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) Å and the Mo-Se separations range from 2.4633 (4) to 2.4693 (5) Å.