| Abstract
| - Polar ordering has been induced by pressure in solid chloroform (trichloromethane), CHCl3, and bromoform (tribromomethane), CHBr3, obtained by isochoric and isothermal freezing in a diamond anvil cell. Structures of these new polymorphs have been determined by single-crystal X-ray diffraction, CHCl3 at 0.62 and 0.75 GPa and CHBr3 at 0.20 and 0.35 GPa. Despite different centrosymmetric structures of all low-temperature phases of CHCl3 (space group Pbcn) and CHBr3 (P63/m, P1̅, and P3̅), the high-pressure phases are isostructural in space group P63. The polar phase of CHBr3 is formed at 295 K, already at the freezing pressure of ∼0.1 GPa, while CHCl3 transforms from the Pbcn phase into the P63 phase between 0.62 and 0.75 GPa. It has been demonstrated that the electrostatic contribution to halogen···halogen and H···halogen interactions in the CHCl3 and CHBr3 molecular crystals is favorable for the polar aggregation and that this effect intensifies with increasing pressure.
|
