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 (<i>N</i>′-(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 [M^III₂(Hhmb)₃­(NCS)₃]·2MeOH·py (M = Y <b>1</b>, Eu <b>2</b>, Gd <b>3</b>, Tb <b>4</b>, Dy <b>5</b>, Ho <b>6</b>), while the second group, Type II, contains two dinuclear complexes with formula [M^III₂(Hhmb)₂­(NCS)₄(MeOH)₂] (M = Er <b>7</b>, and Yb <b>8</b>). Single-crystal X-ray analysis revealed that all M^III 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 <b>5</b>, <b>7</b>, and <b>8</b> exhibiting slow relaxation of the magnetization under an applied optimum dc field. Furthermore, complex <b>8</b> is the first example of a dinuclear Yb-based single-molecule magnet showing field-dependent multiple relaxation processes