Salts of HCN-Cyanide Aggregates: [CN(HCN)2 ]- and [CN(HCN)3 ]

Abstract

Although pure hydrogen cyanide can spontaneously polymerize or even explode, when initiated by small amounts of bases (e.g. CN^- ), the reaction of liquid HCN with [WCC]CN (WCC=weakly coordinating cation=Ph₄ P, Ph₃ PNPPh₃ =PNP) was investigated. Depending on the cation, it was possible to extract salts containing the formal dihydrogen tricyanide [CN(HCN)₂ ]^- and trihydrogen tetracyanide ions [CN(HCN)₃ ]^- from liquid HCN when a fast crystallization was carried out at low temperatures. X-ray structure elucidation revealed hydrogen-bridged linear [CN(HCN)₂ ]^- and Y-shaped [CN(HCN)₃ ]^- molecular ions in the crystal. Both anions can be considered members of highly labile cyanide-HCN solvates of the type [CN(HCN)_n ]^- (n=1, 2, 3 …) as well as formal polypseudohalide ions.

Keywords: hydrogen bonding; hydrogen cyanide; solvates; structure elucidation.