<i>In situ</i> generated 2,5-pyrazinedicarboxylate and oxalate ligands leading to a Eu-MOF for selective capture of C₂H₂ from C₂H₂/CO₂

The separation of C₂H₂/CO₂ mixtures is a very important but highly challenging task due to their comparable physical natures and relative sizes. Herein, we report a europium-based 3D microporous MOF with a 4-connected two-nodal net with <b>{4·5</b>^<b>3</b><b>·6</b>^<b>2</b><b>}</b>_<b>2</b><b>{4</b>^<b>2</b><b>·6</b>^<b>2</b><b>·8</b>^<b>2</b><b>}</b> topology, {[Eu₂(pzdc)(ox)₂(H₂O)₄]·5H₂O}_<i>n</i> (1) (H₂pzdc = 2,5-pyrazinedicarboxylic acid, H₂ox = oxalic acid), prepared by a hydrothermal method involving <i>in situ</i> generation of 2,5-pyrazinedicarboxylate and oxalate ligands. Two different temperatures were utilized to create two porous materials (1a and 1b) with channels of 4.8 × 5.4 Å and 4.1 × 6.3 Å, and 4.8 × 5.4 and 4.6 × 8.7 Ų, respectively. 1b shows a superior ability to selectively capture C₂H₂ from C₂H₂/CO₂ as compared with 1a. At 1 bar and 298 K, 1b takes up 4.10 mmol g^-1 C₂H₂ and 1.84 mmol g^-1 CO₂, respectively. In addition, at 298 K and 1 bar, 1b has a high selectivity for C₂H₂ over CO₂, with an IAST selectivity of 12.7 while the value for 1a is 3.2. The separation of C₂H₂/CO₂ with 1b also exhibits good reusability.