Crystal and molecular structure of cytosine hemitrichloroacetate
The crystal structure of cytosine hemitrichloroacetate (C4H5N3O)2·HOOCCCI3 has been determined at room temperature by X-ray crystallographic analysis. The structure consists of crystallographically independent, centrosymmetric triple hydrogen-bonded cytosine pairs, A and B, and trichloroacetate anions. Base pairing occurs between symmetry-equivalent hemiprotonated cytosines with a proton shared between the N(3) atoms. The observed N(3)⋯ N(3′) distances of 2.755(8) and 2.858(8)Å in base pair A and B, respectively, are typical for asymmetric hydrogen bonds described by an asymmetric double minimum-energy curve. The i.r. spectrum is consistent with that predicted for this type of bridge system.