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<p>In nanoporous materials, guest–host interactions affect the properties and function of
both adsorbent and adsorbate molecules. Due to their structural and chemical diversity, metal-organic frameworks (MOFs), a common class of nanoporous materials, have
been shown to be able to efficiently and, often, selectively adsorb various types of guest
molecules. In this study, we characterize the structure and dynamics of water confined
in ZIF-90. Through the integration of experimental and computational infrared (IR) spectroscopy, we probe the structure of heavy water (D<sub>2</sub>O) adsorbed in the pores,
disentangling the fundamental framework–water and water–water interactions. The experimental IR spectrum of D<sub>2</sub>O in ZIF-90 displays a blue-shifted OD-stretch band
compared to liquid D<sub>2</sub>O. The analysis of the IR spectra simulated at both classical
and quantum levels indicates that the D<sub>2</sub>O molecules preferentially interact with the
carbonyl groups of the framework and highlights the importance of including nuclear
quantum effects and taking into account Fermi resonances for a correct interpretation
of the OD-stretch band in terms of the underlying hydrogen-bonding motifs. Through
a systematic comparison with the experimental spectra, we demonstrate that computational spectroscopy can be used to gain quantitative, molecular-level insights into
framework–water interactions that determine the water adsorption capacity of MOFs
as well as the spatial arrangements of the water molecules inside the MOF pores which,
in turn, are key to the design of MOF-based materials for water harvesting.</p>
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Crystalline metal-organic frameworks (MOFs): synthesis, structure and function