The fourth chapter describes the effect of stepwise ligand substitution and the role of the electron-withdrawing alkynyl ligands on the eight-electron superatom. The role of alkynyl ligands with electron-withdrawing nature in the stability of metal clusters was investigated by gas-phase anion photoelectron spectroscopy on structurally defined superatoms modified with the stepwise ligand substitution. Anion photoelectron spectroscopy on [PdAu24(C≡CArF)18−x(C≡CPh)x]2− (ArF = 3,5-(CF3)2C6H3) with specific x (= 0 − 6) revealed that electron binding energies decreased linearly with x, indicating that the electron-withdrawing CF3 substituents on the alkynyl ligand played a critical role in the electronic stabilization of [PdAu24(C≡CArF)18]2−. Density functional theory calculations reproduced the decrease of electron binding energies and the ligand effect was ascribed to the electrostatic effect of the dipole moment of ligands, which is a similar mechanism to the modulation of the work function of gold films by organic monolayers.