title: Anisotropic elastic properties of flexible metal-organic frameworks: how soft are soft porous crystals?
abstract: We performed ab initio calculations of the elastic constants of five flexible metal-organic frameworks (MOFs): MIL-53(Al), MIL-53(Ga), MIL-47, and the square and lozenge structures of DMOF-1. Tensorial analysis of the elastic constants reveals a highly anisotropic elastic behavior, some deformation directions exhibiting very low Young's modulus and shear modulus. This anisotropy can reach a 400:1 ratio between the most rigid and weakest directions, in stark contrast to the case of nonflexible MOFs such as MOF-5 and ZIF-8. In addition, we show that flexible MOFs can display extremely large negative linear compressibility. These results uncover the microscopic roots of stimuli-induced structural transitions in flexible MOFs, by linking the local elastic behavior of the material and its multistability.
authors.affiliation: CNRS and Chimie ParisTech, 11 rue Pierre et Marie Curie, 75005 Paris, France.
authors.forename: Aurélie U
authors.initials: AU
authors.lastname: Ortiz
authors.forename: Anne
authors.initials: A
authors.lastname: Boutin
authors.forename: Alain H
authors.initials: AH
authors.lastname: Fuchs
authors.forename: François-Xavier
authors.initials: FX
authors.lastname: Coudert