Ajibade Saheed A, Catalano Luca, Kölbel Johanna, Mittleman Daniel M, Ruggiero Michael T
Department of Chemistry, University of Vermont, Burlington, Vermont 05405, United States.
Department of Chemistry, University of Rochester, Rochester, New York 14627, United States.
J Phys Chem Lett. 2024 May 23;15(20):5549-5555. doi: 10.1021/acs.jpclett.4c00706. Epub 2024 May 16.
Porous materials, particularly metal-organic frameworks (MOFs), hold great promise for advanced applications. MIL-53(Al) is an exceptionally well-studied MOF that exhibits a phase transition upon guest capture─in this case, water─resulting in a dramatic change in the pore volume. Despite extensive studies, the structure of the water-loaded narrow-pore phase, MIL-53(Al)-, remains controversial, particularly with respect to the positions of the adsorbed water molecules. We use terahertz spectroscopy, coupled with powder X-ray diffraction and density functional theory simulations, to unambiguously resolve this controversy. We show that the low-frequency (<100 cm) vibrational spectrum depends on weak long-range forces that are extremely sensitive to the orientation of the adsorbed water molecules. This enables definitively determining the correct structure of MIL-53(Al)- while highlighting the extreme sensitivity of terahertz spectroscopy to bulk structure, suggesting its potential as a robust complement to X-ray diffraction for precise characterization of host-guest complexes.
多孔材料，特别是金属有机框架材料（MOFs），在先进应用方面具有巨大潜力。MIL-53(Al)是一种经过深入研究的MOF，它在捕获客体（在此情况下为水）时会发生相变，导致孔体积发生显著变化。尽管进行了广泛研究，但负载水的窄孔相MIL-53(Al)-的结构仍存在争议，特别是关于吸附水分子的位置。我们使用太赫兹光谱，结合粉末X射线衍射和密度泛函理论模拟，来明确解决这一争议。我们表明，低频（<100 cm）振动光谱取决于对吸附水分子取向极为敏感的弱长程力。这使得能够确定MIL-53(Al)-的正确结构，同时突出了太赫兹光谱对整体结构的极端敏感性，表明其作为X射线衍射的有力补充用于主客体复合物精确表征的潜力。
