Porous Organic Cages for Sulfur Hexafluoride Separation

A series of porous organic cages is examined for the selective
adsorption of sulfur hexafluoride (SF6) over nitrogen.
Despite lacking any metal sites, a porous cage, CC3,
shows the highest SF6/N2 selectivity reported
for any material at ambient temperature and pressure, which translates
to real separations in a gas breakthrough column. The SF6 uptake of these materials is considerably higher than would be expected
from the static pore structures. The location of SF6 within
these materials is elucidated by X-ray crystallography, and it is
shown that cooperative diffusion and structural rearrangements in
these molecular crystals can rationalize their superior SF6/N2 selectivity.