Methane Storage in Paddlewheel-Based Porous Coordination Cages

Although gas adsorption properties of extended three-dimensional
metal–organic materials have been widely studied, they remain
relatively unexplored in porous molecular systems. This is particularly
the case for porous coordination cages for which surface areas are
typically not reported. Herein, we report the synthesis, characterization,
activation, and gas adsorption properties of a family of carbazole-based
cages. The chromium analog displays a coordination cage record BET
(Brunauer−Emmett−Teller) surface area of 1235 m2/g. With
precise synthesis and activation procedures, two previously reported
cages similarly display high surface areas. The materials exhibit
high methane adsorption capacities at 65 bar with the chromium­(II)
cage displaying CH4 capacities of 194 cm3/g
and 148 cm3/cm3. This high uptake is a result
of optimal pore design, which was confirmed via powder neutron diffraction
experiments.