Sandglass-like Ln9 Nanoclusters with Magnetocaloric Effect and Lanthanide-Centered Luminescence

It is a challenging work to construct high-nuclear lanthanide nanoclusters with desirable magnetocaloric effects. To this end, a series of Ln₉ nanoclusters with sandglass-like topological structures have been successfully synthesized under solvothermal conditions by using two different alcoholamine ligands and lanthanide (Ln^III) salts, with the molecular formula [Ln₉(L¹)₄(NO₃)₁₂(μ₃-OH)₈(μ₄-OH)₂(CH₃CH₂OH)₄]·4.5CH₃CH₂OH·3Et₃NH (Ln^III = Gd (1-Gd), Eu (1-Eu), Tb (1-Tb)) and [Ln₉(L²)₈(NO₃)₈(μ₃-OH)₈(μ₄-OH)₂]·NO₃ (Ln^III = Gd (2-Gd), Eu (2-Eu), Tb (2-Tb)) (H₂L¹ = N-methyldiethanolamine and HL² = 2-(2-aminoethoxy)ethanol). It is worth noting that both 1-Gd and 2-Gd exhibit intramolecular antiferromagnetic interactions and show typical magnetocaloric effect behavior. At a magnetic field strength of 7 T and a temperature of 3 K, the values of the −ΔS_m^max are 33.65 J kg^–1 K^–1 for 1-Gd and 25.22 J kg^–1 K^–1 for 2-Gd. In addition, 1-Eu, 1-Tb, 2-Eu, and 2-Tb exhibit the characteristic luminescence of Eu^III and Tb^III ions, respectively. For 1-Tb, tunable emission from green to red was achieved by adjusting the doping ratio of lanthanide ions to obtain heterometallic clusters Tb_xEu_9-x, offering the potential for high-fidelity optical barcode applications.