An open capsule-type octanuclear heterometallic sulfide cluster without an intramolecular inversion center [Ru(eta(6)-C6Me6){P(OMe)(3)}{MoO(mu(3)-S)(3)}(Cul)(2)}(2) (5) has been synthesized for the first time by stepwise connection of three mononuclear building blocks, i.e., (i) [RuCl2(eta(6)-C6Me6){P(OMe)(3)}] (1a) as an octahedral terminal building block to control the direction of cluster expansion, (ii) [MoOS3](2-) as a tetrahedral polydentate building block owing to the strong coordination ability of the S atoms, and (iii) a Cul building block to form a trigonal planar (mu-S)(2)Cul unit or to form a linkage unit of two incomplete cubane-type octanuclear frameworks. The stepwise connection was made in the following order: [RuCl2(eta(6)-C6Me6){P(OMe)(3)}] (1a, mononuclear) -> [Ru(eta(6)-C6Me6){P(OMe)(3)}{MoOS(mu(2)-S)(2)}] (2a, dinuclear) -> [Ru(eta(6)-C6Me6){P(OMe)(3)}{MoO(mu(2)-S)(2)(mu(3)-S)}Cul] (3a, butterfly-type trinuclear) -> [Ru(eta(6)-C6Me6){P(OMe)(3)}{MoO(mu(3)-S)(3)}(Cul)(2)](2) (5). When P(OMe)(3) was replaced by P(OEt)(3), which is more bulky than P(OMe)(3), in the starting ruthenium building block [RuCl2(eta(6)-C6Me6){P(OEt)(3))] (1b, mononuclear), only the tetranuclear incomplete single cubane cluster [Ru(eta(6)-C6Me6){P(OEt)(3)}{MoO(mu(3)-S)(3)}(Cul)(2)] (6) was generated, owing to the steric effect of P(OEt)(3).