Ion-Conductive Metallo-Covalent Organic Frameworks Constructed with Tridentate Ligand and Zn Nodes
Fangzheng Chen, Kun Zhang, Yijia Yuan, Walter P. D. Wong, Gang Wang, Xing Li, Lu Wang, Runlai Li, Zhitan Wu, Junhao Lin, Hai‐Sen Xu, Kian Ping Loh
Abstract
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 Zn 2+ ions and in situ-generated tridentate ligands (pdi) yields metallo-COFs with a square-like lattice. In the absence of Zn 2+ ions, a topological isomer COF with a Kagome lattice is instead produced. Thus, the presence or absence of Zn 2+ 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 [Zn 2+ ]/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 [Zn 2+ ]/ligand composition of pdiCOF-Zn-3 (honeycomb) facilitate its application as ion transport channels.