In the last decade, a big effort has been made to understand the nature of the chemical bonding in PCMs for designing materials with enhanced properties. For many years, the chemical bonding in PCMs and related materials, such as pnictogens and chalcogens, was considered to be a rare case of covalent bonding in which occurred a resonant bonding of p-type orbitals [5-8]. In the last decade, the consensus on the chemical bonding in PCMs has been broken as shown by the papers published in 2023 [4,9-13]. Since 2018, Wuttig and coworkers have considered that PCMs feature a new and unconventional type of bond called "metavalent" bond. This bond is different from the resonant bond present in graphite and benzene and is responsible for the extraordinary properties of PCMs and also of lead halide perovskites [1-4,14 . Taking into account that electrons are fully localized in covalent bonding and fully delocalized in metallic bonding, metavalent bonding has been described as a linear or quasi-linear type of two-center one-electron (2c-1e) bonding in which resonant p-type orbitals result in a combination of electrons that are partly localized and partly delocalized; i.e. as an intermediate bonding type between covalent and metallic bonding, hence its name. Therefore, PCMs are considered to be incipient metals, but with unique properties different from those of covalent and metallic materials. On the other hand, other researchers have considered that there is no need to claim a new type of bonding since they consider that PCMs feature a hypervalent bond [20-28]; i.e. the old known electron-rich multicenter bond (ERMB), whose most known example is the three-center four-electron (3c-4e) bond.