2-Iodo-imidazolium receptor binds oxoanions via charge-assisted halogen bonding

A detailed H-1-NMR study of the anion binding properties of the 2-iodo-imidazolium receptor 1 in DMSO allows to fully attribute the observed affinities to strong charge-assisted C-I center dot center dot center dot X- halogen bonding (XB). Stronger binding was observed for oxoanions over halides. Phosphate, in particular, binds to 1 with an association constant of ca. 10(3) M-1, which is particularly high for a single X-bond. A remarkably short C-I center dot center dot center dot O- contact is observed in the structure of the salt 1 center dot H2PO4-.