Lanthanide Molecular Clusters and Metal-Organic Layers Constructed by Manipulation of Substituents

Usually, complexes with different connections and shapes are constructed by regulating the substituents. However, it is extremely challenging to construct two lanthanide complexes with different dimensions by only fine-tuning the substituents of the ligands, especially the substituents (-CH₃ and -CH₂CH₃) with almost similar physical and chemical properties. Herein, by only regulating the substituents of the multidentate chelating ligands, two lanthanide complexes with different dimensions and connection modes were successfully constructed using a multicomponent "one-pot method" under the guidance of the multidentate chelating coordination method (MCC). They are the 11-nuclear lanthanide molecular cluster (Dy) and the metal-organic layer (2D-Dy). Specifically, when the selected ligand is an imidazole-2-carboxaldehyde derivative and its substituent is -CH₃, a layered 2D-Dy is obtained. The linker [Dy(HL¹)₃] with a propeller configuration is formed by chelating the Dy(III) ion with an acylhydrazone ligand (HL¹) formed by the condensation of three salicylhydrazides and 1-methyl-1H-imidazole-2-carboxaldehyde. The above linkers were further linked alternately with propeller-shaped [Dy(NO₃)₃] as a secondary building unit (SBU) to form 2D-Dy. In addition, by changing the -CH₃ on the ligand to -CH₂CH₃, we obtained an example of Dy formed by epitaxial assembly of two Dy(III) ions with an hourglass-shaped Dy₉ as the core, and its molecular formula is [Dy₁₁(HL²)₈(μ₃-OH)₈(μ₄-O)₂(CH₃O)₄(NO₃)₄](NO₃)₅ 18CH₃OH. The cluster Dy was bombarded using high-resolution electrospray ionization mass spectrometry (HRESI-MS) and the molecular ion peaks of various fragments formed were captured. Based on the above molecular ion peaks, the possible fragmentation mechanisms of Dy were inferred to be Dy₁₁ → Dy₄(HL²)₄ → Dy₃(HL²)₂ → Dy₂(HL²)₂ → Dy(HL²)₂ and Dy₁₁ → Dy(HL²)₂/Dy₂(HL²)₂/Dy₃(HL²)₂/Dy₄(HL²)₄. This work is one of the rare examples where fine-tuning of ligand substituents leads to the formation of complexes of different dimensions, which promotes the progress of crystal engineering of lanthanide complexes.