Tetranuclear Lanthanide(III) Complexes Containing a Square‐Grid Core: Synthesis, Structure, and Magnetism

Abstract

The reactions of Ln(NO3)3·5H2O (Ln = Dy3+, Tb3+, Ho3+, Er3+) and a multidentate flexible ligand, (E)‐N′‐[2‐hydroxy‐3‐(hydroxymethyl)‐5‐methylbenzylidene]‐6‐(hydroxymethyl)picolinohydrazide (LH4), in the presence of Et3N in a 1:1:3 molar ratio afforded a series of complexes [Ln4(LH2)4(µ2‐OH)4]·xCH3OH·yH2O (Dy3+, x = 2, y = 2; Tb3+, x = 4, y = 5; Ho3+, x = 0, y = 13; Er3+, x = 4, y = 6). X‐ray diffraction analysis revealed that all the complexes are neutral and possess a distorted [2 × 2] square‐grid core [Ln4(µ2‐O)4(µ2‐OH)4] anchored by the concerted coordination of four doubly deprotonated ligands, (LH2)2–, and four µ2‐OH groups. All the Ln centers adopt a distorted triangular dodecahedral coordination geometry. An ac magnetic susceptibility study revealed undulations of the out‐of‐phase (χM′′) component above 2 K for 1 with a quantum tunnelling of magnetization tail at zero dc field. Surprisingly, a field‐induced temperature dependence of the ac frequencies at which the χM′′ maxima occur implies that the slow relaxation is a result of a mixed contribution from more than one Dy3+ center.