Investigation of single MoFe3S4 cubane cluster: I. First successful synthesis by spontaneous self-assembly reaction and structure of (Et4N) [MoFe3S4(Et2NCSS)5]CH3CN

A single MoFe₃S₄ cubane-like cluster compound has been synthesized through spontaneous self-assembly of simple inorganic salts with organosulfur ligand for the first time. (Et₄N)-(MoFe₃S₄(Et₂NCSS)₅] CH₃CN(1) is quite stable in air. The crystal of 1 is monoclinic with space group P2/c, a=22.897 (3)Å, b= 12.399 (2)Å, c=20.928 (4)Å, β=97.15 (1)°, and Z=4. A full matrix least-squares refinement with 6725 unique reflections for all nonhydrogen atoms gives R=0.068. The anion of 1 is the first isolated single MoFe₃S₄ cubane cluster with core oxidation state MoFe₃S₄]⁴⁺. The distance between the two 6-coordinate metal atoms (Mo, Fe) is 2.624 Å, which is the shortest M-M' bond observed for Mo-Fe-S clusters so far and the only one shorter than similar distances in FeMo-cofactor. The bond orders of this anion were calculated by EHMO method and the results coincide with the general rule. The structural feature and the unusual stability of 1 can be attributed to the bidentate chelating effect of Et₂NCSS-, which leads to high coordination of metal atoms and the various ligated types.