Flexible Coordination Network Exhibiting Water Vapor–Induced Reversible Switching between Closed and Open Phases

That physisorbents can reduce the energy footprint of water vapor capture and release has attracted interest because of potential applications such as moisture harvesting, dehumidification, and heat pumps. In this context, sorbents exhibiting an S-shaped single-step water sorption isotherm are desirable, most of which are structurally rigid sorbents that undergo pore-filling at low relative humidity (RH), ideally below 30% RH. Here, we report that a new flexible one-dimensional (1D) coordination network, [Cu(HQS)(TMBP)] (H₂HQS = 8-hydroxyquinoline-5-sulfonic acid and TMBP = 4, 4′-trimethylenedipyridine), exhibits at least five phases: two as-synthesized open phases, α ⊃ H₂O and β ⊃ MeOH; an activated closed phase (γ); CO₂ (δ ⊃ CO₂) and C₂H₂ (ϵ ⊃ C₂H₂) loaded phases. The γ phase underwent a reversible structural transformation to α ⊃ H₂O with a stepped sorption profile (Type F-IV) when exposed to water vapor at 100 cycles and only mild heating (