Modeling the Effect of Defects and Disorder in Amorphous Metal–Organic Frameworks

Abstract

Amorphous metal–organic frameworks (aMOFs) are a class of disordered framework materials with a defined local order given by the connectivity between inorganic nodes and organic linkers, but absent long-range order. The rational development of function for aMOFs is hindered by our limited understanding of the underlying structure–property relationships in these systems, a consequence of the absence of long-range order, which makes experimental characterization particularly challenging. Here, we use a versatile modeling approach to generate in silico structural models for an aMOF based on Fe trimers and 1,3,5-benzenetricarboxylate (BTC) linkers, Fe-BTC. We build a phase space for this material that includes nine amorphous phases with different degrees of defects and local order. These models are analyzed through a combination of structural analysis, pore analysis, and pair distribution functions. Therefore, we are able to systematically explore the effects of the variation of each of these features, both in isolation and combined, for a disordered MOF system, something that would not be possible through experiment alone. We find that the degree of local order has a greater impact on structure and properties than the degree of defects. The approach presented here is versatile and allows for the study of different structural features and MOF chemistries, enabling the derivation of design rules for the rational development of aMOFs.

The Chemistry of Metal Organic Framework Materials

“…More recently, MOF glasses, a disordered form of MOFs, are finding niche applications. This virtual collection catalogues recent MOF advances featured in Chemistry of Materials from 2022 to 2023, − with an accompanying editorial by Laura Gagliardi and Omar Yaghi that outlines three critical future directions for MOFs …”

“…With the advent of interesting properties that stem from defects in MOFs, there is a strong computational focus on engineering defects into MOFs. Jelfs and co-workers generated in silico structural models for an amorphous MOF based on Fe trimers and 1,3,5-benzenetricarboxylate linkers . Analyzing nine amorphous phases with varying degrees of defects and local order, they concluded that the local order has a greater impact on the properties compared to defectsa new take.…”

“…Jelfs and co-workers generated in silico structural models for an amorphous MOF based on Fe trimers and 1,3,5-benzenetricarboxylate linkers. 20 Analyzing nine amorphous phases with varying degrees of defects and local order, they concluded that the local order has a greater impact on the properties compared to defects�a new take. As a persuasive contribution, Woo and co-workers emphasized the importance of database curation in any data-driven materials discovery effort and offered a massive database of MOFs, the ARC−MOF, which contains density functional theory-derived electrostatic potential and fitted partial atomic charges and reveals the effect of the charge-assignment method on atomistic simulation of gas uptake in MOFs.…”

Computational modeling to assist in the discovery of supramolecular materials

“…We have used this approach to rationalize trends in properties with changing monomer units for PIMs for liquid separations, 68 the separation of hydrocarbons, 69 and selective ion separation for flow batteries 70–72 . We have also recently extended our approach to the simulation of the structures of amorphous MOFs, allowing an explanation of the level of disorder and defects through comparison to experimental scattering measurements 73,74 and unique insight into the effect of defects and disorder on properties that would not be possible through experiment alone 75 …”

Simulating the Breathing Phase Transitions of Metal-organic Frameworks : Volume Control of Nanocrystallites

“…Recently, experimental evidence for a dependence of the breathing effect on the crystallite size has been found, indicating an influence of the system-to-volume ratio [8]. Also, the influence of defects and disorder on the flexibility of MOFs is still being determined [9,10]. From a theoretical point of view, most studies employ artificial periodic boundary conditions (PBCs) to simulate crystalline materials with relatively small unit cells and ideal, nondefective MOF systems leading to a well-defined cell volume, which allows pressure control by barostats [11].…”