From Quasi-Planar B 56 to Penta-Ring Tubular Ca©B 56 : Prediction of Metal-Stabilized Ca©B 56 as the Embryo of Metal-Doped Boron α-Nanotubes.

Motifs of planar metalloborophenes, cage-like metalloborospherenes, and metal-centered double-ring tubular boron species have been reported. Based on extensive first-principles theory calculations, we present herein the possibility of doping the quasi-planar C _2v B ₅₆ (A-1) with an alkaline-earth metal to produce the penta-ring tubular Ca©B ₅₆ (B-1) which is the most stable isomer of the system obtained and can be viewed as the embryo of metal-doped (4,0) boron α-nanotube Ca©BNT _(4,0) (C-1). Ca©BNT _(4,0) (C-1) can be constructed by rolling up the most stable boron α-sheet and is predicted to be metallic in nature. Detailed bonding analyses show that the highly stable planar C _2v B ₅₆ (A-1) is the boron analog of circumbiphenyl (C ₃₈ H ₁₆ ) in π-bonding, while the 3D aromatic C _4v Ca©B ₅₆ (B-1) possesses a perfect delocalized π system over the σ-skeleton on the tube surface. The IR and Raman spectra of C _4v Ca©B ₅₆ (B-1) and photoelectron spectrum of its monoanion C _4v Ca
(©B are computationally simulated to facilitate their spectroscopic characterizations.)