Acta Crystallographica Section C

Crystal Structure Communications

Volume 68, Part 9 (September 2012)

organic compounds

eg3095 scheme

Acta Cryst. (2012). C68, o344-o350    [ doi:10.1107/S0108270112031691 ]

Pseudopolymorphs of chelidamic acid and its dimethyl ester

M. Tutughamiarso, T. Pisternick and E. Egert

Abstract: Different tautomeric and zwitterionic forms of chelidamic acid (4-hy­droxy­pyridine-2,6-dicarb­oxy­lic acid) are present in the crystal structures of chelidamic acid methanol monosolvate, C7H5NO5·CH4O, (Ia), dimethyl­ammonium chelidamate (di­methyl­ammonium 6-carb­oxy-4-hy­droxy­pyridine-2-carboxyl­ate), C2H8N+·C7H4NO5-, (Ib), and chelidamic acid dimethyl sulfoxide monosolvate, C7H5NO5·C2H6OS, (Ic). While the zwitterionic pyridinium carboxyl­ate in (Ia) can be explained from the pKa values, a (partially) deprotonated hy­droxy group in the presence of a neutral carb­oxy group, as observed in (Ib) and (Ic), is unexpected. In (Ib), there are two formula units in the asymmetric unit with the chelidamic acid entities connected by a symmetric O-H...O hydrogen bond. Also, crystals of chelidamic acid dimethyl ester (dimethyl 4-hy­­droxy­pyridine-2,6-dicarboxyl­ate) were obtained as a monohydrate, C9H9NO5·H2O, (IIa), and as a solvent-free mod­ifi­­cation, in which both ester mol­ecules adopt the hy­droxy­pyridine form. In (IIa), the solvent water mol­ecule stabilizes the synperiplanar conformation of both carbonyl O atoms with respect to the pyridine N atom by two O-H...O hydrogen bonds, whereas an anti­periplanar arrangement is observed in the water-free structure. A database study and ab initio energy calculations help to compare the stabilities of the various ester conformations.

Formula: C7H5NO5·CH4O, C2H8N+·C7H4NO5-, C7H5NO5·C2H6OS and C9H9NO5·H2O

hkldisplay filedownload file

Structure factor file (CIF format) (84.4 kbytes)
[ doi:10.1107/S0108270112031691/eg3095Iasup2.hkl ]
Contains datablock Ia

hkldisplay filedownload file

Structure factor file (CIF format) (190.4 kbytes)
[ doi:10.1107/S0108270112031691/eg3095Ibsup3.hkl ]
Contains datablock Ib

hkldisplay filedownload file

Structure factor file (CIF format) (125.3 kbytes)
[ doi:10.1107/S0108270112031691/eg3095Icsup4.hkl ]
Contains datablock Ic

hkldisplay filedownload file

Structure factor file (CIF format) (96.1 kbytes)
[ doi:10.1107/S0108270112031691/eg3095IIasup5.hkl ]
Contains datablock IIa


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