Polymorphism of CBr2Cl2

Maria Barrio; Josep Ll. Tamarit; Philippe Negrier; Luis C. Pardo; Nestor Veglio; Denise Mondieig

doi:10.1039/B708757H

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Polymorphism of CBr₂Cl₂†‡

Maria Barrio,^a Josep Ll. Tamarit,*^a Philippe Negrier,^b Luis C. Pardo,^a Nestor Veglio^a and Denise Mondieig^b

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* Corresponding authors

^a Departament de Física i Enginyeria Nuclear, E.T.S.E.I.B., Universitat Politècnica de Catalunya, Diagonal, 647 08028 Barcelona, Catalonia, Spain
E-mail: jose.luis.tamarit@upc.edu

^b Centre de Physique Moléculaire, Optique et Hertzienne, Université Bordeaux I-UMR 5798 au CNRS, 351, cours de la Libération, Talence Cedex, France

Abstract

The polymorphism of dibromodichloromehtane (CBr₂Cl₂) has been studied by means of a wide set of experimental techniques as a function of temperature and pressure. From the p–V–T diagram and the derived p–T diagram the volume variations at the transition points have been calculated and compared with those obtained by means of X-ray and neutron powder diffraction. By combining the experimental techniques, it has been demonstrated the existence of a high-pressure orientationally disordered rhombohedral phase (a^R ≈ 14.6 ± 0.3 Å and α ≈ 89.2 ± 0.2°). The existence of a glass transition within the monoclinic (C2/c, Z = 32) low-temperature ordered phase associated with the freezing of exchange positions between Cl and Br atoms is analyzed considering the asymmetry of the intermolecular interactions by means of the study of the thermal expansion tensor. The change of the derivative of the aspherism index, previously reported as a possible “fingerprint” for this kind of glass transitions, is found.

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Article information

DOI: https://doi.org/10.1039/B708757H
Article type: Paper
Submitted: 11 Jun 2007
Accepted: 26 Sep 2007
First published: 05 Oct 2007

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New J. Chem., 2008,32, 232-239

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Polymorphism of CBr₂Cl₂

M. Barrio, J. Ll. Tamarit, P. Negrier, L. C. Pardo, N. Veglio and D. Mondieig, New J. Chem., 2008, 32, 232 DOI: 10.1039/B708757H

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