Anhydrous guanine: A synchrotron study

Abstract

Very small crystals of anhydrous guanine (systematic name: 2-amino-l,7-dihydro-6H-purin-6-one), C5H5N5O, were obtained from an attempted solvothermal synthesis of a potassium complex. Data were collected at 120 K using a synchrotron radiation source. There is one essentially planar molecule in the asymmetric unit. Molecules are linked to each other by N-H⋯N and N-H⋯O hydrogen bonds to form sheets, between which there are π-π stacking interactions. This crystal structure determination demonstrates conclusively that, in the absence of any solvent or other molecules, guanine exists as the amino-keto tautomer in the solid state, with H atoms attached to N1 and N7 (purine numbering), unlike its monohydrate, which has H atoms on N1 and N9. © 2006 International Union of Crystallography.