Low-Coordinate Iron(II) Amido Half-Sandwich Complexes with Large Internal Magnetic Hyperfine Fields.

The half-sandwich complex [Cp'Fe{N(dipp)(SiMe)}] (; Cp' = 1,2,4-tri--butylcyclopentadienyl and dipp = 2,6-diisopropylphenyl) and the mixed metallocene [Cp'Fe{(η-CHPr)═N(SiMe)}] () formed in the reaction between [{Cp'Fe(μ-I)}] and [Li{N(dipp)(SiMe)}] were characterized by NMR spectroscopy and X-ray diffraction analysis. complements the series of low-coordinate, quasi-linear iron amido half-sandwich complexes [Cp'Fe{N(Bu)(SiMe)}] () and [Cp'Fe{N(SiMe)}] () reported earlier, and all three compounds were characterized in the solid state by zero-field Fe Mössbauer spectroscopy and magnetic susceptibility measurements, confirming their = 2 electronic ground state. Moreover, the Mössbauer absorption spectra reveal slow paramagnetic relaxation at low temperatures with large internal magnetic hyperfine fields of = 96.4 T (, 20 K), = 101.3 T (, 15 K), and = 96.9 T (, 20 K). The magnetic measurements further confirm that the presence of significant axial zero-field splitting and slow relaxation of magnetization is detected, which is revealed even in the absence of a static magnetic field in the case of . Supplementary and density functional theory calculations were performed and support the experimental data.