Transformations of empty Cu core to CuCuO and CuS cores via oxide and sulfide insertions.

[Cu4(LRh)4]8- ([1]8-; LRh = Δ-[Rh(l-cysteinate)3]3-), with an empty tetrahedral {CuI4}4+ core, was converted to [Cu4O(LRh)4]8- ([2]8-), with a mixed-valent {CuI2CuII2O}4+ core, in aqueous NaOH. A solid sample of the latter compound was converted back to [1]8- by heating under vacuum, while treatment of [1]8- with aqueous NaSH caused conversion to [Cu6S(LRh)4]8- ([3]8-), with a stable octahedral {CuI6S}4+ core.