Halogen Bonds or Not? Reassessing Noncovalent Interactions in Crystals of Periodate Anion from the Cambridge...

This study examines a series of organic-inorganic crystal structures containing the periodate anion (IO₄^-) to clarify the nature of the anion-anion interactions that are frequently referred to as halogen bonds. Our analysis demonstrates that, in many cases, IO₄^- does not develop an electrophilic σ-hole on the iodine center, even in the presence of organic cations, and therefore cannot reliably function as a halogen-bond donor. In its discrete (0D) form, the anion retains its character as a Lewis base. In crystal structures where extended architectures are observed-such as one-dimensional chains, two-dimensional layers, or three-dimensional cage-like assemblies-these structures arise predominantly from strong coulombic interactions with surrounding cations, as the interaction between the anions is intrinsically repulsive in the gas phase. Hydrogen bonding, together with other noncovalent interactions including chalcogen, tetrel, and/or pnictogen bonding, plays a dominant role in stabilizing the anionic arrangements and governing their structural organization.