$$d^1$$: There is no T-S diagram for $$d^1$$ $$d^2$$ $$d^3$$ $$d^4$$ $$d^5$$ $$d^6$$ $$d^7$$ $$d^8$$ $$d^9$$: There is no T-S diagram for $$d^9$$ (??) $$d^10$$: There are no d-d transitions in a $$d^10$$ complex.