Design of a MOF based on octa-nuclear zinc clusters realizing both thermal stability and structural flexibility

An octa-nuclear zinc (Zn8) cluster-based two-fold interpenetrated metal-organic framework (MOF) of [(CH3)2NH2]2[Zn8O3(FDC)6]·7DMF (denoted as Zn8-as; H2FDC = 9H-fluorene-2,7-dicarboxylic acid; DMF = N,N-dimethylformamide) was synthesized by the reaction of a hard base of a curved dicarboxylate ligand (H2FDC) with the borderline acid of Zn(II) under solvothermal conditions. Zn8-as shows significant crystal volume shrinkage upon heating, yielding a solvate-free framework of [(CH3)2NH2]2[Zn8O3(FDC)6] (Zn8-de). Zn8-de displays gated adsorption for C2H2 and type-I adsorption for CO2, attributed to the framework flexibility and the different interactions between the gas molecules and the host framework.