Donor-acceptor duality of the transition-metal-like B 2 core in core-shell-like metallo-borospherenes La 3 &[B 2 @B 17 ] - and La 3 &[B 2 @B 18 ] .

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-borospherene D 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-borospherenes C 2v La 3 &[B 2 @B 17 ] - (2) and D 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 π-donor in the equatorial direction mainly to coordinate three La atoms on the waist and a π/σ-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 of 2 and 3 are computationally simulated to facilitate their spectroscopic characterizations.