The arguments provided in the previous paragraphs can be easily extended to the In 2-and In 3- series, so that bonding electrons must always be an even number. For the In 2-series, evennumbered polyiodides (I2n+2 2-) are stable according to the above even/odd number of bonding electrons in the chain, whereas for the In 3-series, the odd-numbered polyiodides (I2n+3 3-) are favored. Notably, the simplest experimentally encountered polyiodides of 2-and 3-charge are I4 2-, I8 2-(even number of I atoms, even number of chain electrons), and I7 3-(odd number of I atoms, even number of chain electrons). The above even/odd arguments regarding the existence or not of molecules of the In 2-and In 3- series, are also supported by the energetic arguments that we have already discussed for the In - series. Even-numbered In chains have n/2 bonding and n/2 antibonding MOs, while oddnumbered chains have (n-1)/2 bonding, 1 non-bonding, and (n-1)/2 antibonding MOs. Thus, I2n+2 2-and I2n+3 3-series do begin to populate antibonding orbitals, reducing their intrinsic stability. In particular, anions of the I2n+2 2-series fill 2n/2 bonding orbitals and 1 antibonding orbital, while anions of the I2n+3 3-series fill 2n-1 bonding orbitals, 1 non-bonding orbital, and 1 antibonding orbital. In other words, any polyiodide of superior charge would need to put extra electrons in antibonding levels. The energetic instability caused by the population of antibonding orbitals allows to explain why no polyiodides with higher charge are generally experimentally encountered. We have to notice that even the simplest of the I2n+2 2-and I2n+3 3-anions (I4 2-) was predicted to be unstable. Still, its instability with respect to formal I2 and I -components is not marked: even scholars who predicted the anion to be unstable stated that it could be possible for crystal packing and further supramolecular interactions to stabilize the anion. In fact, higher level calculations, a quarter of a century later, have validated I4 2-as a stable adduct. Interestingly, I4 2-, I8 2-and even I7 3-have been experimentally observed at the solid state, often in situations in which ligand/anion shape/size stereo-electronic complementarity was deliberately sought (supramolecular caging of polyiodides type studies, cf. dedicated section in ref. 4). A discussion of suggested the Lewis dot graphs (Figure ) for some of these poly-charged anions is instructive and is briefly presented below. When drawing I4 2-, it is instructive to stop at the I4 neutral chain, in consideration of the fact that extra electrons occupy an antibonding orbital. Note that full EDMB is only possible in extended systems or, equivalently, that bond alternation is more significant in shorter chains. This results in the obvious instability of a neutral I4 chain towards 2 fundamentally not bonded I2 molecules (cf. Figure ). The addition of two further electrons to the I4 system (in order to produce the I4 2- dianion) allows for stabilization of the system at the price of increased electrostatic repulsion. I4 2-dianion is generally depicted as a 2 I -weakly interacting with a central I2 molecule. Beyond electrostatics, the reason for bond alternation can be found in octet rule concerns for atoms 2 and 3: maintaining 2c-2e bonds on both sides would mean reaching a 10-electron count. In that sense, a careful reader could object that atoms 2 and 3 of the I4 2-anion must exceed the 8-electron count (more than atom 2 of the I3 -case); a clever answer would be that exceeding the octet rule comes at the price of stability and that those same extra electrons, as far as MO is concerned, start filling antibonding orbitals, as preventively stated above. This further argument supports the view of chains of p bonding orbitals, rather than d orbitals involvement. Despite the above facts pointing to the limited stability of this anion, the linear I4 2-anion has enough stability to be sometimes isolated in the solid phase thanks to packing forces.