The Crystal Structures of Methylene Dibromide and Methylene Diiodide

Abstract

The crystal structures of methylene dibromide and methylene diiodide (Form II) have been determined by the X-ray diffraction method at about −90°C and about −20°C respectively. Both the crystals are isomorphous, with monoclinic space group C2h6–C2/c. Unit cells containing eight molecules have these dimensions: a=12.239(12), b=4.459(15), c=15.212(16) Å, and β=113.54(7)° for methylene dibromide, and a=13.346(3), b=4.720(90), c=16.479(5) Å, and β=114.48(8)° for methylene diiodide. The orientations of the methylene groups have been obtained by lattice-energy calculations.

Crystal Structure and Spectroscopic Investigation of Bromofluoro‐ and Fluoroiodomethane

“…Two of the overall four CBr···Br angles are closer to a right angle [90.9(1)°and 122.5(1)°], whereas the other two C-Br···Br angles with 160.1(1)°and 167.4(1)°are rather close to 180°. Such contacts are also observed in the crystal structures of methyl bromide [16] and dibromomethane, [17] and they are indicative of a noncovalent bonding type (see below). [21,22] FIM crystallizes in the orthorhombic space group Abm2 with four units per unit cell.…”

“…The C-I bond length of 2.132(12) Å is in the region of C-I bond lengths observed for methyl iodide [2.13(6) Å] [16] and diiodomethane (2.12 Å). [17] The C-F bond length of 1.380 (18) Å is in the region typical of C-F single bonds. [18,19] Figure 3.…”

“…Such I···I interactions are also observed in the solid-state structures of methyl iodide [16] and diiodomethane. [17] Theoretical and experimental studies have shown that dispersion and polarization participate in the molecular interactions of dihalogenomethanes. [8] However, the halogen interactions are believed to be mainly controlled by electrostatics [23] and are Coulombic in nature.…”

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

“…The occurrence of two forms in the freezing region, and their small freezing-point difference of 0.5 K were carefully investigated by Stone (1932). Kawaguchi et al (1973) reported the structure of the monoclinic phase I at 253 K, while according to Torrie et al (1987) and to Prystupa et al (1989) this temperature is close to the phase transition, but on the side of phase II. It was confirmed that the cooling rate is a crucial factor for the transition temperatures (Torrie et al, 1987;Marzocchi et al, 1966) and coexistence of the phases (Prystupa et al, 1989).…”

“…The present study of pressurefrozen CH 2 Br 2 and CH 2 I 2 was aimed at establishing the highpressure structures of these compounds, and comparing them with the low-pressure phases and previously investigated dichloromethane (Podsiadło et al, 2005). The physical and chemical properties of solid dibromo-and diiodomethane have been studied using Raman and IR spectroscopy (Anderson et al, 1987;Brown et al, 1969;Marzocchi et al, 1966;Shimizu, 1985;Torrie et al, 1987;Zhou et al, 1996) and their crystal structures determined at low temperature (Kawaguchi et al, 1973;Prystupa et al, 1989). While the crystals of CH 2 Cl 2 and CH 2 Br 2 are believed to be monomorphic at ambient pressure, several phases of CH 2 I 2 have been observed.…”