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Keywords:

  • ionization potentials;
  • metal–metal bonds;
  • multi-reference configuration interactions;
  • quadruple bonds;
  • relativistic effects
Thumbnail image of graphical abstract

The ties that bind: The electrostatic potential of quadruply bonded W2(hpp)4 and its cation support the idea that the very low ionization energies are due to excitations from the metal–metal bonding core. Theoretical MRCI computations based on CASSCF orbitals show that the relativistic effect influences the lowest four ionization energies, leading to distinct IE sequences: IEδ < IEπ < IEσ in W2(hpp)4, and IEδ < IEσ < IEπ in Mo2(hpp)4.