Metal-organic frameworks based on uranyl and phosphonate ligands

Area of Science:

• Inorganic Chemistry
• Materials Science
• Crystallography

Background:

• Metal-organic frameworks (MOFs) offer tunable properties for various applications.
• Uranyl-based MOFs are of interest due to the unique coordination chemistry of uranium.

Purpose of the Study:

• To synthesize and characterize novel crystalline uranyl-based metal-organic frameworks.
• To investigate the structural diversity and properties of these new MOFs.

Main Methods:

• Reaction of uranyl nitrate with three different phosphonic acids: nitrilotris(methylphosphonic acid) [H6nmp], 1,4-phenylenebis(methylene)diphosphonic acid [H4pmd], and (benzene-1,3,5-triyltris(methylene))triphosphonic acid [H6bmt].
• Single-crystal X-ray diffraction for structural determination.
• FT-IR spectroscopy for solid-state analysis.
• Topological analysis of the network structures.

Main Results:

• Three new uranyl-based MOFs were successfully synthesized and structurally characterized: [(UO2)2F(H3nmp)(H2O)]·4H2O (I), [(UO2)(H2pmd)] (II), and [(UO2)3(H3bmt)2(H2O)2]·14H2O (III).
• Compounds (I) and (III) exhibit diverse uranyl coordination geometries (pentagonal bipyramidal and octahedral) and contain significant solvent-accessible volumes (23.6% and 26.9%, respectively) with distinct cavity shapes.
• Topological studies revealed trinodal (3,6,6- and 4,4,6-connected) and uninodal (4-connected) network structures for compounds (I), (III), and (II), respectively.

Conclusions:

• The study successfully demonstrates the synthesis of novel uranyl-based MOFs with varied structural architectures.
• The characterized MOFs showcase interesting coordination environments and porosity, suggesting potential for further investigation in areas like gas storage or catalysis.
• The findings contribute to the growing field of uranyl-based MOFs, highlighting the versatility of phosphonic acids as ligands.