Reversible pressure-induced amorphization of a zeolitic imidazolate framework (ZIF-4)

Bennett, Thomas D.; Simoncic, Petra; Moggach, Stephen A.; Gozzo, F.; Macchi, Piero; Keen, David A.; Tan, Jin‐Chong; Cheetham, Anthony K.

doi:10.1039/c1cc11985k

Cited by 206 publications

(217 citation statements)

References 15 publications

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“…In the past, a lot of work has focused on the mechanical properties (elastic moduli, hardness) of MOFs and ZIFs, both experimentally [38][39][40] and computationally. 41,42 The occurrence of pressure-induced crystal-to-crystal and crystal-to-amorphous transitions has been solidly established in several frameworks, including ZIF-8, 43 ZIF-4, 44 and the nonporous ZIF-zni. 45 Here, we try to shed light into the generality of this pressure-induced transitions by our systematic approach, modelling the behavior under pressure of 10 different ZIFs with identical chemical composition (Zn(im) 2 ), at the same level of molecular modelling.…”

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confidence: 99%

Thermal and mechanical stability of zeolitic imidazolate frameworks polymorphs

et al. 2014

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Theoretical studies on the experimental feasibility of hypothetical Zeolitic Imidazolate Frameworks (ZIFs) have focused so far on relative energy of various polymorphs, by energy minimization at the quantum chemical level. We present here a systematic study of stability of 18 ZIFs as a function of temperature and pressure, by molecular dynamics simulations. This approach allows us to better understand the limited stability of some experimental structures upon solvent or guest removal. We also find that many of the hypothetical ZIFs proposed in the literature are not stable at room temperature. Mechanical and thermal stability criteria thus need to be considered for the prediction of new MOF structures. Finally, we predict a variety of thermal expansion behavior for ZIFs as a function of framework topology, with some materials showing large negative volume thermal expansion.

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confidence: 99%

Thermal and mechanical stability of zeolitic imidazolate frameworks polymorphs

et al. 2014

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“…Recent studies have revealed that ZIFs may undergo thermally-and/or pressure-induced amorphisation that reinforces the similarity between ZIFs and silica. [3][4][5] However, important differences between ZIFs and silica systems are still ignored in the literature. For example, it is well known that the thermodynamic 'ground state' of the silica system at ambient conditions corresponds to the a-quartz phase (qtz net) 6 , whereas the quartz-like topology is hardly accessible in the Zn(im) 2 (im = imidazolate) system as was shown in our previous ab initio study.…”

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Subtle polymorphism of zinc imidazolate frameworks: temperature-dependent ground states in the energy landscape revealed by experiment and theory

et al. 2013

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We show by variable-temperature X-ray diffraction and differential scanning calorimetry experiments that zinc imidazolates with coi and zni framework topology, respectively represent the thermodynamically stable phase below and above a transition temperature of #360 uC at ambient pressure. The relative stability of the two polymorphs and the experimentally observed strong negative thermal expansion of the coi phase at high temperatures close to the phase transition were successfully modelled using density functional theory calculations. A novel metastable zinc imidazolate with neb framework topology was detected by in situ X-ray diffraction experiments as a transient crystalline phase during solvothermal crystallisation of the stable coi phase.Zeolitic imidazolate frameworks (ZIFs) represent a new class of technology relevant microporous materials that are at the focus of current research efforts. 1,2 Important characteristics of ZIFs are comparatively high thermal and chemical stabilities and the ability to crystallise in a large variety of topologically different frameworks which may be tailored for a specific application in gas storage, separation, sensing or catalysis. ZIFs consist of tetrahedral cationic centres (Zn II , Co II , Fe II , Cd II , and also Li I /B III ) connected by imidazolate-based bridging ligands. Because of the local tetrahedral geometry of metal connectors and the metal-imidazolatemetal bridging angle of #145u ZIFs adopt network topologies common for microporous silica polymorphs and zeolites. Recent studies have revealed that ZIFs may undergo thermally-and/or pressure-induced amorphisation that reinforces the similarity between ZIFs and silica. [3][4][5] However, important differences between ZIFs and silica systems are still ignored in the literature. For example, it is well known that the thermodynamic 'ground state' of the silica system at ambient conditions corresponds to the a-quartz phase (qtz net) 6 , whereas the quartz-like topology is hardly accessible in the Zn(im) 2 (im = imidazolate) system as was shown in our previous ab initio study. 7,8 By considering only unsubstituted imidazolate bridging ligands, nine topologically different Zn(im) 2 frameworks have been experimentally realised to date (zni, coi, cag, mer, gis, dft, crb, zec, nog) 1,2,9 and even more are predicted to be synthetically accessible. 7 However, up to now there was no experimental study which addressed the important question about the thermodynamically most stable phase(s) ('ground state(s)') in the Zn(im) 2 system, which might be either of the two most dense phases zni or coi. Recently, an irreversible single-crystal-to-single-crystal pressureinduced phase transition from the zni to the coi phase was observed at room temperature by Spencer et al. 10 revealing that coi is stable at high pressures (>0.55 GPa). The polymorphs with zni and coi underlying nets crystallise in the tetragonal space groups I4 1 cd and I4 1 , respectively, and are closely related to each other since both frameworks may be considered ...

