Ion-Conductive Metallo-Covalent Organic Frameworks Constructed with Tridentate Ligand and Zn Nodes

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.