The aminodiphosphane molybdenum (IV) cluster complex of formula [Mo3S4Cl3(κ 2 (P,N)-PNP)3]Cl (PNP = bis[(2-di-i-propylphosphino)ethyl]amine) [Mo-1]Cl has been isolated in high yields by reacting [Mo3S4Cl4(PPh3)3(H2O)2] with stoichiometric amounts of the PNP ligand. Characterization of [Mo-1] + by ESI-MS, 31 P{ 1 H} NMR and single-crystal X-ray diffraction confirms that aminodiphosphanes bind as bidentate ligands to the Mo3S4 unit leaving three uncoordinated phosphino groups. The dangling phosphino groups can substitute the chloride ligands and coordinate to the cluster core in the presence of AgBF4 to give the complex of formula [Mo3S4(κ 3-PNP)3](BF4)4 ([Mo-2](BF4)4). The tridentate coordination of the aminodiphosphane ligands to the Mo3S4 cluster unit in ([Mo-2] + is confirmed by 31 P{ 1 H} NMR and elemental analysis.