Dinuclear Lanthanide Complexes Based on a Schiff‐base Ligand: Free Lattice Solvent Inducing the Single Molecule Magnet Behavior of Dy₂ Compound

Abstract

Syntheses, crystal structures and magnetic properties are described for a series of seven-coordinate dinuclear lanthanide complexes of compositions Dy₂ L₂ (1) (H₃ L=2-{[bis(2-hydroxy-3-ethoxybenzyl)(aminoethyl)amino]methyl}phenol) and Ln₂ L₂ ⋅MeCN (Ln=Dy (2), Sm (3), Eu (4), Gd (5), Tb (6), Ho (7)). The reaction of Dy(NO₃ )₃ ⋅6 H₂ O with one equivalent of H₃ L at 70 °C in DMF/EtOH under autogenous pressure gave compound 1. Complexes 2-7 were prepared by means of the same method as that used for 1, except DMF was replaced by MeCN as the reaction solvent and Dy(NO₃ )₃ ⋅6 H₂ O was changed to the corresponding lanthanide salts. Complexes 1-7 possess the similar Ln₂ cores bridged by μ₂ -phenoxyl oxygen atoms. The slight difference between 1 and 2-7 arises from the existence of free MeCN molecule in 2-7. The purposeful introduction of solvent MeCN molecule changes the crystal system from triclinic for 1 to monoclinic for 2 and alters the Dy-O-Dy angles and Dy⋅⋅⋅Dy distances, consequentially resulting into dramatic influences on the magnetic properties of 1 and 2. Complex 1 shows no SMM character, while compound 2 with free MeCN molecule exhibits a field-induced slow magnetization relaxation behavior. Complete active space self-consistent field (CASSCF) calculations were performed on two Dy₂ compounds to rationalize the observed difference in the magnetic behavior. Theoretical calculations reveal that the energy gap between the lowest two Kramers doublets of individual Dy^III fragment for 2 is higher than those of 1 (1_a and 1_b). This conlusion is consistant with the experimental result that complex 2 exhibits better magnetic properties. This work proposes an ingenious strategy for inducing the SMM behavior in the Dy₂ compounds.