5-Chloro-6-hydroxynicotinic Acid （5Cl6HNA) was recrystallized four times from ethanol at 345 K. The obtained white crystalline solid was first dried in a vacuum at 1.3 Pa and 353 K. The crystals were then ground with a mortar and a pestle and further dried for 24 h at 1.3 Pa and 353 K. The powder pattern obtained at 295 ± 1 K was indexed as monoclinic, space group P21/c, with a= 5.478 Å, b= 10.545 Å, c= 11.796 Å, β=97.76°. These results are in agreement with those obtained in this work from single crystal X-ray diffraction experiments carried out at 293 ±2K(P21/c, a ) 5.469 Å, b = 10.529 Å, c= 11.795 Å, β= 97.72°). DSC (fusion, β= 2 K ·min-1 ): Ton= 582.2 K and Tmax= 585.6 K[1].
