3 research outputs found
Polymorphism in HalogenāEthane Derivatives: CCl<sub>3</sub>āCF<sub>2</sub>Cl and CF<sub>3</sub>āCF<sub>2</sub>Cl
Molecular crystals of halogenāethane derivatives
C<sub>2</sub>X<sub>6ā<i>n</i></sub>Y<sub><i>n</i></sub> (X = Cl, Y = F) are known to display orderādisorder
phase
transitions involving changes of the translational, orientational,
and conformational order. The appearance of a high-temperature orientationally
disordered phase with a high symmetry lattice is expected for this
set of compounds in view of their āpseudosphericalā
molecular geometry. In this work, we present a study of polymorphism
of the compounds 1,1,1,2-tetrachloro-2,2-difluoroethane (CCl<sub>3</sub>āCF<sub>2</sub>Cl) and 1-chloro-1,1,2,2,2-pentafluoroethane
(CF<sub>3</sub>āCF<sub>2</sub>Cl), in which conformational
disorder is not present, by combining neutron (D2B and D1B instruments
at the Laue-Langevin Institute) and X-ray scattering experiments.
We show that despite the close molecular shapes and molecular structures
of both compounds, strong differences concerning the disorder appear
in the low-temperature phase. The low-temperature phase for CF<sub>3</sub>āCF<sub>2</sub>Cl is found to be fully ordered, with
a monoclinic <i>P</i>2<sub>1</sub>/<i>n</i> structure
(<i>Z</i> = 4), while that of CCl<sub>3</sub>āCF<sub>2</sub>Cl is found to be orthorhombic <i>Pmna</i> (<i>Z</i> = 4) with a disorder concerning one Cl and one F sites,
each one with a fractional occupancy of 50%. Details related to the
high-temperature orientationally disordered phases (both body-centered-cubic)
are also given
Polymorphism in HalogenāEthane Derivatives: CCl<sub>3</sub>āCF<sub>2</sub>Cl and CF<sub>3</sub>āCF<sub>2</sub>Cl
Molecular crystals of halogenāethane derivatives
C<sub>2</sub>X<sub>6ā<i>n</i></sub>Y<sub><i>n</i></sub> (X = Cl, Y = F) are known to display orderādisorder
phase
transitions involving changes of the translational, orientational,
and conformational order. The appearance of a high-temperature orientationally
disordered phase with a high symmetry lattice is expected for this
set of compounds in view of their āpseudosphericalā
molecular geometry. In this work, we present a study of polymorphism
of the compounds 1,1,1,2-tetrachloro-2,2-difluoroethane (CCl<sub>3</sub>āCF<sub>2</sub>Cl) and 1-chloro-1,1,2,2,2-pentafluoroethane
(CF<sub>3</sub>āCF<sub>2</sub>Cl), in which conformational
disorder is not present, by combining neutron (D2B and D1B instruments
at the Laue-Langevin Institute) and X-ray scattering experiments.
We show that despite the close molecular shapes and molecular structures
of both compounds, strong differences concerning the disorder appear
in the low-temperature phase. The low-temperature phase for CF<sub>3</sub>āCF<sub>2</sub>Cl is found to be fully ordered, with
a monoclinic <i>P</i>2<sub>1</sub>/<i>n</i> structure
(<i>Z</i> = 4), while that of CCl<sub>3</sub>āCF<sub>2</sub>Cl is found to be orthorhombic <i>Pmna</i> (<i>Z</i> = 4) with a disorder concerning one Cl and one F sites,
each one with a fractional occupancy of 50%. Details related to the
high-temperature orientationally disordered phases (both body-centered-cubic)
are also given
Polymorphism in HalogenāEthane Derivatives: CCl<sub>3</sub>āCF<sub>2</sub>Cl and CF<sub>3</sub>āCF<sub>2</sub>Cl
Molecular crystals of halogenāethane derivatives
C<sub>2</sub>X<sub>6ā<i>n</i></sub>Y<sub><i>n</i></sub> (X = Cl, Y = F) are known to display orderādisorder
phase
transitions involving changes of the translational, orientational,
and conformational order. The appearance of a high-temperature orientationally
disordered phase with a high symmetry lattice is expected for this
set of compounds in view of their āpseudosphericalā
molecular geometry. In this work, we present a study of polymorphism
of the compounds 1,1,1,2-tetrachloro-2,2-difluoroethane (CCl<sub>3</sub>āCF<sub>2</sub>Cl) and 1-chloro-1,1,2,2,2-pentafluoroethane
(CF<sub>3</sub>āCF<sub>2</sub>Cl), in which conformational
disorder is not present, by combining neutron (D2B and D1B instruments
at the Laue-Langevin Institute) and X-ray scattering experiments.
We show that despite the close molecular shapes and molecular structures
of both compounds, strong differences concerning the disorder appear
in the low-temperature phase. The low-temperature phase for CF<sub>3</sub>āCF<sub>2</sub>Cl is found to be fully ordered, with
a monoclinic <i>P</i>2<sub>1</sub>/<i>n</i> structure
(<i>Z</i> = 4), while that of CCl<sub>3</sub>āCF<sub>2</sub>Cl is found to be orthorhombic <i>Pmna</i> (<i>Z</i> = 4) with a disorder concerning one Cl and one F sites,
each one with a fractional occupancy of 50%. Details related to the
high-temperature orientationally disordered phases (both body-centered-cubic)
are also given