Hydrolysis-Promoted Building Block Assembly: Structure Transformation from Wheel and Ship to Cage

Accurately controlling the hydrolysis of metal ions can not only yield the desired structure of metal hydroxide clusters but also provide a deeper understanding of the formation process of natural hydroxide minerals. However, the capture of hydrolysis intermediates remains a significant challenge, and metal hydroxide clusters are mainly obtained by employing adventitious hydrolysis. In this study, we realized a hierarchical building block assembly from Y³⁺ ions to large Y₁₂, Y₃₄, and Y₆₀ clusters by controlling the hydrolysis process of lanthanide ions under different pH conditions. Single-crystal structural analysis showed that the Y₁₂ wheel, Y₃₄ ship, and Y₆₀ sodalite cage contain 4, 12, and 24 cubane-like [Y₄(μ₃-OH)₄]⁸⁺ units, respectively. The structure of the Y₆₀ cluster can be attributed to two Y₃₄ clusters or six Y₁₂ clusters linked by vertices. These clusters can be synthesized through the hydrolysis of Y³⁺ under different pH conditions, and Y₆₀ can be prepared from the obtained Y₁₂ or Y₃₄ crystals by the simple addition of Y³⁺ ions. The capture and conversion of the intermediates of lanthanide series hydroxide clusters, Y₁₂ or Y₃₄, during the assembly from Y³⁺ ions to Y₆₀ can facilitate an understanding of the formation process of high-nuclearity lanthanide clusters.

Two Lanthanide Metal⁻Organic Frameworks Based on Semi-Rigid T-Shaped Tricarboxylate Ligand: Syntheses, Structures, and Properties

By using a semi-rigid tripodal ligand 5-(4-carboxybenzyloxy)isophthalic acid (H3L) and lanthanide metal ions (Nd3+, Tb3+), two novel lanthanide metal-organic frameworks, namely, {[Nd2L2(DMF)4] DMF}n (1), and {TbL(DMF)(H2O)}n (2), were synthesized under mild solvothermal conditions and structurally characterized by X-ray single crystal diffraction. Compounds 1 and 2 are isostructural, in which L3- ligands linked dinuclear lanthanide metal-carboxylate units to form non-interpenetrated 3D network with (3,6)-connected topology. Luminescent investigations reveal that compound 1 displays the near-infrared emission at room temperature, and compound 2 can be employed as selective probe for Cr2O72- anion in aqueous solution based on luminescence quenching. Moreover, compound 2 exhibits catalytic activity for cyclo-addition of CO2 and epoxides under relatively mild conditions.