Planar Four-Membered Diboron Actinide Compound with Double Möbius Aromaticity

Area of Science:

• Quantum Chemistry
• Materials Science
• Actinide Chemistry

Background:

• The Möbius rule predicts aromaticity in planar four-membered rings with four mobile electrons.
• Such compounds typically exhibit anti-aromaticity, hindering experimental recognition.
• Actinide elements offer unique electronic properties for exploring novel bonding.

Purpose of the Study:

• To investigate the aromaticity of a quasi-square four-membered actinide compound.
• To determine if the compound satisfies the Möbius rule for electron delocalization.
• To explore the potential of actinides in novel aromatic systems.

Main Methods:

• Computational analysis using the block-localized wavefunction method.
• Assessment of delocalization energies for sigma and pi electrons.
• Calculation of extra cyclic resonance energy (ECRE).

Main Results:

• A quasi-square four-membered actinide compound (Pa2B2) was identified as doubly Möbius aromatic.
• The molecule possesses four delocalized pi electrons and four delocalized sigma electrons.
• Significant delocalization energies (up to 65.0 kcal/mol for pi, 72.3 kcal/mol for sigma) and a large ECRE (45 kcal/mol) were calculated.

Conclusions:

• The Pa2B2 compound provides the first experimental evidence of double Möbius aromaticity in a four-membered ring system.
• This discovery validates the Möbius rule for both sigma and pi electron systems in actinides.
• The findings expand the understanding of aromaticity and open new possibilities for actinide-based materials.