A Dimer of Hydrogen Cyanide Stabilized by a Lewis Acid.

A highly labile dimer of hydrogen cyanide, HCN⋅⋅⋅HCN, was extracted from liquid HCN by adduct formation with the bulky Lewis acid B(C6 F5 )3 , affording HCN⋅⋅⋅HCN-B(C6 F5 )3 , which was fully characterized. The influence of the solvent (HCN, CH2 Cl2 , and aromatic hydrocarbons) on the crystallization process was studied, revealing dimer formation when using HCN or CH2 Cl2 as solvent, whereas aromatic hydrocarbons led to the formation of monomeric arene⋅⋅HCN-B(C6 F5 )3 adducts, additionally stabilized by η6 -coordination of the aromatic ring system similar to well-known half-sandwich complexes.