Six closely related 4,6-disubstituted 2-amino-5-formyl­pyrimidines: different ring conformations, polarized electronic structures, and hydrogen-bonded assembly in zero, one, two and three dimensions

In each of ethyl N-{2-amino-5-formyl-6-[meth­yl(phen­yl)amino]­pyrimidin-4-yl}glycinate, C₁₆H₁₉N₅O₃, (I), N-{2-amino-5-formyl-6-[meth­yl(phen­yl)amino]­pyrimidin-4-yl}glycin­amide, C₁₄H₁₆N₆O₂, (II), and ethyl 3-amino-N-{2-amino-5-formyl-6-[meth­yl(phen­yl)amino]­pyrimidin-4-yl}propionate, C₁₇H₂₁N₅O₃, (III), the pyrimidine ring is effectively planar, but in each of methyl N-{2-amino-6-[benz­yl(meth­yl)amino]-5-formyl­pyrimidin-4-yl}glycinate, C₁₆H₁₉N₅O₃, (IV), ethyl 3-amino-N-{2-amino-6-[benz­yl(meth­yl)amino]-5-formylpyrimidin-4-yl}propionate, C₁₈H₂₃N₅O₃, (V), and ethyl 3-amino-N-[2-amino-5-formyl-6-(piperidin-4-yl)pyrimidin-4-yl]propionate, C₁₅H₂₃N₅O₃, (VI), the pyrimidine ring is folded into a boat conformation. The bond lengths in each of (I)-(VI) provide evidence for significant polarization of the electronic structure. The mol­ecules of (I) are linked by paired N-H...N hydrogen bonds to form isolated dimeric aggregates, and those of (III) are linked by a combination of N-H...N and N-H...O hydrogen bonds into a chain of edge-fused rings. In the structure of (IV), mol­ecules are linked into sheets by means of two hydrogen bonds, both of N-H...O type, in the structure of (V) by three hydrogen bonds, two of N-H...N type and one of C-H...O type, and in the structure of (VI) by four hydrogen bonds, all of N-H...O type. Mol­ecules of (II) are linked into a three-dimensional framework structure by a combination of three N-H...O hydrogen bonds and one C-H...O hydrogen bond.

5-Methyl-N-[2-nitro-4-(trifluoro­methyl)phen­yl]-1H-pyrazole-3-amine: a chain of hydrogen-bonded R₂²(6) and R₂²(16) rings

The mol­ecular skeleton of the title compound, C₁₁H₉F₃N₄O₂, is almost planar and exhibits a polarized (charge-separated) electronic structure in the nitro­aniline portion. Mol­ecules are linked by N-H...N and C-H...O hydrogen bonds to form a chain in which centrosymmetric R₂²(6) and R₂²(16) rings alternate.