Metal Encapsulation Engineered Aromaticity Modulation: Transforming Cyclo[16]Carbon From Dual Antiaromaticity to Conflicting or Dual Aromaticity

The inherent instability of a recently synthesized cyclo[16]carbon (C₁₆) ring, arising from its dual antiaromatic 4n π-electron systems, is strategically mitigated through encapsulation of light lanthanides (La-Nd) and actinide metals (Th-Np). This approach transforms C₁₆'s dual antiaromaticity into tunable aromatic or conflicting aromatic states. The magnitude of aromatic character induced by metal encapsulation reveals an evolution trend that correlates with metal reducibility, thereby offering insights into the interactions between f-block metals and carbon-based materials. Multifaceted computational analyses, including topological, natural population, interaction region indicator (IRI), and spin density assessments, demonstrate that metal confinement fundamentally reconstructs the π electron distribution. Crucially, light actinides (Th-Np) impart dual aromaticity through uniform electron delocalization and bond-length equalization, while lanthanides (La-Nd) induce conflicting aromaticity. Frontier molecular orbital and magnetically induced current analyses provide definitive evidence for these metal-dependent electronic transitions. We thus establish a metal-encapsulation paradigm for precise aromaticity engineering in carbon nanorings, unlocking transformative pathways for tailored quantum materials and single-molecule electronics.