Hydroxyphenyl- and octoxyphenyl-substituted dipyrazinylpyridine complexes of ruthenium(II), iron(II) and nickel(II)

Abstract A water-soluble, hydroxyphenyl-substituted dipyrazinylpyridine (HOL) and its liposoluble, n -octylated derivative (C 8 OL) were prepared in short sequences and good yields. The monocarbonyldichlororuthenium(II) complex (C 8 OL)Ru(CO)Cl 2 were obtained in cis and trans isomeric forms, which could be distinguished by their absorption, 13 C NMR and 15 N NMR spectra. The octahedral homoleptic complexes [(C 8 OL) 2 M] 2+ (M = Ru II , Fe II ) and five-coordinate (HOL)NiCl 2 are also described. Density functional theory is used to derive optical geometries, optical spectra, a molecular orbital description and the electronic structure. The time-dependent calculations reveal that the strong visible-region absorption responsible for the color of the homoleptic Fe II and Ru II species arises mainly from an internal ligand charge-transfer process and only to a small degree from the expected metal-to-ligand CT process. The crystal structures of free C 8 OL, trans -(C 8 OL)Ru(CO)Cl 2 , [(C 8 OL) 2 Fe](FeCl 4 ) 2 and (HOL)NiCl 2 were also obtained. Electrochemical data are also presented and discussed.