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 (<b>soc</b>) topology. The new MOF, formulated as [In₃O­(<b>L</b>)_1.5(H₂O)₂Cl]·n­(solv) (<b>1</b>), features the oxo-centered trinuclear clusters, [In₃(μ₃-O)­(−COO)₆], acting as trigonal-prismatic 6-connected nodes that linked together with the metalloligand <i>trans</i>-[PdCl₂(PDC)₂] (<b>L</b>^<b>4–</b>) (PDC: pyridine-3,5-dicarboxylate) to form a 3D network. After successful activation of <b>1</b> 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 <i>Q</i>_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(<b>L</b>)]·<i>n</i>(solv) (<b>2</b>). This MOF is constructed from pseudotetrahedral, mononuclear [In­(−COO)₄] nodes bridged by four <b>L</b>^<b>4–</b> linkers, resulting in a 3D network with <b>PtS</b> topology