B. B. Hassine, P. Négrier, M. Barrio
Jul 8, 2015
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Journal
Crystal Growth & Design
Abstract
The polymorphism of 1-adamantane-methanol C11H18O has been investigated by differential thermal analysis and single-crystal and powder X-ray diffraction. Below the melting temperature (389.5 ± 0.4 K), this compound exhibits an orthorhombic phase (phase I, Pnnm, Z = 12, Z′ = 1.5). The melting enthalpy was determined to be 20.5 ± 0.4 kJ mol–1, i.e., with an entropy change of (6.34 ± 0.13)R, which is much higher than the quoted value from Timmermans for the melting orientationally disordered phases (2.5R), thus supporting the orientationally ordered character of phase I. This orthorhombic phase I exhibits a statistical disorder of the hydrogen atom related to the oxygen atom, due to the position of one independent molecule on the mirror. At ca. 272 K, phase I transforms continuously through an order–disorder transition to a low-temperature monoclinic phase II (P21/n, Z = 12, Z′ = 3). The monoclinic and orthorhombic phases are related by a group–subgroup relationship, which perfectly agrees with the continuou...