The FERMO concept was successfully applied to the Pearson's Hard and Soft acid-base principle for four ambidentate ligands. Using an intuitive statement based on the HOMO-LUMO approach to the hardness and softness, the FERMO-LUMO gaps correctly describe the soft and hard sites in the studied systems. Moreover, Kohn-Sham and Hartree-Fock MOs lead to same conclusions.
HSAB; FERMO; molecular orbitals; HOMO-LUMO
