The reaction of [Mo3S4(H2O)(9)](4+) with Bi-III in, the presence of BH4- (rapid), or with Bi metal shot (3-4 days), gives a heterometallic cluster product. The latter has been characterized as the corner-shared double cube [Mo-6 BiS8(H2O)(18)](8+) by the following procedures. Analyses by ICP-AES confirm the Mo:Bi:S ratio as 6:1:8. Elution from a cation-exchange column by 4 M Hpts (Hpts = p-toluenesulfonic acid), but not 2 M Hpts (or 4 M HClO4), is consistent with a high charge. The latter is confirmed as 8+ from the 3:1 stoichiometries observed for the oxidations with [Co(dipic)(2)](-) or [Fe(H2O)(6)](3+) yielding [Mo3S4(H2O)(9)](4+) and Bi-III as products. Heterometallic clusters [Mo(6)MS(8)(H2O)(18)](8+) are now known for M = Hg, In, Tl, Sn, Pb, Sb, and Bi and are a feature of the P-block main group metals. The color of [Mo6BiS8(H2O)(18)](8+) in 2.0 M Hpts (turquoise) is different from that in 2.0 M HCl (green-blue). Kinetic studies (25 degrees C) for uptake of a single chloride k(f) = 0.80 M(-1) s(-1), I = 2.0 M (Hpts), and the high affinity for Cl- (K > 40 M(-1)) exceeds that observed for complexing at Mo. A specific heterometal interaction of the Cl- not observed in the case of other double cubes is indicated. The Cl- can be removed by cation-exchange chromatography with retention of the double-cube structure. Kinetic studies with [Co(dipic)(2)](-) and hexaaqua-Fe-III as oxidants form part of a survey of redox properties of this and other clusters. The Cl- adduct is more readily oxidized by [Co(dipic)(2)](-) (factor of similar to 10) and is also more air sensitive.