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

Abstract

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.

The Zeolitic Imidazolate Framework ZIF‐4 under Low Hydrostatic Pressures

“…This experimental limitation related to DACs has large implications when interested in accurately determining bulk moduli of MOFs. For MOFs, amorphization processes can occur at pressures below p = 0.3 GPa, pressures at which typically only a few datapoints have been measured, thus limiting the accuracy of the derived bulk modulus by DACs.…”

Controlling interpenetration through linker conformation in the modulated synthesis of Sc metal–organic frameworks

“…Driven by our interest in the modulation of Zr MOFs 13,29,47 and the relatively limited research into Sc MOFs in comparison, we sought to extend modulated syntheses to Sc MOFs containing bpdc and bpydc ligands (Fig. 1b) in an attempt to: (i) conrm the structure and level of interpenetration of the reported Sc-bpdc MOF, 42 (ii) examine the extent of structural diversity, as seen for the Sc-bdc MOFs, in this series, and (iii) control the physical properties of the resulting materials.…”

Models Facilitating the Design of a New Metal‐Organic Framework Catalyst for the Selective Decomposition of Formic Acid into Hydrogen and Carbon Dioxide

“…To examine the mechanistic aspects responsible for the selective decomposition of formic acid into H 2 and CO 2 via reaction steps I and II within the catalytic cycle (Scheme 1a), DFT energy profiles have been determined for five systems: (i) [(phen*)Cu(H)] 2À , 1 d (Scheme 1d), which has been experimentally investigated in the gas phase (Figure 1), (ii) [(bipy)Cu(H)], 1 e (Scheme 1d); (iii) [(bipy*)Cu(H)], 1 f (Scheme 1d), which contains the organic linker present in MOF UiO-67, and capped as a diester; and models for MOF UiO-67 [21] in which the octahedron is simplified as a square consisting of three biphenyl organic linkers, one (bipy*)Cu(H) organic linker containing the catalytic site and four Zr 6 O 4 (OH) 4 (COOH) 10 Table 1 compares the energies of all key species for all model systems. The most noteworthy aspect of comparing the energy profiles and associated structures is that the mechanistic features are similar for all model systems, with small perturbations to the energetics.…”