Infrared and laser Raman studies of l-phenylalanine l-phenylalaninium perchlorate and bis( dl-phenylalaninium) sulphate monohydrate

Both crystals under study have two phenylalanine groups in the cationic part of the complex. In the l-phenylalanine l-phenylalaninium perchlorate crystal, two phenylalanine groups share one proton and become monoprotonated. In the bis( dl-phenylalaninium) sulphate monohydrate crystal, on the other hand, both the phenylalanine groups are protonated. This leads to several differences in the infrared and Raman spectra of these two crystals. The presence of both the carbonyl and the ionized carboxylic groups has been identified in the perchlorate crystal, while the sulphate crystal has only the carbonyl group. Extensive hydrogen bonding further leads to the shifting of bands due to several stretching and bending modes. It also reduces the T d symmetry of the anions to C 2 v symmetry causing the degeneracies of several modes to be removed.