# Molecular orbital diagram for I₃⁺ cation

Do I need to go through the whole process of reducible representations/projection operator method to come up with the bent SALCs for the $$\ce{[I3]+}$$ molecule? Or is it simpler than that?

• How is this unusual ion created ? Is it not $\ce{I_3^-}$ ? Because this ion $\ce{I_3^-}$ does exist. Never heard of $\ce{I_3^+}$ !! – Maurice Apr 13 '20 at 9:40
• @Maurice Apparently it is iodonium cation. sciencedirect.com/science/article/abs/pii/S0032386101004906 – Nilay Ghosh Apr 13 '20 at 12:45
• Yes I already found information on I3- but thank you. In a homework we are asked to compare the bond orders of I3- and I3+ after creating their MO diagrams. After much searching and trying to figure out the MO diagram for I3-, I found out that it's very easy and only involves the three 5pz orbitals in a "4 electron 3 center bond." But I don't know if I3+ is similar. I3+ is a different geometry, so I feel like there may be other bonding involved? – Kameron Shrum Apr 13 '20 at 13:01
• I suspect the intent of the exercise is for you to compare the linear and bent structures and determine which is more likely based on MO occupancy. One way to do this is to start with the linear I3- MOs and consider how they are perturbed by bending. Look up Walsh diagrams if you're not familiar with doing that sort of perturbation. – Andrew Apr 13 '20 at 14:28
• I do know about Walsh diagrams, which I've seen for water and BeH2. Linear vs bent for water wouldn't be the same for I3- and I3+ though, it's a different set of orbitals involved. And the homework asks me to construct and MO diagram for I3+, which I don't understand how to do. – Kameron Shrum Apr 14 '20 at 14:15