Abstract
Single crystals of two new compounds, (l-CysH···l-Cys)(HC2O4) (I) and (l-CysH···l-Cys···l-CysH)(HC2O4)2·0.5H2O (II), were obtained. Crystal structures were solved and refined using single-crystal X-ray diffraction, and compared with the previously known orthorhombic and monoclinic modifications of the simple salt (l-CysH)(HC2O4). Compound (I) crystallizes in the triclinic crystal system (space group P1, Z=2) and contains (l-CysH···l-Cys) dimeric cations with very short O···O interatomic distance of 2.434(2) Å. Hydrogen oxalate anions form head-to-tail type chains with very short hydrogen bonds, characterized by O···O distances of 2.422(2) Å and 2.417(3) Å. The crystal lattice of (II) is monoclinic with the space group C2, Z=4. It contains a new type of cation, that has never been observed before for cysteine salts, i.e. trimeric (l-CysH···l-Cys···l-CysH) cation. Protonated l-cysteinium cations are connected to the zwitterionic l-cysteine moiety through the same oxygen atom of the carboxylate group via hydrogen bonds, with O···O distances of 2.6410(18) Å and 2.4888(19) Å. Similar to the structure (I), the hydrogen oxalate anions form head-to-tail type chains linked by short hydrogen bonds with O···O distances of 2.4369(17) Å and 2.4330(17) Å, respectively. The crystals were characterized by IR and Raman spectroscopy. The batches obtained on crystallization were also characterized by X-ray powder diffraction, in order to check the phase purity of all the sample.
Published Version
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