Partial transfer of bridging atom in halogen-bonded complexes

Abstract

Ab initio calculations assess the displacement of the bridging atom within halogen-bonded complexes and comparison is made with proton transfers within H-bonds. Lewis acid units considered include CX, FX, NX, and OX bonds within the context of F3CX, FX, F2NX, FOX, and F2NOX where X = Cl, Br, and I, and H in the corresponding H-bonded complexes. NMe3 and NCl3. were both taken as bases due to their widely differing nucleophilicity. The degree of transfer is small even when a strong acid is combined with a strong base. This reluctance to transfer is due in part to the fact that such a transfer would lead to a high-energy ion pair. Cl shifts its position the most within most of these complexes, followed by Br and then I; the proton is more resistant to transfer.