Anhydrous versus hydrated N-4-substituted 1H-pyrazolo[3,4-d]pyrimidine-4,6-diamines: hydrogen bonding in two and three dimensions

Ten new N-4-substituted 1H-pyrazolo[3,4-d]pyrimidine-4,6-diamines have been synthesized and the structures of nine of them are reported here, falling into two clear groups, those which are stoichiometric hydrates and those which crystallize in solvent-free forms. In each of N-4-methyl-N-4-phenyl-1H-pyrazolo[3,4-d]pyrimidine-4,6-diamine, C12H12N6 (I), N-4-cyclohexyl-N-4-methyl-1H-pyrazolo[3,4-d]pyrimidine-4,6-diamine, C12H18N6 (II), and N-4-(3-chlorophenyl)-1H-pyrazolo[3,4-d]pyrimidine-4,6-diamine, C11H9ClN6 (III), the molecules are linked into hydrogen-bonded sheets. The molecules of 2-{4-(6-amino-1H-pyrazolo[3,4-d]pyrimidin-4-yl)piperazin-1-yl}ethanol, C11H17N7O (IV), are linked into a three-dimensional framework, while the structure of N-4-methyl-N-4-(4-methylphenyl)-1H-pyrazolo[3,4-d]pyrimidine-4,6-diamine monohydrate, C13H14N6 center dot H2O (V), is only two- dimensional despite the presence of five independent hydrogen bonds. The stoichiometric hemihydrates N-4-ethyl-N-4-phenyl-1H-pyrazolo[3,4-d]pyrimidine-4,6-diamine hemihydrate, C13H14N6 center dot 0.5H(2)O (VI) and N-4-(4-methoxyphenyl)-N-4-methyl-1H-pyrazolo[3,4-d]pyrimidine-4,6-diamine hemihydrate, C13H14N6O center dot 0.5H(2)O (VII), exhibit remarkably similar sheet structures, despite different space groups and Z' values, Z' = 0.5 in C2/c for (VI) and Z' = 1 in P (1) over bar for (VII). N-4-4-Benzyl-N-4-phenyl-1H-pyrazolo[3,4-d]pyrimidine-4,6-diamine monohydrate, C18H16N6.H2O (VIII), crystallizes with Z' = 2 in P2(1)/n, and the four independent molecular components are linked into sheets by a total of 11 intermolecular hydrogen bonds. The sheet structure in {4-(pyrrolidin-1-yl)-1H-pyrazolo[3,4-d]pyrimidine-6-amine} ethanol hemisolvate hemihydrate, C9H12N6 center dot 0.5C(2)H(6)O center dot 0.5H(2)O (IX), is built from the pyrimidine and water components only; it contains eight independent hydrogen bonds, and it very closely mimics the sheets in (VI) and (VII); the ethanol molecules are pendent from these sheets. The N-4-alkyl-N-4-aryl-4-aminopyrazolopyrimidine molecules in (I), (V)-(VIII) all adopt very similar conformations, dominated in each case by an intramolecular C-H center dot center dot center dot pi(arene) hydrogen bond: this interaction is absent from (III) where the molecular conformation is entirely different and probably dominated by the intermolecular hydrogen bonds.