Halogen Bonding in Solution: Under Pressure

The first study of the high-pressure behavior of organic halogen bond donors in solution is presented: HP-NMR titrations were performed in various solvents, primarily with a neutral tridentate halogen bond donor and an orthoamide or halides as Lewis bases. While the orthoamide showed stronger binding upon increased pressure in CDCl₃, CD₂Cl₂, acetone-d₆, and THF-d₈, the halides unexpectedly featured decreased association constants for the first three solvents. For comparison, bromide was also titrated against dicationic halogen and chalcogen bond donors as well as a thiourea as a representative hydrogen bond donor, with the latter showing weaker binding at elevated pressure. Qualitative agreement with this data was achieved via thermodynamic modeling using PC-SAFT. These findings stress the important role of the solvent in halogen-bonded complexes involving charged species and are expected to provide the basis for a rational application of high pressure in applications of halogen bonding in solution.