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“…For comparison, we have also investigated the thermal effects on the vibrational spectra of ZIF-8 (whose linker is mIm = 2-methylimidazolate), which does not amorphize thermally. 21 It is worth noting that these materials can also amorphize through other sources of external stimuli, such as pressure 22 and mechanical impact. 23 However, it has been suggested that the mechanisms for the various routes to amorphization are different, with a shear instability being the likely cause of the mechanically induced amorphization.…”

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Tracking thermal-induced amorphization of a zeolitic imidazolate framework via synchrotron in situ far-infrared spectroscopy

et al. 2017

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We present the first use of in situ far-infrared spectroscopy to analyze the thermal amorphization of a zeolitic imidazolate framework material. We explain the nature of vibrational motion changes during the amorphization process and reveal new insights into the effect that temperature has on the Zn-N tetrahedra.Vibrational spectroscopy has been shown to be an excellent method of analyzing framework materials and gaining a better understanding of their molecular structure. The mid-infrared (MIR) region of the vibrational spectra is related to the local characteristic vibrations (e.g. localized bond stretching and bending) and is therefore of limited interest for providing information regarding lattice dynamics of a specific framework. However, there has recently been a strong focus on the framework specific vibrational motions located in the far-infrared (FIR) region (< 700 cm -1 ), which have been shown to reveal the nature of quasi-localized and collective modes.One group of framework materials exhibiting a particularly rich variety of collective vibrational motions are metal-organic frameworks (MOFs), 1, 2 which are a topical class of hybrid (inorganic-organic) crystalline materials. Their nanoscale pore structures and long-range order have attracted significant scientific and industrial interest, which originates from their wide range of potential applications including, carbon sequestration, photonics and microelectronics, and drug encapsulation and delivery. 3,4 The diverse structural behavior of MOFs 5, 6 results in the FIR region of the vibrational spectra providing a gateway to understanding the physical behavior and underlying flexibility of these highly promising next-generation functional materials.We have shown that inelastic neutron scattering (INS) and synchrotron-based FIR spectroscopy, in conjunction with ab initio density functional theory (DFT) can be used to explain these framework specific motions. 7 Specifically, we related quasi-local vibrations to the deformation of the organic linkers and Zn-based coordination polyhedra (ZnN4) in zeolitic imidazolate frameworks (ZIFs), 8 and linked them to various physical phenomena, including "gate-opening", "breathing" and shear destabilization modes. 7 We also reported molecular rotational dynamics, trampoline-like vibrational motions, and demonstrated how collective vibrations can be connected to the elasticity and mechanical stability of the framework structure, revealing the origin of auxeticity (negative Poisson's ratio), in the copper paddle-wheel MOF, HKUST-1. 9 Unlike in situ MIR spectroscopy, 10, 11 which can be performed via benchtop equipment, detailed characterization of the FIR region in situ requires a more sophisticated experimental setup, explaining the relative absence of reports to date.The structural dynamics of MOFs, at the molecular level, is of increasing importance. For example, phase transitions in ZIF-7 upon exchange of guest molecules and ZIF-8 upon gas adsorption have been ascribed to "breathing" and "gate-opening" mechanisms...

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Reversible pressure-induced amorphization of a zeolitic imidazolate framework (ZIF-4)

Cited by 206 publications

References 15 publications

Thermal and mechanical stability of zeolitic imidazolate frameworks polymorphs

Thermal and mechanical stability of zeolitic imidazolate frameworks polymorphs

Subtle polymorphism of zinc imidazolate frameworks: temperature-dependent ground states in the energy landscape revealed by experiment and theory

Tracking thermal-induced amorphization of a zeolitic imidazolate framework via synchrotron in situ far-infrared spectroscopy

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