Heptacoordinate transition-metal-decorated metallo-borospherenes and multiple-helix metallo-boronanotubes.

The recent discovery of lanthanide-metal-decorated metallo-borospherenes LMB (LM = La, Tb) marks the onset of a new class of boron-metal binary nanomaterials. Using the experimentally observed or theoretically predicted borospherenes as ligands and based on extensive first-principles theory calculations, we predict herein a series of novel chiral metallo-borospherenes Ni ∈ B (1), Ni ∈ B (3), Ni ∈ B (4), Ni ∈ B (5), and Ni ∈ B (6) as the global minima of the systems decorated with quasi-planar heptacoordinate Ni (phNi) centers in η-B heptagons on the cage surfaces, which are found to be obviously better favoured in coordination energies than hexacoordinate Ni centers in previously reported Ni ∈ B (2). Detailed bonding analyses indicate that these phNi-decorated metallo-borospherenes follow the σ + π double delocalization bonding pattern, with two effective (d-p)σ coordination bonds formed between each phNi and its η-B ligand, rendering spherical aromaticity and extra stability to the systems. The structural motif in elongated axially chiral Ni ∈ B (4), Ni ∈ B (5), and Ni ∈ B (6) can be extended to form the metallic phNi-decorated boron double chain (BDC) double-helix Ni ∈ B (2, 0) (4̄2) (8), triple-helix Ni ∈ B (3, 0) (3̄1) (9), and quadruple-helix Ni ∈ B (4, 0) (4) (10) metallo-boronanotubes, which can be viewed as quasi-multiple-helix DNAs composed of interconnected BDCs decorated with phNi centers in η-B heptagons on the tube surfaces in the atomic ratio of Ni : B = 1 : 7.