A reaction system containing FeCl3/Li2S/Li(S-t-Bu)/LiOMe in methanol solution in the initial mole ratios 6:9:(4-8): 12 affords the hexanuclear cluster [Fe6S9(S-t-Bu)2]4-, which has been obtained in 50-70% purified yield as its (Me3NCH2Ph)+ salt. The compound (Me3NCH2Ph)4[Fe6S9(S-t-Bu)2]·MeOH crystallizes in the triclinic space group [formula omitted] with a = 17.617 (10) Å, b = 19.958 (10) Å, c = 10.162 (7) Å, α = 98.73 (4)°, β = 101.97 (3)°, γ = 72.54 (3)°, and Z = 2 (T = 125 K). On the basis of 4864 unique data (Fo2 > 3σ(Fo2)) the structure has been refined to R = 5.9%. The [Fe6S9]2- core of the cluster is formed of eight nonplanar Fe2S2 rhombs that are fused by edge sharing to give four Fe(μ2-S)(μ3-S)Fe, two Fe(μ2-S)(μ4-S)Fe, and two Fe(μ3-S)(μ4-S)Fe subunits. Their arrangement produces a structure of idealized symmetry in which the twofold axis contains the μ4-S atom and is normal to the Fe4 plane of a pyramidal Fe4(μ4-S) fragment, the central portion of the structure. All Fe atoms are present in tetrahedral FeS4 sites; the thiolates are terminally coordinated to two Fe atoms at the exterior of the structure. The cluster is mixed valence but does not contain localized Fe(II,III) sites. The [Fe6S9]2- core represents a new structural type in iron-sulfide-thiolate chemistry, and [Fe6S9(S-t-Bu)2]4- is the only discrete cluster known to contain three types of bridging sulfur atoms. Other significant properties of [Fe6S9(S-t-Bu)2]4-include chemically reversible redox reactions affording a 3-/4-/5- electron-transfer series and ligand substitution with 2 equiv of benzenethiol to give [Fe6S9(SPh)2]4-, which has been characterized in Me2SO solution. Large excesses of the thiol (≲28 equiv) degrade the initial cluster to [Fe4S4(SPh)4]2- and [Fe2S2(SPh)4]2-, which are formed in a ∼1.8:1 ratio. Properties common to the three known types of Fe/S/SR clusters, containing Fe2S2, Fe4S4, and Fe6S9 core units, are briefly summarized.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry