A Flexible Microporous Hydrogen-Bonded Organic Framework for Gas Sorption and Separation

A microporous
three-dimensional hydrogen-bonded organic framework
(HOF-5) has been constructed from a new organic linker 4,4′,4″,4‴-tetra­(2,4-diamino-1,3,5-triazin-6-yl)­tetraphenylethene.
Activated HOF-5a exhibits a stepwise N2 adsorption isotherm
at 77 K, suggesting framework flexibility. The structure of activated
HOF-5a has been established by powder X-ray diffraction studies, indicating
a significant framework contraction from as-synthesized HOF-5 to activated
HOF-5a of ∼21% by volume. HOF-5a shows moderately high porosity
with a Brunauer–Emmett–Teller (BET) surface area of
1101 m2/g, and takes up a large amount of acetylene and
carbon dioxide under ambient conditions. Powder neutron diffraction
studies and theoretical calculations reveal that suitable pore sizes,
curvatures, and functional sites collectively enable HOF-5a to encapsulate
a high density of carbon dioxide molecules packed in a pseudo-one-dimensional
array along the pore channel.