Beyond the Multicomponent Debus–Radziszewski Route: Two-Component Cyclocondensation Constructing a 12 + 3‑Connected aea Topology Three-Dimensional Imidazole-Linked COF for Sustainable Wastewater Treatment

The rational construction of high-connectivity three-dimensional
covalent organic frameworks (3D COFs) remains a central challenge
in reticular chemistry, holding immense promise for advancing framework
rigidity, porosity, and functional integration. From both fundamental
and application standpoints, diversifying the linkage chemistry of
such high-connectivity COFs beyond the archetypal imine bond is essential,
as imidazole linkages impart superior chemical resilience, enhanced
π-delocalization, and intrinsic polarity compared with imine
linkages. Here, we report TU-123, the first 12 + 3-connected 3D imidazole-linked
COF with aea topology, synthesized via a two-component
cyclocondensation between a D3-symmetric
hexakis-aldehyde and a D3h-symmetric hexaamine
building block. Unlike conventional imidazole-linked COFs derived
from multicomponent Debus–Radziszewski reactions, TU-123 forms
through direct imidazole ring formation from aldehyde and amine precursors
via an imine intermediate, intramolecular cyclization, and oxidative
aromatization. This strategy, previously limited to 2D frameworks,
is extended herein to a highly connected 3D network for the first
time. Benefiting from its rigid and polarized imidazole framework,
TU-123 exhibits a cationic surface character at neutral pH, arising
from protonation of nitrogen sites within the imidazole linkages,
which enables selective adsorption of anionic dyes such as acid orange
7, with a maximum adsorption capacity of 495.07 mg g–1 and 86.08% removal efficiency under optimized conditions. The adsorption
process follows pseudo-second-order kinetics and Langmuir isotherm
behavior, highlighting the framework’s potential for sustainable
wastewater purification.