Methylthioirontricarbonyl dimer, also known as methanethiolatoirontricarbonyl dimer, is an organometallic compound with the formula Fe2(SCH3)2(CO)6. It is a red volatile solid that is classified as a transition metal thiolate complex. It exists as air-stable red crystals with two isomers, where the methyl groups are either anti (isomer A) or syn (isomer B) with respect to each other.[1]
It was first synthesized 1940[2] with the discovery of isomers in 1962.[3] Synthesis involves treating triiron dodecacarbonyl with dimethyl disulfide:
2 Fe3(CO)12 + 3 (CH3)2S2 → 3 [Fe(CO)<sub>3</sub>SCH<sub>3</sub>]2 + 6 COIt can be purified by recrystallization or by sublimation. The isomers can be separated by chromatography.
The methylthioirontricarbonyl dimer is a butterfly cluster compound, consisting of two iron atoms with distorted square pyramidal coordination geometry. The geometry is octahedral if the Fe-Fe bond is included. Each iron has three terminal carbon monoxide ligands and two bridging methylthiolate ligands. The Fe-Fe distance is 2.537 Å with an average Fe-S bond length of 2.259 Å. The average Fe-S-Fe bond angle is relatively small at 68.33°. Three isomers are possible but only the diequatorial and axial-equatorial isomers are seen. The diaxial isomer is disfavored due to steric hindrance.[4] [5] The structurally related compound [Fe(CO)<sub>3</sub>S]2 has idealized C2v symmetry.