A heterometallic metal–organic framework based on multi-nuclear clusters exhibiting high stability and selective gas adsorption

Abstract

The design and synthesis of porous heterometallic metal–organic frameworks (MOFs) with high thermal and chemical stability is a challenging task at present. In this work, by the heterometallic cooperative crystallization (HCC) approach, an original heterometallic MOF based on a tetra-carboxylic ligand has been solvothermally synthesized [In₆O₃Tb₃O(CBDA)₃]·18DMF·3H₂O (In/Tb-CBDA) [CBDA = 5,5′-(carbonylbis(azanediyl))-diisophthalic acid, DMF = N,N-dimethylformamide]. The framework of In/Tb-CBDA is cooperatively assembled from the rarely reported tetra-nuclear In₄O₂(COO)₄ and tri-nuclear Tb₃O(COO)₆ clusters, and an organic ligand. Topological analysis indicates that In/Tb-CBDA exhibits a new (4,4,6)-connected topology with the Schläfli symbol (4·6³·8²)₆(4³·6⁹·8³)₂(6²·8⁴)₃. Noteworthy, forming multi-nuclear metal clusters prompts the framework to maintain high stability under the conditions of heating to 150 °C, exposure to air, and soaking in acidic and basic aqueous solutions for 12 h. After desolvation, In/Tb-CBDA shows permanent porosity proved by N₂ adsorption isotherms. In addition, theoretical ideal adsorption solution theory (IAST) calculation indicates that In/Tb-CBDA displayed high selective adsorption of CO₂/CH₄, C₂H₆/CH₄ and C₃H₈/CH₄ at room temperature. This work shows a striking example of a porous heterometallic MOF material with high thermal and chemical stability, which exhibits high-efficiency selective gas adsorption behaviour.