Structures and Bonding of Lanthanide-Doped Endohedral Borospherenes Ln@B400/+ (Ln = Ce, Pr, Nd, Pm, Sm, Eu, Gd)

Metal-doped endohedral borospherenes M@B₄₀ have attracted considerable attention since the discovery of the first boroshphenes B₄₀^−/0 in 2014. Systematical density functional theory investigations performed herein unveil the ground-state structures and coordination bonding patterns of a series of lanthanide-doped endohedral borospherenes Ln@B₄₀^0/+, including the doublet C_2v Ce@B₄₀⁺ (1, ²B₁), triplet C_2v Ce@B₄₀ (2, ³A₂), quartet C_2v Pr@B₄₀ (3, ⁴B₁), quintet C_2v Nd@B₄₀ (4, ⁵A₁), sextet C₂ Pm@B₄₀ (5, ⁶A), septet C_2v Sm@B₄₀ (6, ⁷A₂), octet D_2d Eu@B₄₀ (7, ⁸B₁), and octet C_2v Gd@B₄₀⁺ (8, ⁸A₂). Detailed principal interaction spin orbital (PISO) and adaptive natural density partitioning (AdNDP) bonding pattern analyses indicate that, with the number of unpaired α-electrons changing from n_α = 1, 2, 3, 4, 5, 6, 7, to 7 in the series, their coordination bonding energies decrease monotonically from E_c = 7.22, 6.93, 5.67, 4.85, 4.67, 4.29, 4.02, to 2.07 eV, respectively, with the dominating percentage contributions of the Ln 5d-involved PISOs to the overall E_c increasing almost monotonically from 66 to 83%, while the minor contributions of the Ln 4f-involved PISOs varying between 0.3% and 12.1% and that of Ln 6s-involved PISO pairs remaining basically unchanged in a narrow range between 6% and 8%. In average, the dominating 5d-invloved PISOs in Ln@B₄₀ contribute about 72.8% to the overall E_c, 19.3% higher than that (53.4%) of the 6d-involved PISOs in the newly reported actinide-doped An@B₄₀^+/0/−, while the minor 4f-involved PISOs in Ln@B₄₀ contribute about 6.1% to E_c, 15.7% lower than that (21.8%) of the 5f-invloved PISOs in An@B₄₀^+/0/−, quantitatively unveiling the differences in coordination bonding patterns between Ln@B₄₀^+/0 and An@B₄₀^+/0/−.

Graphical Abstract