Synthesis, structural and spectroscopic properties of a new Schiff base ligand N,N′-bis(trifluoromethylbenzylidene)ethylenediamine

The Schiff base compound, NA,-bis(trifluoromethylbenzylidene)ethylenediamine (C18H14F6N2) (1), CF3C6H4CHNCH2CH2NCHC6H4CF3 has been synthesized by adding a solution of ethylenediammine (en), 0.1 mmol in chloroform to 4-(trifluoromethyl)-benzaldehyde, CF3C6H4CHO (0.2 mmol) and the product was crystallized in ethanol with the mp, 109.2 degrees C and 75% yield. The crystal structure was investigated by a single-crystal X-ray diffraction study at 150 K. The compound crystallizes in monoclinic space group, P2(1)/c with a = 9.295(3), b = 5.976(5), c = 15.204(9) angstrom and alpha = 90 degrees, beta = 96.56(5)' and gamma = 90 degrees. The crystal structure is stabilized by intermolecular C-H... F hydrogen bonds. The asymmetric unit contains only one-half of the molecule related to the center of symmetry coinciding with C(1)-C(1') and as a whole, the title molecule is in the staggered conformation. The phenyl rings and the C=N imine bonds are co-planar. The infrared spectrum showed a sharp peak at 1640 cm(-1) which is typical of the conjugated C=N stretching and strong peaks at 800-1400 cm-1 regions are due to the C-C and C-H stretching modes. Electronic absorption spectra exhibits strong absorption in the UV region (240 nm wavelength) which have been ascribed to pi-pi(*)(1), pi-pi(*)(2) and pi-pi(*)(3) electronic transitions. The H-1 NMR spectra showed three distinct peaks at 2.5, 7.8 and 8.5 ppm which are assigned based on the splitting of resonance signals and are clearly confirmed by the X-ray molecular structure. The aromatic protons appear at about 7.8 ppm and the imine protons at 8.5 ppm. The sharp singlet at about 3.95 ppm is assigned to the CH2-CH2 protons. Mass spectra of the titled compound showed the molecular ion peak at We 372 (M+), and fragments at m/e 353 (M-F), 342 (M-2F), 200 (M-CF3C6H4CHN), 186 (M-CF3C6H4CHNCH2). (c) 2006 Elsevier B.V. All rights reserved.