Crystal structures of three halide salts of L-asparagine : an isostructural series

de Moraes, Lygia S. and Kennedy, Alan R. and Logan, Charlie R. (2018) Crystal structures of three halide salts of L-asparagine : an isostructural series. Acta Crystallographica Section E: Structure Reports, 74 (Part 1). ISSN 1600-5368

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    Abstract

    The structures of three monohydrated halide salt forms of L-asparagine are presented, viz.L-asparaginium chloride monohydrate, C4H9N2O3+·Cl−·H2O, (I), L-asparaginium bromide monohydrate, C4H9N2O3+·Br−·H2O, (II), and L-asparaginium iodide monohydrate, C4H9N2O3+·I−·H2O, (III). These form an isomorphous and isostructural series. The C—C—C—C backbone of the amino acid adopts a gaucheconformation in each case [torsion angles for (I), (II) and (III) = −55.4 (2), −55.6 (5) and −58.3 (7)°, respectively]. Each cation features an intra­molecular N—H⋯O hydrogen bond, which closes an S(6) ring. The extended structures feature chains of cations that propagate parallel to the b-axis direction. These are formed by carb­oxy­lic acid/amide complimentary O—H⋯O + N—H⋯O hydrogen bonds, which generate R22(8) loops. These chains are linked by further hydrogen bonds mediated by the halide ions and water mol­ecules to give a layered structure with cation and anion layers parallel to the ab plane. Compound (III) was refined as an inversion twin.