Issue 5, 2019

Mapping the polymorphic transformation gateway vibration in crystalline 1,2,4,5-tetrabromobenzene

Abstract

The thermosalient behavior of 1,2,4,5-tetrabromobenzene (TBB) is related to a temperature-induced polymorphic structural change. The mechanism behind the phase transition has been investigated in this work using low-frequency (10–250 cm−1) Raman spectroscopy and solid-state density functional theory simulations. Careful adjustments of the probing laser power permitted thermal control of the polymorph populations and enabled high-quality Raman vibrational spectra to be obtained for both the β (low temperature) and γ (high temperature) forms of TBB. Numerous well-defined vibrational features appear in the Raman spectra of both polymorphs which could be assigned to specific motions of the solid-state TBB molecules. It was discovered that the lowest-frequency vibration at 15.5 cm−1 in β-TBB at 291 K is a rotational mode that functions as a gateway for inducing the polymorphic phase transition to γ-TBB, and serves as the initiating step in the storage of mechanical strain for subsequent macroscopic release. Computationally mapping the potential energy surface along this vibrational coordinate reveals that the two TBB polymorphs are separated by a 2.40 kJ mol−1 barrier and that γ-TBB exhibits an enhanced cohesion energy that stabilizes its structure.

Graphical abstract: Mapping the polymorphic transformation gateway vibration in crystalline 1,2,4,5-tetrabromobenzene

Supplementary files

Article information

Article type
Edge Article
Submitted
31 Aug. 2018
Accepted
22 Nov. 2018
First published
23 Nov. 2018
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2019,10, 1332-1341

Mapping the polymorphic transformation gateway vibration in crystalline 1,2,4,5-tetrabromobenzene

A. J. Zaczek, L. Catalano, P. Naumov and T. M. Korter, Chem. Sci., 2019, 10, 1332 DOI: 10.1039/C8SC03897J

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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