Engineering Metal Pyrazolate Coordination Polymers for Highly Selective Direct Air Capture via Metal-Ligand...

Direct air capture (DAC) of CO2 has emerged as an indispensable negative emission technology, yet current sorbents remain constrained by the persistent trade-off between intrinsic capture capacity and regeneration energy alongside the extrinsic challenge of atmospheric moisture inhibition. Herein, engineering of crystalline and thermally stable alkali metal pyrazolate coordination polymers (MRPyr) is established as a novel paradigm for the metal-ligand cooperative (MLC), moisture-gated, and highly selective capture of CO2 from ambient air streams. While inert in low-humidity air, activation of solid-state MRPyr by atmospheric moisture unlocks exceptional CO2-capture capacities (7.4-9.2 mmol/g) and realizes a substantial CO2:pyrazolate stoichiometry (0.83-0.89) through formation of metal carbamate (MRCarbamate). To elucidate the operative mechanism, crystallographic snapshots and in/ex situ spectroscopic analyses unveil that MLC hydration of KMePyr yielding KMePyr·H2O triggers a substantial structural rearrangement from a compact double-ladder chain into an expanded zig-zag architecture. This moisture-gated transformation relieves steric shielding and unleashes intrinsic nucleophilicity of pyrazolate ligands to initiate CO2 capture via a thermodynamically favored displacement of bound water. Finally, quantitative regeneration of MRPyr from CO2-saturated MRCarbamate adducts and demonstrated multiple-cycle recyclability under a temperature-vacuum swing adsorption process position the robust MRPyr platform as a paradigm-shifting class of sorbents for sustainable DAC applications.