  We show clear experimental evidence of co-operative terahertz (THz) dynamics
observed below 3 THz (~100 cm-1), for a low-symmetry Zr-based metal-organic
framework (MOF) 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 (DFT) calculations. For completeness, we obtained Raman
spectra and characterized the alterations to the complex pore architecture
caused by the THz rotations. We discovered an array of soft modes with
trampoline-like motions, which could potentially be the source of anomalous
mechanical phenomena, such as negative linear compressibility and negative
thermal expansion. Our results also demonstrate coordinated shear dynamics
(~2.5 THz), a mechanism which we have shown to destabilize MOF crystals, in the
exact crystallographic direction of the minimum shear modulus (Gmin).
