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...π(arene) hydrogen bonds; those of (II), (IV) and (V), which all crystallize in the space groupP\overline{1}, 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...π(arene) hydrogen bond; finally, the molecules of (VI) are linked by a single C—H...O hydrogen bond to form a simple chain.