I certainly can't disagree that such a high extinction coefficient is unusual for a d-d transition. The greater detail in looking at molecular orbitals etc is definitely well beyond HSC or IB chemistry.This has got me interested. I can't find reliable data on the identity of the complex I.e tetrahedral or octahedral which is strange for such a common complex; nevertheless the extinction coefficient of around 4000 is very high for an d-d transition. I suspect it might be a charge transfer band, metal to ligand, but I can't be sure. If anyone has any more information, I would be very interested to hear it.