X-ray absorption spectroscopy systematics at the tungsten L-edge

Area of Science:

• Inorganic Chemistry
• Materials Science
• Spectroscopy

Background:

• Accurate determination of metal oxidation states is crucial for understanding chemical and physical properties.
• Tungsten compounds exhibit diverse oxidation states and electronic structures, often posing interpretation challenges.
• X-ray absorption spectroscopy (XAS) is a powerful tool for probing electronic structures of metal complexes.

Purpose of the Study:

• To establish reference tungsten L-edge X-ray absorption spectra (XAS) for various oxidation states (0 to +VI).
• To demonstrate the utility of these reference spectra for interpreting complex tungsten compounds, including those with redox-active ligands.
• To assess the effective metal oxidation state (Zeff) in tungsten compounds with ambiguous electronic structures.

Main Methods:

• Tungsten L-edge X-ray absorption spectroscopy (XAS) was performed on a series of well-defined mononuclear six-coordinate tungsten compounds.
• The series spanned formal oxidation states from 0 to +VI, featuring inert chloride and phosphine ligands.
• Spectra were analyzed by correlating L3,2-edge branching ratios and L1 rising-edge energies with metal Zeff.

Main Results:

• Tungsten L-edge XAS spectra clearly correlated with the formal oxidation states of the reference compounds.
• The established reference spectra were successfully applied to interpret the XAS of [W(IV)(mdt)2(CO)2] and [W(IV)(mdt)2(CN)2](2-), confirming effective W(IV) states.
• Ligand type, particularly π-acceptors (e.g., CO) and π-donors, can influence the difference between formal oxidation state and Zeff.

Conclusions:

• Tungsten L-edge XAS provides reliable reference data for determining metal oxidation states and electronic structures.
• This spectroscopic approach is valuable for characterizing tungsten compounds with complex or redox-active ligands.
• Combined analysis with other techniques, like ligand K-edge XAS, enhances the interpretation of metal L-edge XAS data for uncertain formulations.