Recent progress in boron nanoclusters: from borophene to boron buckminsterfullerene

Boron nanoclusters remain an especially rich arena in chemistry because they continue to reveal unusual structures, novel bonding motifs, aromaticity, and dimensional transformations. Significant experimental progress has been made over the past several years that has substantially reshaped our understanding of these remarkable nanosystems. While the discovery of the B₄₀ borospherene established that all-boron fullerene-like cages can exist, subsequent studies showed that larger boron clusters do not follow a simple fullerene growth path. Instead, B₄₁ ^- and B₄₂ ^- remain quasi-planar with borophene-like vacancy motifs, B₄₈ ^- adopts a bilayer structure, and B₄₆ ^- marks the onset of three-dimensional core-shell structures. The investigation of B₅₆ ^- further revealed the emergence of the B₁₂ icosahedral motif characteristic of bulk boron, providing a direct molecular-scale link to the structural chemistry of elemental boron. Following the discovery of borospherene, metal incorporation was found to be an additional route to create boron cages, in which the metal atoms become integral components of the cage surface. Most recently, photoelectron spectroscopy of B₈₀ ^- has provided compelling evidence for boron buckminsterfullerene, representing a striking culmination of this structural evolution. This perspective discusses these recent developments and highlights how photoelectron spectroscopy in conjunction with theoretical calculations reveals the evolving structural principles that underlie borophene motifs, bulk-like boron units, metallo-borospherenes, and boron buckminsterfullerene.