Supramolecular structure of unnatural nucleobases: Revised structure of (2:1) 6-methylisocytosinium dihydrogen monophosphate adduct

The solid-state supramolecular structure of 6-methylisocytosine dihydrogen monophosphate adduct [2-NH(2)-6-CH(3)-C(4)H(2)N(2)O(2)](2)(+) center dot H(2)PO(4)(-), has been determined by single-crystal X-ray diffraction at room temperature. In this paper a revised model, based on single proton transfer from one molecule of phosphoric acid to the pyridine N atoms opposite to the methyl substituent of the two aminooxo tautomers of 6-methylisocytosine, has been used for the crystal structure analysis of the ionic complex. 6-Methylisocytosine molecules form hemiprotonated centrosymmetric pairs by complementary WC triple hydrogen bonds. Dihydrogen phosphate anions act as bridges between charged WC dimers to generate ribbons via four cation-to-anion N-H center dot center dot center dot O hydrogen bonds. Ribbons are then interconnected to form a three-dimensional network by means of a further series of O-H center dot center dot center dot O anion-to-cation hydrogen bonds. (C) 2011 Elsevier B.V. All rights reserved.