Hydrogen Bonds between an NH 4 ⊕ Ion and a Carbanion—Crystal Structure of Ammonium 1,2,4‐Tricyanocyclopentadienide

The H 3 N ⊕ H ⃛C hydrogen bond found for the first time in the crystalline state is consistent with concepts developed by Cram for the mechanism of the D/H exchange which proceeds with unusually high retention ( k A / k rac = 148) on reaction of a fluorenyl derivative with NH 3 . Each nitrile N atom of the title compound is bound via an H bond to an NH   4 ⊕ion, and each NH   4 ⊕ion forms three H bonds to nitrile N atoms and one hydrogen bond to a cyclopentadienide C atom. The picture on the right shows a section of the crystal structure (in hydrogen bond).