The role of phonons in switchable MOFs: a model material perspective

Hoffman, Alexander E. J.; Senkovska, Irena; Abylgazina, Leila; Bon, Volodymyr; Grzimek, Veronika; Dominic, Anna Maria; Russina, Margarita; Kraft, Marvin; Weidinger, Inez M.; Zeier, Wolfgang G.; Speybroeck, Véronique Van; Kaskel, Stefan

doi:10.1039/d3ta02214e

Cited by 6 publications

(4 citation statements)

References 74 publications

(126 reference statements)

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“…All materials exhibiting NGA thus far are isoreticular and extremely structurally complex: the “parent” DUT-49 compound, with 1728 atoms per cubic unit cell of length 46.6 Å, is large enough to make systematic calculations, beyond relaxed structure and energetic, unfeasible. For example, harmonic vibration modes, second-order elastic tensor, and other linear response properties frequently used in the characterization of soft porous crystals are not readily accessible . This is a strong limitation for the application of DFT-based methodology that is generally considered the most comprehensive available for the computational characterization of crystalline materials.…”

Section: Resultsmentioning

confidence: 99%

“…For example, harmonic vibration modes, second-order elastic tensor, and other linear response properties frequently used in the characterization of soft porous crystals are not readily accessible. 12 This is a strong limitation for the application of DFT-based methodology that is generally considered the most comprehensive available for the computational characterization of crystalline materials.…”

Section: How Do Linkers Buckle? a Microscopic Viewmentioning

confidence: 99%

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Challenges and Opportunities of Molecular Simulations for Negative Gas Adsorption

Evans,

Coudert

2024

Acc. Mater. Res.

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Metrics & MoreArticle Recommendations CONSPECTUS: Negative gas adsorption (NGA) is a particularly eye-catching phenomenon, involving the spontaneous desorption of gas upon pressure increase during adsorption in a flexible nanoporous material. The material undergoes a structural transition from an "open-pore" phase to a contracted "closedpore" phase upon gas adsorption, leading to macroscopic gas desorption visible to the naked eye. It was initially evidenced experimentally in 2016 for the adsorption of methane and n-butane in the DUT-49 metal−organic framework (DUT = Dresden University of Technology) and later demonstrated to be a general phenomenon, occurring for different gases and in a variety of materials with the same topology. NGA materials belong to the category of metamaterials, displaying behavior that is not found (or rarely observed) in "natural" or simple materials. The negative adsorption transition takes place outside of thermodynamic equilibrium, and its characterization requires the use of many complementary experimental techniques (adsorption measurements, in situ X-ray diffraction, EXAFS, NMR, etc.), as well as molecular simulation techniques. In order to obtain a full and consistent picture of the NGA phenomenon, it is indeed necessary to combine computational modeling with a variety of methods, at different scales, in order to understand the microscopic behavior of the host framework and guest molecules to the macroscopic experimental results. At the smallest scale, density functional theory calculations have been used to understand the energetics and structure of the NGA materials, as well as the micromechanical properties of their organic linkers: the buckling of these linkers explains the large metastability of the open-pore phase and gives rise to the NGA transition. At a larger scale, classical grand canonical Monte Carlo simulations in the "rigid host" structures can predict the adsorption capacity of different phases, elucidating the driving force behind the structural transition. To explicitly couple the flexibility of the framework and the adsorption of guest molecules, molecular dynamics simulations (relying on a classical force field for the flexible metal−organic framework) can be coupled with free energy methods to investigate the thermodynamics of NGA, obtaining free energy profiles that determine the relative stability of different phases with varying amounts of adsorbed gas. Finally, mesoscopic-scale modeling methods are required in order to understand the phenomenon at a scale larger than one unit cell and explain experimental findings about the influence of crystal size effects on the NGA transition. This Account summarizes the computational approaches that have been used so far to better understand negative gas adsorption and highlights open questions and perspectives in this field of research.

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Section: Resultsmentioning

confidence: 99%

Section: How Do Linkers Buckle? a Microscopic Viewmentioning

confidence: 99%

Challenges and Opportunities of Molecular Simulations for Negative Gas Adsorption

Evans,

Coudert

2024

Acc. Mater. Res.

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“…Studies on structural phase transitions and various physical and chemical properties of the DUT-8(Ni) framework, as well as its lattice dynamics, were carried out earlier in many works. − DUT-8 with different metal ions, like other switchable MOFs, belong to third-generation materials in which structural transformation is accompanied by switching between metastable phases. The combination of different metal ions and organic ligands gives freedom to both structural and physical properties (such as spin, charge, or photonic properties), and different elastic factors can represent a synergistic effect on the porous structure.…”

Section: Introductionmentioning

confidence: 99%

Theoretical Insights into the Mechanical Properties of DUT-8(Ni) MOF in the Open and Closed Pore Phases

Yushina,

Matveychuk,

Krylov

2024

Crystal Growth & Design

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Insights into the mechanical properties of DUT-8(Ni) MOF crystals capable of structural phase transitions are presented. The open and closed pore phases of DUT-8(Ni) are drastically different in their mechanical behavior. For the openpore phase, a huge anisotropy of compressibility and shear modulus is observed, caused by the presence of two orthogonal motives formed by aromatic linkers bound with Ni atoms via Ni− O bonds. The possibility of easy shifting of linkers with breaking and formation of new Ni−O and Ni−N bonds at the application of shear stress, which is at the same time more stable at uniaxial stress, is shown on the basis of the stiffness tensor analysis. This fact assumes the flexibility of the open-pore phase crystals and their ability for structural transformation. The less prominent anisotropy of elastic moduli and the increased values of these moduli for the closed-pore phase crystals indicate the predominantly hardness and absence of flexibility of this phase.

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“…Lattice dynamics serves as a pivotal component in elucidating the dynamic and thermodynamic properties of materials, including thermal conductivity, − thermal expansion, − heat capacity, vibrational energy and entropy, and characteristics related to structural phase transformations. − The concept of phonons, as an analogue of vibrational modes in molecules, has been introduced as correlated vibrations of atoms in crystalline materials. Phonons are described as collective, quantized lattice vibrations, providing a framework for understanding the dynamics within solid materials .…”

Section: Introductionmentioning

confidence: 99%

Correlating Phonons and Deformations: A Method for Structural Phase Transformation Analysis in Metal–Organic Frameworks

Formalik,

Fischer,

Kuchta

2023

Crystal Growth & Design

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The role of phonons in switchable MOFs: a model material perspective

Abstract: The large cell volume changes of switchable metal-organic frameworks (MOFs) render them as promising functional materials. Low-frequency phonon modes are known to influence the dynamic response of these materials. The...

Cited by 6 publications

References 74 publications

Challenges and Opportunities of Molecular Simulations for Negative Gas Adsorption

Challenges and Opportunities of Molecular Simulations for Negative Gas Adsorption

Theoretical Insights into the Mechanical Properties of DUT-8(Ni) MOF in the Open and Closed Pore Phases

Correlating Phonons and Deformations: A Method for Structural Phase Transformation Analysis in Metal–Organic Frameworks

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