Hydration/Dehydration phase transition mechanism in organic crystals investigated by ab initio crystal structure determination from powder diffraction data

Abstract

The study of organic crystals is a very active field. Molecules in a crystal are responsive to environmental changes, such as temperature, humidity, and irradiation. The motion of these molecules in response to the external stimuli may result in chemical reactions, in addition to altering their arrangement in the crystal. Such structural rearrangements can only be understood by crystal structure comparison before and after the change. However, disintegration of crystal order due to the molecular motion may make structural investigation difficult. Recently, by using the structure determination from powder diffraction data (SDPD) technique, the study of dynamic structural phenomena is possible using X-rays. In this chapter, three such crystal structure rearrangements, which can only be revealed by the SDPD technique, are reviewed. They are the dehydration and hydration mechanism of pharmaceutical crystals, organic Vapor-Induced dehydration and polymorphic structure change, and photochemical reaction in organic crystal.