Defect-dependent colossal negative thermal expansion in UiO-66(Hf) metal–organic framework

Cliffe, Matthew J.; Hill, Joshua A.; Murray, Claire; Coudert, François‐Xavier; Goodwin, Andrew L.

doi:10.1039/c5cp01307k

Cited by 139 publications

(170 citation statements)

References 59 publications

(119 reference statements)

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“…E in each case lies above those of other highly porous MOFs, and indeed approaches the mechanical response expected of dense hybrid frameworks 25. The large differences in elasticity with relatively small changes in SAV may allow fine‐tuning of mechanical response in these highly porous systems, though the effect of defects upon the properties of such materials remains an issue 14a, 26. The unexpected increase in resistance to pressure and the large decrease in the elastic modulus for UiO‐abdc compared to UiO‐67 are both ascribed to the presence of the azobenzene linker, which bows out of the horizontal plane.…”

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confidence: 69%

A Computational and Experimental Approach Linking Disorder, High‐Pressure Behavior, and Mechanical Properties in UiO Frameworks

et al. 2016

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Whilst many metal–organic frameworks possess the chemical stability needed to be used as functional materials, they often lack the physical strength required for industrial applications. Herein, we have investigated the mechanical properties of two UiO‐topology Zr‐MOFs, the planar UiO‐67 ([Zr6O4(OH)4(bpdc)6], bpdc: 4,4′‐biphenyl dicarboxylate) and UiO‐abdc ([Zr6O4(OH)4(abdc)6], abdc: 4,4′‐azobenzene dicarboxylate) by single‐crystal nanoindentation, high‐pressure X‐ray diffraction, density functional theory calculations, and first‐principles molecular dynamics. On increasing pressure, both UiO‐67 and UiO‐abdc were found to be incompressible when filled with methanol molecules within a diamond anvil cell. Stabilization in both cases is attributed to dynamical linker disorder. The diazo‐linker of UiO‐abdc possesses local site disorder, which, in conjunction with its longer nature, also decreases the capacity of the framework to compress and stabilizes it against direct compression, compared to UiO‐67, characterized by a large elastic modulus. The use of non‐linear linkers in the synthesis of UiO‐MOFs therefore creates MOFs that have more rigid mechanical properties over a larger pressure range.

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A Computational and Experimental Approach Linking Disorder, High‐Pressure Behavior, and Mechanical Properties in UiO Frameworks

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“…44,45 Recently, Goodwin and co-workers showed that correlations between defects can be introduced and controlled, yielding nanoscale defect structures. 46 The presence of these defects may alter the catalytic properties, 47,48 thermal stability, 49 proton conductivity, 50,51 and adsorption behavior 43,52−55 of the host material. While recent work also indicates a decrease in bulk modulus and hence robustness upon the introduction of defects, 54,56 it remains to be investigated how the precise molecular nature of these defects alters the pressure-induced disorder in UiO-66-type materials.…”

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confidence: 99%

Thermodynamic Insight in the High-Pressure Behavior of UiO-66: Effect of Linker Defects and Linker Expansion

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In this Article, we present a molecular-level understanding of the experimentally observed loss of crystallinity in UiO-66-type metal–organic frameworks, including the pristine UiO-66 to -68 as well as defect-containing UiO-66 materials, under the influence of external pressure. This goal is achieved by constructing pressure-versus-volume profiles at finite temperatures using a thermodynamic approach relying on ab initio derived force fields. On the atomic level, the phenomenon is reflected in a sudden drop in the number of symmetry operators for the crystallographic unit cell because of the disordered displacement of the organic linkers with respect to the inorganic bricks. For the defect-containing samples, a reduced mechanical stability is observed, however, critically depending on the distribution of these defects throughout the material, hence demonstrating the importance of judiciously characterizing defects in these materials.

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“…Examples exist, however, such as the defect dependent NTE in UIO-66, 109 where a combination of configurational disorder together with vibrational entropy account for the material's properties. The first step towards an elaborate understanding of entropy is the analysis of each contribution and its importance within the system as a whole.…”

Section: Entropy As Design Principle?mentioning

confidence: 99%

Organised chaos: entropy in hybrid inorganic–organic systems and other materials

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Defect-dependent colossal negative thermal expansion in UiO-66(Hf) metal–organic framework

Cited by 139 publications

References 59 publications

A Computational and Experimental Approach Linking Disorder, High‐Pressure Behavior, and Mechanical Properties in UiO Frameworks

A Computational and Experimental Approach Linking Disorder, High‐Pressure Behavior, and Mechanical Properties in UiO Frameworks

Thermodynamic Insight in the High-Pressure Behavior of UiO-66: Effect of Linker Defects and Linker Expansion

Organised chaos: entropy in hybrid inorganic–organic systems and other materials

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