Synthesis and spectroscopic studies of the optically active copper(II), cobalt(II) and nickel(II) complexes with Schiff bases N,N′-(1R,2R)(−)-1,2-cyclohexylenebis(3-methoxybenzylideneiminato), N,N′-(1R,2R)(−)-1,2-cyclohexylenebis(5-methoxybenzylideneimina

Schiff bases obtained from N,N′-(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(II) and nickel(II). The complexes were characterized with UV–Vis, circular dichroism (CD), IR and 1H and 13C 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 π → π*, 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 λ conformation of the cyclohexane bridge. The 1H NMR paramagnetic spectra of Co(II) complexes revealed the most upfield shifted resonance at −60 ppm assigned to CHN 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 CHN. 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 CH2. 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].

Schiff bases obtained from N,N′-(1R,2R)-cyclohexanediamine and 2-hydroxy-3-methoxy-benzaldehyde, 2-hydroxy-5-methoxybenzaldehyde or 2-hydroxy-5-methylbenzaldehyde have been used as ligands for copper(II), cobalt(II) and nickel(II). The complexes were characterized with UV–Vis, circular dichroism (CD), IR and 1H and 13C 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 π → π*, 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 λ conformation of the cyclohexane bridge.Figure optionsDownload as PowerPoint slide