Salt or Cocrystal? Using XRPD to Infer Proton Transfer in Three Adducts of Iodoxybenzoic Acid by Analyzing Iodine-Oxygen Bond Lengths

2-Iodoxybenzoic acid (IBX) is a versatile oxidant, which has been used for a plethora of reactions through the years. Its explosive properties and low solubility, the major limitations to a more widespread use of this reactant, have led to the search for derivatives, adducts, or mixtures with comparable oxidative properties but better characteristics. In this paper, different adducts of IBX, in particular with pyridine (PIBX), quinoline (QUIBX), and nicotinamide (B3-IBX), have been structurally characterized using state-of-the-art X-ray powder diffraction (XRPD) methods. Their oxidative properties have been tested and compared to those of pristine IBX. While generally structure determination from XRPD does not allow us to investigate the proton position, a strategy was devised based on the investigation of iodine-oxygen exocyclic bond lengths to discriminate between single and double iodine- oxygen bonds. The final aim was to attempt to use XRPD to answer an elusive question: salt or cocrystal?