Regulating the magnetic dynamics of mononuclear β-diketone Dy(III) single-molecule magnets through the substitution effect on capping N-donor coligands

A series of five mononuclear beta-diketonate-Dy(III) complexes, with formulas Dy(ntfa)(3)(Br-bpy) (1), Dy(ntfa)(3)(Br-2-bpy) (2), Dy(ntfa)(3)(5,5-(CH3)(2)-bpy) (3), Dy(ntfa)(3) (4,4-((CH3)(3))(2)-bpy) (4) and Dy(ntfa)(3)(4,4-(CH3)(2)-bpy) (5) (ntfa = 4,4,4-triftuoro-1-(2-naphthyl)-1,3-butanedione, Br-bpy = 5-bromo-2,2'-bipyridine, Br-2-bpy = 4,4'-dibromo-2,2'-bipyridine, 5,5-(CH3)(2)-bpy = 5,5'-di-methyl-2,2'-bipyridine, 4,4-((CH3)(3))(2)-bpy = 4,4'-di-tert-butyl-2,2'-bipyridine, and 4,4-(CH3)(2)-bpy = 4,4'-di-methyl-2,2'-bipyridine), have been prepared by altering the capping N-donor coligands. Dy(III) ions in all complexes possess N2O6 octa-coordinated environments, displaying a distorted square antiprismatic D-4d symmetry in complexes 1-4, as well as a triangular dodecahedron D-2d symmetry in 5. Magnetic investigations evidence the SIM behavior in the five complexes with the energy barriers (U-eff) of 104.19 K (1), 122.93 K (2), 84.20 K (3), 64.16 K (4) and 80.23 K (5) under zero applied dc field. The potential QTM effects in the title complexes are successfully suppressed in the presence of the extra applied fields. The crystal field parameters and orientations of the magnetic easy axes were obtained from the simulation of the magnetic data and the electrostatic model calculation. The distinct electronic effects originating from the subtle changes of the substituents on the capping N-donor coligands induce varying coordination microenvironments and geometries on the Dy(III) sites, further drastically impacting the overall magnetic properties of the title complexes. The disparities of the uniaxial anisotropy and the magnetic dynamics for 1-5 have been elucidated by ab initio calculations as well.

Automated summary

A series of five mononuclear beta-diketonate-Dy(III) complexes have been synthesized by altering the capping N-donor coligands. Magnetic investigations show single-ion magnet behavior in these complexes, with quantum tunneling effects successfully suppressed in the presence of extra applied fields. The distinct electronic effects from subtle changes in the coligands drastically impact the overall magnetic properties.