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

The reaction of 4 equiv. of Li(N[double bond, length as m-dash]C( t Bu)Ph) with Fe II Cl 2 results in isolation of [Li(Et 2 O)] 2 [Fe II (N[double bond, length as m-dash]C( t Bu)Ph) 4 ] (1), in good yields. The reaction of 1 with 1 equiv. of I 2 leads to formation of [Fe IV (N[double bond, length as m-dash]C( t Bu)Ph) 4 ] (2), in moderate yields. 57 Fe 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.