Abstract
<jats:p> We report the synthesis and characterization of a pair of homoleptic cerium tris(amidinate) complexes, [Ce <jats:sup>III</jats:sup> {PhC(N <jats:sup>t</jats:sup> Bu) <jats:sub>2</jats:sub> } <jats:sub>3</jats:sub> ] and [Ce <jats:sup>IV</jats:sup> {PhC(N <jats:sup>t</jats:sup> Bu) <jats:sub>2</jats:sub> } <jats:sub>3</jats:sub> ][Al(OC <jats:sub>4</jats:sub> F <jats:sub>9</jats:sub> ) <jats:sub>4</jats:sub> ], containing cerium in both its trivalent (Ce <jats:sup>III</jats:sup> ) and tetravalent (Ce <jats:sup>IV</jats:sup> ) oxidation states. To the best of our knowledge, these represent the first examples of a lanthanide-amidinate system where both trivalent and tetravalent complexes have been isolated and structurally characterized in such a congruent ligand coordination. With electronic structure and bond analysis, we demonstrate that while the metal-ligand bonding in both species is dominated by interactions involving Ce <jats:italic toggle="yes">5d</jats:italic> valence orbitals, there is a measurable participation of the <jats:italic toggle="yes">4f</jats:italic> orbitals specifically within the Ce <jats:sup>IV</jats:sup> homolog. Ce L <jats:sub>3</jats:sub> -edge high-energy resolution X-ray absorption near edge structure (HR-XANES) and valence band resonant inelastic X-ray scattering (VB-RIXS) are employed to evaluate the bonding properties and are complemented with quantum chemical calculations based on density-functional theory (DFT). Crucially, the high-resolution nature of these spectroscopic techniques, coupled with theoretical modelling, enables a quantitative deconvolution of the bonding interaction directly from the experimental data. This approach allows us to partition the individual contributions of both the <jats:italic toggle="yes">4f</jats:italic> and <jats:italic toggle="yes">5d</jats:italic> electrons to the metal-ligand interaction. Our findings highlight the increased role of 4f electron density in stabilizing high-valent lanthanide complexes, due to improved energetic and spatial overlap between nitrogen donor lone pairs and the Ce <jats:sup>IV</jats:sup> acceptor manifold. </jats:p>