The halogen bond made visible: experimental charge density of a very short intermolecular Cl⋯Cl donor–acceptor contact

Abstract

[ZnCl(2)(3,4,5-trichloropyridine)(2)] features short intermolecular Cl···Cl contacts between halogen atoms of different nature, and a charge density study provides experimental evidence for the accepted model of the halogen bonds: an arene-bonded Cl atom acts as a donor of electron density towards the "sigma hole" of a chlorido ligand attached to a neighbouring Zn(II) cation.

Supramolecular Cl⋅⋅⋅H and O⋅⋅⋅H Interactions in Self‐Assembled 1,5‐Dichloroanthraquinone Layers on Au(111)

“…We performed ab initio density functional calculations (DFT) using the VASP code 25. 26 Interactions between ions and electrons were approximated by the projector‐augmented wave (PAW) potential 28.…”

“…Therefore, the σ‐hole of a Cl ligand is weaker than that of a Br ligand. However, recent reports have shown that Cl⋅⋅⋅Cl halogen bonds are formed in molecules such as hexachlorobenzene, 2‐chloro‐3‐chloromethyl‐8‐methylquinoline, and 3,4,5‐trichloropyridine 23–25. On the basis of X‐ray crystallography analyses, these reports demonstrated that Cl ligands are reasonable donors and acceptors for halogen bonds in the bulk crystals of these molecules…”

Halogen Bonding in Isostructural Co(II) Complexes with 2-Halopyridines

“…Cu, Zn, Co, Cd, etc.) [16][17][18][19][20][21][22][23], represent a large family of coordination compounds which reveal a clear trend to form XB in a solid state. Surprisingly, the analysis of previously published XRD data indicates that complexes with 2-halopyridines (2-XPy) are less studied than those with 3-, 4-or polysubstituted pyridines.…”

Charge Density of Intra‐ and Intermolecular Halogen Contacts

“…Already in our first communication concerning the very short Cl ··· Cl interactions in 8 ,14 we pointed out that “the roles for density donor D and acceptor halogen X... are at first sight counterintuitive”, and it was no surprise that our report has stimulated discussion: M. A. A. Ibrahim (University of Manchester, UK and Minia University, Egypt) has investigated a single molecule of 8 by theoretical methods.…”

“…Charge density studies concerning short interhalogen contacts will be the main focus of this article: Our experimental results have been obtained by diffraction studies on the compounds shown in Scheme and Scheme . The experimental charge densities for 1 – 4 and 7 17 and for 8 and 9 14 have already been communicated. Scheme summarizes coordination polymers in which intra‐ and inter‐strand X ··· X contacts can be expected ( 1 – 4 ) and the chemically related compounds ( 5 – 7 ) without such interactions.…”