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Porous Coordination-Polymer Crystals with Gated Channels Specific for Supercritical Gases
Summary:
The authors from Kyoto University developed two flexible nanoporous coordination polymers (1a & 2) with “gated” channels that open/close only at super-critical gas pressures, achieving unprecedented gate-controlled CO₂/CH₄/O₂/N₂ uptake and release at 298 K.
Background:
1. To address the trade-off between rigid zeolite-like stability and selective guest recognition, previous workers built robust MOFs but lost dynamic response; flexible frameworks showed guest-induced breathing yet lacked gate-pressure tunability for super-critical gases.
2. The team now proposes an “interdigitated 2D” and “interpenetrated 3D” design motif that couples π–π sliding with weak coordination hinges, yielding crystal-to-crystal gate transitions whose threshold pressure is dictated by guest polarizability.
Research Content:
1. Synthesis:
Layering aqueous Cu(NO₃)₂ with ethanolic H₂dhbc/4,4′-bpy (for 1a) or bdc/4,4′-bpy (for 2) gives plate-like green crystals within days at room temperature.
2. Characterizations:
1) BET: closed form 1b ≈ 24 m² g⁻¹; gate-open 1a reaches 320 m² g⁻¹ (N₂, 298 K).
2) SEM: single-crystal plates 50–200 µm; XRPD confirms single-crystal-to-single-crystal gliding (Δ2θ ≈ 2°) upon dehydration.
3) High-pressure gravimetric analyses: gate-opening pressures 0.4 atm (CO₂) → 50 atm (N₂); reversible 20-cycle hysteresis.
3. Application:
The materials act as pressure-selective valves, separating CO₂ from CH₄/O₂/N₂ streams by choosing operating windows between 0.2–50 atm without external heating.
4. Mechanism:
Guest–π interactions trigger sliding of interdigitated dhbc rings or interpenetrated grids, expanding 1D/3D channels from 3.3 Å to 4.2 Å; DFT shows dispersion energy scales linearly with gate-opening pressure, validating a “molecular force-balance” model.
Outlook:
This study demonstrates the first super-critical gas specific “gate-opening” crystals, providing a new platform for pressure-swing gas separation, sensors and actuators operating under ambient temperature.
Porous Coordination-Polymer Crystals with Gated Channels Specific for Supercritical Gases
Authors: Ryo Kitaura, Kenji Seki, George Akiyama, Susumu Kitagawa
DOI: 10.1002/anie.200390130
Link: https://onlinelibrary.wiley.com/doi/10.1002/anie.200390130
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