The above chemical compositions indicate that there is a difference in the number of SO3 t Bu ligand between S@Ag54 and I@Ag54. Ligand-protected metal clusters are generally formed when the total number of valence electrons is even. In this study, SC-XRD and electrospray ionization (ESI) mass spectrometry of the low mass region showed that no TFA -, which could be a counter ion, was observed in either S@Ag54 or I@Ag54, suggesting that these clusters were neutral. In this case, because S@Ag54S20(S t Bu)20(SO3 t Bu)12 has an even number of valence electrons, I@Ag54 with the same ligand combination (I@Ag54S20(S t Bu)20(SO3 t Bu)12) should have an odd number of valence electrons. Therefore, it can be considered that I@Ag54 was formed with one fewer SO3 t Bu ligand than S@Ag54 to prevent destabilization due to the odd number of valence electrons.