Crystal Field Splitting of the Ground State of Terbium(III) and Dysprosium(III) Complexes with a Triimidazolyl Tripod Ligand and an Acetate Determined by Magnetic Analysis and Luminescence

Abstract

Terbium­(III) and dysprosium­(III) complexes with a tripodal N₇ ligand containing three imidazoles (H₃L) and a bidentate acetate ion (OAc^–), [Ln^III(H₃L)­(OAc)]­(ClO₄)₂·MeOH·H₂O (Ln = Tb, <b>1</b>; Ln = Dy, <b>2</b>), were synthesized and studied, where H₃L = tris­[2-(((imidazol-4-yl)­methylidene)­amino)­ethyl]­amine. The Tb^III and Dy^III complexes have an isomorphous structure, and each Tb^III or Dy^III ion is coordinated by the tripodal N₇ and the bidentate acetate ligands, resulting in a nonacoordinated capped-square-antiprismatic geometry. The magnetic data, including temperature dependence of the magnetic susceptibilities and field dependence of the magnetization, were analyzed by a spin Hamiltonian, including the crystal field effect on the Tb^III ion (4f⁸, <i>J</i> = 6, <i>S</i> = 3, <i>L</i> = 3, <i>g</i>_<i>J</i> = 3/2, ⁷F₆) and the Dy^III ion (4f⁹, <i>J</i> = 15/2, <i>S</i> = 5/2, <i>L</i> = 5, <i>g</i>_<i>J</i> = 4/3, ⁶H_15/2). The Stark splittings of the ground states ⁷F₆ of the Tb^III ion and ⁶H_15/2 of the Dy^III ion were evaluated from the magnetic analyses, and the energy diagram patterns indicated an easy axis (Ising type) anisotropy for both complexes, which is more pronounced for <b>2</b>. The solid-state emission spectra of both complexes displayed sharp bands corresponding to the f–f transitions, and the fine structures assignable to the ⁵D₄ → ⁷F₆ transition for <b>1</b> and the ⁶F_9/2 → ⁶H_15/2 transition for <b>2</b> were related to the energy diagram patterns from the magnetic analyses. <b>1</b> and <b>2</b> showed an out-of-phase signal with frequency dependence in alternating current (ac) susceptibility under a dc bias field of 1000 Oe, indicative of a field-induced SIM