Ferrocene analogues of sandwich M(CrB₆H₆)₂: a theoretical investigation

The stability and electronic structures of the new sandwich compounds M(CrB6H6)2 (M = Cr, Mn(+), Fe(2+)) are investigated by density functional theory. All the investigated sandwich complexes are in D(6d) symmetry and all of them are thermodynamically stable according to the large HOMO-LUMO gap, binding energy, vertical ionization potential and vertical electron affinity analyses, as well as Fe(C5H5)2 and Cr(C6H6)2, following the 18-electron principle. The natural bond orbital, detailed molecular orbitals and adaptive natural density partitioning analyses suggest that the spd-π interaction plays an important role in the sandwich compounds. This work challenges the traditional chemical bonding of the inorganic metal compound, investigates first the bonding style of the d atom orbital interacting with the π MO which was formed by p-d atomic orbitals, and indicates that the metal-doped borane ring can also be an ideal type π-electron donor ligand to stabilize the transition metal.