Spectroscopic Identification of an Fe^III Center, not Fe^IV, in the Crystalline Sc–O–Fe Adduct Derived from [Fe^IV(O)(TMC)]²⁺

The apparent Sc3+ adduct of [FeIV(O)­(TMC)]2+ (1, TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) has been synthesized in amounts sufficient to allow its characterization by various spectroscopic techniques. Contrary to the earlier assignment of a +4 oxidation state for the iron center of 1, we establish that 1 has a high-spin iron­(III) center based on its Mössbauer and EPR spectra and its quantitative reduction by 1 equiv of ferrocene to [FeII(TMC)]2+. Thus, 1 is best described as a ScIII–O–FeIII complex, in agreement with previous DFT calculations (Swart, M. Chem. Commun. 2013, 49, 6650.). These results shed light on the interaction of Lewis acids with high-valent metal-oxo species.