Multifaceted Modularity: A Key for Stepwise Building of Hierarchical Complexity in Actinide Metal–Organic Frameworks

Growing
necessity for efficient nuclear waste management is a driving
force for development of alternative architectures toward fundamental
understanding of mechanisms involved in actinide (An) integration
inside extended structures. In this manuscript, metal–organic
frameworks (MOFs) were investigated as a model system for engineering
radionuclide containing materials through utilization of unprecedented
MOF modularity, which cannot be replicated in any other type of materials.
Through the implementation of recent synthetic advances in the MOF
field, hierarchical complexity of An-materials was built stepwise,
which was only feasible due to preparation of the first examples of
actinide-based frameworks with “unsaturated” metal nodes.
The first successful attempts of solid-state metathesis and metal
node extension in An-MOFs are reported, and the results of the former
approach revealed drastic differences in chemical behavior of extended
structures versus molecular species. Successful utilization of MOF
modularity also allowed us to structurally characterize the first
example of bimetallic An–An nodes. To the best of our knowledge,
through combination of solid-state metathesis, guest incorporation,
and capping linker installation, we were able to achieve the highest
Th wt % in mono- and biactinide frameworks with minimal structural
density. Overall, the combination of a multistep synthetic approach
with homogeneous actinide distribution and moderate solvothermal conditions
could make MOFs an exceptionally powerful tool to address fundamental
questions responsible for chemical behavior of An-based extended structures
and, therefore, shed light on possible optimization of nuclear waste
administration.