Free‐Standing Halogen‐Bonded Nanosheets Formed by Ultrasonic Liquid Exfoliation

Abstract Strong in‐layer interactions are typically considered a key requirement for exfoliating layered materials to form nanosheets. Here, the formation of free‐standing nanosheets held together by halogen bonding interactions is reported for the first time. Layered co‐crystals are synthesized using either iodo‐ or bromo‐functionalized halogen bond donors with pyridyl functionalized acceptors. Sonication resulted in dissolution in a range of polar organic solvents; however, stable suspensions showing Tyndall scattering are observed for the iodo‐systems after exfoliation in water. Atomic force microscopy confirms the formation of micron‐sized nanosheets approaching monolayer thickness. Powder X‐ray diffraction of the nanosheets shows preferred orientation along the (1 1 0) plane, which confirms that the nanosheets are composed of halogen‐bonded chains in one dimension, and π – π stacking interactions in the second. The iodo‐nanosheets are stable in acidic and alkaline conditions and when heated at 80 °C for 48 h. Comparisons between the iodo‐ and bromo‐ analogues confirm that stronger halogen bonding is likely responsible for the difference in stability. The remarkable stability shown by these nanosheets held together by only supramolecular interactions calls for re‐evaluation of the conventional understanding of the requirements for forming 2D materials and establishes halogen‐bonded nanosheets as an exciting new class of materials.