The mixed-metal cluster compound (Me2NH2)6[(SCN)9W3S4SnCl3].0.5H2O (1) with the cubane-type [W3(mu3-S)4Sn] core has been prepared by reacting W3S44+ in aqueous HCI solution with SnCl2.2H2O in the presence of Me2NH2Cl and NaSCN. 1 was characterized by X-ray crystallography and by Sn-119 Mossbauer, photoelectron, and electronic absorption spectroscopy. Crystals of 1 are monoclinic, of space group C2/c, with a = 42.792(10) angstrom, b = 11.988(2) angstrom, c = 21.725(3) angstrom, beta = 95.24(2)-degrees, and Z = 8. The structure was refined by full-matrix least-squares techniques to R = 0.069 and R(w) = 0.071 for 7690 reflections with F > 4sigma(F). The formation of 1 is due to a synergetic effect : The affinity of the W3S4 ligand for cations like Sn2+ is increased as its electron-donor strength is increased by the reducing cation itself. An alternative description would be to insert a plug formed mainly from the Sn 5s level into a socket formed from acceptor levels localized on the W3 triangle, which is equivalent to a novel type of host pest interactions.