THE ABINITIO CRYSTAL-STRUCTURE DETERMINATION OF ALPHA-MALONIC ACID FROM NEUTRON POWDER DIFFRACTION DATA

The crystal structure of the alpha phase of malonic acid has been determined ab initio from high-resolution neutron powder diffraction data at 373 K. The structure is orthorhombic: a=7.64800(1) angstrom, b=5.02111(1) angstrom, c=11.55803(2) angstrom, V(c)=443.84 angstrom3 with four molecules in the unit cell and is characterised by hydrogen bonded dimeric units linked through symmetry equivalent carboxyl groups. The molecules form zig-zag chains along the c-axis direction but in contrast to the triclinic ambient temperature beta phase there is a twisting of the carboxylic groups rendering them equivalent and related by a twofold axis.