Substantial π-aromaticity in the anionic heavy-metal cluster [Th@Bi₁₂]⁴

Area of Science:

• Inorganic Chemistry
• Materials Science
• Physical Chemistry

Background:

• Aromaticity, defined by Hückel's rule (4n+2 π-electrons), was initially observed in organic molecules like benzene.
• π-aromaticity has been extended to various organic and inorganic non-metal compounds.
• Metallic systems were previously limited to small clusters (3-5 atoms) exhibiting aromaticity.

Purpose of the Study:

• To synthesize and characterize a large metal ring system with significant π-aromaticity.
• To investigate the electronic properties and stability of a novel heterometallic cluster.
• To explore the potential for designing substantial π-aromaticity in heavy-metal cycles.

Main Methods:

• Synthesis of a heterometallic anion [Th@Bi12]4- under highly reducing conditions.
• Characterization of the 12-atom bismuth ring structure and its electronic properties.
• Comparison of the ring current and aromaticity with known organic aromatic systems like benzene and porphine.

Main Results:

• Successful synthesis of a 12-atom metal ring, [Th@Bi12]4-, exhibiting 2π-aromaticity.
• The synthesized metal ring displays a significantly stronger ring current than benzene (6π) and is comparable to porphine (26π).
• The interstitial Th4+ ion stabilizes the Bi128- moiety, facilitating large-scale π-aromaticity in a metallic system.

Conclusions:

• It is feasible to design and generate substantial π-aromaticity in large metal rings.
• The discovered π-aromatic heavy-metal cycles offer new possibilities for cluster-based reactions.
• This work expands the understanding of aromaticity beyond traditional organic and non-metal systems into metallic clusters.