Electronic absorption spectra Allowed vs forbidden transitions

Transitions in d 1 and d 2 complexesEd xz d xy d yzd x 2 -y 2 d z 2 d xz d xy d yzd x 2 -y 2 d z 2 d x 2 -y 21d xzd xyd yzd x 2 -y 2 d z 2 d x 2 -y 2d z 2d xz d xy d yz1d xy d x 2 -y 21d xz1d xz 1 d z 2 1 d yz 1 d z 2 1d xy 1 d z 2 1 d yz 1 d x 2 -y 21d xz d xy d yzd x 2 -y 2 d z 2d x 2 -y 2 d z 2d xz d xy d yzSome compounds are very highly coloredbecause of charge transfer transitions – evensome with no d electrons● There can be electronic transitions in the visible region that donot involved d-electrons− MnO 4- (purple) and CrO 42-(yellow) are intensely coloredbecause electrons in filled oxygen based orbitals areexcited into empty d-orbitals (LMCT)− Ligand to Metal Charge Transfer (LMCT) bands have fewselection rule restrictions and are typically very intense● Metal to Ligand Charge Transfer (MLCT) bands may also occurfor complexes with d-electrons.− There are few selection rules and the high intensity of thesebands may mask d-d transitions.