Probing the SO$_2$ adsorption mechanism in Hofmann clathrates via inelastic neutron scattering and density functional theory calculations

TL;DR

This study investigates the SO2 adsorption mechanism in a Hofmann-like coordination polymer using inelastic neutron scattering and DFT calculations, revealing spectral shifts linked to gas binding and steric effects.

Contribution

It combines experimental neutron scattering with theoretical DFT analysis to elucidate the molecular-level adsorption mechanism of SO2 in the polymer.

Findings

Blueshift of the low energy peak at 100 cm-1 upon SO2 adsorption

Increase in force constant of cyanide out-of-plane movement due to gas binding

Negligible effect on internal pyrazine vibrations, indicating physisorption

Abstract

The adsorption mechanism of SO2 in the Hofmann-like coordination polymer Fe(pz)[Pt(CN)4] is studied using inelastic neutron scattering and density functional theory calculations. We find that the most important spectral change upon gas adsorption is the blueshift of the low energy peak found at 100 cm-1, a feature that is fully confirmed by the computed neutron-weighted phonon density of states. Our calculations suggest that the origin of this change is twofold: i) an increase in the force constant of the cyanide out-of-plane movement due to the binding of the gas onto the Pt(CN)4 plane, and ii) the hampered rotation of the pyrazine due to steric hindrance. The high energy region of the neutron scattering data whose spectral weight is dominated by the internal vibrations of the pyrazine is negligibly affected by the presence of the gas as expected from a physisorption type of binding.