Crystal Structure Solution from Powder X-ray Diffraction Data: The Development of Monte Carlo Methods To Solve the Crystal Structure of the γ-Phase of 3-Chloro-trans-cinnamic Acid†

Many important crystalline materials do not form single crystals of sufficient size and/or quality for single-crystal diffraction studies, and in such cases it is essential that the crystal structure can be solved from powder diffraction data; however, there are many difficulties associated with solving crystal structures, ab initio, from powder diffraction data. In this paper, we report the successful application of a Monte Carlo technique to solve the (previously unknown) crystal structure of the γ-phase of 3-chloro-trans-cinnamic acid from powder X-ray diffraction data. The “structural fragment” used in the Monte Carlo calculation comprised a rigid trans-cinnamic acid molecule (with the chlorine and hydrogen atoms omitted) with its oxygen atoms at a fixed distance from the crystallographic center of symmetry, and with the center of symmetry lying in the molecular plane. The structural fragment was rotated by a random angular displacement around a random axis constrained to pass through the center of sy...