Diversified Lanthanide-Directed Self-Assembly of Tritopic Tetradentate Acylhydrazone Ligand

Abstract

Lanthanide-organic assemblies exhibit considerable promise for optical, electronic, magnetic, and catalytic applications, yet their preparation remains challenging. Herein, we present a comprehensive study of lanthanide directed coordination self assembly using the tritopic tetradentate acylhydrazone ligand H6L3. Assembly of H6L3 with a broad range of lanthanide ions under varying conditions produced diverse outcomes, characterized by NMR spectroscopy, ESI-TOF-MS, and single crystal X-ray diffraction. Under neutral conditions, early lanthanide ions (Ln: LaIII, CeIII) rarely adopted an orthogonal coordination, yielding tetranuclear Ln4(H3L3)2 and trinuclear Ln3(H3L3)2 species. For the middle lanthanide ion (EuIII), Eu6(H3L3)4 complex would convert into anti-triangular prismatic Eu6(H3L3')6 during crystallization or a mixture of Eu3(H3L3)2 and Eu4(H3L3)2 when the metal-to-ligand ratio was increased to 3:2. In the presence of base, the orthogonal coordination is observed to minimize steric hindrance and octahedral Ln6L34 were accessed across the entire lanthanide series. Interestingly, the homochiral Δ6/Λ6-Ce6L34 and Δ6/Λ6-Lu6L34 display different binding sequence toward alkylammonium cation. The rich structural diversity and size selectivity toward guests were attributed to the differences in lanthanide ions radii and coordination strength. These findings furnish general design principles for coordination driven self-assembly of multinuclear lanthanide architectures.