The Crystal Structure of Dipicolinic Acid Monohydrate

Abstract

Abstract The crystal structure of the dipicolinic acid monohydrate has been determined by the method of X-ray diffraction. The crystal is orthorhombic, with a space group of P212121 and with cell dimensions of a=12.233, b=9.399, and c=6.817 Å. The crystal structure was solved by an inspection of the Patterson map. The final R value was 5.67% for 964 observed reflections. The pyridine ring has the C2v symmetry within the limits of experimental error. The protonation does not occur on the nitrogen atom of the pyridine ring, and two carboxyl groups consist of carbonyl and hydroxyl groups. There is a simple relation between the C–O bond length and the C–C–O bond angle. The molecules are arranged in layers closely parallel to the (0 0 1) plane. Each molecule on the same plane is hydrogen-bonded to form an endless chain along the b axis. These two chains on the planes at z=1⁄8 and 3/8 are linked together by the O–H···N hydrogen bond between the water and pyridine ring to form a double chain along the b axis. In this case, the angle between the N···H(7) vector of the hydrogen bond and the plane of the pyridine ring is 28°. This situation can be explained by the fact that two adjacent and bulky carboxyl groups wrap up the nitrogen atom as an acceptor of the hydrogen bond. The double chains are packed only by the van der Waals forces. The thermal diffuse scattering observed on Weissenberg photographs can be explained by this hydrogen-bond system.