Expanded spherical trihedral metallo-borospherenes of transition-metal doped boron clusters: TM3B15q (TM = Zr, Hf; q = −1, 0, +1)

•Discovery of a new spherical trihedron metallo-borospherenes of TM3B15+/0/–.•Compared with Ln3B18–, TM3B15 has an open electronic shell and a new bonding mode. The discoveries of D3h Ln3B18– (Ln = La, Tb) , of which all the La or Tb and B atoms are integral parts of the cage surface, represent an unprecedented class of metallo-borospherenes. Based on particle swarm optimisation (PSO) algorithm and densityfunctionaltheory (DFT) calculations, a smaller spherical trihedral metallo-borospherene D3h TM3B15q (TM = Zr, Hf; q = -1, 0, +1) is designed, where the two B6 triangles of B18 framework in D3h Ln3B18– are remained but interconnected by three B atoms instead of three B2 units, resulting in each TM atom conjoined an equivalent η8–B8 ring. The high stability of proposed structure has been rationalized in terms of large average binding energy, low relative energy and geometric integrity at high temperature. Detailed orbital and bonding analysis of TM3B15 obtain that three localized 2c-2e B–B σ bonds and one delocalized 15c-2e B–B π bond are missing, and its HOMO is semi-occupied with the comparison of Ln3B18–. The most stable cationic and anionic isomers, formed from unoccupied or fully occupied HOMO of TM3B15, respectively, also have the D3h symmetry metallo-borospherene structures with similar molecular orbital shapes and bonding patterns. In addition, their IR and Raman spectra are simulated to facilitate the experiment characterizations in future.