Oxidation States: Intrinsically Ambiguous?

Area of Science:

• Inorganic Chemistry
• Computational Chemistry
• Quantum Chemistry

Background:

• The oxidation state formalism is widely used but has limitations.
• Interpreting oxidation states computationally for transition metal (TM) complexes requires careful consideration.

Purpose of the Study:

• To develop a broadly applicable and user-friendly computational procedure for deriving oxidation states.
• To introduce the Intrinsic Oxidation State (IOS) method based on localized orbitals.
• To analyze bonding in TM complexes, particularly cobalt complexes, using the IOS framework.

Main Methods:

• Utilizing quantum chemical calculations.
• Employing localized orbitals to define the Intrinsic Oxidation State (IOS).
• Applying the IOS method to a cobalt complex studied by Hunter et al.

Main Results:

• The calculated IOS for the cobalt complex matched the formal oxidation state, consistent with experimental findings.
• Analysis revealed an "inverted" ligand field in the Co(III) complex, despite classically dative bonds.
• A more restrictive definition of (locally) inverted bonding is proposed.

Conclusions:

• The IOS method provides a reliable computational tool for determining oxidation states in TM complexes.
• The study highlights complex bonding scenarios in high-valent TM complexes.
• New bonding descriptors (σ-gain and π-loss) within the Intrinsic Bonding Orbital (IBO) framework facilitate covalency quantification.