On crystallization from CHCl3, CCl4, CH 2ClCH2Cl and CHCl2CHCl2, 6-chloro-5-hydr-oxy-2-pyridone, C5H4ClNO2, (I), under-goes a tautomeric rearrangement to 6-chloro-2,5-di-hy-droxy-pyridine, (II). The resulting crystals, viz. 6-chloro-2,5-di-hy-droxy-pyridine chloro-form 0.125-solvate, C5H4ClNO2·0.125CHCl 3, (IIa), 6-chloro-2,5-dihydroxy-pyridine carbon tetra-chloride 0.125-solvate, C5H4ClNO2.·0.125CCl 4, (IIb), 6-chloro-2,5-di-hy-droxy-pyridine 1,2-dichloro-ethane solvate, C5H4ClNO2·C2H 4Cl2, (IIc), and 6-chloro-2,5-dihydroxy-pyri-dine 1,1,2,2-tetra-chloro-ethane solvate, C5H4ClNO 2·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 mol-ecules form R 2 2(8) dimers via pairs of N - H⋯O hydrogen bonds. The dimers are linked by O - H⋯O hydrogen bonds into R 4 6(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 mol-ecules form an R 2 2(8) dimer via a pair of O - H⋯N hydrogen bonds. One mol-ecule is further linked by O - H⋯O hydrogen bonds to two 41 screw-related equivalents to form a helical motif parallel to the c axis. The other independent mol-ecule is O - H⋯O hydrogen bonded to two related equivalents to form tetra-meric R 4 4(28) rings. The dimers are π-π stacked with inversion-related dimers, which in turn stack the R 4 4(28) rings along c to form continuous solvent-accessible channels. CHCl3, CCl4, CH2ClCH2Cl and CHCl2CHCl 2 solvent mol-ecules are able to occupy these channels but are disordered by virtue of the site symmetry within the channels.
|Journal||Acta Crystallographica Section C: Crystal Structure Communications|
|State||Published - 2009|
ASJC Scopus subject areas
- Biochemistry, Genetics and Molecular Biology (all)