Different conformations and packing motifs in the crystal structures of four thio­phene–carbohydrazide–pyridine derivatives

The crystal structures of four thio­phene–carbohydrazide–pyridine derivatives, viz. N′-[(E)-pyridin-3-yl­methyl­idene]thio­phene-2-carbohydrazide, C11H9N3OS, (I), N′-[(E)-pyridin-2-yl­methyl­idene]thio­phene-2-carbohydrazide, C11H9N3OS, (II), N-methyl-N′-[(E)-pyridin-2-yl­methyl­idene]thio­phene-2-carbohydrazide, C12H11N3OS, (III) and N′-[(E)-pyridin-2-yl­methyl­idene]-2-(thio­phen-2-yl)ethano­hydrazide, C12H11N3OS, (IV) are described. The dihedral angles between the thio­phene ring and the pyridine ring are 21.4 (2), 15.42 (14), 4.97 (8) and 83.52 (13)° for (I)–(IV), respectively. The thio­phene ring in (IV) is disordered over two orientations in a 0.851 (2):0.149 (2) ratio. Key features of the packing include N—H⋯Np (p = pyridine) hydrogen bonds in (I), which generate C(7) chains propagating in the [001] direction; N—H⋯Np links also feature in (II), but in this case they lead to C(6) [001] chains; in (IV), classical amide (C4) N—H⋯O links result in [010] chains; in every case adjacent mol­ecules in the chains are related by 21 screw axes. There are no classical hydrogen bonds in the extended structure of (III). Various weak C—H⋯X (X = O, N, S) inter­actions occur in each structure, but no aromatic π–π stacking is evident. The Hirshfeld surfaces and fingerprint plots for (I)–(IV) are compared.