Question

What does a small homo-lumo gap of transitonmetal have to do with its catalytic reactivity?

Answer 1

HOMO is the highest occupied molecular orbitals consisting of electron in it and exist below the energy level of LUMO which is lowest occupying molecular orbital having no lectrons before excitation. Now the diiference between the energy level of both tends to affect the certain properties such as optical and catalytic properties. As due to low HOMO-LUMO gap exhibiting in transition metals make them to show colour usually. Small gap will allow the electron to jump to excited/LUMO state over low energy supply suggesting its stability along with catalytic reactivity because what catalyst do, it provides a different pathway having lower energy for a reaction. Also the small gap results in π electron mobility i.e larger the mobility leads to the larger distribution of energy through the molecule, hence lower the HOMO-LUMO gap, lesser the energy, is required for catalysts/transition metals ,more easily the electron will be excited and to provide lower energy pathway for the reaction to happen.