Reticular chemistry: occurrence and taxonomy of nets and grammar for the 27 design of frameworks

The structures of all 1127 three-periodic extended metal-organic frameworks (MOFs) reported in the Cambridge Structure Database have been analyzed, and their underlying topology has been determined. It is remarkable that among the almost infinite number of net topologies that are available for MOFs to adopt, only a handful of nets are actually observed. The discovery of this inversion between expected and observed nets led us to deduce a system of classification ªtaxonomyº for interpreting and rational-izing known MOF structures, as well as those that will be made in future. The origin of this inversion is attributed to the different modes with which MOF synthesis has been approached. Specifi-cally, three levels of complexity are defined that embody rules ªgrammarº for the design of MOFs and other extended structures. This system accounts for the present proliferation of MOF struc