Understanding the Magnetic Relaxation Mechanism in Mixed-Valence Dilanthanide Complexes with Metal-Metal Bonding: A Theoretical Investigation.

Theoretical investigations on mixed-valence dilanthanide complexes (Cp iPr5 ) 2 Ln 2 I 3 (Ln = Tb, Dy, and Ho) indicate that the total spin of the 4f shell couples preferentially to the σ electron spin and then to the orbital angular momentum, improving the strength of spin-orbit coupling (SOC) for each magnetic center. On the other hand, the concentration of negative charges containing the delocalized σ electron in the axial direction leads to a large crystal-field (CF) splitting. Both strong SOC and large CF splitting lead to the largest energy barrier U eff of such complexes up to now. In addition, our calculations show that the introduction of σ electron can better suppress the quantum tunneling of magnetization in the ground spin-orbit state, and the U eff of (Cp iPr5 ) 2 Ln 2 I 3 is expected to originate from the contribution of both Ln ions under such strong Ln-σ exchange coupling.