Single-Molecule Magnetism in Three Dy2 Complexes from the Use of a Pentadentate Schiff Base Ligand and Different Benzoates.

Three dinuclear dysprosium(III) complexes, [Dy2 L2 (O2 CPh)2 ]⋅2 MeOH (1), [Dy2 L2 {(2-NO2 )O2 CPh}2 ] (2), and [Dy2 L2 {(2-OH)O2 CPh}2 ]⋅MeOH⋅MeCN (3) (H2 L=N1 ,N3 -bis(4-chlorosalicyladehyde)diethylenetriamine), have been synthesized and structurally characterized. Complexes 1-3 possess similar Ln2 cores and differ in substituents at the benzyl rings of benzoates. Direct current (dc) magnetic susceptibility studies in the 2-300 K range showed weak antiferromagnetic interactions between two dysprosium(III) ions in 1-3. The alternating current (ac) magnetic susceptibility measurements indicated that they all exhibited SMM behavior. The strategic attachment of the -NO2 group (in 2) and the -OH functionality (in 3) on the skeleton of the benzoic acid led to subtle variations of the bond lengths and bond angles in the coordination environments of the central dysprosium(III) ions, consequently resulting in the enhancement of the energy barriers for 2 and 3. Complete-active-space self-consistent field (CASSCF) calculations were employed to rationalize the experimental outcomes. Theoretical calculations confirm the existence of antiferromagnetic interactions in 1-3, and the calculated dc magnetic susceptibility data agree well with those obtained experimentally. The computational results reveal more axial g tensors, as well as higher first excited Kramers doublets in 2 and 3; thus resulting in higher energy barriers in compounds 2 and 3.