Crystal and Molecular Structure of ω-Amino Acids, ω-Aminosulfonic Acids and Their Derivatives. I. The Crystal and Molecular Structure of γ-Guanidinobutyric Acid Hydrochloride and Hydrobromide

The crystals of γ-guanidinobutyric acid (GGBA) hydrochloride and hydrobromide, C5H12O2N3Cl and C5H12O2N3Br, are both triclinic, space group P1, with two molecules in a unit cell with the following dimensions; hydrochloride: a=7.41, b=9.12, c=7.25 Å, α=101.5°, β=112.4°, γ=65.2°; hydrobromide: a=7.94, b=9.36, c=7.78 Å, α=103.2°, β=115.5°, γ=61.5°. The X-ray structure analysis was carried out by the application of heavy atom method and refined by three dimensional least-squares method. Since GGBA hydrochloride and hydrobromide are isomorphous, the structure analysis was started by using of X-ray data of the hydrobromide to determine the rough atomic coordinates of its molecule, and the data of hydrochloride were used for the further refinement. The positions of the involved twelve hydrogen atoms were located by a three dimensional difference Fourier analysis. GGBA cation, +NH2(NH2)CNH(CH2)3COOH, and Cl− ion were almost perfectly on the (201) plane and formed a pararell sheet structure with six hydrogen bonds. The possible resonance structures were also discussed.