title: Enantiotropically related polymorphs of gaboxadol hydrochloride.
abstract: Gaboxadol hydrochloride, also known as THIP hydrochloride (systematic name: 3-hydroxy-4,5,6,7-tetrahydro-1,2-oxazolo[5,4-c]pyridin-6-ium chloride), C6H9N2O2(+)·Cl(-), exists as two enantiotropically related polymorphs. Transformation between the polymorphs occurs in a single-crystal-to-single-crystal manner at 221 K, and the enthalpy of transformation from the high-temperature form to the low-temperature form is -0.7 kJ mol(-1). Single-crystal structures have been determined at 298 and 220 K. At 298 K, the structure is triclinic (space group P overline 1), with two formula units in the crystallographic asymmetric unit. At 220 K, the structure is monoclinic (space group I2/a), with one formula unit in the asymmetric unit. The structures contain identical hydrogen-bonded layers and the transformation between the polymorphs corresponds to a shift of adjacent layers relative to each other. The transformation is shown to be reversible by differential scanning calorimetry and variable-temperature powder X-ray diffraction.
authors.affiliation: H. Lundbeck A/S, Ottiliavej 9, DK-2500 Valby, Denmark.
authors.forename: Heidi
authors.initials: H
authors.lastname: Lopez de Diego
authors.forename: Vishal
authors.initials: V
authors.lastname: Koradia
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Bond
mesh_terms: D003460:Crystallization; D007555:Isoxazoles / Q000737:chemistry*; D008958:Models, Molecular; D013696:Temperature; D014961:X-Ray Diffraction
chemical_list: D007555:Isoxazoles; C015542:gaboxadol
keywords: THIP hydrochloride; crystal structure; enantiotropically related polymorphs; gaboxadol hydrochloride; phase transition