Crystal structures of dibromodichloromethane and bromotrichloromethane

Abstract

The neutron powder profiles for CBr2C12 and CBrC13 have been recorded at temperatures ranging from about 260 K to 5 K. The profiles at theo highest temperatures are consistent with fcc structures with a = 8.597(2) A and a = 8.526(2) A respectively. CBrC13 has a second plastic phase observed at 245 K. The remaining profiles, below 250 K for CBr2CI2, or below 225 K for CBrC13, can be analysed in terms of the C2/c space group with 2 = 32. This is the same as for the ordered phases of CBr4 and CC14. Orientational disorder of the molecules leads to the structural similarity of all members of the family, Tests for partial ordering were not successful.

Comparison of the atomic level structure of the plastic crystalline and liquid phases of CBr2Cl2: neutron diffraction and reverse Monte Carlo modelling

“…In this special phase the molecular centres are located in a highsymmetry lattice (face centered cubic, body centered cubic or rhombohedral), but the molecules can rotate around their equilibrium position. The three characteristic phases (ordered, plastic crystalline and liquid) have been studied extensively for each halomethane mentioned above [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16].…”

Monoclinic mixed crystals of halogenomethanes CBr4−nCln (n=0,…,4)

“…Next, the procedure was applied to CBrCl 3 and CBr 2 Cl 2 pure compounds, following the model used by Binbrek et al [6] which is briefly detailed. Structural parameters of CBr 4 were used as the starting point for the atomic coordinates of the four independent molecules in the asymmetric unit cell.…”

“…For the halogenomethanes with T d molecular symmetry, a high number of experimental and molecular dynamics simulation studies have been published [9 12,19,20,24] while for the compounds with lower symmetry (C 3V or C 2V ) only a few preliminary experiments have been done [6,7,23].…”

“…The crystal structures of the low-temperature phases of CBrCl 3 and CBr 2 Cl 2 were attempted by Binbrek et al [6] from neutron powder diffraction experiments. They described the structure of these phases on the basis of the hypothesis of the isostructural character of the low-temperature ordered phases for all four members of the CBr 4 n Cl n (n 0,. .…”

The plastic and liquid phases of CCl3Br studied by molecular dynamics simulations

“…Compounds with lower symmetry (C 3v or C 2v ) have attracted so far some attention from the experimental groups 12,[18][19][20] , but very little work has been done from a computational point of view. 21,22 The polymorphism of CCl 3 Br (C 3v molecular symmetry) has been studied by several methods such as calorimetry 18 and neutron scattering, 19 X-ray diffraction and densitometry 20 . The low-temperature phase III (monoclinic) transforms at 238 K to the OD phase II (rhombohedral).…”