Absorption Spectra and Circular Dichroisms of Metal Complexes. I. Platinum(II)-, Palladium(II)- and Gold(III)-Complexes Containing Optically Active Diamines

Abstract

Abstract In order to study the nature of absorption bands in square-planar metal complexes of d8 type, a number of platinum (II), palladium (II) and gold(III) complexes containing l-propylenediamine and l-cyclohexanediamine were prepared and their circular dichroism (CD) and rotatory dispersion (RD) as well as absorption spectra (AB) were measured. Three or four absorption bands corresponding to d–d transitions were observed for each platinum(II) and palladium(II) complex. All the complexes, except for [Au(l-pn)2]Cl3, [Au(l-chxn)2]Cl3 and [PdCl2(l-pn)], give two possitive CD bands in the wavelength region from visible to 210 mμ, which are assigned to the spin-forbidden and spin-allowed A1→E transition. Both [Au(l-pn)2]Cl3and [Au(l-chxn)2]Cl3 exhibit only one strong positive CD band corresponding to the ligand field transition probably mixed with charge transfer transition. [PdCl2(l-pn)] gives a weak negative and a strong positive band corresponding to the transitions, A1→A2 and A1→E, respectively. The CD strength of the bis-l-diamine complexes is almost twice those of the mono-l-diamine complexes. The vicinal effect of l-cyclohexanediamine was about twice as strong as that of l-propylenediamine. Absorption spectra of the [MX4]n− (M=Pt2+, Pd2+ and Au3+, X=Cl− and Br−) show a shoulder and two bands in the ultraviolet region adjacent to the ligand field bands. The shoulder band was assigned to the symmetry forbidden, and the two strong bands to the symmetry allowed pπ→dx2−y2 and pσ→dx2−y2 charge transfer transitions. In the [MBr4]n−, the pπ→dx2−y2 band splits into two components, corresponding to A1g→A1u and the other A1g→Eu transition.