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

The crystal structures of four thiophene--carbohydrazide--pyridine derivatives, it viz. N$^-[(it E)-pyridin-3-ylmethylidene]thiophene-2-carbohydrazide, C$1$H$$N$$OS, (I), it N$^-[(it E)-pyridin-2-ylmethylidene]thiophene-2-carbohydrazide, C$1$H$$N$$OS, (II), it N-methyl-it N$^-[(it E)-pyridin-2-ylmethylidene]thiophene-2-carbohydrazide, C$2$H$1$N$$OS, (III) and it N$^-[(it E)-pyridin-2-ylmethylidene]-2-(thiophen-2-yl)ethanohydrazide, C$2$H$1$N$$OS, (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)$^ for (I)--(IV), respectively. The thiophene ring in (IV) is disordered over two orientations in a 0.851(2):0.149(2) ratio. Key features of the packing include N---H$N$sb p$ (p = pyridine) hydrogen bonds in (I), which generate it C(7) chains propagating in the [001] direction; N---H$N$sb p$ links also feature in (II), but in this case they lead to it C(6) [001] chains; in (IV), classical amide (it C4) N---H$O links result in [010] chains; in every case adjacent molecules in the chains are related by 2$$ screw axes. There are no classical hydrogen bonds in the extended structure of (III). Various weak C---H$it X (it X = O, N, S) interactions occur in each structure, but no aromatic $--$ stacking is evident. The Hirshfeld surfaces and fingerprint plots for (I)--(IV) are compared.