Structural Rearrangement Through Lanthanide Contraction in Dinuclear Complexes

A new series of lanthanide complexes
was synthesized, and the geometry
and preliminary magnetic measurements of the complexes were explored.
The specific ligand used (N′-(2-hydroxy-3-methoxybenzylidene)­benzhydrazide)
(H2hmb) was synthesized using a Schiff-base approach and
was employed due to the presence of a coordination pocket that is
able to accommodate magnetically selective lanthanide ions. The series
can be divided into two groups that are categorized by a drastic structural
rearrangement. The first group, Type I, contains six analogous complexes
with the formula [MIII2(Hhmb)3­(NCS)3]·2MeOH·py (M = Y 1, Eu 2, Gd 3, Tb 4, Dy 5, Ho 6), while the second group, Type II, contains two dinuclear
complexes with formula [MIII2(Hhmb)2­(NCS)4(MeOH)2] (M = Er 7, and Yb 8). Single-crystal X-ray analysis revealed
that all MIII ions in Type I exhibit monocapped distorted
square antiprismatic geometries, while those of Type II exhibit distorted
dodecahedron geometry. The direct current and alternating current
magnetic measurements were carried out on all complexes, with 5, 7, and 8 exhibiting slow relaxation
of the magnetization under an applied optimum dc field. Furthermore,
complex 8 is the first example of a dinuclear Yb-based
single-molecule magnet showing field-dependent multiple relaxation
processes.