Cyclooctatetraene dianion--an artifact?

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Organic Chemistry

Background:

• The aromaticity of cyclooctatetraene dianion (COT(2-)) is debated, with some studies suggesting planarity and aromatic character.
• Contrasting reports indicate that COT(2-) may be non-planar and non-aromatic, challenging its established properties.

Purpose of the Study:

• To conduct a detailed computational analysis of the cyclooctatetraene dianion (COT(2-)) to resolve the debate on its structure and aromaticity.
• To investigate the impact of various computational parameters on the calculated properties of COT(2-).

Main Methods:

• Systematic investigation of the influence of different theoretical approximations and basis sets on the geometry and electronic structure of COT(2-).
• Quantum chemical calculations were employed to analyze the structural and electronic characteristics of the cyclooctatetraene dianion.

Main Results:

• Certain computational approximations were found to produce misleading results, incorrectly depicting COT(2-) as planar and aromatic.
• The study identified specific calculation conditions that lead to the erroneous representation of COT(2-) adopting its neutral, non-planar structure.
• Evidence suggests that the planar COT(2-) structure may be an artifact of specific computational descriptions, particularly basis set effects.

Conclusions:

• The planar, aromatic structure of COT(2-) is highly dependent on the computational methodology employed.
• The results indicate that COT(2-) is likely not a stable, experimentally observable species in its planar form.
• The dianion should be considered an artificial construct arising from specific theoretical treatments rather than a genuine chemical entity.