We know that polynuclear carbonyls are colored and their intensity increases with increase in metal ions. But why does the color arise?
I am aware that this is due to some transition between electronic energy levels; but, what sort of transition takes place? Is it due to transition between orbitals that are largely localized on the ligands i.e. CO, or is due to transition between orbitals localized on metal frame work?
I have tried gathering some information about the same and I have found something called metal to ligand charge transfer (MLCT) that is responsible for colors in complexes, but I am not sure whether this is applicable in this case or not.