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 2 L 2 ( 1 ) (H 3 L=2 ‐ {[bis(2‐hydroxy‐3‐ethoxybenzyl)(aminoethyl)amino]methyl}phenol) and Ln 2 L 2 ⋅MeCN (Ln=Dy ( 2 ), Sm ( 3 ), Eu ( 4 ), Gd ( 5 ), Tb ( 6 ), Ho ( 7 )). The reaction of Dy(NO 3 ) 3 ⋅6 H 2 O with one equivalent of H 3 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 3 ) 3 ⋅6 H 2 O was changed to the corresponding lanthanide salts. Complexes  1 – 7 possess the similar Ln 2 cores bridged by μ 2 ‐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 2 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 Dy 2 compounds.