3D Cage COFs: A Dynamic Three-Dimensional Covalent Organic Framework with High-Connectivity Organic Cage Nodes

Three-dimensional
(3D) covalent organic frameworks (COFs) are rare
because there is a limited choice of organic building blocks that
offer multiple reactive sites in a polyhedral geometry. Here, we synthesized
an organic cage molecule (Cage-6-NH2) that was used as a triangular prism node to yield the first
cage-based 3D COF, 3D-CageCOF-1. This COF adopts an unreported
2-fold interpenetrated acs topology and exhibits reversible
dynamic behavior, switching between a small-pore (sp)
structure and a large-pore (lp) structure. It also shows
high CO2 uptake and captures water at low humidity (<40%).
This demonstrates the potential for expanding the structural complexity
of 3D COFs by using organic cages as the building units.