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–), [LnIII(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 TbIII and DyIII complexes have an isomorphous
structure, and each TbIII or DyIII 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 TbIII ion (4f8, J = 6, S =
3, L = 3, gJ = 3/2, 7F6) and the DyIII ion (4f9, J = 15/2, S = 5/2, L = 5, gJ = 4/3, 6H15/2). The Stark splittings
of the ground states 7F6 of the TbIII ion and 6H15/2 of the DyIII 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 6F9/2 → 6H15/2 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.