title: 3,3'-[Biphenyl-4,4'-diylbis(-oxy)]diphthalic acid.
abstract: In the title mol-ecule, C(28)H(18)O(10), the two central benzene rings form a dihedral angle of 31.0 (1)°. In the phthalic acid fragments, the carb-oxy groups in the meta positions are approximately coplanar with the attached benzene rings, being inclined to their planes at 2.7 (1) and 10.3 (1)°, while the carb-oxy groups in the ortho positions are twisted from the benzene ring planes by 83.5 (1) and 75.4 (1)°. In the crystal, O-H⋯O hydrogen bonds link the mol-ecules into layers parallel to the bc plane. Weak C-H⋯O hydrogen bonds and π-π inter-actions between the aromatic rings [centroid-centroid distance = 3.7674 (3) Å] further consolidate the crystal packing.
authors.affiliation: Department of Chemistry and Chemical Engineering, University of Science and Technology Beijing, Beijing 100083,  People's Republic of China.
authors.forename: Ningning
authors.initials: N
authors.lastname: Zhao
authors.forename: Wenjun
authors.initials: W
authors.lastname: Li
authors.forename: Zhidong
authors.initials: Z
authors.lastname: Chang
authors.forename: Changyan
authors.initials: C
authors.lastname: Sun
authors.forename: Hongxia
authors.initials: H
authors.lastname: Fan