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

Michel Fleck,^a,* Christian Lengauer,^a Ladislav Bohatý^b and Ekkehart Tillmanns^a

^a Institut für Mineralogie und Kristallographie, Universität Wien, Althanstr. 14, A-1090 Vienna, Austria
^b Institut für Kristallographie, Universität zu Köln, Zülpicher Str. 49b, D-50674 Cologne, Germany
* Corresponding author: E-mail: michel.fleck@univie.ac.at

Abstract
Two new L-alanine compounds (alanine alaninium triiodide (1), s.g. P212121, a = 8.366(2) Å, b = 8.912(2) Å, c = 41.889(8) Å and alanine SrCl₂∙3H₂O (2), s.g. P21, a = 8.540(2) Å, b = 7.167(1) Å, c = 8.769(2) Å, β = 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.

Keywords: Alanine, crystal structure, amino-acid, coordination compounds, thermal properties