[XIm][FeI(CO)3(SnI3)2] (XIm: EMIm, EHIm, PMIm) containing a barbell-shaped FeSn2-carbonyl complex

Abstract

By reacting Fe(CO)₅ and SnI₄ in the ionic liquids [XIm][NTf₂] (XIm: 1-ethyl-3-methylimidazolium/EMIm, 1-ethyl-imidazolium/EHIm, 1-propyl-3-methylimidazolium/PMIm; NTf₂: bistrifluoridomethansulfonimide), the compounds [XIm][FeI(CO)₃(SnI₃)₂] are obtained as transparent, dark red crystals. According to single-crystal structure analysis, the title compounds crystallize monoclinically and contain the anionic carbonyl complex [FeI(CO)₃(SnI₃)₂]⁻ as well as [EMIm]⁺, [EHIm]⁺ or [PMIm]⁺ cations. The anionic carbonyl is composed of a Sn–Fe–Sn barbell-shaped building unit with Fe–Sn distances of 252.0(1) pm. Herein, tin is coordinated distorted tetrahedrally by iodine; iron is coordinated pseudo-octahedrally by three carbonyl ligands, one iodine atom and two tin atoms. Bonding situation and valence state are investigated in detail for [EMIm][FeI(CO)₃(SnI₃)₂] based on bond-lengths considerations, infrared spectroscopy, Mössbauer spectroscopy, density functional theory and DFT-based Mulliken population analysis. Hence, the formal oxidation state of the metal atoms can be concluded to Fe^±0 and Sn³⁺.