The structure of solid carbon tetrafluoride

Abstract

The structure of phase II of CF 4 has been refined in the monoclinic space group C2/n (No. 15) from high-resolution powder neutron diffraction data. At 1.5 Κ the lattice parameters are a = 8.4098(2) Â, b = 4.3022(1) A, c = 8.3506(2) Â, and β = 119.588(1)°, Ζ = 4. An error in the table of coordinates in the original report of the structure, which was improperly corrected in a subsequent paper, has been rectified. The refined structure of phase II is in excellent agreement with recent theoretical calculations of the crystal static energy and molecular dynamics simulations. The unit cell of the orientationally disordered phase I has been indexed as rhombohedral, a = 11.577(9) Â, α = 89.49(1)° at 80 K. It is likely that this phase is isostructural with phase lb of CC1 4 .

W(CO)6 in cryogenic solids: A comparative study of vibrational properties

“…In order to probe another crystallographic environment with molecular "spher- is a well-ordered crystal and the lattice structure changes to monoclinic [24].…”

The origin of diffuse scattering in crystalline carbon tetraiodide

“…Among the crystalline CX 4 halides that do not contain iodine (CF 4 , CCl 4 , CBr 4 ), monoclinic (CF 4 [1,2,3,4,5], CCl 4 [6] and CBr 4 [7]), face-centered cubic (CCl 4 [8] and CBr 4 [9]) and rhombohedral phases (CF 4 [4], CCl 4 [6] and CBr 4 [10]) are common. Over a long period of time, the structure of carbon tetraiodide has been debated; initially it was classified as cubic (see the reference of [11]) or monoclinic [12], analogous with the above carbon-tetrahalides.…”

“…Another interesting feature of this class of materials is the possible presence of plastic crystalline phases, appearing as the rhombohedral phase of carbon tetrafluoride [4], and the face centered cubic phases of carbon tetrachloride [6,21] and carbon tetrabromide [9]. The common feature of these phases is that while the centres of the molecules maintain translational (i.e., crystalline) symmetry, the molecules can rotate (for CF 4 , see [22]).…”

Phase Transition of Solid CF4 under High Pressure.

“…Below 89.5 K, it crystallizes into a disordered non-cubic plastic phase referred to as phase I [1]. At temperatures below 76.2 K, it transforms into well-ordered monoclinic phase referred to as phase II, whose crystal lattice is a C2/c one with four molecules per unit cell [2,3]. The crystal structure of the disordered phase I has been recently determined to be rhombohedral, which is isostructural with the phase lb of CC14 [3].…”