# Why do isomeric complexes often have different colors? [duplicate]

For example, $\ce{[Cr(NH3)2Cl2]+}$

One isomer is green and the other is violet. Why is this so? The ligands are the same, the oxidation state is the same, and so is the coordination number. The only reason I can think of is that if two $\ce{NH3}$ ligands are trans to each other, they repel the 3d orbitals differently than if they were cis. But I don't know why this would occur.

The explanation given in the other question involves anti-bonding orbitals, and I simply have no idea what these are. I'd like an answer which uses highschool chemistry so that I can understand (albeit perhaps in a flawed way ) whats going on.

• Sorry for the late followup - if you want an easier answer, please place a bounty on the duplicate question, requesting for an easier answer. When something is marked as a duplicate, that is simply because the question has been asked before; it does not take into account the kind of answer requested. Thanks for understanding. – orthocresol May 16 '17 at 13:21
• I can't see the option for adding a bounty.. – John May 16 '17 at 15:47
• You seem to have figured it out? :) – orthocresol May 16 '17 at 15:54
• Yeah, just read 'on the duplicate question'. Hopefully this is something which is explainable to a highschooler.. – John May 16 '17 at 15:56