A homoleptic Fe(iv) ketimide complex with a low-lying excited state

Abstract

The reaction of 4 equiv. of Li(NC(^tBu)Ph) with Fe^IICl₂ results in isolation of [Li(Et₂O)]₂[Fe^II(NC(^tBu)Ph)₄] (1), in good yields. The reaction of 1 with 1 equiv. of I₂ leads to formation of [Fe^IV(NC(^tBu)Ph)₄] (2), in moderate yields. ⁵⁷Fe Mössbauer spectroscopy confirms the Fe(IV) oxidation state of 2, and X-ray crystallography reveals that 2 has a square planar coordination geometry along with several intramolecular H⋯C interactions. Furthermore, SQUID magnetometry indicates a small magnetic moment at room temperature, suggestive of an accessible S = 1 state. Both density functional theory and multiconfigurational calculations were done to elucidate the nature of the ground state. Consistent with the experimental results, the ground state was found to be an S = 0 state with an S = 1 excited state close in energy.