L-Cysteine halogenides: A new family of salts with an l-cysteine"l-cysteinium dimeric cation

Two l-cysteinium-halogenides with (l-cysteine···l-cysteinium) dimeric cations have been obtained, (l-Cys"l-Cys⁺)·Cl^-, and (l-Cys"l-Cys⁺)·Br^-. Both salts crystallize in monoclinic space group P2₁. Although these salts have the same dimeric cations and isotypical halogen anions, crystal packing is different. The main difference between the two salts rests in the conformation of (l-Cys"l-Cys⁺) dimeric cation, which also differs from that of the dimeric cation in the previously reported compound l-Cys⁺(l-Cys"l-Cys⁺)·F^-·(F^-"HF). The dimeric cation is formed by a very short O-H"O hydrogen bond with d(O···O) of 2.449(2) Å and 2.435(11) Å in the chloride and bromide, respectively. In addition to crystal structure analysis, Infrared and Raman spectra have been registered and discussed with a particular focus on intermolecular interactions. The l-Cys⁺·Br^-·H₂O salt with a simple l-cysteinium cation was also obtained and the crystal structure solved. It resembles its chloride analogue, l-Cys⁺·Cl^-·H₂O.