ABSTRACT We observed characteristic CD bands at 450, 550, and 650 nm assigned to be d-d transitions of achiral copper(II) Schiff base complexes induced by chiral nickel(II) Schiff base complexes in the mixed solutions for the first time. We used a chiral nickel(II) complex, bis(N-R-1-phenylethyl-3,5-dichlorosalicydenaminato) nickel(II) (Ni-phen), as a chiral source, and achiral copper(II) complexes, bis(N-2-phenylethyl-salicydenaminato) copper(II) (Cu-2phen) and bis(N-3-aminoquinoline-salicydenaminato)copper(II), (Cu-3amq) as known reference samples. We investigated dependence of conditions, namely solvents (methanol, acetone, and chloroform), concentration (0.01, 0.1, and 1 mM), and the ratio of complexes (Ni:Cu = 1: 0.1, 0.2, 0.5, 1, 2, 5, and 10), and molecular shapes (Cu-2phen and Cu-3amq). We plotted and compared all CD spectra and the corresponding absorption spectra of individual components, their calculated sum, and experimentally mixed solutions of nickel(II) and copper(II) complexes to find induced CD peaks obviously. The results indicated clear effect of solvent polarity among them. Furthermore, we attempted to estimate molecular structures of achiral copper(II) complexes by means of these induced CD spectra. We used two copper(II) complexes prepared newly (abbreviated as Cu-acac and Cu-sal). Although the induced CD bands did not exhibit clear differences, the maximum of the Ni:Cu ratios suggested mononuclear (Cu-sal) or binuclear (Cu-acac) structures. The chiral transfer phenomenon occurred in organic solutions, and it could not be observed in carboxymethylcellulose (CMC) cast films even if we used bis(N-R-1-naphthylethyl-3,5-dichlorosalicydenaminato)nickel(II) complex (Ni-naph) having more extended π-ligands. This fact suggests that intermolecular interaction (non-bonding contact) may be important for this phenomenon.
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