Quantum tunneling rotor as a sensitive atomistic probe of guests in a metal-organic framework

Quantum tunneling rotors in a zeolitic imidazolate framework ZIF-8 can provide insights into local gas adsorption sites and local dynamics of porous structure, which are inaccessible to standard physisorption or x-ray diffraction sensitive primarily to long-range order. Using in situ high-resolution inelastic neutron scattering at 3 K, we follow the evolution of methyl tunneling with respect to the number of dosed gas molecules. While nitrogen adsorption decreases the energy of the tunneling peak, and ultimately hinders it completely (0.33 meV to zero), argon substantially increases the energy to 0.42 meV. Ab initio calculations of the rotational barrier of ZIF-8 show an exception to the reported adsorption sites hierarchy, resulting in anomalous adsorption behavior and linker dynamics at subatmospheric pressure. The findings reveal quantum tunneling rotors in metal-organic frameworks as a sensitive atomistic probe of local physicochemical phenomena.

Automated summary

Using in situ high-resolution inelastic neutron scattering, the study investigated the dynamic changes of quantum tunneling rotors in ZIF-8 with gas adsorption. It was found that nitrogen adsorption decreases the energy of the tunneling peak, ultimately hindering it completely, while argon significantly increases the energy. Ab initio calculations revealed an exception to the reported adsorption sites hierarchy and anomalous adsorption behavior in ZIF-8.