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.