Perfect cubic metallo-borospherenes TM8B6 (TM = Ni, Pd, Pt) as superatoms following the 18-electron rule

Abstract

Transition-metal (TM)-doped metallo-borospherenes exhibit unique structures and bonding in chemistry which have received considerable attention in recent years. Based on extensive global minimum searches and first-principles theory calculations, we predict herein the first and smallest perfect cubic metallo-borospherenes O_h TM₈B₆ (TM = Ni (1), Pd (2), Pt (3)) and O_h Ni₈B₆⁻ (1⁻) which contain eight equivalent TM atoms at the vertexes of a cube and six quasi-planar tetra-coordinate face-capping boron atoms on the surface. Detailed canonical molecular orbital and adaptive natural density partitioning bonding analyses indicate that O_h TM₈B₆ (1/2/3) as superatoms possess nine completely delocalized 14c–2e bonds following the 18-electron principle (1S²1P⁶1D¹⁰), rendering spherical aromaticity and extra stability to the complex systems. Furthermore, Ni₈B₆ (1) can be used as building blocks to form the three-dimensional metallic binary crystal NiB (4) (Pmm) in a bottom-up approach which possesses a typical CsCl-type structure with an octa-coordinate B atom located exactly at the center of the cubic unit cell. The IR, Raman, UV-vis and photoelectron spectra of the concerned clusters are computationally simulated to facilitate their experimental characterization.