Fluorinated linkers enable the synthesis of flexible MOFs with 1D alkaline earth SBUs and a temperature-induced phase transition

Abstract

Fluorination as a functionalization of organic linkers in MOFs has shown surprising effects both on the structure of the linker itself as well as on the topology and properties of the resulting framework materials. 4,4′,4′′-Benzene-1,3,5-triyl-tris-(benzoate), typically abbreviated to BTB, is a well-known linker in the construction of MOFs. It is expected to be planar due to a complete sp² hybridisation of its carbon atoms. However, some flexibility is frequently observed by twists of the outer carboxylate groups as well as by the benzoate rings. The latter is mainly influenced by substituents of the inner benzene ring. Herein, we present two novel alkaline earth metal based MOFs [EA(II)₅(3F-BTB)₃OAc(DMF)₅] (EA(II) = Ca, Sr) utilizing a fluorinated derivative of the BTB-linker (perfluorination of the inner benzene ring) with a unique topology, crystalline sponge behaviour and a low temperature induced phase transition.