Conversion Between 2- and 3-Dimensional Halogen-Bonded Networks Formed From a Single N-Oxide/Iodoalkyne Building Block

Despite their promise as porous supramolecular materials, permanently porous halogen-bonded frameworks have not been realized, and progress in the field is limited by a lack of understanding of what happens when these materials are activated via solvent exchange or under vacuum. In the current work, a single building block bearing complementary iodoalkyne halogen bond donors and pyridine-N-oxide acceptors is described. Crystallization is solvent dependent, with initial experiments giving networks containing unwanted hydrogen bonding interactions between components. Subsequent optimization of conditions enabled the generation of a 3D network assembled by only halogen bonds. Upon solvent exchange, the 3D network undergoes an unprecedented single-crystal transformation to a new 2D phase. Synchrotron far-infrared spectroscopy was employed to identify diagnostic signals for the phase transition. These results add to our understanding of the dynamic nature of halogen-bonded network materials.