High‐Connectivity 3D Covalent Organic Frameworks with pdp Net for Efficient C2H2/CO2 Separation

High‐connectivity 3D covalent organic frameworks (COFs) have garnered significant attention due to their structural complexity, stability, and potential for functional applications. However, the synthesis of 3D COFs using mixed high‐nodal building units remains a substantial challenge. In this work, we introduce two novel 3D COFs, JUC‐661 and JUC‐662, which are constructed using a combination of D2h‐symmetric 8‐nodal and D3h‐symmetric 6‐nodal building blocks. These COFs feature an unprecedented [8+6]‐c pdp net with rare mesoporous polyhedral cages (~3.9 nm). Remarkably, JUC‐661 and JUC‐662 exhibit outstanding separation capabilities, achieving adsorption selectivities of 4.3 and 5.9, respectively, for C2H2/CO2 (1/1, v/v) mixtures. Dynamic breakthrough experiments confirm their excellent separation capability, maintaining this performance even under conditions of 100% humidity. Monte Carlo simulations and DFT calculations indicate that the exceptional adsorption performance is attributed to the well‐defined pore cavities of the COFs, with fluorination of the building unit further enhancing C2H2 selectivity through improved electrostatic and host‐guest interactions. This study expands the structural diversity of COFs and highlights their potential for low‐energy separation processes.