Theoretical study on exohedral complexes C₆H₆TMB₄₀ (TM = Sc-Ni)

Exohedral borospherene complexes comprised of 3d transition metal (TM) atoms with borospherene B₄₀ and benzene (C₆H₆) molecules, C₆H₆TMB₄₀, were systematically studied by using density functional theory (DFT). Results show that in the ground states, the bonding type between TM and B₄₀ changes from η⁷ (TM = Sc-V) to η⁶ (TM = Cr-Fe) and then to η⁷ (TM = Co, Ni) with the increasing number of d electrons. Except for C₆H₆TiB₄₀ and C₆H₆FeB₄₀ being triplets, all C₆H₆TMB₄₀ clusters have the lowest spin. Namely, the ground spin state with an even number of electrons is a singlet state, and the ground spin state with an odd number of electrons is a doublet state. The investigated C₆H₆TMB₄₀ clusters (TM = Sc-Ni) possess higher stabilities through the ionic-covalent interactions between transition metals, benzene and the B₄₀ cage.