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

The reactions of Ln(NO 3 ) 3 · 5H 2 O (Ln = Dy 3+ , Tb 3+ , Ho 3+ , Er 3+ ) and a multidentate flexible ligand, ( E )‐ N′ ‐[2‐hydroxy‐3‐(hydroxymethyl)‐5‐methylbenzylidene]‐6‐(hydroxymethyl)picolinohydrazide (LH 4 ), in the presence of Et 3 N in a 1:1:3 molar ratio afforded a series of complexes [Ln 4 (LH 2 ) 4 (µ 2 ‐OH) 4 ] · x CH 3 OH · y H 2 O (Dy 3+ , x = 2, y = 2; Tb 3+ , x = 4, y = 5; Ho 3+ , x = 0, y = 13; Er 3+ , x = 4, y = 6). X‐ray diffraction analysis revealed that all the complexes are neutral and possess a distorted [2 × 2] square‐grid core [Ln 4 (µ 2 ‐O) 4 (µ 2 ‐OH) 4 ] anchored by the concerted coordination of four doubly deprotonated ligands, (LH 2 ) 2– , and four µ 2 ‐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 ( χ M ′′ ) 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 χ M ′′ maxima occur implies that the slow relaxation is a result of a mixed contribution from more than one Dy 3+ center.