Can you break the oxo-wall? A multiconfigurational perspective.

Area of Science:

• Inorganic Chemistry
• Computational Chemistry
• Materials Science

Background:

• The oxo-wall theory posits limitations on high-valent metal-oxo species.
• Synthesizing true high-valent cobalt-oxo species (Co^IV=O) remains challenging.
• Co^IV=O and Co^III-O˙ are considered electromers, with potential for resonance-like mixing.

Purpose of the Study:

• To quantify the electromeric mixing between Co^IV=O and Co^III-O˙ species.
• To investigate the influence of spin states and ligand architectures on this mixing.
• To develop a predictive tool for estimating the Co^III-O˙ character in cobalt-oxo species.

Main Methods:

• Employed density functional theory (DFT) and ab initio CASSCF/NEVPT2 methods.
• Studied six different metal-oxo species, including Fe^IV=O and Mn^IV=O.
• Analyzed four distinct ligand architectures for cobalt-oxo species.

Main Results:

• Electromeric mixing is negligible for Fe^IV=O and Mn^IV=O (pre-oxo-wall examples).
• Substantial Co^IV=O ↔ Co^III-O˙ mixing occurs in cobalt-oxo species across various geometries.
• Co^IV=O dominates in the S = 3/2 spin state, while Co^III-O˙ character increases in the S = 1/2 state.
• A linear correlation was found between the % of Co^III-O˙ and a ratio of axial bond lengths (R_d).

Conclusions:

• The oxo-wall theory may need refinement regarding cobalt-oxo species due to significant electromeric mixing.
• The developed R_d ratio provides a geometrically portable method for qualitatively assessing Co^III-O˙ character.
• This work offers insights into the electronic structure and reactivity of high-valent cobalt-oxo complexes.