The crystal structure of cytosine monohydrate

Abstract

The crystal structure of cytosine monohydrate, CdHsNaO.H20, has been determined from threedimensional photographic data. The cytosine molecules are hydrogen-bonded in parallel ribbons which are linked into a three-dimensional network by hydrogen-bonding through the water molecules. Each water molecule is bonded to three cytosines, two through the carbonyl oxygens at 2-78 and 2.85 A and one to the amino group at 2.97 A, in a coordination which is approximately trigonal planar. The cytosine molecules are slightly distorted from planarity in a way which suggests that the distortion is due to a rather close interaction between the water molecules and the methylene carbon atoms at 3-19 and 3-29 A.