title: First order temperature dependent phase transition in a monoclinic polymorph crystal of 1,6-hexanedioic Acid: an interpretation based on the landau theory approach.
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.
authors.affiliation: Crystallography Unit, School of Physics, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia. hkfun.c@ksu.edu.sa.
authors.forename: Hoong-Kun
authors.initials: HK
authors.lastname: Fun
authors.affiliation: Department of Chemistry, Faculty of Science, Prince of Songkla University, Hat-Yai, Songkhla 90112, Thailand. suchada.c@psu.ac.th.
authors.forename: Suchada
authors.initials: S
authors.lastname: Chantrapromma
authors.affiliation: Crystallography Unit, School of Physics, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia.
authors.forename: Lye-Hock
authors.initials: LH
authors.lastname: Ong
mesh_terms: D000272:Adipates / Q000737:chemistry*; D006358:Hot Temperature; D008962:Models, Theoretical; D044367:Phase Transition
chemical_list: D000272:Adipates; C029900:adipic acid