For the isoelectronic series[V(CO)6]-, Cr(CO)6, and [Mn(Co)6]+, does the energy of the metal to ligand charge-transfer bands increase or decrease with increasing charge on the complex? Why?
Although this involves molecular orbitals, if we want to address this question rigorously, we can apply a simplification without changing the conclusion. Three degenerate orbitals of the metal, dxy, dxz and dyz, interact with the pi* orbitals of CO, causing the energy of the former to go down and ...
The solution applies a simplification to explain the question of increasing or decreasing charge on an isoelectric series in terms of orbital set energies as clearly as possible.