Mixed hierarchical local structure in a disordered metal\u2013organic framework

Adam F Sapnik,Duncan N Johnstone,Kim E Jelfs,Philip A Chater,Matthew A Addicoat,Sean M Collins,Andrew J Smith,Timothy Johnson,Giorgio Divitini,Thomas D Bennett,Irene Bechis,David A Keen

doi:10.1038/s41467-021-22218-9

Abstract

Amorphous metal–organic frameworks (MOFs) are an emerging class of materials. However, their structural characterisation represents a significant challenge. Fe-BTC, and the commercial equivalent Basolite® F300, are MOFs with incredibly diverse catalytic ability, yet their disordered structures remain poorly understood. Here, we use advanced electron microscopy to identify a nanocomposite structure of Fe-BTC where nanocrystalline domains are embedded within an amorphous matrix, whilst synchrotron total scattering measurements reveal the extent of local atomic order within Fe-BTC. We use a polymerisation-based algorithm to generate an atomistic structure for Fe-BTC, the first example of this methodology applied to the amorphous MOF field outside the well-studied zeolitic imidazolate framework family. This demonstrates the applicability of this computational approach towards the modelling of other amorphous MOF systems with potential generality towards all MOF chemistries and connectivities. We find that the structures of Fe-BTC and Basolite® F300 can be represented by models containing a mixture of short- and medium-range order with a greater proportion of medium-range order in Basolite® F300 than in Fe-BTC. We conclude by discussing how our approach may allow for high-throughput computational discovery of functional, amorphous MOFs.

Highlights

Amorphous metal–organic frameworks (MOFs) are an emerging class of materials
The use of advanced electron microscopy identified that Fe-BTC possesses a nanocomposite structure, containing both crystalline and amorphous domains
Synchrotron pair distribution function (PDF) analysis revealed the presence of tetrahedral assemblies in Fe-BTC

Summary

Introduction

Amorphous metal–organic frameworks (MOFs) are an emerging class of materials. their structural characterisation represents a significant challenge. We use a polymerisation-based algorithm to generate an atomistic structure for Fe-BTC, the first example of this methodology applied to the amorphous MOF field outside the well-studied zeolitic imidazolate framework family. Metal–organic frameworks (MOFs) are hybrid materials composed of metal centres bridged by organic linkers Our understanding of their structure–property relationships enables the rational design of functional materials through the selection of structural building units with specific chemistries and connectivities. The absence of structural periodicity precludes the use of single crystal diffraction techniques routinely employed in the structure solution of crystalline materials Since it is the atomic-scale structure of materials, often regardless of the degree of long-range order, that drives functionality, the comparatively poor understanding of amorphous MOFs prevents their rational design and hinders their development towards possible applications. This entry was from a study of aZIF-4 using neutron and X-ray total scattering data with reverse Monte Carlo (RMC)

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Conclusion