Hydrogen-bonded assembly in six closely related pyrazolo­[3,4-b]pyridine derivatives; a simple chain, three types of chains of rings and a complex sheet structure

Six closely related pyrazolo­[3,4-b]pyridine derivatives, namely 6-chloro-3-methyl-1,4-diphenyl­pyrazolo­[3,4-b]pyridine-5-carbaldehyde, C₂₀H₁₄ClN₃O, (I), 6-chloro-3-methyl-4-(4-methyl­phenyl)-1-phenylpyrazolo­[3,4-b]pyridine-5-carbaldehyde, C₂₁H₁₆ClN₃O, (II), 6-chloro-4-(4-chloro­phenyl)-3-methyl-1-phenyl­pyrazolo­[3,4-b]pyridine-5-carbaldehyde, C₂₀H₁₃Cl₂N₃O, (III), 4-(4-bromo­phenyl)-6-chloro-3-methyl-1-phenyl­pyrazolo­[3,4-b]pyridine-5-carbaldehyde, C₂₀H₁₃BrClN₃O, (IV), 6-chloro-4-(4-meth­oxy­phenyl)-3-methyl-1-phenyl­pyrazolo­[3,4-b]pyridine-5-carbaldehyde, C₂₁H₁₆ClN₃O₂, (V), and 6-chloro-3-methyl-4-(4-nitro­phenyl)-1-phenyl­pyrazolo[3,4-b]pyridine-5-carbaldehyde, C₂₀H₁₃ClN₄O₃, (VI), which differ only in the identity of a single small substituent on one of the aryl rings, crystallize in four different space groups spanning three crystal systems. The mol­ecules of (I) are linked into a chain of rings by a combination of C-H...N and C-H...[pi](arene) hydrogen bonds; those of (II), (IV) and (V), which all crystallize in the space group P, are each linked by two independent C-H...O hydrogen bonds to form chains of edge-fused rings running in different directions through the three unit cells; the mol­ecules of (III) are linked into complex sheets by a combination of two C-H...O hydrogen bonds and one C-H...[pi](arene) hydrogen bond; finally, the mol­ecules of (VI) are linked by a single C-H...O hydrogen bond to form a simple chain.