A focus on coordination chemistry at chlorine

Abstract

A highlight of the recent report on the remarkable outcomes of the seemingly simple reaction of pyridines with chlorine gas.

Halogen Bonds of Halogen(I) Ions─Where Are We and Where to Go?

“…Riedel and co-workers have used an analogous strategy for the production of [bis(pyridine)chlorine(I)] + and bis(luthidine)chlorine(I)] + Cl 3 − crystals from −196 to −40 °C, 64 which has been a truly impressive achievement considering that such a complex could previously only be studied in solution at −80 °C. 19,67 In summary, halogen-bonded halogen(I) complexes can be produced through a variety of robust synthetic routes; however, one needs to carefully exclude moisture and avoid the use of protic solvents to obtain pure products. For their characterization in solution, the detection of 15 N NMR chemical shifts is strongly recommended as the 1 H and 13 C NMR spectra of the halogen(I) and proton complexes are often similar.…”

“…Bromine(I) complexes decompose within hours in solution, whereas chlorine(I) complexes can only be studied at low temperatures. 19,64,67 The 3c4e halogen-bond complexes of electron-rich ligands are more stable those of electron-poor ones. 62 The complexes of bidentate ligands, such as (1,2-bis(pyridin-2-ylethynyl)benzene), are comparably stable to their monodentate analogues, whether a symmetric or asymmetric halogen bond is formed.…”

“…This redox reaction does not generate a pure product in high yield, but the product can be isolated through careful crystallization. Riedel and co-workers have used an analogous strategy for the production of [bis­(pyridine)­chlorine­(I)] + and bis­(luthidine)­chlorine­(I)] + Cl 3 – crystals from −196 to −40 °C, which has been a truly impressive achievement considering that such a complex could previously only be studied in solution at −80 °C. , …”

“…Iodine­(I) complexes can be stored for months as solids when dry, and they survive days in dry solutions in aprotic solvents. Bromine­(I) complexes decompose within hours in solution, whereas chlorine­(I) complexes can only be studied at low temperatures. ,, The 3c4e halogen-bond complexes of electron-rich ligands are more stable those of electron-poor ones . The complexes of bidentate ligands, such as (1,2-bis­(pyridin-2-ylethynyl)­benzene), are comparably stable to their monodentate analogues, whether a symmetric or asymmetric halogen bond is formed. , The most common cause of decomposition of [D···X···D] complexes is the presence of moisture or a protic solvent.…”