Protonated Hydrogen Cyanide

Trimethylsilylcyanide reacts with superacidic solutions AF/MF 5 (A=H, D; M=As, Sb) to form their corresponding salts [ACNA] + [MF 6 ] − , which are protonated forms of hydrogen cyanide and Me 3 SiF as by‐product. The salts have been characterized by vibrational spectroscopy and a single‐crystal X‐ray structure analysis. [DCND] + [AsF 6 ] − crystallizes in the triclinic space group P‐1 with one formula unit in the unit cell. The disordered cations are linked with two strong hydrogen bonds to [SbF 6 ] − anions to form chains. The crystal structure and the vibrational spectra are compared to the quantum‐chemically calculated (PBE1PBE/6‐311++G(3df,3dp)) [HCNH(HF) 2 ] + and [DCND(HF) 2 ] + units which simulate the H⋅⋅⋅F hydrogen bridges found in the solid state. The vibrational modes of the [DCND] + cation are strongly mixed. For their discussion 13 C and 15 N isotopomers have been prepared by the reaction of KCN isotopomers with the superacidic solution AF/AsF 5 .