Molecular and Electronic Structure of a Mixed-spin Diiron “wedged” Metallacarborane, [(CH₃)₂C₂B₄H₄] 2(Feᴵᴵ(low Spin))(Feᴵᴵ(high Spin))L₂ [L₂ = 2THF Or (OCH₃)₂C₂H₄], an Oxidative Fusion Intermediate

An X-ray diffraction study of the purple paramagnetic title compound established it as a dimetallic complex having one iron atom sandwiched between two (CH3)2C2B4H4 2- ligands (as in the previously characterized red diamagnetic monoiron compound [(CH3)2C2B4H4] 2FeH2) with the second iron in a wedging location, coordinated to the complex via four Fe-B interactions. The “outer” iron atom is also bound to a 1,2-dimethoxyethane solvent ligand. The Fe-Fe distance of 2.414 (4) Å is well within bonding range, but the existence of a direct iron-iron bond is in doubt. From magnetic susceptibility and Mössbauer measurements, both iron atoms are assigned 2+ oxidation states with one metal in a low-spin (diamagnetic) configuration and the other high-spin with four unpaired electrons. Comparison with the red monoiron species, from which the diiron complex is prepared by insertion of Fe2+, suggests that the paramagnetism arises from the outer iron atom. The bis(tetrahydrofuran) analogue of the title compound, [(CH3)2C2B4H4] 2Fe2(THF)2, is an intermediate in the conversion of [(CH3)2C2B4H4] 2FeH2 to (CH3)4C4B8H8 via oxidative fusion, as described in the preceding article. © 1982 American Chemical Society.