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

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, 1; Ln = Dy, 2), 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, J = 6, S = 3, L = 3, g_J = 3/2, ⁷F₆) and the Dy^III ion (4f⁹, J = 15/2, S = 5/2, L = 5, g_J = 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 2. 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 1 and the ⁶F_9/2 → ⁶H_15/2 transition for 2 were related to the energy diagram patterns from the magnetic analyses. 1 and 2 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.