LAUSR

The spherical trihedral metallo-borospherene D3h B18Ln3- (Ln = La, Tb), in which both Ln and B atoms are integral parts of the cage surface, represents a brand new geometric structure. On the basis of particle swarm optimization searches and density functional theory calculations, a large spherical trihedral metallo-borospherene D3h B20TM3 (TM = Sc, Y) is predicted herein, of which the B20 framework can be viewed as two equivalent B7 triangles, rather than two routine equivalent B6 triangles in B18Ln3-, connected by three B2 units. More interestingly, an additional TM can be embedded into the center of surface cage, first designing the co-existence of empty and endohedral spherical trihedral metallo-borospherene, of which the stability is further enhanced and the energy gaps of 1.25 and 1.20 eV are enlarged to 2.86 and 2.61 eV at the PBE0 level for Sc and Y as dopants, respectively. Detailed orbital and bonding analyses show that B20TM4 resembles B18Ln3-, except for the six missing 2c-2e B-B σ bonds, the 10 more 3c-2e B-B σ bonds, and the lack of one delocalized π bonds for the B20 skeleton, where the absence of two totally delocalized Sc-B bonds lead to the relative instability of B20Sc3. The novel hollow geometric structure can be expanded to their charged states with one or three negative charges and to the systems doped by three Ti, Zr, or Hf atoms. Their infrared and Raman spectra are theoretically simulated to facilitate the experimental characterizations in future. Our findings enrich the family of trihedral metallo-borospherene and provide a B7 triangular motif for the B-framework.