Biphenyl-2,4,4′,6-tetracarboxylic acid monohydrate

In the title compound, C16H10O8·H2O, the dihedral angle between the benzene rings is 71.59 (8)°. The COOH groups make dihedral angles of 10.3 (2), 30.8 (2), 11.3 (2) and 42.3 (2)° with their attached rings. In the crystal, O—H⋯O hydrogen bonds link the components forming a three-dimensional supramolecular network.

Biphenyl-2,4,4′,6-tetracarboxylic acid monohydrate Ye-Nan Wang and Jun Zhao Comment Aromatic carboxylates have been proven to be effective building blocks for the design and construction of coordination polymers exhibiting remarkable polymeric structural motifs due to their rich coordination modes (Yaghi et al.,2003;Zhao et al., 2012). Recently, we attempted to synthesize an Sm III complex with the ligand in hydrothermal synthesis conditions. However the title organic salt was obtained, its structure is reported here.

Experimental
All chemicals were of reagent grade quality obtained from commercial sources and used without further purification. A mixture of bipheny1,2,4,4′6-tetracarboxylic acid (0.0370 g, 0.1 mmol), Sm(NO 3 ) 3 .6H 2 O (0.0444 g, 0.1 mmol) and water (12 ml) were placed in a 23 ml Teflon-lined stainless steel reactor and heated at 393 K for 2 days, and then cooled to room temperature at 10 K h -1 to obtain colorless prism-shaped crystals suitable for X-ray analysis.

Refinement
The H atoms bonded to C and carboxylate O atoms were positioned geometrically (C-H = 0.93, O-H = 0.82 Å) and allowed to ride on their parent atoms, with U iso (H) value equal to 1.2U eq (C) or 1.5U eq (O). The H atoms bonded to water were located in a difference Fourier map and refined with O-H distance restraint of 0.85±0.01 Å, U iso (H) = 1.5U eq (O).  The molecular structure of the title compound with displacement ellipsoids at the 50% probability level.

Figure 2
Part of the crystal structure with hydrogen bonds shown as dashed lines.

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 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.