Dysprosium Clusters from 3-Ethoxysalicylidene Terminal-Decorated Acylhydrazone Ligands: In Situ Ligand Transformation-Assisted Assembly and Zero-Field Single-Molecule Magnet Behaviors

Abstract

High-performance polynuclear lanthanide single-molecule magnets (Ln-SMMs) are still scarce now. Herein, we report the assembly of three novel DyIII clusters, where in situ ligand transformation-assisted assembly offered a system with high SMM performance successfully. These clusters, [Dy6(bepho)3(NO3)6(CH3OH)3(H2O)3]·5CH3OH·CH3CN·2H2O (1), [Dy4(bepho)2(H3epho)2 (CH3OH)2]·2CH3OH (2), and [Dy5(eehz)3(eqzl)(μ-CH3O)(μ3-CH3O)2(μ4-O)(CH3OH)]·2CH3OH (3), were all assembled from 3-ethoxysalicylidene terminal-decorated acylhydrazones. H4bepho, H5epho, H3eehz, and Heqzl represent N,N′-bis(3-ethoxysalicylicdene)pyridine-2,6-dicarbohydrazide N-oxide, N-(3-ethoxysalicylidene)pyridine-2,6-dicarbohydrazide N-oxide, N-(3-ethoxysalicylicdene)-2-(3-ethoxysalicylideneamino)benzohydrazide, and 3-(3-ethoxysalicylicdeneamino)quinazolinone, respectively. Cluster 1 is built by H4bepho directly, showing a hexanuclear zig-zag chain structure, while for 2 and 3, their original ligands all undergo unprecedented in situ transformations during the assembly. H5epho featuring asymmetric chelating arms and Heqzl bearing the quinazolinone parent are formed in 2 and 3, respectively, and participate in the assembly of clusters along with original ligands. In 2, H4bepho and H5epho construct a quasi-linear {Dy4} topology. A unique pentanuclear core of 3 is assembled by H3eehz and Heqzl. It consists of a [Dy4] tetrahedron and a [Dy3] triangle unit sharing an edge. Clusters 1–3 all show zero-field SMM behaviors, and 2 displays two distinct relaxation processes. Strikingly, the quantum tunneling of magnetization (QTM) effect in 3 might be suppressed by intramolecular magnetic interactions associated with its unique cluster topology. The zero-field energy barrier (Ueff) of 3 reaches up to 211.3 K, which is among the high values for all polynuclear Ln-SMM species and also the second largest one in the {Ln5}-SMM family.