Evolution of Zr nodes in metal–organic frameworks

The predefined geometries of metal–organic framework (MOF) building blocks, which consist of secondary building units (SBUs) and organic linkers, are integral to the rational design of new structures. In contrast to that of organic linkers, access to new SBUs is a daunting challenge because of their complex chemistry during MOF synthesis. Here, we present novel opportunities for molecular clusters to bring future SBUs in MOF chemistry. This opinion article summarizes recently emerging structural types of Zr SBUs and provides an understanding of Zr molecular clusters, suggesting them as new SBU candidates. A structural library of Zr molecular clusters will accelerate the discovery of new Zr-based MOFs and motivate similar analysis on various classes of MOFs.