Exploring The Photochemistry and Bonding of Trivalent Americium within Metal–Organic Constructs

Metal-organic frameworks (MOFs) are suitable platforms for studying the fundamental properties of the transuranium (TRU) elements. While the material properties that are common to MOFs, (e.g., structural variability, high surface area, and permanent porosity), are often exploited for their functionality, our motivations for studying TRU-MOFs are fundamental in nature. These robust, crystalline constructs are attractive hosts for immobilizing the scarce and often, highly radioactive isotopes of the TRU elements, providing both structural stability and a platform to explore structure–property relationships. The trivalent lanthanide (Ln(III)) containing MOF-76 family is of particular interest in this regard, given its high thermal stability and unique optical properties, which have been explored for use in color tuning and analyte sensing. The MOF-76 family is constructed from Ln(III) ions (where Ln = Eu, Sm, Tb, Nd…) and 1,3,5-tricarboxylic acid (BTC) ligands, forming a porous, three-dimensional architecture. Perhaps more importantly, the synthetic routes for preparing MOF-76(Ln(III)) are robust, being able to accommodate nearly all the 4f elements, and as such, is an ideal entry point for studying the trivalent actinides, like americium. An overview of this synthetic strategy and the crystal structure of MOF-76(Am) will be presented. Moreover, the utility of this platform for studying the optical properties of Am(III) will be highlighted. To this end, the focus will be in differentiating 4f vs. 5f element behavior with respect to ligand-to-metal resonance energy transfer and photoluminescence quenching.