Pentanuclear Yb(III) cluster-based metal-organic frameworks as heterogeneous catalysts for CO2 conversion

Two porous metal-organic frameworks (MOFs) incorporating pentanuclear Yb(III) clusters and pyridyl-supported tetracarboxylates or pyridyl carboxylic acid-supported tetracarboxylates, Yb-DDPY and Yb-DDIA, are presented, in which the pentanuclear Yb(III) cluster shows uncommon trigonal bipyramidal geometry. Furthermore, the pentanuclear Yb(III) clusters are extended by tetracarboxylates to form a 3D porous framework with uniform M12L8-cages constructed by 12 pentanuclear Yb(III) clusters and 8 tetracarboxylates with the size of ca. 20 Å × 17 Å. Their highly CO2 uptake capacity and the existence of Lewis acidic sites make these MOFs promising catalysts for the chemical conversion of CO2. These MOFs demonstrate good catalytic activities and recyclability in the cycloaddition of CO2 and epoxides at 60 °C under 1.0 MPa pressure or at room temperature and atmospheric pressure. In addition, the synergistic effect of the Brønsted acidic –COOH groups and the Lewis acidic Yb(III) sites makes Yb-DDIA exhibit higher catalytic activity towards the cycloaddition of CO2 and epoxides.