Double-chain chemistry of boron in planar borophenes, cage-like borospherenes, boron nanotubes, and their metal-doped heteronanostructures

Boron-based nanomaterials have attracted considerable attention in recent years. We present herein the latest combined experimental and theoretical investigations on cage-like borospherenes Bnq (q=n-40, n=36-42), metal-doped heteroborospherenes Nin∈B40 (n=1-6), planar borophenes, metal-doped Ni2∈B14 heteroborophenes, tubular molecular rotors B2-Ta@B18-, B3-Ta@B18, and B4-Ta@B18+, and the tubular to cage-like structural transition in metal-centered boron clusters at Ta@B22- which is the smallest axially chiral endohedral metalloborospherene with the record coordination number of CN=22. These nanostructures which are dominated with the double-chain chemistry of boron exhibit unique structural fluctuations due to the bonding fluctuations originated from the electron deficiency of the systems. Boron double chains（BDCs）appear to be equivalent to carbon single chains (CSCs) in these boronanostructures. Boron-based nanostructures possess properties complementary to carbon nanostructures and may find wide applications in catalysis, energy-storage, and electronics materials.