Trinuclear clusters of formula [M3Se4X3(dmpe)3]PF6, M = Mo with X = Cl (1), M = Mo with X = Br (2) and M = W with X = Br (3) have been synthesized by excision of polymeric {M3Se7X4}x phases with dmpe in acetonitrile. Cu(I) is readily incorporated into the molybdenum selenide clusters in organic solvents to give [Mo3CuSe4Cl4(dmpe)3]PF6 (4) and [Mo3CuSe4Br4(dmpe)3]PF6 (5). These are the first reported complexes with [Mo3CuSe4] units. No reaction with Cu(I) has been observed for the tungsten cluster. In contrast with the aquo cuboidal seleno derivatives these trinuclear, 1–3, and tetranuclear, 4 and 5, clusters are air stable making easier their full characterization. X-Ray structural analysis of complexes 1 and 3 shows that the overall geometry of the [M3Se4] core is basically the same as for the [Mo3S4] units. Structures 1 and 3 do not present the weak dimerization through Se–Se bonds observed for the previously reported [M3Se4] cyano and thiocyanato cluster complexes. The addition of a Cu atom to [Mo3Se4] results in cluster compounds with single cube type structures. The six intermetallic distances within the [Mo3Cu] tetrametallic unit in 4 are statistically the same. The Mo–Cu bond distance in 5 is 0.02 Å longer than the Mo–Mo bond length. Electrochemical reduction processes of compounds 1–5 have been investigated by cyclic voltammetry. Cu insertion into complexes 1 and 2 to give 4 and 5 results in an anodic shift potential of 0.25 V for the first reduction process.
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