Water-induced pseudo-quadruple hydrogen-bonding motifs in xanthine-inorganic acid complexes.

In xanthinium nitrate hydrate [systematic name: 2,6-dioxo-1,2,3,6-tetrahydro-9H-purin-7-ium nitrate monohydrate], C(5)H(5)N(4)O(2)(+)·NO(3)(-)·H(2)O, (I), and xanthinium hydrogen sulfate hydrate [systematic name: 2,6-dioxo-1,2,3,6-tetrahydro-9H-purin-7-ium hydrogen sulfate monohydrate], C(5)H(5)N(4)O(2)(+)·HSO(4)(-)·H(2)O, (II), the xanthine molecules are protonated at the imine N atom with the transfer of an H atom from the inorganic acid. The asymmetric unit of (I) contains a xanthinium cation, a nitrate anion and one water molecule, while that of (II) contains two crystallographically independent xanthinium cations, two hydrogen sulfate anions and two water molecules. A pseudo-quadruple hydrogen-bonding motif is formed between the xanthinium cations and the water molecules via N-H···O and O-H···O hydrogen bonds in both structures, and leads to the formation of one-dimensional polymeric tapes. These cation-water tapes are further connected by the respective anions and aggregate into two-dimensional hydrogen-bonded sheets in (I) and three-dimensional arrangements in (II).