A new Fe(IV) superoxide: The perferrate isomerization re-examined

Area of Science:

• Inorganic Chemistry
• Computational Chemistry
• Quantum Chemistry

Background:

• The iron perferrate anion [FeVIIO4]- is an elusive species analogous to permanganate.
• Previous computational studies failed to accurately predict the stability trend between peroxide and perferrate species.
• Key questions regarding the stability and isomerization of iron perferrate remain unresolved.

Purpose of the Study:

• To computationally revisit the manifold of possible structures for iron perferrate and related species.
• To accurately reproduce the stability trend observed between peroxide and perferrate anions.
• To identify the most stable structural configuration of the [FeO4]- system.

Main Methods:

• Utilized a high-level theoretical method: MRCISD+Q/x2c-TZVP//CASPT2(25,17)/ANO-RCC-VDZP.
• Generated gas-phase [FeO4]- ions using electrospray ionization.
• Probed ion structures and stability via collision-induced dissociation mass spectrometry.

Main Results:

• The computational approach successfully reproduced the correct stability trend: [FeVO2(η2-O2)]- > [FeVIIO4]-.
• Identified a cyclometalated superoxide, [FeIVO2(η2-O2)]-, as the most stable species.
• Perferrate was found to be less stable by +29.2 kcal mol-1 compared to the cyclometalated superoxide.
• Experimental data provided complementary evidence for O-O motifs in generated ions, aligning with computational findings.

Conclusions:

• The study resolves discrepancies in the predicted stability of iron perferrate and related species.
• A cyclometalated superoxide structure is computationally identified as the most stable form of the [FeO4]- anion.
• Experimental evidence supports the computational findings regarding the presence of O-O bonds in the investigated iron-oxygen anions.