Exploring Energy-Density Relationships in Uranyl nun-Topology MOFs and Their Topological Isomers

Metal–organic frameworks (MOFs) offer a tunable and controlled environment to investigate uranium chemistry, though the development of specific design rules for uranyl-containing MOFs remains necessary. Here, we explore the previously reported low-density uranyl MOF, NU-1301, to investigate the formation of additional topologically unique products and their thermodynamic relationships. By adjusting the temperature, modulator, and reaction time, we selectively synthesized three distinct phases: NU-1301-A, NU-1301-B, and NU-1301-C. We further examined their energetic relationships by analyzing the conditions that trigger the transitions between them. This approach was applied to the synthesis and study of an isoreticular analogue, NU-1308, and its topological isomer, NU-1309. Our findings reveal that the lower density nun topologies, NU-1301-A and NU-1308, are kinetic products, while the higher density structures, NU-1301-B, NU-1301-C, and NU-1309, are thermodynamically more stable. Understanding these energetic profiles is valuable for the reproducible synthesis of low-density MOFs and for identifying structure-energy relationships in the crystallization of actinide-containing materials.