posted on 2023-11-13, 18:35authored byFangzheng Chen, Kun Zhang, Yijia Yuan, Walter Peide Wong, Gang Wang, Xing Li, Lu Wang, Runlai Li, Zhitan Wu, Junhao Lin, Hai-Sen Xu, Kian Ping Loh
Metallo-covalent organic frameworks
(metallo-COFs) are organometallic
scaffolds in which covalently bonded organic frameworks are interwoven
with metal-coordinated pendant groups. Unlike the rigid ligands traditionally
used for metal coordination, the utilization of “soft”
ligands allows for configurable topology and pore structure in metallo-COFs,
particularly when the ligands are generated in situ during dynamic
synthesis. In this study, we present the rational synthesis of metallo-COFs
based on pyridine-2,6-diimine (pdi), wherein the incorporation of
Zn2+ ions and in situ-generated tridentate ligands (pdi)
yields metallo-COFs with a square-like lattice. In the absence of
Zn2+ ions, a topological isomer COF with a Kagome lattice
is instead produced. Thus, the presence or absence of Zn2+ ions allows us to switch between two distinct morphologies corresponding
to metallo-COF or COF. In comparison to Brønsted acid-catalyzed
COF, which necessitates postmetallization for loading metal ions,
the metal-templated COF synthesis method yields COFs with improved
crystallinity and approximately 1:1 [Zn2+]/ligand composition.
Building upon the metal-templated COF synthesis approach, we successfully
synthesized pdiCOF-Zn-2 and pdiCOF-Zn-3, which possess square-like
and honeycomb lattices, respectively. The enhanced crystallinity and
near 1:1 [Zn2+]/ligand composition of pdiCOF-Zn-3 (honeycomb)
facilitate its application as ion transport channels.