Heterometallic In(III)-Pd(II) Porous Metal-Organic Framework with Square-Octahedron Topology Displaying High CO2 Uptake and Selectivity toward CH4 and N2.

Abstract

The targeted synthesis of metal-organic frameworks (MOFs) with open metal sites, following reticular chemistry rules, provides a straightforward methodology toward the development of advanced porous materials especially for gas storage/separation applications. Using a palladated tetracarboxylate metalloligand as a 4-connected node, we succeeded in synthesizing the first heterobimetallic In(III)/Pd(II)-based MOF with square-octahedron (soc) topology. The new MOF, formulated as [In3O(L)1.5(H2O)2Cl]·n(solv) (1), features the oxo-centered trinuclear clusters, [In3(μ3-O)(-COO)6], acting as trigonal-prismatic 6-connected nodes that linked together with the metalloligand trans-[PdCl2(PDC)2] (L4-) (PDC: pyridine-3,5-dicarboxylate) to form a 3D network. After successful activation of 1 using supercritical CO2, high-resolution microporous analysis revealed the presence of small micropores (5.8 Å) with BET area of 795 m2 g-1 and total pore volume of 0.35 cm3 g-1. The activated solid shows high gravimetric (92.3 cm3 g-1) and volumetric (120.9 cm3 cm-3) CO2 uptake at 273 K and 1 bar as well as high CO2/CH4 (15.4 for a 50:50 molar mixture) and CO2/N2 (131.7 for a 10:90 molar mixture) selectivity, with moderate Qst0 for CO2 (29.8 kJ mol-1). Slight modifications of the synthesis conditions led to the formation of a different MOF with an anionic framework, having a chemical formula [Me2NH2][In(L)]· n(solv) (2). This MOF is constructed from pseudotetrahedral, mononuclear [In(-COO)4] nodes bridged by four L4- linkers, resulting in a 3D network with PtS topology.