[Fe(4)S(4)](q) cubane clusters (q = 4+, 3+, 2+) with terminal amide ligands

Bis(trimethylsilyl)amide-ligated iron-sulfur cubane clusters [Fe(4)(mu(3)-S)(4)(N{SiMe(3)}(2))(4)](z) (z = 0, 1-, 2-) are accessible by the reaction of FeCl(N{SiMe(3)}(2))(2)(THF) (1) with 1 equiv of NaSH (z = 0), followed by reduction with either 0.25 (z = 1-) or 1 equiv (z = 2-) of Na(2)S as needed. The anionic clusters are obtained as the sodium salts [Na(THF)(2)][Fe(4)S(4)(N{SiMe(3)}(2))(4)] and [Na(THF)(2)](2)[Fe(4)S(4)(N{SiMe(3)}(2))(4)]; in the solid state, these two clusters both possess a unique contact ion pair motif in which individual sodium ions each coordinate to a cluster core sulfide, an adjacent amide nitrogen, and two THF donors. The monoanionic cluster can also be prepared as the lithium salt [Li(THF)(4)][Fe(4)S(4)(N{SiMe(3)}(2))(4)] by the reaction of 1 with 1:0.5 LiCl/Li(2)S. The characterization of the three-membered redox series allows an analysis of redox trends, as well as a study of the effects of the amide donor environment on the [Fe(4)S(4)] core. Bis(trimethylsilyl)amide terminal ligation significantly stabilizes oxidized cluster redox states, permitting isolation of the uncommon [Fe(4)S(4)](3+) and unprecedented [Fe(4)S(4)](4+) weak-field cores.