Evolution from a single relaxation process to two-step relaxation processes of Dy2 single-molecule magnets via the modulations of the terminal solvent ligands

Y To explore the influences of magnetic interactions on the relaxation dynamics of single-molecule magnets (SMMs) and to understand the relationship between single-ion relaxation and the relaxation of a molecular entity, it is very important to design dinuclear lanthanide-based SMMs with two-step relaxation processes. Here, three Dy-2 complexes of compositions [Dy-2(L)(2)(NO3)(2)(MeOH)(2)] (1), [Dy-2(L)(2)(NO3)(2)(EtOH)(2)] (2), and [Dy-2(L)(2)(NO3)(2)(DMF)(2)]center dot 0.5EtOH (3) (H2L = 2-(((2-hydroxy-3-methoxybenzyl)imino)methyl)-4-methoxyphenol) were successfully synthesized via elaborately introducing different terminal solvent ligands. X-ray single-crystal diffraction analyses revealed that complexes 1-3 are isostructural. The two Dy-III ions of 1 and 2 both adopt D-2d symmetry, while the two Dy-III centres of 3 display D-2d and D-4d symmetries, respectively. The magnetic property studies of 1-3 indicated that all three complexes exhibit single-molecule magnet (SMM) behaviours with energy barriers of 104 K for 1, 98.94 K for 2, and 76.28 K and 45.54 K for 3 under zero dc field. The target of assembling Dy-2 SMMs with two-step relaxation processes was achieved by gradually increasing the sizes of the terminal solvent ligands. Complex 3 exhibits two-step relaxation processes. Complete active space self-consistent field (CASSCF) calculations were performed on 1-3 to rationalize the observed differences in the magnetic behaviour. It is found that both the angles theta between the magnetic axis and the vector connecting two Dy-III ions and the symmetries of Dy-III ions are vital factors that affect the energy barriers of 1-3. The high local symmetries of the central metals in 1 and 2 make the complexes act as SMMs with higher energy barriers, while the smaller theta angle and different symmetries of the two Dy-III ions render complex 3 as a SMM with a two-step relaxation process. This work demonstrates a new methodology for preparing SMMs with two-step relaxation processes by fine-tuning the terminal solvent ligands.

Automated summary

By elaborately designing different terminal solvent ligands, three Dy-2 complexes were successfully synthesized with single-molecule magnet behaviors. The observed differences in the magnetic behavior of the complexes were rationalized by performing CASSCF calculations. The complexes with higher local symmetries of central metals acted as SMMs with higher energy barriers, while a smaller theta angle and different symmetries of the Dy-III ions resulted in a complex with a two-step relaxation process.