a C 2 -axis at [x, 3/4, z]. Intermolecular O-H···O interactions between adjoining centrosymmetry-related carboxylic groups form a hydrogen-bonded ribbon running along the [010] direction. C-H···F interactions connect the ribbons into a two-dimensional supramolecular array.
Experimental 5-Fluoroisophthalic acid and solvents for synthesis and analysis were commercially available and used as received. Single crystals suitable for X-ray diffraction were obtained by slow evaporation of the methanol solution of the title compound.

Refinement
Benzene H atoms were assigned to calculated positions with C-H = 0.93 Å, and refined using a riding model, with Uiso(H) = 1.2Ueq(C). H atoms bound to carboxylic O atoms were located in difference maps and refined as riding with U iso (H) = 1.5 U eq (O). Fig. 1. The molecular structure of the title compound drawn with 30% probability ellipsoids.

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 supplementary materials sup-3 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.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )