Jelfs and co-workers have outlined a simple system of nomenclature in which building blocks with complementary functionality, depending on the covalent bond being targeted (e.g. aldehyde and amine for imines, boronic acid and diol for boronic esters), are assigned as ditopic (Di), tritopic (Tri), or tetratopic (Tet) based on the number of reactive end groups. The stoichiometry of building blocks in the resultant assembly will be determined by their topicity, following analogous principles to Lehn's maximal site occupancy, e.g. a ditopic unit combined with a tritopic unit will likely give species with a 2:3 ratio ([2n+3n]) of Tri and Di units (Tri 2n Di 3n ), with the precise formula dependent on the building block structures and external factors (Fig. ). It is noted, however, that there are exceptions to this rule, in which the stoichiometry of building blocks in a POC does not align with the ratio of their reactive groups. By careful design of the building blocks, topologically comparable structures can be assembled using different reactions (Fig. ). Triformylbenzene, 15, and diamine 16 assemble to form the [4+6] (or Tri 4 Di 6 ) tetrahedron 17; 78 alternatively triamine 18 and dialdehyde 19 also form a [4+6] imine-based tetrahedron ( ), whilst a boronic ester analogue (23) was formed from the combination of tris-diol 21 and bisboronic acid 22. 80 Fig. The topologies of POCs formed through DCCs can be designated formulations based on the number of reactive groups on the building blocks. Reproduced from reference 76 with permission from the Royal Society of Chemistry. Through careful design, topologically analogous systems can be prepared with functional groups on different building blocks or using alternative reactions. R groups omitted from SCXRD structures for clarity.