Uranyl Coordination Mediates Structure Evolution of Supramolecular Assemblies of Carbazole Tricarboxylic Acid

Abstract

As a class of typical metal-organic framework materials(MOFs), actinide-based MOFs feature their unique actinide-ligand bonds. However, how these coordination interactions participate in and affect the lattice assembly process of organic ligands remains less studied. In this work, the coordination assembly of carbazole tricarboxylic acid organic ligands and uranyl ions was taken as a showcase study, and the regulation of uranyl coordination on the assembly process of carbazole tricarboxylic acid in lattice by controlling the synthesis conditions was studied in detail. Single-crystal analyses show that with the introduction of uranyl metal nodes, the assembly of carbazole tricarboxylic acid has realized a gradual evolution from a hydrogen bond-organic framework structure to a metal-organic network. In this regulation process, the connection of hydrogen bonds between different carbazole tricarboxylic acids is gradually replaced by uranyl coordination. The two-dimensional network structure also changes from sextuple intercatenated non-planar network through planar supramolecular network to final coordination network. The related transformation process is mainly manifested in gradual participation of the carboxyl groups in the coordination of uranyl center, which has also been confirmed by infrared spectroscopy. This work reveals the molecular mechanism of the synthesis of inorganic-organic porous materials through uranyl-ligand coordination and the detailed process of material structure evolution.

Keywords

• actinides
• uranyl
• metal-organic framework
• coordination bonds
• supramolecular assembly
• structure regulation