Mechanical Properties of Nanoporous Metal - Organic Framework Materials

Mechanical Properties of Nanoporous Metal-Organic Framework Materials [2012]

 

 

Given their vast potential for gas separations and storage, sensing, and drug delivery applications, detailed knowledge of the mechanical behaviour of MOFs is highly desirable from both a scientific and technological perspective.

Here, for the first time, we use laser Brillouin scattering to measure the single-crystal elastic constants (Cij’s) of an inorganic-organic (hybrid) framework material: ZIF-8, a prototypical imidazole-based MOF exhibiting a large accessible pore volume. The elastic constants are fundamentally important as they reflect the intrinsic interatomic bonding that governs the structure and stability of solids.

Tensorial analysis of the elastic constants (Figure) reveals the complete picture of the anisotropic elasticity in cubic ZIF-8. We discover that ZIF-8 has a remarkably low shear modulus (~1 GPa), which is the lowest yet reported for a single-crystalline extended solid. Using ab initio computations, we further demonstrate that ZIF-8’s elastic constants can be reliably predicted. The underlying elastic deformation mechanism is governed by the pliant coordination tetrahedra, whose distortion is being accommodated by the large porosity. Our results shed new light on the role of elastic constants for establishing the fundamental structural stability of MOF-type materials, and thus their suitability for commercial applications.