Crystal structure of triclinic colchiceine hemihydrate

Triclinic crystals of colchiceine hemihydrate, C21H23N06.!H20, belong to the space group PI with a 8 .211(1), b 8·361(1), c16 ·898(2) A, a 92 ·35(1)", J3 93 ·93(1)", l' 121·35(1)" and Z 2. The structure was solved by direct methods and successive difference syntheses with diffractometer data measured with CuKa radiation. Refinement converged at R 0·053 for 2798 observed reflections. The two tautomers, one of the isoco1chiceine and the other of the colchiceine form, exist as independent entities in the crystal; the angles between the normals to the plane of the benzene and troponoid rings are 44·5(4)" and 51· 5(5)" respectively. The hydroxyl and N-acetyl groups are oriented to form channels along the a-axis which accommodate the water molecules.