Benchmark C 2 H 2 /CO 2 Separation in an Ultra‐Microporous Metal–Organic Framework via Copper(I)‐Alkynyl Chemistry

Separation of acetylene from carbon dioxide remains a daunting challenge because of their very similar molecular sizes and physical properties. We herein report the first example of using copper(I)‐alkynyl chemistry within an ultra‐microporous MOF (Cu I @UiO‐66‐(COOH) 2 ) to achieve ultrahigh C 2 H 2 /CO 2 separation selectivity. The anchored Cu I ions on the pore surfaces can specifically and strongly interact with C 2 H 2 molecule through copper(I)‐alkynyl π‐complexation and thus rapidly adsorb large amount of C 2 H 2 at low‐pressure region, while effectively reduce CO 2 uptake due to the small pore sizes. This material thus exhibits the record high C 2 H 2 /CO 2 selectivity of 185 at ambient conditions, significantly higher than the previous benchmark ZJU‐74a (36.5) and ATC‐Cu (53.6). Theoretical calculations reveal that the unique π‐complexation between Cu I and C 2 H 2 mainly contributes to the ultra‐strong C 2 H 2 binding affinity and record selectivity. The exceptional separation performance was evidenced by breakthrough experiments for C 2 H 2 /CO 2 gas mixtures. This work suggests a new perspective to functionalizing MOFs with copper(I)‐alkynyl chemistry for highly selective separation of C 2 H 2 over CO 2 .