Tuning Pore Size in Square-Lattice Coordination Networks for Size-Selective Sieving of CO₂

Porous materials capable of selectively capturing CO₂from flue-gases or natural gas are of interest in terms of rising atmospheric CO₂levels and methane purification. Size-exclusive sieving of CO₂over CH₄and N₂has rarely been achieved. Herein we show that a crystal engineering approach to tuning of pore-size in a coordination network, [Cu(quinoline-5-carboxyate)₂]_n(Qc-5-Cu) ena+bles ultra-high selectivity for CO₂over N₂(S_CN≈40 000) and CH₄(S_CM≈3300). Qc-5-Cu-sql-β, a narrow pore polymorph of the square lattice (sql) coordination network Qc-5-Cu-sql-α, adsorbs CO₂while excluding both CH₄and N₂. Experimental measurements and molecular modeling validate and explain the performance. Qc-5-Cu-sql-β is stable to moisture and its separation performance is unaffected by humidity.