Crystal structure of two N′-(1-phenyl­benzyl­idene)-2-(thio­phen-3-yl)acetohydrazides

The synthesis, spectroscopic data, crystal and mol­ecular structures of two N′-(1-phenyl­benzyl­idene)-2-(thio­phen-3-yl)acetohydrazides, namely N′-[1-(4-hy­droxy­phen­yl)benzyl­idene]-2-(thio­phen-3-yl)acetohydrazide, C(13)H(10)N(2)O(2)S, (3a), and N′-[1-(4-meth­oxy­phen­yl)benzyl­idene]-2-(thio­phen-3-yl)acetohydrazide, C(14)H(14)N(2)O(2)S, (3b), are described. Both compounds differ in the substituent at the para position of the phenyl ring: –OH for (3a) and –OCH(3) for (3b). In (3a), the thio­phene ring is disordered over two orientations with occupancies of 0.762 (3) and 0.238 (3). The configuration about the C=N bond is E. The thio­phene and phenyl rings are inclined by 84.0 (3) and 87.0 (9)° for the major- and minor-occupancy disorder components in (3a), and by 85.89 (12)° in (3b). Although these dihedral angles are similar, the conformation of the linker between the two rings is different [the C—C—C—N torsion angle is −ac for (3a) and −sc for (3b), while the C6—C7—N9—N10 torsion angle is +ap for (3a) and −sp for (3b)]. A common feature in the crystal packing of (3a) and (3b) is the presence of N—H⋯O hydrogen bonds, resulting in the formation of chains of mol­ecules running along the b-axis direction in the case of (3a), or inversion dimers for (3b). The most prominent contributions to the surface contacts are those in which H atoms are involved, as confirmed by an analysis of the Hirshfeld surface.