The Crystal Structure of Trimellitic Acid for the Pseudo-cell

Abstract

Abstract The crystal structure of trimellitic acid(benzene-1,2,4-tricarboxylic acid) for the pseudo-cell was determined by the method of X-ray diffraction. The crystal is monoclinic, with the space group of I2/c and with a=15.91, b=61.35, c=8.99 Å, and β=95.4°. The appearence of diffraction patterns strongly indicated the existence of the pseudo-cell with b⁄5 and with the space group of I2/c. The structure of the pseudo-cell was determined by the symbolic addition method. The final R value is 13.6%. There is no intramolecular hydrogen bond between the adjacent carboxyl groups, and one of these carboxyl groups twists greatly out of the plane of a benzene ring so that the repulsion between the oxygen atoms is reduced. Each molecule is joined, through three kinds of hydrogen bonds, with three neighboring molecules. These hydrogen bonds are formed between the carboxyl groups related by the center of symmetry and the two-fold axis. The molecular dimensions and packing obtained by the refinement for the pseudo-cell do not seem to contain unacceptable results.