Search

Dibromomethane, CH2Br2, and diiodomethane, CH2I2, have been in situ pressure-crystallized in a diamond–anvil cell and their structures determined by single-crystal X-ray diffraction at 0.61 and 0.16 GPa, respectively. The pressure-frozen CH2Br2 crystal is isostructural with its C2/ c phase obtained by cooling. CH2I2 is known to form several phases at low temperature, one of which is isostructural with CH2Br2. However, pressure freezing leads to the polar Fmm2 phase. The formation of the polar CH2I2 structure at 0.16 GPa has been rationalized by the electrostatic and anisotropic van der Waals interactions of the I atoms. No ferroelectric behaviour of the Fmm2 polar phase II of CH2I2 has been determined. The diffraction, calorimetric and dielectric constant studies reveal considerable temperature hysteresis of transformations between the CH2I2 phases, as well as metastable regions strongly dependent on the sample shape and history. [ABSTRACT FROM AUTHOR]

The structure of 1,2,3-trichloropropane, ClCH2CHClCH2Cl, in-situ crystallized in a diamond–anvil cell, has been determined by single-crystal X-ray diffraction at 0.28 and 0.35 GPa. A melting point at 295 K and 0.22 GPa has been determined. The molecular conformation of aliphatic chain and terminal Cl atoms is approximately C2 symmetric. Of the intermolecular contacts, the tightest are the Cl⋯Cl and then the Cl⋯H contacts, whereas the H⋯H distances are considerably longer than the sum of the van der Waals radii and leave narrow voids in the structure. The elevated pressure reduces the H⋯H separations but hardly affects the Cl⋯Cl distances. The crystal growth rates, compression and types of intermolecular interactions in the structures can be correlated with the directions of the Cl⋯Cl contacts, which can be considered the main motif responsible for the molecular arrangement in the structure. [ABSTRACT FROM AUTHOR]