Asymmetric {Dy4} metallogrid and double-layered {Dy8} cage clusters from carboxylic decorated o-vanillin Schiff bases: syntheses, topological variation, and single molecule magnet behaviors

Abstract

There is still great potential to be tapped for polynuclear lanthanide single-molecule magnets (Ln-SMMs) for performance. Toward this goal, the exploration of polynuclear lanthanide clusters (PLnCs) with novel special topologies is critical. Herein, two novel PLnCs, [Dy₄(ov6ca)₆(CH₃OH) (H₂O)₂]·6CH₃OH·CH₃CN·H₂O (1) and [Dy₈(ov5ca)₆(a5ca)₄(ov)₂(μ-OH)₆]·6CH₃OH (2), have been synthesized, where ov6ca²⁻, ov5ca²⁻, a5ca⁻, ov⁻ represent the ions of 2-[(o-vanillidene)amino]-6-chlorobenzoic acid, 2-[(o-vanillidene)amino]-5-chlorobenzoic acid, 2-amino-5-chlorobenzoic acid and o-vanillin, respectively. Carboxylic decorated o-vanillin Schiff base ligands H₂ov6ca and H₂ov5ca, were constructed as 1 and 2, respectively, and only differ in the position of a Cl-substituent. However, this tiny difference has induced great variation in the nuclearity and topology between 1 and 2. Cluster 1 features a {Dy₄} metallogrid core, where four Dy^III ions are bridged by two O_phenol and two carboxylate groups from ov6ca²⁻ ligands but show different coordination geometries. To our knowledge, it is the first {Ln₄} cluster with such an asymmetric metallogrid topology. While 2 displays a rare double-layered cage cluster topology, in which a pair of butterfly-shaped {Dy₄} units were linked together by four carboxylate groups from ov5ca²⁻ ligands. Magnetic measurements revealed that both 1 and 2 exhibit slow magnetic relaxation behavior, with efficient energy barrier (U_eff) values of 93.06 and 66.92 K, respectively.