Molecular interactions in crystalline dibromomethane and diiodomethane, and the stabilities of their high-pressure and low-temperature phases

Abstract

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.

Thermodynamic and Acoustic Properties of Mixtures of Dibromomethane + Heptane

“…Broken lines mark the shortest distances between the molecules. Picture generated using Mercury 2.3 program from the data reported in the Cambridge Structural Database [28] temperature and pressure [24]. Since the electrostatic potential is negative along the ring perpendicular to the C-Br bond and positive at the both ends beyond C and Br atoms [25], the C-H and C-Br bonds of the nearest-neighboring molecules are nearly perpendicular to one another rather than arranged in a line, while the dipole moments remain parallel (Fig.…”

High-pressure crystallography

“…On the other hand, these huge pressures are comparable to the intermolecular interactions in crystal structures. Molecular crystals are formed by a very large group of organic compounds and it has already been recognized that pressure is an efficient method of generating new polymorphs (Boldyreva, 1990(Boldyreva, , 2004Allan et al, 1998;Allan & Clark, 1999;Allan et al, 2002;Boldyreva, Shakhtshneider, Ahsbahs, Sowa & Uchtmann, 2002;Boldyreva et al, 2003;Fabbiani et al, 2005;Podsiadło et al, 2005Podsiadło et al, , 2006Gajda et al, 2006;Gajda & Katrusiak, 2007;Bujak et al, 2007) and binary systems characteristic for high-pressure conditions only (Loubeyre et al, 1993(Loubeyre et al, , 1994Loubeyre, 1996;Kuhs, 2004). The higher the pressure, the further-reaching are the structural modifications.…”

High-pressure diffraction studies of molecular organic solids. A personal view

“…Later, many examples were published in the papers by several groups (Fourme, 1968;Weir et al, 1969;Fourme et al, 1971;Allan et al, 1998;Allan & Clark, 1999a,b;Allan et al, 1999Allan et al, , 2001Allan et al, , 2002aKatrusiak et al, , 2007Podsiadło et al, 2005Podsiadło et al, , 2006Lozano-Casal et al, 2005;Gajda et al, 2005Gajda et al, , 2006Oswald, Allan, Day et al, 2005;Budzianowski et al, 2005;Budzianowski & Katrusiak, 2006a,b;Budzianowski et al, 2006;McGregor et al, 2006;Bujak et al, 2007;Dziubek et al, 2007;. Sometimes, the same polymorph is formed as a result of crystallization on cooling and with increasing pressure; examples are 1,2-dichloromethane (Podsiadło et al, 2005), and carbon disulfide .…”

“…The analysis of the high-pressure forms as compared to the lowtemperature ones, as well as of the anisotropy of compression of the crystals with increasing pressure, makes it possible to reveal the structures, in which the halogen-halogen interactions can be considered as the main cohesive forces responsible for the molecular arrangements (Podsiadło & Katrusiak, 2006;Bujak et al, 2007), and the structures in which halogenhalogen interactions are not attractive at all Gajda et al, 2006). Very interesting information was obtained for series of substituted dihalomethanes (CH 2 XY, where X, Y = Br, Cl, I), 1,2-dihalotetrafluoroethanes X(CF 2 ) 2 Y (X = Br, I; Y = Br, I) and dichloroacetic acid, which show clearly systematic isostructural relations resulting from the specific intermolecular interactions in their pressure-crystallized phases (Podsiadło et al, 2006;Katrusiak et al, 2007). Studies of the effect of pressure on the halogenated organic compounds could be compared with the effect of pressure on the electron lone pairs in inorganic oxides (Grzechnik et al, 2002;Dinnebier et al, 2003;Orosel et al, 2004).…”