Origin and switch of different colors: Thermo-isomerism and crystal structure of (1E,2E)-bis[1-(4-nitrophenyl)ethylidene] hydrazine
Abstract
A new symmetric branched 4-nitrophenyl hydrazine compound has been prepared in one-step procedure by direct condensation of aromatic ketone with hydrazine in MeOH. The synthesized compound, red isomer, was characterized by IR, 1H and 13C NMR spectroscopy, Elemental analyses, Mass spectrometry and X-ray crystallography. Refluxing in MeOH solution led to thermo-isomerism offering a white isomer product that was characterized by X-ray crystallography. The red isomer crystallizes in the orthorhombic system having space group Pbcn, with a = 12.7612(4), b = 11.5197(3), c = 20.1586(7) Å, V = 2963.42(16) Å 3, Z = 8 while the white isomer crystallizes in the triclinic system having space group P −1, with a = 7.8007(4), 8.5966(7), 12.224 (1) Å, α= 71.133(7), β= 81.281(5), γ= 74.895(5) ∘, V = 746.86(9) Å 3, Z = 2. Molecules of both compounds are twisted at N2–N3 bond with the C7-N2-N3-C9 torsion angle of 155.23(12) and −113.36(18) ∘, respectively. The crystal structures of both compounds are stabilized by weak intramolecular C—H …N contacts and intermolecular C—H …O hydrogen bonding interactions. In addition, π– π stacking interactions are observed between the same aromatic rings of molecules. Graphical Abstract Hydrazone undergoes trans-cis isomerism when heated in an appropriate solvent. The reverse trans-cis thermo-isomerism can be driven also by light or thermally in the dark