The crystal structure of α-pyrazinamide

Abstract

ex-Pyrazinamide, C5H5N30, obtained from alcohol-water solution, is monoclinic, space group P2tfa, with four molecules in a unit cell of dimensions a=23·07, b=6·73, c=3·73 A, P=101·0°. The detailed crystal structure has been determined by two-dimensional difference syntheses and least squares based on (hlcO) and (hOl) reflexions. The pyrazine ring is completely planar, with mean C-N = 1·348 and C-C = 1·383 A, and makes an angle about 5° to the amide group (C-0 = 1·244 and C-N = 1·312 A). The molecules are connected by NH-0 hydrogen bonds, 2·90 A, forming dimers, and there are indications of NH-N hydrogen bonds, 3·14 A, linking the dimers into endless chains extended along [Oil]. Anisotropic thermal vibration parameters of each atom were obtained, and they were interpreted by dividing into translational and angular oscillation of the rigid molecule. It was observed that the amide group makes probably a torsional motion.