Anion–Cation Redox Competition and the Formation of New Compounds in Highly Covalent Systems

Abstract The increase in energy of the sp anionic band on going from oxides to the less electronegative sulfides, selenides, or tellurides (with a similar trend in neighboring columns) facilitates anion–cation redox interactions involving the d levels of transition metal cations and the sp levels of anionic species. The interactions can induce phase transitions or gradual change within a given structural model. When a cation is reduced by electron transfer to its d levels from the sp band, holes appear at the top of the latter. Interesting soft chemistry can be carried out based on redox processes that neutralize the holes with electrons. This approach also allows particular structural types to be stabilized. Three structural domains can be recognized amongst the transition elements: 1) on the left‐hand side of the periodic table layered structures are observed involving M 4 + and (chalcogen) 2‐ ions; 2) formation of sets of metal‐metal bonds is then observed, the geometry of which depends on both the initial electron population and the electron transfer to the metal; 3) on the right‐hand side the metals in their highest oxidation state are no longer active, and the holes at the top of the sp band are taken up by a catenation of the anions, which can lead to full polymerization of the anionic sublattice.