Two copper-mercury-chalcogenide clusters [Hg15Cu20E25(PPr3)(18)] (1, E = S; 2, E = Se) are synthesized in good yield from the reaction of (Pr3P)(3)Cu-ESiMe3 and (Pr3P)(2).Hg(OAc)(2) at low temperatures. Single-crystal X-ray analyses illustrate that the two ternary clusters are isomorphous and consist of a phosphine-stabilized core of mixed Hg, Cu, and E centers. Thermolysis of 1 leads to the formation of mercury metal and various forms of copper-sulfide. The copper-indium-sulfide cluster [Cu(6)ln(8)S(13)Cl(4)(PEt3)(12)] (3) is similarly prepared in 50% yield from (Et3P)(3)Cu-SSiMe3, InCl3, and S(SiMe3)(2).