X-ray structural studies on two forms of β-cyclodextrin barbital complexes

The crystal structures of two forms of -cyclodextrin barbital complexes (Form I and Form II) were investigated by X-ray analysis. In Form I crystal, two -cyclodextrin(-CyD) molecules including two barbital molecules form a dimeric structure by the hydrogen bonds among their secondary hydroxyl groups. The unit cell volume of Form II is about twice as large as that of Form I and there exist two -CyD dimers in Form II. Although the (Host)/(Guest) ratio is 1/1, only one barbital molecule can be found in Form II at the present stage. The sinilarities and differences between the two crystal structures are mainly discussed here.