A statistical analysis of halide · · · H–A (A = OR, NR2, N+R3) hydrogen bonding interactions in the solid state

Abstract

The interaction between F^–, Cl^–, Br^– and I^– and organic H-bond donors OH, NH and N⁺H are examined in detail using the Cambridge Structural Database. The ammonium group is shown to be the most effective H-bond donor to the halides, followed by the hydroxy group and neutral NH. Comparison of the H-bonding requirements of the anions in each case shows trends in X^– · · · HA distances (r), with the Δr interval between F^– and Cl^– being the greatest, and that between Cl^– and Br^– the least. Mean H-bonding angles ∠AHX^– are ca. 160 ° and tend towards greater linearity with increasing quality of the hydrogen bond. Interactions of halide ions with macrocyclic H-bonding receptors and the potential for host selectivity are discussed.