Aliovalent solid solutions of metal–organic frameworks

Metal–organic frameworks (MOFs) are amenable to the formation of solid solutions by the isomorphous substitution of the organic linker and/or the metal ion. In the case of metal substitution, the incorporation of aliovalent species, i.e., species having a different oxidation state than the original ion, leads to the generation of excess charges in the framework, which must be compensated. Depending on the charge compensation mechanism, new properties can emerge. Although limited work has been done so far in this research area, aliovalent substitution has the potential to become an important tool to fine-tune the physico-chemical properties of MOFs and should be investigated more systematically. Here, the available literature on the aliovalent solid solutions of MOFs is critically analysed under the lens of inorganic solid-state chemistry.