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Molecules 2014, 19(7), 10137-10149; doi:10.3390/molecules190710137
Article

First Order Temperature Dependent Phase Transition in a Monoclinic Polymorph Crystal of 1,6-Hexanedioic Acid: An Interpretation Based on the Landau Theory Approach

1,2,* , 3,*  and 1
1 Crystallography Unit, School of Physics, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia 2 Department of Pharmaceutical Chemistry, College of Pharmacy, King Saud University, Riyadh 11451, Kingdom of Saudi Arabia 3 Department of Chemistry, Faculty of Science, Prince of Songkla University, Hat-Yai, Songkhla 90112, Thailand
* Authors to whom correspondence should be addressed.
Received: 28 May 2014 / Revised: 1 July 2014 / Accepted: 8 July 2014 / Published: 11 July 2014
(This article belongs to the Section Molecular Diversity)
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Abstract

Crystals of 1,6-hexanedioic acid (I) undergo a temperature-dependent reversible phase transition from monoclinic P21/c at a temperature higher than the critical temperature (Tc) 130 K to another monoclinic P21/c at temperature lower than Tc. The phase transition is of first order, involving a discontinuity and a tripling of the b-axis at Tc whereas the other unit cell parameters vary continuously. The transition is described by the phenomenological Landau theory. The crystal structure analyses for data collected at 297(2) K and 120.0(1) K show that there is half of a molecule of (I) in the asymmetric unit at 297(2) K whereas there are one and a half molecules of (I) in the asymmetric unit at 120.0(1) K. At both temperatures, 297(2) and 120.0(1) K, intermolecular O-H···O hydrogen bonds link the molecules of I into infinite 1D chains along [101] direction. However there are significantly more O-H···O hydrogen bonds presented in the 120.0(1) K polymorph, thereby indicating this phase transition is negotiated via hydrogen bonds. The relationship of the conformational changes and hydrogen bonding for these two polymorphs are explained in detail.
Keywords: adipic acid; crystal structure; Landau theory; phase-transition adipic acid; crystal structure; Landau theory; phase-transition
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).

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Fun, H.-K.; Chantrapromma, S.; Ong, L.-H. First Order Temperature Dependent Phase Transition in a Monoclinic Polymorph Crystal of 1,6-Hexanedioic Acid: An Interpretation Based on the Landau Theory Approach. Molecules 2014, 19, 10137-10149.

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