Impact of Alkyl-Functionalized BTC on Properties of Copper-Based Metal–Organic Frameworks

Highly porous metal–organic frameworks (MOFs)
[Cu3(MBTC)2(H2O)3]n (where MBTC is methyl-1,3,5-benzenetricarboxylate)
and [Cu3(EBTC)2(H2O)3]n (where EBTC is ethyl-1,3,5-benzenetricarboxylate)
have been solvothermally synthesized. The MOFs are isostructural to
each other but do not form the same framework as HKUST-1 (CuBTC) due
to the steric impact of the alkyl-functionalized ligands. The new
MOFs are formed by two different [Cu2(O2CR)4] units (where R is an aromatic ring), which create the three-dimensional
framework with open-metal sites and high surface areas. Compared with
HKUST-1, these MOFs adsorb comparable amounts of carbon dioxide and
methane at pressures up to 5 bar. However, water adsorption is significantly
lower compared to HKUST-1 due to the hydrophobic functional groups.
This work indicates that the strong adsorption preference of water
on open-metal sites can be limited with the proper choice of the hydrophobic
functional groups, without losing the strong interaction with other
gases.