The crystal structure of one modification of trimesic acid (benzene-l,3,5-tricarboxylic acid) has been determined. The crystals are monoclinic, space group C2/c, with a= 26.52, b= 16.42, c=26.55 A, and ,8=91-53°; there are 48 molecules in the cell and, hence, 6 in the asymmetric unit. Intensities were estimated visually from Weissenberg photographs; about 11,500 were recorded of which 3200 were too weak to be observed. The structure was derived by consideration of Patterson maps, optical transforms and molecular packing; refinement was by multiple-matrix least squares. In all, 979 parameters were refined, including anisotropic temperature factors for the heavy atoms and coordinates and isotropic temperature factors for the hydrogen atoms. The final R index is 0.068 and the standard deviation of fit is 1.49. The basic structural motif is a continuous, two-dimensional network comprising large, open rings formed by six molecules of trimesic acid bonded together through pairs of O-H. • • O hydrogen bonds. The networks are not planar, pleats involving dihedral angles of about 70 ° being formed

No abstract

The development of a flexible intra-and intermolecular empirical potential function is described, which is designed for investigating the geometric structure of large molecular systems. The intramolecular components in the potential consist of harmonic bond stretching and angle bending terms, out-of-plane deformation terms, and torsional terms; intermolecular components include nonbonding, hydrogen bonding, and electrostatic terms. Bond lengths, angles, and torsional angles are predicted to within 2% of experiment, with most cases being within 1%. The suitability of the intermolecular potential was tested by crystal packing calculations; in all cases the results obtained were in excellent agreement with experiment.

No abstract

No abstract