title: Exceptionally low shear modulus in a prototypical imidazole-based metal-organic framework.
abstract: Using Brillouin scattering, we measured the single-crystal elastic constants (C(ij)'s) of a prototypical metal-organic framework (MOF): zeolitic imidazolate framework (ZIF)-8 [Zn(2-methylimidazolate)(2)], which adopts a zeolitic sodalite topology and exhibits large porosity. Its C(ij)'s under ambient conditions are (in GPa) C(11)=9.522(7), C(12)=6.865(14), and C(44)=0.967(4). Tensorial analysis of the C(ij)'s reveals the complete picture of the anisotropic elasticity in cubic ZIF-8. We show that ZIF-8 has a remarkably low shear modulus G(min) < or approximately 1 GPa, which is the lowest yet reported for a single-crystalline extended solid. Using ab initio calculations, we demonstrate that ZIF-8's C(ij)'s can be reliably predicted, and its elastic deformation mechanism is linked to the pliant ZnN(4) tetrahedra. Our results shed new light on the role of elastic constants in establishing the structural stability of MOF materials and thus their suitability for practical applications.
authors.affiliation: Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge CB2 3QZ, United Kingdom.
authors.forename: Jin-Chong
authors.initials: JC
authors.lastname: Tan
authors.forename: Bartolomeo
authors.initials: B
authors.lastname: Civalleri
authors.forename: Chung-Cherng
authors.initials: CC
authors.lastname: Lin
authors.forename: Loredana
authors.initials: L
authors.lastname: Valenzano
authors.forename: Raimondas
authors.initials: R
authors.lastname: Galvelis
authors.forename: Po-Fei
authors.initials: PF
authors.lastname: Chen
authors.forename: Thomas D
authors.initials: TD
authors.lastname: Bennett
authors.forename: Caroline
authors.initials: C
authors.lastname: Mellot-Draznieks
authors.forename: Claudio M
authors.initials: CM
authors.lastname: Zicovich-Wilson
authors.forename: Anthony K
authors.initials: AK
authors.lastname: Cheetham