“…Boron as a prototypical electron-deficient element exhibits unique structures and bonding in bulk allotropes, polyhedral molecules, and gas-phase clusters. − Combined photoelectron spectroscopy (PES) and first-principles theory investigations in the past two decades have unveiled a rich landscape for size-selected boron clusters (B n –/0 ) from planar or quasi-planar species ( n = 3–38, 41, and 42) to cage-like borospherenes ( C 3 / C 2 B 39 – and D 2d B 40 –/0 ) featuring delocalized multicenter two-electron (mc-2e) σ and π bonds, with B 39 – being the only boron cluster monoanion possessing a cage-like global minimum (GM). − Seashell-like C 2 B 28 –/0 and C s B 29 – were later observed in PES measurements as minor isomers coexisting with their quasi-planar GM counterparts. , Endohedral M@B 40 (Ca, Sr, Sc, Y, and La) and exohedral M&B 40 (M = Be and Mg) metallo-borospherenes were proposed in theory shortly after the discovery of D 2d B 40 –/0 . , Endohedral D 2 Ta@B 22 – and D 2d U@B 40 were predicted to be superatoms following the 18-electron rule and 32-electron principle, respectively. , Other cage-like B n clusters ( n = 20, 30, 38, 40, 50, and 60) and related Ti-doped species have also been predicted in theory. , Joint ion-mobility measurements and density functional theory (DFT) investigations indicated that B n + boron cluster monocations possess double-ring tubular structures in the size range between n = 16 and 25 . Extensive GM searches and DFT calculations showed that B 46 is the smallest core–shell boron cluster with a B 4 core at the center (B 4 @B 42 ), while B 48 , B 54 , B 60 , and B 62 are the first bilayer boron clusters predicted to date. , Encouragingly, bilayer B 48 –/0 has been very recently confirmed in gas-phase PES measurements, revealing a new structural domain in boron nanoclusters and nanomaterials…”