Anisotropic Elastic Properties of Flexible Metal-Organic Frameworks: How Soft are Soft Porous Crystals?

Aurélie Ortiz (1) , Anne Boutin (2) , Alain Fuchs (1) , François-Xavier Coudert (1)

1 LECIME - Laboratoire d'Electrochimie, Chimie des Interfaces et Modélisation pour l'Energie (LECIME - UMR 7575)
2 PASTEUR - Processus d'Activation Sélective par Transfert d'Energie Uni-électronique ou Radiatif (UMR 8640)

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.

Domaines: Chimie; Chimie théorique et/ou physique; Matériaux

Aurélie Ortiz, Anne Boutin, Alain Fuchs, François-Xavier Coudert. Anisotropic Elastic Properties of Flexible Metal-Organic Frameworks: How Soft are Soft Porous Crystals?. Physical Review Letters, 2012, 109, pp.195502. ⟨10.1103/PhysRevLett.109.195502⟩. ⟨hal-02310172⟩