Glycine hydrogen fluoride: Remarkable hydrogen bonding in the dimeric glycine glycinium cation

Crystals of glycine hydrogen fluoride (Gly·HF) were prepared from an aqueous solution containing stoichiometric quantities of the components. The crystal structure of Gly·HF was determined, IR and Raman spectra were registered and are discussed. Gly·HF crystallizes in the orthorhombic space group Pbca with Z = 32. The most remarkable feature of the structure is the existence of symmetric dimeric glycine–glycinium cations with short hydrogen bonds (O⋯O distance of 2.446 Å), charge-counterbalanced by hydrogen bifluoride (FH⋯F)− anions – in addition to the expected glycinium cations and fluoride anions. These results were compared with previously published data on crystals grown in the system glycine–HF–H2O.