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

The recent discovery of lanthanide-metal-decorated metallo-borospherenes LM 3 B 18 - (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 C 2 Ni 6 ∈ B 39 - (1), C 1 Ni 6 ∈ B 41 + (3), C 2 Ni 6 ∈ B 42 2+ (4), C 2 Ni 6 ∈ B 42 (5), and C 2 Ni 8 ∈ B 56 (6) as the global minima of the systems decorated with quasi-planar heptacoordinate Ni (phNi) centers in η 7 -B 7 heptagons on the cage surfaces, which are found to be obviously better favoured in coordination energies than hexacoordinate Ni centers in previously reported D 2d Ni 6 ∈ B 40 (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 7 -B 7 ligand, rendering spherical aromaticity and extra stability to the systems. The structural motif in elongated axially chiral Ni 6 ∈ B 42 2+ (4), Ni 6 ∈ B 42 (5), and Ni 8 ∈ B 56 (6) can be extended to form the metallic phNi-decorated boron double chain (BDC) double-helix Ni 4 ∈ B 28 (2, 0) ( P 4̄ m 2) (8), triple-helix Ni 6 ∈ B 42 (3, 0) ( P 3̄ m 1) (9), and quadruple-helix Ni 8 ∈ B 56 (4, 0) ( P 4 mm ) (10) metallo-boronanotubes, which can be viewed as quasi-multiple-helix DNAs composed of interconnected BDCs decorated with phNi centers in η 7 -B 7 heptagons on the tube surfaces in the atomic ratio of Ni : B = 1 : 7.