Complementary Features of Inorganic (M–X) and Organic (C–X′) Halogens in C–X′···X–M Halogen Bonds: A Study Based on Structure, Energy, and Topological Electron Density

Abstract

A family of 10 compounds, each containing a MX2–pyrazine carboxylate complex anion and a protonated halo– (X′−) amino pyridine cation (MX2 = ZnCl2, ZnBr2, ZnI2, HgBr2, and HgI2; X′ = Cl, Br, I), are presented; a suitable system for pursuing C–X′···X–M halogen bonding (XB). The influence of halogen manipulation, metal ion and coordination variation on the nature and strength of C–X′···X–M interactions was discussed in terms of geometrical parameters, binding energies and charge density analysis with emphasis on the Laplacian of the electron density, ∇2ρ. Interplay of XBs with other noncovalent interactions, mainly N–H···X–M and Npy–H+···O– bonds, in supramolecular assemblies, were also investigated. The C–X′···X–M and N–H···X–M bonds have rationally been modified in strength upon changing the halogens involved, leading to systematic variations in the crystal packing.