Expanding Actinide Crystal Chemistry through Synthesis and Radiolytic Studies of Actinide Metal-Organic Frameworks and Construction of a Structural Hierarchy

The field of actinide metal-organic frameworks (MOFs), specifically transuranic MOFs, is vastly underexplored. The first transuranic MOF was reported in 2018 and although others have since been reported, understanding of their chemistry lags behind those of early actinides and transition metals. This is in part due to their potent radioactivity and strategic importance, in addition to the need for dedicated facilities to study these elements.

In this work, the subset of thorium MOFs is expanded by exposing this actinide element to synthetic conditions typical of MOFs. A thorium MOF containing organic linkers with extended pi systems was synthesized, characterized, and irradiated. Gamma and He-ion irradiation studies reveal exceptional radiation resistance.

Neptunium MOFs are also investigated. Synthesis and characterization of multiple Np MOFs underscore that unprecedented clusters and structural units are stabilized in MOFs. This is achieved using a variety of organic linkers with diverse structures and geometries. Gamma-irradiation studies of one Np MOF indicated the interesting reactivity of transuranic structures when irradiated.

To relate these novel Np MOFs to the published body of literature on neptunium crystal chemistry, an expanded structural hierarchy of neptunium crystal structures was constructed. By sorting crystal structures based on oxidation state and dimensionality of the structural unit, structural trends and similarities are identified. Additionally, I develop a graphical notation system for neptunyl compounds coordinated by organic ligands and apply it to this subset of compounds to facilitate its comparison to structures coordinated by oxyanions.