Work

Lattice‐Matched Polyoxometalates Direct Crystallization of Cationic Covalent Organic Frameworks

Year: 2026

Type: article

Abstract: Cationic covalent organic frameworks (COFs) hold great potential for ion conduction and catalysis, yet poor crystallinity from interlayer electrostatic repulsion severely limits their performance. Herein, we demonstrate that lattice-matched polyoxometalates (POMs) as multifunctional counterions can direct the crystallization of cationic COFs and introduce functional sites. In situ incorporation of Keggin-type POMs affords highly crystalline honeycomb frameworks (POM@vCOF-CR), whereas post-synthetic ion exchange yields amorphous materials. Further investigations reveal that POMs play multiple roles during the crystallization process: in-plane, they modulate monomer release to promote ordered growth; out-of-plane, they act as electrostatic anchoring centers to facilitate ordered stacking. Crucially, lattice-matching between the POM sublattice and the COF framework eliminates configurational degeneracy and dictates long-range ordering. This principle is further validated in a square-lattice pvCOF, where only the larger Preyssler-type POM can form a matched square sublattice that enables crystallization, whereas smaller Keggin-type POMs lead to orientational disorder and amorphous products. Benefiting from the ordered functional sites and transport pathways, the crystalline POM@vCOF-CR exhibits significantly enhanced electrocatalytic activity for ethylbenzene oxidation and improved lithium-ion conductivity compared to its amorphous counterpart. This work establishes a rational solution for constructing crystalline cationic COFs by using lattice-matched POMs, thereby enabling functional frameworks with enhanced performance.

Source: Small

DOI: 10.1002/smll.75327