A “Solvent-Free” Crystal Structure of [FeN(SiMe$_3$)$_2$}$_3$] – Synthesis, Structure and Properties

For the synthesis of the ferric bis(trimethylsilyl)amido complex [Fe{N(SiMe3)2}3] literature gives differing synthetic protocols based on crystallization from solution. In this report we present a ‘solvent‐free’ structural phase of [Fe{N(SiMe$_{3}$)$_{2}$}$_{3}$] which was isolated by sublimation of the product obtained from the reaction of 2 eq FeCl$_{3}$ with 3 eq LiN(SiMe$_{3}$)$_{2}$ in benzene. It could be characterized by single crystal as well as powder XRD and elemental analysis. However, $_{57}$Fe Mößbauer spectroscopy suggests a contamination of the main product with an Fe(II) species. Also, a part of the solid reaction byproducts from the reactions in solution were identified by powder XRD and $_{7}$Li MAS NMR which indicate distinct redox side reactions between oxidizing FeCl$_{3}$ and reducing LiN(SiMe$_{3}$)$_{2}$, a fact which rationalizes the lower than expected yields and the observation of an Fe(II) impurity compound. AC magnetic measurements of [Fe{N(SiMe$_{3}$)$_{2}$}$_{3}$] ave been performed in an extended frequency range up to 10$^{4}$ s$^{-1}$ allowing for a more precise evaluation of the magnetic relaxation parameters when compared to previously published measurements.