A Novel Class of Aromatic Compounds: Metal‐Centered Planar Cations [Fe(Sb 5 )] + and [Fe(Bi 5 )] +

Iron enters the pentagon : Quantum chemical calculations using gradient‐corrected DFT predict that the cations [Fe(Sb 5 )] + and [Fe(Bi 5 )] + in the electronic singlet state have planar ( D 5 h ) equilibrium geometries (see scheme). Analysis of the electronic structure shows that the molecules are metal‐centered six‐π‐electron aromatic species with strong iron–ligand π bonds which involve the d(π) atomic orbitals of the Fe center and the degenerate π orbital of the ring. The calculated 57 Fe NMR chemical shifts indicate extremely high deshielding of the metal nucleus.