Pressure‐Induced Amorphization of MOF‐5: A First Principles Study

Erkartal, Mustafa; Durandurdu, Murat

doi:10.1002/slct.201801381

Cited by 20 publications

(16 citation statements)

References 66 publications

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“…Distributions of (a) C–O P bond lengths and (b) O P –C–O P bond angles of the carboxylate group. Small variations in b (C–O P ) negate the possibility of bond-breaking, in agreement with the predictions of Erkartal et al (c) Zn–O bond lengths and (d) O–Zn–O bond angles of ZnO 4 tetrahedra, indicating topological disordering of structural units with ϵ h while maintaining the local coordination environment.…”

Section: Resultsmentioning

confidence: 99%

Flat Phonon Band-Based Mechanism of Amorphization of MOF-5 at Ultra-low Pressures

Bhogra

Waghmare

2021

J. Phys. Chem. C

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MOF-5 is a crystalline metal–organic framework (MOF) with large pore volume and exceptional thermal stability. However, it undergoes irreversible amorphization at surprisingly low pressures of about 10 MPa. While such disruption of framework-topology was attributed to the rupture of −C–O– bonds of the carboxylate groups in its rigid secondary building units (SBUs), these energy-intensive bond-breaking events are unlikely to occur at minuscule pressures of a few MPa. Using first-principles theoretical phonon-spectral analysis, we demonstrate that thermally stable MOF-5 crystal cannot sustain hydrostatic compression, primarily because of pressure-induced symmetry-lowering torsional forces that destabilize its octahedral SBUs. Group-theoretical analysis of phonons of MOF-5 unravels the role of normal modes in mid-frequency range (ω ∼ 1.6–3.2 THz), which become unstable and form dispersionless phonon bands at very small compressive strains (∼−0.3%), leading to an order-to-disorder structural phase transition. At slightly larger strains, structures distorted with random combinations of localized modes in the flat bands of these unstable phonons and associated instabilities of the transverse acoustic branches relax to lower-energy states that exhibit structural shearing at the nanoscale. This results in the loss of long-range order and irreversible amorphization of the MOF-5 crystal, while preserving the local structural coordination environment in this topologically disordered state. Our work will stimulate exploration of this microscopic mechanism of amorphization in other MOFs that consist of high-symmetry directionally constrained rigid building units in their network structure.

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Section: Resultsmentioning

confidence: 99%

Flat Phonon Band-Based Mechanism of Amorphization of MOF-5 at Ultra-low Pressures

Bhogra

Waghmare

2021

J. Phys. Chem. C

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“…For a MOF, the dense phase can be more difficult to conceptualize due to the directionality of the ligands, but denser, amorphous phases of some MOFs, achieved thermally, are known, [22][23][24][25] and other structures transition to denser amorphous phases with the application of pressure. [26][27][28] Figure 1: Metastability of Porous Materials. A) Enthalpic penalty relative to a dense phase versus molar unit cell volume per Zn or Si for porous materials including zeolites, mesoporous silicas, ZIFs, and MOF-5.…”

Section: The Energetic Penalty For Porositymentioning

confidence: 99%

Kinetic stability of metal–organic frameworks for corrosive and coordinating gas capture

2019

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Metal-organic frameworks (MOFs) have demonstrated their utility for a variety of applications involving the storage, separation, and sensing of weakly interacting gases of high purity. Exposure to more realistic, impure gas streams and interactions with corrosive and coordinating gases raises the question of chemical robustness, which remains a paramount concern for practical applications of MOFs. However, factors that determine the stability of MOFs remain incompletely understood. Although past researchers attempted to categorize framework materials as either thermodynamically stable or kinetically stable, recent work has elucidated an energetic penalty for porosity for all materials in this class with respect to a dense material. The metastability of porous phases has important implications for the design of materials for gas storage, heterogeneous catalysts, and electronic materials. Here, we focus on two main strategies for stabilization of the porous phase, either by using inert metal ions, or by increasing the heterolytic metal-ligand bond strength, both of which increase the activation barrier for framework collapse. These two strategies have led to exceptionally robust materials for the capture of coordinating and corrosive gases such as water vapor, ammonia, H2S, SO2, NOx, and even elemental halogens, and we review the progress in designing stable materials for these gases. Looking forward, we envision that the continued pursuit of strategies for kinetic stabilization in the synthesis of new MOFs will provide increasing numbers of robust frameworks suited to harsh conditions, and that short-term stability towards these challenging gases will be predictive of long-term stability for applications in less demanding environments.

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“…The first work studied the MOF-5 amorphization under hydrostatic pressure by investigating the change in structural and electronic properties and provided the first amorphous MOF-5 atomistic model ever reported. 36 The second one investigated pressure-induced amorphization of ZIF-8 both under hydrostatic and uniaxial stress. The resulting amorphous ZIF-8 was obtained without bond-breaking, and the method was validated by comparing the RDF with experimental data.…”

Section: Erkartal Et Al Developed An Ad Hoc Technique That Proceeds B...mentioning

confidence: 99%

Atomistic Models of Amorphous Metal-Organic Frameworks

Castel,

Coudert

2022

Preprint

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There is an increasing interest in the amorphous states of metal-organic frameworks (MOFs) and porous coordination polymers, which can be produced by pressure-induced amorphization, temperature-induced amorphization, melt-quenching, ball-milling, irradiation, etc. They can exhibit useful physical and chemical properties, distinct from those achievable in the crystalline states, along with greater ease of processing, and intrinsic advantages over crystals and powders, such as high transparency and mechanical robustness. However, these amorphous states are particularly challenging to characterize, and the determination of their framework structure at the microscopic scale is difficult, with only indirect structural information available from diffraction experiments. In this Perspective, we review and compare the existing methodologies available for the determination of microscopic models of amorphous MOFs, based on both experimental data and simulation methods. In particular, the atomistic models that can be obtained using Reverse Monte Carlo (RMC) methods, Continuous Random Networks (CRN), classical and ab initio molecular dynamics, reactive force fields, and simulated assembly/polymerization algorithms.

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Pressure‐Induced Amorphization of MOF‐5: A First Principles Study

Cited by 20 publications

References 66 publications

Flat Phonon Band-Based Mechanism of Amorphization of MOF-5 at Ultra-low Pressures

Flat Phonon Band-Based Mechanism of Amorphization of MOF-5 at Ultra-low Pressures

Kinetic stability of metal–organic frameworks for corrosive and coordinating gas capture

Atomistic Models of Amorphous Metal-Organic Frameworks

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