Tandem structural transformations from 4-fold to 5-fold interpenetrated Cd(II) metal-organic frameworks

Abstract Three pseudo-polymorphic isomers of metal-organic frameworks (MOFs) [Cd(2-eiba)2](solvent) (MOFs 1–3, Heiba ​= ​4-(2-ethyl-1H-imidazol-1-yl)benzoic acid) were prepared with different synthesis approaches, including layer diffusion and solvothermal synthesis. Layer diffusion method afforded MOF 1, which showed 2 ​+ ​2 → 4-fold interpenetrating pattern. Empolyment of solvothermal syntheses via different temperatures (60 and 100 ​°C) gave rise to MOFs 2 and 3, featuring 2 ​+ ​2’ → 4-fold and 5-fold interpenetrating structures, respectively. All MOFs displayed dia topological networks. Interestingly, tandem structural transformations occurred to result in the switching of network interpenetration degrees (from 2 ​+ ​2 → 4-fold, to 2 ​+ ​2’ → 4-fold, and to 5-fold). The mechanism proposed for these structural conversions can be appropriately interpreted by the rotation of 2-eiba ligand in the crystallographic lattice. In addition, MOFs 1–3 showed luminescent sensing effect to nitrobenzene and Fe(III) ion.