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Detecting Molecular Rotational Dynamics Complementing the Low-Frequency Terahertz Vibrations in a Zirconium-Based Metal-Organic Framework

DOI: 10.1103/PhysRevLett.118.255502 DOI Help

Authors: Matthew R. Ryder (University of Oxford; ISIS Facility; Diamond Light Source) , Ben Van De Voorde (KU Leuven) , Bartolomeo Civalleri (University of Turin) , Thomas D. Bennett (University of Cambridge) , Sanghamitra Mukhopadhyay (ISIS Facility) , Gianfelice Cinque (Diamond Light Source) , Felix Fernandez-alonso (ISIS Facility; University College London) , Dirk De Vos (KU Leuven) , Svemir Rudic (ISIS Facility) , Jin-chong Tan (University of Oxford)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Physical Review Letters , VOL 118

State: Published (Approved)
Published: June 2017
Diamond Proposal Number(s): 10215

Abstract: We show clear experimental evidence of cooperative terahertz (THz) dynamics observed below 3 THz (∼100  cm−1), for a low-symmetry Zr-based metal-organic framework structure, termed MIL–140A [ZrO(O2C−C6H4−CO2)]. Utilizing a combination of high-resolution inelastic neutron scattering and synchrotron radiation far-infrared spectroscopy, we measured low-energy vibrations originating from the hindered rotations of organic linkers, whose energy barriers and detailed dynamics have been elucidated via ab initio density functional theory calculations. The complex pore architecture caused by the THz rotations has been characterized. We discovered an array of soft modes with trampolinelike motions, which could potentially be the source of anomalous mechanical phenomena such as negative thermal expansion. Our results demonstrate coordinated shear dynamics (2.47 THz), a mechanism which we have shown to destabilize the framework structure, in the exact crystallographic direction of the minimum shear modulus (Gmin).

Subject Areas: Physics

Instruments: B22-Multimode InfraRed imaging And Microspectroscopy