4′-Hydroxybiphenyl-4-carboxylic acid

The title compound, C13H10O3, has potential oxygen donor and acceptor sites. Intermolecular hydrogen bonding between neighboring carboxylate groups leads to the formation of hydrogen-bonded dimers [graph-set motif R 2 2(8)]. A second hydrogen-bonding interaction between the hydroxy groups generates a chain and extends the structure into a lamellar layer. One of the benzene rings is disordered over two positions with an occupancy ratio of 0.57 (2):0.43 (2).

The title compound, C 13 H 10 O 3 , has potential oxygen donor and acceptor sites. Intermolecular hydrogen bonding between neighboring carboxylate groups leads to the formation of hydrogen-bonded dimers [graph-set motif R 2 2 (8)]. A second hydrogen-bonding interaction between the hydroxy groups generates a chain and extends the structure into a lamellar layer. One of the benzene rings is disordered over two positions with an occupancy ratio of 0.57 (2):0.43 (2).

Data collection
Bruker APEXII area-detector diffractometer Absorption correction: none 6310 measured reflections 1800 independent reflections 854 reflections with I > 2(I) R int = 0.063 Refinement R[F 2 > 2(F 2 )] = 0.058 wR(F 2 ) = 0.183 S = 1.01 1800 reflections 160 parameters 24 restraints H-atom parameters constrained Á max = 0.18 e Å À3 Á min = À0.19 e Å À3 Table 1 Hydrogen-bond geometry (Å , ). Hydrogen-bonding interactions between ligands are specific and directional. When present in metal complexes they usually do not rely on the properties of the metal ions, but they play an important role in the overall structures and functions of the complexes and the way in which they pack in the solid state (Zwier et al., 1996;Datta & Pati, 2006). In this context we report here the crystal structure of the title compound, (I).
The molecular structure of (I) is shown in Fig. 1. The C-O and C-C bond distances show no remarkable features. The title molecular structure acts as both a hydrogen bonding donor and acceptor, forming dimers with neighboring molecules through O-H···O hydrogen bonding with a R 2 2 (8) graph set motif (Bernstein et al., 1995). A second hydrogen bonding interaction by the hydroxyl groups forms a chain and extends the structure into a lamellar layer (Table 1, Fig. 2).
Experimental 4-Hydroxyl-biphenyl-4'-carboxylic acid was dissolved in a hot ethanol-water solution (1:1; v/v) with stirring. Colorless single crystals suitable for X-ray diffraction were obtained at room temperature by slow evaporation of the solvent over a period of several days.

Refinement
In the initial refinement with disorder not taken into account one of phenyl rings showed significantly elongated thermal ellipsoids indicating disorder, the dihedral angle between two phenyl rings is 5.66 (2) /%A, and the adjacent distances of C-H···C-H interactions in the biphenylene are 2.044 (1) and 2.077 (1) /%A, respectively, thus leading to a static repulsion between two phenyl rings,and the phenyl ring was thus refined as being disordered over two positions. The occupancy ratio refined to 0.57 (2) to 0.43 (2). The adps of the disordered atoms were restrained to be close to isotropic and those of equivalent atoms were set to be identical. Carbon-bound, hydroxyl and carboxylate group H atoms were placed at calculated positions and were treated as riding on their parent C or O atoms with C-H = 0.93 Å, with U iso (H) = 1.2 U eq (C); O-H = 0.82 Å and with U iso (H) = 1.5 U eq (O). Fig. 1. The structure of (I), showing the atom-numbering scheme and displacement ellipsoids drawn at the 30% probability level.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > 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.