6-Amino-2-iminiumyl-4-oxo-1,2,3,4-tetrahydropyrimidin-5-aminium sulfate monohydrate

The title compound, C4H9N5O2+·SO4 2−·H2O, is the monohydrate of the commercially available compound `C4H7N5O·H2SO4·xH2O'. It is obtained by reprecipitation of C4H7N5O·H2SO4·xH2O from dilute sodium hydroxide solution with dilute sulfuric acid. The crystal structure of anhydrous 2,4,5-triamino-1,6-dihydropyrimidin-6-one sulfate is known, although called by the authors 5-amminium-6-amino-isocytosinium sulfate [Bieri et al. (1993). Private communication (refcode HACDEU). CCDC, Cambridge, England]. In the structure, the sulfate group is deprotonated, whereas one of the amino groups is protonated (R 2C—NH3 +) and one is rearranged to a protonated imine group (R 2C=NH2 +). This arrangement is very…