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Acta Crystallogr C Struct Chem. 2015 Aug;71(Pt 8):733-41. doi: 10.1107/S2053229615013601. Epub 2015 Jul 25.

Unusual hydrogen bonding in L-cysteine hydrogen fluoride.

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Novosibirsk State University, Pirogova 2, Novosibirsk 630090, Russian Federation.
Institute of Applied Problems of Physics, NAS of Armenia, 25 Nersessyan Str., 0014 Yerevan, Armenia.


L-Cysteine hydrogen fluoride, or bis(L-cysteinium) difluoride-L-cysteine-hydrogen fluoride (1/1/1), 2C3H8NO2S(+)·2F(-)·C3H7NO2S·HF or L-Cys(+)(L-Cys···L-Cys(+))F(-)(F(-)...H-F), provides the first example of a structure with cations of the 'triglycine sulfate' type, i.e. A(+)(A···A(+)) (where A and A(+) are the zwitterionic and cationic states of an amino acid, respectively), without a doubly charged counter-ion. The salt crystallizes in the monoclinic system with the space group P2(1). The dimeric (L-Cys···L-Cys(+)) cation and the dimeric (F(-)···H-F) anion are formed via strong O-H···O or F-H···F hydrogen bonds, respectively, with very short O···O [2.4438 (19) Å] and F···F distances [2.2676 (17) Å]. The F···F distance is significantly shorter than in solid hydrogen fluoride. Additionally, there is another very short hydrogen bond, of O-H···F type, formed by a L-cysteinium cation and a fluoride ion. The corresponding O···F distance of 2.3412 (19) Å seems to be the shortest among O-H···F and F-H···O hydrogen bonds known to date. The single-crystal X-ray diffraction study was complemented by IR spectroscopy. Of special interest was the spectral region of vibrations related to the above-mentioned hydrogen bonds.


IR spectroscopy; amino acid salt; bond/angle distribution; crystal structure; dimeric cation; l-cysteine hydrogen fluoride; short hydrogen bonds

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