Journal
INORGANICA CHIMICA ACTA
Volume 358, Issue 13, Pages 3642-3652Publisher
ELSEVIER SCIENCE SA
DOI: 10.1016/j.ica.2005.06.032
Keywords
optically active Schiff bases; cobalt; copper; nickel; crystal structure
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Schiff bases obtained from NN'-(1R,2R)-cyclohexanediamine and 2-hydroxy-3-methoxybenzaldehyde, 2-hydroxy-5-methoxybenzaldehyde or 2-hydroxy-5-methylbenzaldehyde have been used as ligands for copper(II), cobalt(11) and nickel(II). The complexes were characterized with UV-Vis, circular dichroism (CD), IR and H-1 and C-13 NMR spectroscopy and X-ray crystal structure was solved for [Cu(II)(1R, 2R)(-)chxn(5-methylba)(2)]. CD spectra in acetonitrile solution revealed exciton coupled pi-pi*, LMCT and d-d transitions in Ni(II), Co(II) and Cu(II) complexes. CD data are characteristic for tetrahedral distortion from the planarity of the chelate ring and. conformation of the cyclohexane bridge. The 1H NMR paramagnetic spectra of Co(11) complexes revealed the most upfield shifted resonance at -60 ppm assigned to -CH=N- and at -28 ppm to C(5')H of the phenyl ring. NOE NMR of the Schiff bases and nickel complexes were measured with the saturation of proton at -CH=N-. NOE experiment revealed interaction of the azomethine hydrogen with protons from cyclohexyl groups, phenyl ring hydrogen and with the hydroxyl group Schiff bases, while in the nickel complexes with the phenyl ring hydrogen atom and with the cyclohexyl CH,. Results of spectral analyses suggest central ions in a distorted square planar geometry with N2O2 chromophore group. The X-ray crystallography study confirmed tetrahedral distortion from the planarity in [Cu(II)(1R,2R)(-)chxn(5-methylba)(2)]. (c) 2005 Elsevier B.V. All rights reserved.
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