Donor-acceptor duality of the transition-metal-like B₂ core in core-shell-like metallo-borospherenes La₃&[B₂@B₁₇]^- and La₃&[B₂@B₁₈]^-

Transition-metal doping induces dramatic structural changes and leads to earlier planar -> tubular -> spherical -> core-shell-like structural transitions in boron clusters. Inspired by the newly discovered spherical trihedral metallo-borosphereneD(3h)La(3)&B-18(-)(1) (Chen,et al., Nat. Commun., 2020,11, 2766) and based on extensive first-principles theory calculations, we predict herein the first and smallest core-shell-like metallo-borospherenesC(2v)La(3)&[B-2@B-17](-)(2) andD(3h)La(3)&[B-2@B-18](-)(3) which contain a transition-metal-like B(2)core at the cage center with unique donor-acceptor duality in La-3&B(n)(-)spherical trihedral shells (n= 17, 18). Detailed energy decomposition and bonding analyses indicate that the B(2)core in these novel complexes serves as a pi-donor in the equatorial direction mainly to coordinate three La atoms on the waist and a pi/sigma-acceptor in the axial direction mainly coordinated by two B(6)triangles on the top and bottom. These highly stable core-shell complexes appear to be spherically aromatic in nature in bonding patterns. The IR, Raman, and photoelectron spectra of2and3are computationally simulated to facilitate their spectroscopic characterizations.