Conformational Polymorphism: The Missing Phase of 1,1,2,2-Tetrachloroethane (Cl<sub>2</sub>HC–CHCl<sub>2</sub>)

Negrier, Ph.; Barrio, Marı́a; Tamarit, J. Ll.; Mondieig, D.; Zuriaga, Mariano; Pérez, S.C.

doi:10.1021/cg400235b

Cited by 19 publications

(26 citation statements)

References 40 publications

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“…The experimental volume and the perfect crystalline structure determined by X-ray diffraction were used as initial configuration. 15,16 The system was formed by 800 molecules (6400 atoms), and some tests with a larger system of 6400 molecules (51200 atoms) were done in order to discard finite-size effects. Runs of 7 20000 ps were done, taking averages over the last 5000 ps.…”

Section: Molecular Simulationsmentioning

confidence: 99%

“…17 At ambient pressure, the thermodynamically stable phase of TCE below 231 K is orthorhombic (P2 1 2 1 2 1 , Z = 8, Z' = 2), with all the molecules in the gauche + conformation. 15,16 A metastable solid form is known, which is obtained by recrystallization upon heating the structural glass obtained by rapid cooling of the liquid, and which is observed in a limited temperature range; this metastable phase was found to be monoclinic (P2 1 /c) with Z = 8 molecules in the unit cell and Z' = 2 in the asymmetric unit, with both gauche + and gaucheconformers coexisting in the asymmetric unit. 16 Finally, at high pressures (above 0.5 4 GPa at room temperature) the stable phase is a monoclinic phase (P2 1 /c, Z = 2, Z' = 0.5) in which all molecules are in the trans conformation.…”

Section: Introductionmentioning

confidence: 99%

“…15,16 A metastable solid form is known, which is obtained by recrystallization upon heating the structural glass obtained by rapid cooling of the liquid, and which is observed in a limited temperature range; this metastable phase was found to be monoclinic (P2 1 /c) with Z = 8 molecules in the unit cell and Z' = 2 in the asymmetric unit, with both gauche + and gaucheconformers coexisting in the asymmetric unit. 16 Finally, at high pressures (above 0.5 4 GPa at room temperature) the stable phase is a monoclinic phase (P2 1 /c, Z = 2, Z' = 0.5) in which all molecules are in the trans conformation. 15 Molecular reorientational dynamics were reported in the orthorhombic phase consisting only of gauche + conformers, where a full assignment of the dynamics was so far not possible, 18 and in the high-pressure monoclinic phase, where the trans conformers undergo rotational motions in which the C-C bond changes its spatial orientation while the chlorine atoms interchange their positions in the crystal structure (in what could be termed a "positional-exchange" reorientation).…”

Section: Introductionmentioning

confidence: 99%

“…15,16 Under ambient conditions TCE is liquid and consists both of gauche and trans isomers, with the gauche conformers being slightly more stable than the trans one. 17 At ambient pressure, the thermodynamically stable phase of TCE below 231 K is orthorhombic (P2 1 2 1 2 1 , Z = 8, Z' = 2), with all the molecules in the gauche + conformation.…”

Section: Introductionmentioning

confidence: 99%

“…The capacitor was then loaded within a nitrogen-gas flow cryostat for temperature control. To obtain the orthorhombic phase of (1,1,2,2)tetrachloroethane, the sample was cooled down to 130 K and then warmed up to below 230 K to avoid melting of the solid phase, 16 and isothermal spectra were then taken always below this temperature.Isothermal dielectric spectra were acquired using a Novocontrol Alpha analyzer in the frequency (f) range between 10 -2 and 5•10 6 Hz. The imaginary part ε"(f) of the complex permittivity, called dielectric loss spectrum, carries information on the dipolar molecular dynamics processes taking place in the sample, with processes of distinct origin appearing in different characteristic frequency ranges.…”

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confidence: 99%

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Orientational relaxations in solid (1,1,2,2)tetrachloroethane

Tripathi

Mitsari

Romanini

et al. 2016

The Journal of Chemical Physics

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We employ dielectric spectroscopy and molecular dynamic simulations to investigate the dipolar dynamics in the orientationally disordered solid phase of (1,1,2,2)tetrachloroethane. Three distinct orientational dynamics are observed as separate dielectric loss features, all characterized by a simply activated temperature dependence. The slower process, associated to a glassy transition at 156±1 K, corresponds to a cooperative motion by which each molecule rotates by 180º around the molecular symmetry axis through an intermediate state in which the symmetry axis is oriented roughly orthogonally to the initial and final states. Of the other two dipolar relaxations, the intermediate one is the Johari-Goldstein precursor relaxation of the cooperative dynamics, while the fastest process corresponds to an orientational fluctuation of single molecules into a higher-energy orientation. The Kirkwood correlation factor of the cooperative relaxation is of the order of one tenth, indicating that the molecular dipoles maintain on average a strong antiparallel alignment during their collective motion. These findings show that the combination of dielectric spectroscopy and molecular simulations allows studying in great detail the orientational dynamics in molecular solids. 2 INTRODUCTIONWhile conventional (atomic) solids are made of atomic constituents with only translational degrees of freedom, so that their structure is totally determined by translation symmetry and fundamental excitations are vibrational in character, in molecular solids the constituent molecules possess also orientational (as well as internal) degrees of freedom, which lead to a richer variety of possible solid phases and to the existence of rotational excitations such as librations and orientational relaxations. A molecular solid can display complete translational and rotational order, as in a molecular crystal, or complete rototranslational disorder, as in a molecular glass. In between these two extremes, molecular solids also display phases (known as Orientationally disordered (OD) phases are generally formed by relatively small globular molecules such as derivatives of methane, 1,2,3 neopentane, 4 adamantane 5 or fullerene, 6 or by small linear ones such as ethane derivatives 7,8,9 and dinitriles. 10 OD solids exhibit many of the phenomenological features of glass formers, displaying in particular a cooperative rotational motion, called α relaxation, that undergoes a continuous, dramatic slow-down upon cooling, 11,12 leading in some cases to a glass-like 3 transition associated with rotational freezing. 13,14 Contrary to structural glasses, which do not exhibit any long-range order, OD phases are characterized by a translationally ordered structure and can therefore be more thoroughly characterized with the help of methods that exploit the translational symmetry such as Bragg diffraction, lattice models, or solid-state NMR spectroscopy. Even more importantly, since as mentioned OD phases are generally formed by molecular species with a simple structure ...

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Section: Molecular Simulationsmentioning

confidence: 99%