Understanding MOF Flexibility: An Analysis Focused on Pillared Layer MOFs as a Model System

Abstract

Flexible porous frameworks are at the forefront of materials research. A unique feature is their ability to open and close their pores in an adaptive manner induced by chemical and physical stimuli. Such enzyme-like selective recognition offers a wide range of functions ranging from gas storage and separation to sensing, actuation, mechanical energy storage and catalysis. However, the factors affecting switchability are poorly understood. In particular, the role of building blocks, as well as secondary factors (crystal size, defects, cooperativity) and the role of host-guest interactions, profit from systematic investigations of an idealized model by advanced analytical techniques and simulations. The review describes an integrated approach targeting the deliberate design of pillared layer metal-organic frameworks as idealized model materials for the analysis of critical factors affecting framework dynamics and summarizes the resulting progress in their understanding and application.

Unravelling abnormal in-plane stretchability of two-dimensional metal–organic frameworks by machine learning potential molecular dynamics

“…and other related flexible MOFs have been computationally and experimentally proved to exhibit significant anisotropy in their Young's modulus and/or shear modulus at the origin of their anomalous mechanical properties. 13–20…”

Stimulus-Induced Dynamic Behavior Regulation of Flexible Crystals through the Tuning of Module Rigidity

“…During previous explorations, it has been recognized that pillared-layer structures have highly potential for the targeted synthesis of flexible MOFs. 29,30 Encouragingly, Eddaoudi et al employed a supermolecular building layer (SBL) strategy to systematically enrich the types of pillared-layer MOFs. 31,32 Although five edge-transitive SBLs, i.e., sql, kgm, hcb, hex, and kgd, are frequently observed in pillar-layered MOFs, flexible features are typically found in MOFs that are built from sql layers.…”

“…31,32 Although five edge-transitive SBLs, i.e., sql, kgm, hcb, hex, and kgd, are frequently observed in pillar-layered MOFs, flexible features are typically found in MOFs that are built from sql layers. 29 MOFs is formed by connecting 2D square grids with pillar linkers to form a primitive structure with an underlying pcu topology. Such structures can undergo reversible conformational transformations based on a shrinkage/swelling motion of the square lattice.…”

Phase switching and shape-memory effect in a molecular material: revisiting the Werner complex [Ni(4-MePy)4(NCS)2]

“…Soft porous crystals that exhibit guest-induced structural transformations, 1,2 especially flexible metal-organic materials (FMOMs), [3][4][5][6][7][8][9][10][11] are of interest thanks to their potential utility in gas storage [12][13][14][15][16] and hydrocarbon separation. [17][18][19][20][21][22] A feature of some FMOMs is that they can undergo reversible structural transformation(s) between their activated (desolvated) and guest-loaded phases induced by guest sorption, [23][24][25][26][27][28][29][30] often with varying levels of hysteresis. [12][13][14][15][16][17][18][19][20][21][22][31][32][33][34][35][36] The shape-memory effect (SME) is a related phenomenon whereby a shape-memory material (SMM) transforms to a ne...…”