For the neutral I6 chain, the argument of instability towards 3 I2 molecules also applies, as for the neutral I4 chain. The I6 2-dianion (Figure center) is instead a special case and, despite correct (even) chain electron count, it is the most experimentally elusive anion of the I2n 2- series. Although it might seem that the anion can form a chain with 2n electrons distributed in n bonds, as our model easily shows, the cause of instability is to be found in the impossibility of ERMB to extend beyond 3 centers, making I6 2-unstable towards 2 I3 -anions (understood as formal displacement of the central black/blue electron pair in Figure to reinforce bonds 2-3 and 4-5, leading to two independent I3 -units with their corresponding 3c-4e bonds).