Sandwich complexes of the Sb42− aromatic ring with some transition metals

The equilibrium geometries, energies, harmonic vibrational frequencies, molecular orbital (MO), stability, and nucleus independent chemical shifts (NICS) of the new type sandwich structures [Sb4MSb4]n− (M = Fe, Ru, Os, Co, Rh, and Ir; n = 1, or 2) are researched at the B3LYP level of theory. The calculations reveal that the [Sb4MSb4]n− complexes adopt the staggered D4d conformers as their stable structures, and the Sb42− ring of them exhibit σ and π aromaticity. Some of MOs for [Sb4MSb4]n− originated from the interactions between the orbitals of the ligands and the atomic orbitals of the metal, and the other directly inherited from the ligands, and once the sandwich complexes are formed, the Sb42− square properties remain unchanged. The addition of sodium to [Sb4MSb4]2− (M = Fe, Ru, and Os) can yield stabilization toward electron detachment, and the sandwich structures are all stable thermodynamically because the dissociations of [Sb4MSb4]n− and [Sb4MSb4Na]− into separated fragments are both endothermic reaction.