Dinuclear Lanthanide Complexes Based on a Schiff-base Ligand: Free Lattice Solvent Inducing the Single Molecule Magnet Behavior of Dy 2 Compound.

Syntheses, crystal structures and magnetic properties are described for a series of seven-coordinate dinuclear lanthanide complexes of compositions Dy L (1) (H L=2-{[bis(2-hydroxy-3-ethoxybenzyl)(aminoethyl)amino]methyl}phenol) and Ln L ⋅MeCN (Ln=Dy (2), Sm (3), Eu (4), Gd (5), Tb (6), Ho (7)). The reaction of Dy(NO ) ⋅6 H O with one equivalent of H 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(NO ) ⋅6 H O was changed to the corresponding lanthanide salts. Complexes 1-7 possess the similar Ln cores bridged by μ -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 Dy 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 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 Dy compounds.