ABSTRACT
A series of lanthanide-titanium oxo clusters (LnTOCs), Ln2Ti8-Ac, Ln2Ti8-p-Toluic, and Ln2Ti8-Anthra (Ln = Eu and Tb), were prepared based on acetic acid (HAc), p-toluic acid (Hp-Toluic), and anthracene-9-carboxylic acid (HAnthra). Crystal structural analysis showed that these clusters possess the same metal topology framework, in which eight Ti4+ ions form a cube and two Ln3+ ions are located on the opposite faces of the cube. The luminescence investigation discovered that the Eu2Ti8-Ac displays the highest quantum yields with 15.6%, and the conjugation effect of ligand substituents can lower the triplet state energy of ligands, thus regulating the luminescence quantum yield of the Ln2Ti8 clusters. These results suggest that the triplet excited-state energy of the ligands should match well with the energy levels of Ln3+ to enhance the luminescence.
ABSTRACT
Three heterometallic lanthanide-titanium oxo clusters (LnTOCs) formulated as Eu2Ti4(µ3-O)4(tbba)12(acac)2 (Eu2Ti4, 1, Hacac = acetylacetone), Eu5Ti4(µ3-O)6(tbba)20(Htbba)(THF)2 (Eu5Ti4, 2), and Eu8Ti10(µ3-O)14(Ac)2(tbba)34(H2O)4(THF)2(Htbba)2 (Eu8Ti10, 3) were prepared through the reactions of 4-tert-butylbenzoate (Htbba), rare-earth salts, and Ti(OiPr)4. The solution luminescence investigation discovered a size-dependent quantum yield phenomenon in solution. A solid-state luminescence study showed that these three LnTOCs display temperature-dependent photoluminescent properties. Interestingly, the Eu5Ti4 cluster exhibited the highest quantum yield of 94.9% in the solid state among the reported 3d-4f clusters.
ABSTRACT
Three homometallic high-nuclearity clusters, formulated as [(CO3)2@Ln37(LH3)8(CH3COO)21(CO3)12(µ3-OH)41(µ2-H2O)5(H2O)40]·(ClO4)21·(H2O)100 (abbreviated as Ln37, Ln = Gd (1); Tb (2); Eu (3), LH3 = 1,2,3-cyclohexanetriol) and featuring a double cage-like structure, were obtained through the reaction of 1,2,3-cyclohexanetriol, acetate ligand, and Ln(ClO4)3. The largest odd-numbered lanthanide cluster Gd37 exhibits an entropy change (-ΔSm) of 38.7 J kg-1 K-1.
