Tautomerism and hydrogen bonding in guaninium phosphite and guaninium phosphate salts.

The crystal structures of three similar guaninium salts, guaninium monohydrogenphosphite monohydrate, C(5)H(6)N(5)O(+).H(2)O(3)P(-).H(2)O, guaninium monohydrogenphosphite dihydrate, C(5)H(6)N(5)O(+).H(2)O(3)P(-).2H(2)O, and guaninium dihydrogenmonophosphate monohydrate, C(5)H(6)N(5)O(+).H(2)O(4)P(-).H(2)O, are described and compared. The crystal structures have been determined from accurate single-crystal X-ray data sets collected at 100 (2) K. The two phosphite salts are monoclinic, space group P2(1)/c, with different packing and the monophosphate salt is also monoclinic, space group P2(1)/n. An investigation of the hydrogen-bond network in these guaninium salts reveals the existence of two ketoamine tautomers, the N9H form and an N7H form.