Syntheses, Crystal Structures and Thermal Behaviour of Novel L-Alanine Halogenide Compounds

Two new L-alanine compounds (alanine alaninium triiodide (1), s.g. P212121, a = 8.366(2) A, b = 8.912(2) A, c = 41.889(8) A and alanine SrCl2 3H2O (2), s.g. P21, a = 8.540(2) A, b = 7.167(1) A, c = 8.769(2) A, Beta= 95.02(3)°) have been prepared and characterised by X-ray single crystal analysis. The crystal structure of (1) features the presence of two independent molecules of alanine, alaninium and triiodide, respectively, in the asymmetric unit, with a very strong hydrogen bond between the carboxylate groups of alanine and alaninium. Compound (2) is composed of infinite zig-zag chains of [SrO7Cl]-polyhedra, with alanine molecules and chloride ions in the interstices. By the study of the thermal behaviour of (1) via thermogravimetry and temperature resolved X-ray powder diffraction it was found that the compound is stable up to approx. 363 K and that the thermal expansion along c is only about 1/3 compared to a and b.