Record Complexity in the Polycatenation of Three Porous Hydrogen-Bonded Organic Frameworks with Stepwise Adsorption Behaviors

Hydrogen-bonded
organic frameworks (HOFs) show great potential
in many applications, but few structure–property correlations
have been explored in this field. In this work, we report that self-assembly
of a rigid and planar ligand gives rise to flat hexagonal honeycomb
motifs which are extended into undulated two-dimensional (2D) layers
and finally generate three polycatenated HOFs with record complexity.
This kind of undulation is absent in the 2D layers built from a very
similar but nonplanar ligand, indicating that a slight torsion of
ligand produces overwhelming structural change. This change delivers
materials with unique stepwise adsorption behaviors under a certain
pressure originating from the movement between mutually interwoven
hexagonal networks. Meanwhile, high chemical stability, phase transformation,
and preferential adsorption of aromatic compounds were observed in
these HOFs. The results presented in this work would help us to understand
the self-assembly behaviors of HOFs and shed light on the rational
design of HOF materials for practical applications.