Single-Determinant Ground State in Ce⁴⁺ Imidophosphorane Complexes

Area of Science:

• Materials Science
• Quantum Chemistry
• Spectroscopy

Background:

• X-ray spectroscopy is vital for understanding high-valent lanthanide electronic structures.
• Interpreting multipeaked features at the lanthanide L3-edge is challenging across material classes.
• Ligand field perturbations are often considered for ground-state electronic structure.

Purpose of the Study:

• To investigate the origin of multipeaked features at the Ce L3-edge in tetravalent cerium complexes.
• To determine if ligand field perturbation influences the ground state electronic structure.
• To elucidate the electronic behavior responsible for observed spectral features.

Main Methods:

• Synthesis of structurally related Ce4+ imidophosphorane complexes.
• UV-vis spectroscopy and electrochemistry to tune and verify electronic properties.
• High-energy resolution fluorescence-detected X-ray absorption near-edge structure (HERFD-XANES) spectroscopy.
• Resonant inelastic X-ray scattering (RIXS) to visualize spectral features.
• Large complete active space configuration interaction singles and doubles (CASCISD) calculations.

Main Results:

• Ligand derivatization successfully tuned electronic properties, confirmed by spectroscopy and electrochemistry.
• Ce L3-edge HERFD-XANES spectra showed consistent features across all complexes, irrespective of ligand variation.
• RIXS confirmed the visualization of observed features in HERFD-XANES spectra.
• CASCISD calculations indicated that the ground state of all complexes is well-described by a single determinant wave function.

Conclusions:

• The multipeaked feature at the Ce L3-edge is attributed to excited-state multiconfigurational behavior.
• This behavior is independent of ligand variation in these Ce4+ imidophosphorane complexes.
• The findings clarify the interpretation of L3-edge XANES spectra for high-valent lanthanides, distinguishing excited-state from ground-state effects.