Two thiosemicarbazones derived from salicylaldehyde: very specific hydrogen‐bonding interactions of the N—H...S=C type

The molecular structures of two salicylaldehyde thiosemicarbazone derivatives, namely salicylaldehyde 4‐phenylthiosemicarbazone, C₁₄H₁₃N₃OS, (I), and 4‐methoxysalicylaldehyde 4‐phenylthiosemicarbazone, C₁₅H₁₅N₃O₂S, (II), both of potential pharmacological interest, are found in the keto (thione) tautomeric form. The first compound represents a second triclinic polymorph of composition β‐C₁₄H₁₃N₃OS. Although both polymorphs crystallize in the same space group (P), the α‐polymorph Seena, Kurup & Suresh (2008). J. Chem. Crystallogr. 38 , 93–96] differs from the β form in its unit‐cell volume at 293 K. The molecules in the crystal structures of (I) and (II) are linked into centrosymmetric R²₂(8) dimers by hydrogen bonds of the N—H...S=C type. These dimers are connected through π–π stacking and T‐shaped C—H...π interactions into three‐dimensional networks.