Molecular Dynamics Simulations of Gas Selectivity in Amorphous Porous Molecular Solids

Some organic cage molecules have
structures with protected, internal
pore volume that cannot be in-filled, irrespective of the solid-state
packing mode: that is, they are intrinsically porous. Amorphous packings
can give higher pore volumes than crystalline packings for these materials,
but the precise nature of this additional porosity is hard to understand
for disordered solids that cannot be characterized by X-ray diffraction.
We describe here a computational methodology for generating structural
models of amorphous porous organic cages that are consistent with
experimental data. Molecular dynamics simulations rationalize the
observed gas selectivity in these amorphous solids and lead to insights
regarding self-diffusivities, gas diffusion trajectories, and gas
hopping mechanisms. These methods might be suitable for the de novo
design of new amorphous porous solids for specific applications, where
“rigid host” approximations are not applicable.