STRUCTURE OF AN INTERMOLECULAR COMPLEX BETWEEN CYTOSINE AND 5-FLUOROURACIL

Crystals of an intermolecular complex containing cytosine and 5-fluorouracil in 1:1 molar ratio have been isolated from an aqueous solution containing these components. The structure of the crystal has been determined using single-crystal X-ray diffraction techniques. The crystals belong to the space group P1 with one molecule each of cytosine and 5-fluorouracil in the asymmetric unit. The two molecules are joined together by two hydrogen bonds to form a cyclic dimer. These cyclic dimers are in turn joined by hydrogen bonds across centers of symmetry to other such cyclic dimers to form infinite sheets so that the crystal is a layered structure. In each unit cell of this structure there is a centrosymmetric cavity that contains two disordered water molecules. © 1969, American Chemical Society. All rights reserved.