title: Conformational dimorphism in o-nitrobenzoic acid: alternative ways to avoid the O...O clash.
abstract: Polymorphism is a challenging phenomenon and the competitive packing alternatives which are characteristic for polymorphs may be encountered for essentially rigid molecules. A second crystal form of the well known compound o-nitrobenzoic acid, C7H5NO4, an important intermediate in the production of dyes, pharmaceuticals and agrochemicals, is described. Although obtained serendipitously, its intra- and intermolecular features match expectations from database searches and theoretical calculations. O-H...O hydrogen-bonded carboxylic acid dimers represent the building blocks in both polymorphs. For steric reasons and in agreement with a calculated potential energy surface, the carboxylic acid and nitro groups cannot simultaneously be coplanar with the benzene ring but have to tilt. In the well established crystal form, this out-of-plane torsion is more pronounced for the nitro substituent. In contrast, the new polymorph is characterized by a major tilt of the carboxylic acid group. The molecules in both alternative crystal forms achieve a similar compromise with respect to acceptable intramolecular O...O contacts.
authors.affiliation: Institute of Bioorganic Chemistry, Academy of Sciences of Uzbekistan, Tashkent, Uzbekistan.
authors.forename: Aziz
authors.initials: A
authors.lastname: Ibragimov
authors.affiliation: Institute of Bioorganic Chemistry, Academy of Sciences of Uzbekistan, Tashkent, Uzbekistan.
authors.forename: Jamshid
authors.initials: J
authors.lastname: Ashurov
authors.affiliation: Institute of Bioorganic Chemistry, Academy of Sciences of Uzbekistan, Tashkent, Uzbekistan.
authors.forename: Bakhtiyar
authors.initials: B
authors.lastname: Ibragimov
authors.affiliation: Institut für Anorganische Chemie, RWTH Aachen University, Landoltweg 1, 52074 Aachen, Germany.
authors.forename: Ai
authors.initials: A
authors.lastname: Wang
authors.affiliation: Institut für Physikalische Chemie, RWTH Aachen University, Landoltweg 2, 52074 Aachen, Germany.
authors.forename: Halima
authors.initials: H
authors.lastname: Mouhib
authors.affiliation: Institut für Anorganische Chemie, RWTH Aachen University, Landoltweg 1, 52074 Aachen, Germany.
authors.forename: Ulli
authors.initials: U
authors.lastname: Englert
keywords: 2-nitrobenzoic acid; computational chemistry; conformation; crystal structure; disappearing polymorph; polymorphism; potential energy surface