Crystal structures of 2-[5-nitrothien-2-yl)- CH=N-NR-CO(CH2)n]thiophene compounds (R = H or Me; n=0 or 1)

The crystal structures of four acylhydrazonyl derivatives of thiophene, 2-(ArCH=N-NHCO)-thiophene, (1a), 2-(ArCH=N-NMeCO)-thiophene, (2a), 2-(ArCH=N-NHCOCH2)-thiophene, (3a) and 2-(ArCH=N-NMeCOCH2)-thiophene, (4a) [in each case Ar = 5-nitrothien-2-yl] are reported. The molecular conformations of 1a and 2a are near planar, while those of 3a and 4a exhibit bends at the methylene carbon. Methylations at the hydrazonyl groups in 1a and 3a, to give 2a and 4a, do not result in any significant changes in the molecular conformations. Each of the four molecular conformations possesses a Z(C(O)NR)/E-(C=N) arrangement about the C(O)-NR-N=C(H, aryl) fragment (R = H or Me). The dominant intermolecular interactions in 1a and 3a are N-H center dot center dot center dot O(carbonyl) hydrogen bonds, with other intermolecular interactions being weaker interactions: C-H center dot center dot center dot O and N-O center dot center dot center dot pi in 1a and C-H center dot center dot center dot X (X = O, S, pi) and pi-pi interactions in 3a. In the N-methylated compounds, the intermolecular interactions are restricted to weaker C-H center dot center dot center dot O hydrogen bonds in 2a and C-H center dot center dot center dot X (X = O or pi) interactions in 4a.