2D Covalent Organic Frameworks with cpt-defect topology Enabled by a Node-Splitting Strategy.

Reticular chemistry provides a robust platform for the construction of two-dimensional covalent organic frameworks (2D COFs) with tailored architectures and functionalities. A key synthetic challenge lies in the integration of densely arranged functional moieties without compromising long-range structural order. Herein, we report a node-splitting strategy in which half of the 6-connected C₃-symmetric nodes in the cpt topology are replaced by trios of 2-connected C_2v-symmetric nodes, generating a new cpt-defect topology. Directional hydrogen bonding among the C_2v nodes drives the formation of well-defined hydrogen-bonded nanotraps while preserving crystalline periodicity. The resulting COFs exhibit remarkable performance in gold ion (Au³⁺) recovery, with COF-36 achieving a maximum adsorption capacity of 1725 mg g^-1 and over 99% removal efficiency under strongly acidic conditions. Density functional theory (DFT) calculations attribute this high affinity to the geometric complementarity between the nanotrap cavity and the [AuCl₄]^- anion, enabling the formation of multiple stabilizing hydrogen bonds. This work establishes node splitting as a versatile approach for topological and functional engineering in COFs, broadening their potential for advanced applications.