Tuning the Porosity, Solubility, and Gas-Storage Properties of Cuboctahedral Coordination Cages via Amide or Ester Functionalization

The
molecular nature of porous coordination cages can endow these
materials with significant advantages as compared to extended network
solids. Chiefly among these is their solubility in volatile solvents,
which can be leveraged in the synthesis, characterization, modification,
and utilization of these adsorbents. Although cuboctahedral, paddlewheel-based
coordination cages have shown some of the highest surface areas for
coordination cages, they often have limited solubility. Here, we show
that amide and ester functionalization, which has been widely utilized
in porous solids to tune material properties, can be used to tune
the solubility, porosity, and bulk adsorbent properties of copper-,
chromium-, and molybdenum-based cuboctahedral coordination cages.
In addition, we demonstrate that the solubility of a set of diphenylamide-functionalized
cages can be utilized to increase their bulk densities for gas storage
applications. For a subset of these cages, we further show that amide
and ester functional groups can be added postsynthetically, a strategy
that is particularly important for the latter where direct cage syntheses
with these groups are challenging.