Al Rahal Okba, Kariuki Benson M, Hughes Colan E, Williams P Andrew, Xu Xiaoyan, Gaisford Simon, Iuga Dinu, Harris Kenneth D M
School of Chemistry, Cardiff University, Park Place, Cardiff, Wales CF10 3AT, U.K.
Department of Pharmaceutics, School of Pharmacy, University College London, 29-39 Brunswick Square, London, England WC1N 1AX, U.K.
Cryst Growth Des. 2023 Apr 12;23(5):3820-3833. doi: 10.1021/acs.cgd.3c00223. eCollection 2023 May 3.
Phase transitions in crystalline molecular solids have important implications in the fundamental understanding of materials properties and in the development of materials applications. Herein, we report the solid-state phase transition behavior of 1-iodoadamantane (1-IA) investigated using a multi-technique strategy [synchrotron powder X-ray diffraction (XRD), single-crystal XRD, solid-state NMR, and differential scanning calorimetry (DSC)], which reveals complex phase transition behavior on cooling from ambient temperature to ca. 123 K and on subsequent heating to the melting temperature (348 K). Starting from the known phase of 1-IA at ambient temperature (phase ), three low-temperature phases are identified (phases , , and ); the crystal structures of phases and are reported, together with a re-determination of the structure of phase . Remarkably, single-crystal XRD shows that some individual crystals of phase transform to phase , while other crystals of phase transform instead to phase . Results (from powder XRD and DSC) on cooling a powder sample of phase are fully consistent with this behavior while also revealing an additional transformation pathway from phase to phase . Thus, on cooling, a powder sample of phase transforms partially to phase (at 229 K), partially to phase (at 226 K) and partially to phase (at 211 K). During the cooling process, each of the phases , , and is formed from phase , and no transformations are observed phases , , and . On heating the resulting triphasic powder sample of phases , , and from 123 K, phase transforms to phase (at 211 K), followed by the transformation of phase to phase (at 255 K), and finally, phase transforms to phase (at 284 K). From these observations, it is apparent that different crystals of phase , which are ostensibly identical at the level of information revealed by XRD, must actually differ in other aspects that significantly influence their low-temperature phase transition pathways. This unusual behavior will stimulate future studies to gain deeper insights into the specific properties that control the phase transition pathways in individual crystals of this material.
结晶分子固体中的相变对于深入理解材料特性以及材料应用的发展具有重要意义。在此,我们报告了采用多技术策略[同步辐射粉末X射线衍射(XRD)、单晶XRD、固态核磁共振以及差示扫描量热法(DSC)]对1-碘代金刚烷(1-IA)固态相变行为的研究,该研究揭示了从室温冷却至约123 K以及随后加热至熔点(348 K)过程中复杂的相变行为。从室温下1-IA的已知相(相α)开始,确定了三个低温相(相β、相γ和相δ);报告了相β和相γ的晶体结构,以及对相α结构的重新测定。值得注意的是,单晶XRD表明,相α的一些单晶转变为相β,而相α的其他晶体则转变为相γ。(粉末XRD和DSC)对相α粉末样品冷却的结果与这种行为完全一致,同时还揭示了从相α到相δ的另一条转变途径。因此,在冷却时,相α的粉末样品部分转变为相β(在229 K),部分转变为相γ(在226 K),部分转变为相δ(在211 K)。在冷却过程中,相β、相γ和相δ均由相α形成,未观察到相β、相γ和相δ之间的转变。将所得的相β、相γ和相δ的三相粉末样品从123 K加热时,相δ在211 K转变为相γ,随后相γ在255 K转变为相β,最后,相β在284 K转变为相α。从这些观察结果可以明显看出,相α的不同晶体,在XRD揭示的信息层面上看似相同,但实际上在其他方面必定存在差异,这些差异显著影响它们的低温相变途径。这种不寻常的行为将激发未来的研究,以更深入地了解控制该材料单个晶体中相变途径的具体特性。