The Crystal Structure of Dinicotinic Acid

Abstract

Abstract The crystal structure of dinicotinic acid has been determined by X-ray diffraction method. Two kinds of twinning crystals were obtained by changing the pH of the aqueous solution by recrystallization. The crystals are monoclinic with the space group of P21/c and with cell dimensions of a=9.702, b=11.153, c=6.587 Å, and β=107.8°. The crystal structure was solved by an inspection of the sharpened Patterson map. The final R value is 5.93% for 1181 observed reflections. The dinicotinic acid molecule takes an intermediate structure between the neutral molecule and the zwitter ion with an approximate C2v symmetry. The bond lengths and angles related by the C2v symmetry are equal within the limits of experimental error for those of the two carboxyl groups. The C(2)–N(1)–C(6) bond angle is 119.8°, which lies between those of protonated and unprotonated species of the pyridine ring. The molecules lie approximately on planes parallel to the (001) plane at z=1⁄4 and 3/4. Each molecules on the same plane is joined through two kinds of hydrogen bonds (O–H···O; 2.594 Å, O···H···N; 2.515 Å), related by two-fold screw axes, with four neighboring molecules. In the O···N hydrogen bond, the hydrogen bonding distance and angle are 2.515 Å and 174° and the O–H and N–H distances are 1.23 and 1.29 Å, which are equal within the limits of experimental error. Therefore, it may be considered as an example of the single minimum hydrogen bond of the O–H···N hydrogen-bond type. The existence of two kinds of twins may be interpreted on the basis of the layer structure.