Simulation Meets Experiment: Unraveling the Properties of Water in Metal-Organic Frameworks Through Vibrational Spectroscopy

<div> <div> <div> <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 (D₂O) adsorbed in the pores, disentangling the fundamental framework–water and water–water interactions. The experimental IR spectrum of D₂O in ZIF-90 displays a blue-shifted OD-stretch band compared to liquid D₂O. The analysis of the IR spectra simulated at both classical and quantum levels indicates that the D₂O 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> </div> </div> </div>

Simulation Meets Experiment: Unraveling the Properties of Water in Metal-Organic Frameworks Through Vibrational Spectroscopy

<div> <div> <div> <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 (D₂O) adsorbed in the pores, disentangling the fundamental framework–water and water–water interactions. The experimental IR spectrum of D₂O in ZIF-90 displays a blue-shifted OD-stretch band compared to liquid D₂O. The analysis of the IR spectra simulated at both classical and quantum levels indicates that the D₂O 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> </div> </div> </div>

Understanding Fermi resonances in the complex vibrational spectra of the methyl groups in methylamines

Vibrational spectra of the methyl groups in mono-methylamine (MMA), dimethylamine (DMA), and trimethylamine (TMA) monomers and their clusters were measured to capture their spectral features as a result of bend/umbrella-stretch Fermi resonance (FR).

Криоспектроскопическое исследование резонансных мультиплетов ν-=SUB=-s-=/SUB=- ~2ν-=SUB=-b-=/SUB=- в молекуле CHF-=SUB=-3-=/SUB=-

The sequences of Fermi resonances vs~2vb in the IR spectrum of a solution of fluoroform (CHF3) in liquefied krypton are investigated. Here vs is the CH stretching vibration, vb is the bending vibration. It is shown that for a correct description of resonance multiplets (polyads) at a high degree of vibrational excitation, it is necessary to use an extended set of spectroscopic parameters. In particular, it is necessary to take into account the dependence of the anharmonic interaction constant asbb on the vibrational quantum numbers. The conclusions are generalized for the arbitrary case of the CH-chromophore CHX3.