Ligand Geometry Regulated Architecture of Ultra‐Microporous Flexible Guanidinium‐Based Hydrogen‐Bonded Organic Frameworks for Highly Selective Nitrous Oxide/Nitrogen Separation

The efficient separation of nitrous oxide (N 2 O) from nitrogen (N 2 ) 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 N 2 O/N 2 separation—The Ideal Adsorbed Solution Theory (IAST) selectivities of 1091 and 782 for 50:50 and 10:90 (v/v) mixtures—and outstanding N 2 O 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 N 2 O separation.