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

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] (L^4–) (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 Q_st⁰ 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 L^4– linkers, resulting in a 3D network with PtS topology.