Tetra-μ(3)-selen-ido-1:2:3κ(3)Se;1:2:4κ(3)Se;1:3:4κ(3)Se;2:3:4κ(3)Se-tetrakis-[(η(5)-methyl-cyclo-penta-dien-yl)molybdenum(III)](6 Mo-Mo).

The title cluster compound, [Mo(4)(η(5)-C(5)H(4)Me)(4)(μ(3)-Se)(4)], was synthesized from the reaction of [Mo(η(5)-C(5)H(4)Me)(CO)(3)](2) with grey selenium in refluxing xylene solution under a nitro-gen atmosphere. The complete cluster is generated by a crystallographic twofold axis and contains an Mo(4)Se(4) cubane-like core surrounded by four η(5)-methylcyclo-pentadienyl ligands. In the core, the four molybdenum atoms are connected to each other to form a tetra-hedron, with a selenium atom capping each face. The Mo-Mo bond lengths vary from 2.9857†(5) to 3.0083†(3)†à and the Mo-Se separations range from 2.4633†(4) to 2.4693†(5)†à .