Zr- and Hf-Based Metal–Organic Frameworks: Tracking Down the Polymorphism

Six novel Zr(IV)- and Hf(IV)-based MOFs, namely DUT-67, DUT-68, and DUT-69 (DUT, Dresden University of Technology) were obtained using a modulated synthesis approach with the acetic acid as a modulator and the bent 2,5-thiophenedicarboxylate (tdc2–) as a ligand. The modulator not only increases the size of the MOF crystallites but also plays a role of a structure directing agent, affecting both the secondary building unit (SBU) connectivity and topology of the resulting frameworks. The structure of DUT-67 is based on the reo underlying net, characteristic for its cuboctahedral and octahedral pores and is therefore isoreticular to DUT-51. The DUT-68 material has a more complicated hierarchical pore system including rhombicuboctahedral mesopore, surrounded by cuboctahedral, square-antiprismatic and octahedral microcages. DUT-69 is the first example of Zr-based MOF containing 10-connected SBU. DUT-69 has bct topology, possessing octahedral cages and channels running along one crystallographic direction. In a...