The crystal structure of thymine monohydrate

Crystals of thymine monohydrate are monoclinic with space group P21/c; the unit cell dimensions are: a=6.077, b=27.862,c=3.816A; fl=94 ° 19'.The crystal structure was refined on the basis of three-dimensional intensity data obtained with copper radiation.The structural parameters for the heavy atoms, including anisotropic temperature factors, were refined by the least-squares method; the positions of the hydrogen atoms were located from a three-dimensional difference synthesis.The final R factor was 0.078 for 1068 observed reflections and the standard deviations in the positional parameters for the heavy atoms are about 0-0023 A.A surprising feature is the amount of the water of crystallization, which is about 83% of the theoretical value.An arrangement of the water molecules is proposed which accounts for the observed X-ray data.