Engineering Metal Pyrazolate Coordination Polymers for Highly Selective Direct Air Capture via Metal–Ligand Cooperativity and Moisture-Gated Mechanism

Abstract

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 (M R Pyr) 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 M R Pyr 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 (M R Carbamate). To elucidate the operative mechanism, crystallographic snapshots and in/ex situ spectroscopic analyses unveil that MLC hydration of K Me Pyr yielding K Me Pyr·H 2 O 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 M R Pyr from CO2-saturated M R Carbamate adducts and demonstrated multiple-cycle recyclability under a temperature-vacuum swing adsorption process position the robust M R Pyr platform as a paradigm-shifting class of sorbents for sustainable DAC applications.