Acta Crystallographica Section C

Volume 65, Part 10 (October 2009)

organic compounds

mx3019 scheme

Acta Cryst. (2009). C65, o529-o533 [ doi:10.1107/S0108270109036476 ]

Channel-forming solvates of 6-chloro-2,5-dihydroxypyridine and its solvent-free tautomer 6-chloro-5-hydroxy-2-pyridone

S. R. Parkin and E. J. Behrman

Abstract: On crystallization from CHCl₃, CCl₄, CH₂ClCH₂Cl and CHCl₂CHCl₂, 6-chloro-5-hydroxy-2-pyridone, C₅H₄ClNO₂, (I), undergoes a tautomeric rearrangement to 6-chloro-2,5-dihydroxypyridine, (II). The resulting crystals, viz. 6-chloro-2,5-dihydroxypyridine chloroform 0.125-solvate, C₅H₄ClNO₂·0.125CHCl₃, (IIa), 6-chloro-2,5-dihydroxypyridine carbon tetrachloride 0.125-solvate, C₅H₄ClNO₂.·0.125CCl₄, (IIb), 6-chloro-2,5-dihydroxypyridine 1,2-dichloroethane solvate, C₅H₄ClNO₂·C₂H₄Cl₂, (IIc), and 6-chloro-2,5-dihydroxypyridine 1,1,2,2-tetrachloroethane solvate, C₅H₄ClNO₂·C₂H₂Cl₄, (IId), have I4₁/a symmetry, and incorporate extensively disordered solvent in channels that run the length of the c axis. Upon gentle heating to 378 K in vacuo, these crystals sublime to form solvent-free crystals with P2₁/n symmetry that are exclusively the pyridone tautomer, (I). In these sublimed pyridone crystals, inversion-related molecules form R²₂(8) dimers via pairs of N-HO hydrogen bonds. The dimers are linked by O-HO hydrogen bonds into R⁴₆(28) motifs, which join to form pleated sheets that stack along the a axis. In the channel-containing pyridine solvate crystals, viz. (IIa)-(IId), two independent host molecules form an R²₂(8) dimer via a pair of O-HN hydrogen bonds. One molecule is further linked by O-HO hydrogen bonds to two 4₁ screw-related equivalents to form a helical motif parallel to the c axis. The other independent molecule is O-HO hydrogen bonded to two $\overline{4}$ related equivalents to form tetrameric R⁴₄(28) rings. The dimers are [pi] - [pi] stacked with inversion-related dimers, which in turn stack the R⁴₄(28) rings along c to form continuous solvent-accessible channels. CHCl₃, CCl₄, CH₂ClCH₂Cl and CHCl₂CHCl₂ solvent molecules are able to occupy these channels but are disordered by virtue of the $\overline{4}$ site symmetry within the channels.

Formula: C₅H₄ClNO₂, C₅H₄ClNO₂·0.125CHCl₃ and C₅H₄ClNO₂·0.125CCl₄


	Structure factor file (CIF format) (65.7 kbytes) [ doi:10.1107/S0108270109036476/mx3019Isup2.hkl ] Contains datablock I

	Structure factor file (CIF format) (143.8 kbytes) [ doi:10.1107/S0108270109036476/mx3019IIasup3.hkl ] Contains datablock IIa

	Structure factor file (CIF format) (115.5 kbytes) [ doi:10.1107/S0108270109036476/mx3019IIbsup4.hkl ] Contains datablock IIb

	Structure factor file (CIF format) (144.0 kbytes) [ doi:10.1107/S0108270109036476/mx3019IIcsup5.hkl ] Contains datablock IIc

	Structure factor file (CIF format) (117.5 kbytes) [ doi:10.1107/S0108270109036476/mx3019IIdsup6.hkl ] Contains datablock IId

	Structure factor file (CIF format) (67.0 kbytes) [ doi:10.1107/S0108270109036476/mx3019IRTsup7.hkl ] Contains datablock IRT

	Structure factor file (CIF format) (149.7 kbytes) [ doi:10.1107/S0108270109036476/mx3019IIdRTsup8.hkl ] Contains datablock IIdRT

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