Triangular dodecahedral Dy(III) single-ion magnets with pseudo-mono-axial ligand field

Taking advantage of a bulky heptadentate organic ligand tris{[2-((imidazol-4-yl)methyl)amino]ethyl}amine (L) weakly binding to the central Dy(III) ion, two new eight-coordinate triangular dodecahedral Dy(III) complexes, [Dy(L)(F₅PhO)₂](BPh₄)₂·2CH₃CN (F₅PhOH = pentafluorophenol, 1) and [Dy(L)(2,6-dichloro-4-nitro-PhO)](BPh₄)₂·CH₃CN (2,6-dichloro-4-nitro-PhOH = 2,6-dichloro-4-nitrophenol, 2), were synthesized and characterized by X-ray diffraction, magnetic measurements, and theoretical calculations. Complexes 1 and 2 exhibit typical single-molecule magnet (SMM) behavior, with effective energy barriers of 69(6) K and 35(1) K, respectively. Detailed ab initio calculations were performed to further elaborate on the electronic and magnetic structures of the low-lying energy levels for both complexes. The theoretical results indicate that the presence of strongly electron-withdrawing substituents such as fluorine, chlorine, and nitro groups in the axial ligands leads to the reduction of the negative charge distribution in the axial ligand field, thus weakening the magnetic anisotropy of the oblate-shaped Dy(III) ion, which is also confirmed by the analysis of magneto-structural relationship.