Multi-site CO₂ fixation in triazolates: cooperative O,N binding enhanced by solvation and counter-ion effects

The cooperative interaction of nitrogen and oxygen centers in aromatic heterocycles provides an effective pathway for charge-assisted CO₂ capture. Building on the pioneering work of Luo et al. on hydroxy-pyridine systems and our recent PCCP study on hydroxy-substituted N-heterocycles, this work extends the O,N-cooperative binding concept to triazolate frameworks. Density functional theory (DFT) and molecular electrostatic potential (MESP) analyses were performed on neutral, monoanionic, and dianionic 1,2,3- and 1,2,4-triazoles to elucidate how charge, counter-ion and solvation govern CO₂ adsorption. Deprotonation generates anionic and dianionic triazolates with enhanced negative potential at N and O sites, enabling O-carboxylate and N-carboxylate formation. While gas-phase dianions capture multiple CO₂ molecules through cooperative charge delocalization and carbonate-chain growth (up to three CO₂ with ΔG_ad ≈ -54 kcal mol^-1), the inclusion of ethanol solvation and tetramethylphosphonium counter-ions reveals that these species remain strongly exergonic. Reaction modeling shows that both mono- and dianionic triazolates undergo spontaneous CO₂ fixation in solution (ΔG ≈ 24 to -61 kcal mol^-1), forming ion-paired poly(carboxylate) complexes with up to six CO₂ molecules. These results demonstrate that even under polar, solvated conditions, counter-cation-stabilized triazolates preserve high-affinity, multi-site CO₂ capture, identifying them as realistic and promising building blocks for molecular CO₂-activation strategies.