Halogen Bonded Three-Dimensional Uranyl–Organic Compounds with Unprecedented Halogen–Halogen Interactions and Structure Diversity upon Variation of Halogen Substitution

Actinide-based metal–organic
materials have drawn much attention
due to their intriguing 5f bonding properties and promising applications
in nuclear fuels and other fields. Introduction of weak interactions,
such as halogen bonds, into actinide–organic hybrid materials
will provide them with more flexibility and dynamics. The first case
of halogen bonded three-dimensional (3D) uranyl–organic supramolecular
frameworks with regular nanoscale channels has been obtained from
multifunctional halogen-substituted isonicotinic acids. Distinct from
conventional halogen bonded uranyl–organic frameworks, the
supramolecular networks obtained here consist of three-component cocrystals
and have been assemblied by intensive supramolecular networks to obtain
an extended 3D geometry. Moreover, secondary “X3” and “X6” halogen–halogen
interactions resulting from the driving forces of primary hydrogen
bonds have been found and analyzed by quantum chemical calculation,
indicating their feature of weak bonding and special geometry. It
is notable that this unprecedented type of “X6”
synthon, especially for “Br6”, represents
a new pattern of halogen–halogen interaction. When halogen
substitution of the organic precursor is changed, another type of
halogen bonded and hydrogen bonded 3D uranyl–organic framework
with two-dimensional layered networks and cross-linking agents formed in situ was acquired. Finally, reversible transformation
of 3D uranyl–organic supramolecular frameworks is available
through loss and regain of water involving in hydrogen bonding networks
and thus affords them structural dynamics.