Ionic Radius-Dependent Self-Assembly of Lanthanide Organic Polyhedra: Structural Diversities and Luminescent Properties

Abstract

The synthesis of nonclassical polyhedra is at the forefront of supramolecular research for their unique anisotropic interior cavities. However, due to the difficulty in controlling the topology of Ln supramolecular systems, the preparation of nonclassical lanthanide organic polyhedral (LOPs) remains a challenge. Herein, we explore the ionic radius dependent self-assembly of LOPs using rectangular tetra-tropic ligand L. Due to the rectangular, other than square, geometry of the ligand panels, the assembly of it with lanthanide ions located in the middle of Ln series affords the irregular tetragonal antiprismatic Ln8L4 (Ln = Sm3+, Eu3+, Tb3+, Dy3+ and Ho3+) with two faces are unoccupied by ligands L. Interestingly, such tetragonal antiprism possesses an oblate internal cavity, which binds four THF molecules in the solid-state structure. With an increase in radius, the larger La3+ and Nd3+ ions, produces a distinct architecture, the sandwich square, Ln4L2. In contrast, the smaller Er3+ and Lu3+ ions give rise to a mixture of both Ln8L4 and Ln6L3. Once adding excess Ln3+ ions, the structure transformation from Ln8L4 to Ln6L3 occur. Structural comparisons of La4L2 and Sm8L4 reveal that the differences in architecture within these systems are governed by both the ionic radii of the lanthanides and the conformational flexibility of the ligands. Photophysical investigations disclose that the ligand L exhibits a sensitizing ability toward Sm3+, Tb3+ and Dy3+ ions, displaying their characteristic luminescence emission, with a new record-setting luminescent quantum yield of 92.74% being observed for Tb8L4. This work provides new insights to understand the effect of lanthanide size on the resulting assemblies and opens new avenues to develop nonclassical LOPs.