The Crystal Structure of Cinchomeronic Acid

Abstract

Abstract The crystal structure of cinchomeronic acid (3,4-pyridinedicarboxylic acid) has been determined by the method of X-ray diffraction. The crystals are orthorhombic, with a space group of P212121, and with cell dimensions of a=11.211, b=11.206, and c=5.285 Å. The structure was determined by the method of symbolic addition. The final R value was 5.90% for 828 observed reflections. The molecule takes the form of a zwitter ion in the crystal. The pyridine ring has, approximately, the C2v symmetry. One carboxyl group consists of C=O and C–O (H) groups, while the other consists of two O(Remark: Graphics omitted.)O groups. These carboxyl groups twist out of the plane of a pyridine ring by 39.6° and 73.0° respectively. The hydrogen bonds are in the forms of two spirals around the two-fold screw axes parallel to the c axis, thus linking the molecules three-dimensionally. There are four molecules per turn of the spiral along the c axis. The carbonyl oxygen atom O(2) is free from the hydrogen bond, while the nitrogen atom N(l) in the pyridine ring participates in it. The relations between the C–N–C bond angle of the pyridine ring and the N···H distance, and also between the net charge on the nitrogen atom calculated by the “complete neglect of differential overlap” (GNDO) method and the O···N distance for a hydrogen bond are discussed in connection with five pyridine-carboxylic acids.