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

Article abstract of DOI:10.1016/j.ica.2011.04.018

A water-soluble, hydroxyphenyl-substituted dipyrazinylpyridine (HOL) and its liposoluble, n-octylated derivative (C₈OL) were prepared in short sequences and good yields. The monocarbonyldichlororuthenium(II) complex (C₈OL)Ru(CO)Cl₂ were obtained in cis and trans isomeric forms, which could be distinguished by their absorption, ¹³C NMR and ¹⁵N NMR spectra. The octahedral homoleptic complexes [(C ₈OL)₂M]²⁺ (M = Ru^II, Fe ^II) and five-coordinate (HOL)NiCl₂ 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 C₈OL, trans-(C₈OL)Ru(CO)Cl₂, [(C₈OL)₂Fe](FeCl₄)₂ and (HOL)NiCl₂ were also obtained. Electrochemical data are also presented and discussed.