Abstract-Identifying the role of terahertz vibrations in metalorganic frameworks: From gate-opening phenomenon to shear-driven structural destabilization

Matthew R. Ryder, Bartolomeo Civalleri, Thomas D. Bennett, Sebastian Henke, Svemir Rudić, Gianfelice Cinque, Felix Fernandez-Alonso, and Jin-Chong Tan

http://journals.aps.org/prl/accepted/99077Yb0If312d3dd7a20130212ad398366d46c9c

We present an unambiguous identification of low-frequency terahertz (THz) vibrations in the archetypal imidazole-based metal-organic framework (MOF) materials: ZIF-4, ZIF-7 and ZIF-8, all of which adopt a zeolite-like nanoporous structure. Using inelastic neutron scattering and synchrotron radiation far-infrared absorption spectroscopy, in conjunction with density functional theory (DFT), we have pinpointed all major sources of vibrational modes. Ab initio DFT calculations revealed the complex nature of the collective THz modes, which enable us to establish detailed correlations with experiments. We discover that low-energy conformational dynamics offers multiple pathways to elucidate novel physical phenomena observed in MOFs. New evidence demonstrates that THz modes are intrinsically linked, not only to anomalous elasticity underpinning gate opening and pore breathing mechanisms, but also to shear-induced phase transitions and the onset of structural instability.