The treatment of a Mo(0) complex with a tetraphosphine co-ligand [Mo(kappa(4)-P4)(Ph(2)PCH(2)CH(2)PPh(2))] (P4 = meso-o-C(6)H(4)(PPhCH(2)CH(2)PPh(2))(2)) with H(2)S gas in toluene at room temperature afforded [Mo(SH)(2)(kappa(4)-P4)] (1), which demonstrates the first Mo(II) bis(hydrosulfido) complex. Its trigonal-prismatic structure rarely observed for Mo(II) complexes has been determined by X-ray analysis. The reactions of 1 with [RhCl(CO)(2)](2) and [IrCl(CO)(2)(p-toluidine)] in the presence of NEt(3) resulted in the formation of the sulfido-bridged trinuclear clusters [Mo(kappa(4)-P4)(mu(3)-S)(2){Rh(CO)(2)}(2)] (4) and [Mo(kappa(4)-P4)(mu(3)-S)(2){Ir(CO)(2)}(2)] (5), respectively. The X-ray diffraction study has disclosed that the MoRh(2) cluster 4 in the solid state exists in two isomeric forms arising from the different orientation of P4 to the trigonal-prismatic Mo center, whereas the crystals of the Ir analogue 5 contains the molecules corresponding to only one of the two isomers observed for 4. The fluxional features of 1, 4, and 5 in solution have been confirmed by VT NMR studies.