Very strong −N–X+⋯−O–N+ halogen bonds

Abstract

A new ⁻N–X⁺⋯⁻O–N⁺ paradigm for halogen bonding is established by using an oxygen atom as an unusual halogen bond acceptor. The strategy yielded extremely strong halogen bonded complexes with very high association constants characterized in either CDCl₃ or acetone-d₆ solution by ¹H NMR titrations and in the solid-state by single crystal X-ray analysis. The obtained halogen bond interactions, R_XB, in the solid-state are found to be in the order of strong hydrogen bonds, viz. R_XB ≈ R_HB.