Ligand Geometry Regulated Architecture of Ultra-Microporous Flexible Guanidinium-Based Hydrogen-Bonded Organic...

The efficient separation of nitrous oxide (N₂O) from nitrogen (N₂) is crucial for recovering valuable gases and mitigating industrial greenhouse gas emissions, yet remains a formidable challenge. A ligand geometry engineering strategy is reported herein to fabricate a series of guanidinium-based hydrogen-bonded organic frameworks (HOFs) with layered, ordered ultramicroporous and densely packed architectures. Among them, guanidinium 1,3,5-tris(4-carboxyphenyl)benzene (G-BTB) is distinguished by its unique snowflake-like polar ultra-micropores and corrugated, wavy layered stacking architecture. It delivers exceptional N₂O/N₂ separation-The Ideal Adsorbed Solution Theory (IAST) selectivities of 1091 and 782 for 50:50 and 10:90 (v/v) mixtures-and outstanding N₂O adsorption capacity of 3.70 mmol g^-1 at 298.0 K and 4.0 MPa, with distinct self-enhancement. Density functional theory (DFT) simulations and in situ X-ray diffraction (XRD) analysis reveal that this remarkable performance stems from a multilevel synergy: ultra-microporous confinement, strong electrostatic interactions from polar (C═O) pore walls, and host-guest adaptability. This multipath, stimuli-responsive structural evolution, underpinned by the ligand geometry modulation strategy, provides critical guidance for the directional design of HOF structures and the exploitation of advanced adsorbents for efficient N₂O separation.