Organic Vapor‐Induced Microscopic Behaviors in Molecular Crystals

ABSTRACT Understanding and controlling the phase transitions of molecular crystals remain one of the most challenging, important issues in molecular science and technology. In this study, confocal laser microscopy and single‐crystal X‐ray diffraction were used together to observe an organic vapor‐induced single‐crystal‐to‐single‐crystal phase transition of fac ‐[Re(CO) 3 Br(ppt)] (ppt = 2‐pyridyl‐4‐phenylthiazole) crystals. The inclusion of CHCl 3 vapor molecules induced dynamic, microscopic, cooperative single‐crystal‐to‐single‐crystal phase transition processes in > 50 µm‐sized non‐solvated crystals. CHCl 3 vapor exposure caused recrystallization of 2–10 µm‐sized crystals, whereas CHCl 3 vapor‐induced deliquescence was observed for ≤2 µm‐sized crystals. These findings deepen scientific understanding of solid‐state phase transitions at the molecular level.