ABSTRACT
The title compound has been first synthesized and fully characterized as both tetraphenylborate and perchlorate salt. Its 300-900 nm absorption spectrum, recorded in nitromethane, water, and dimethyl sulfoxide, reveals the peculiar existence of two distinct bands whose intensities depend on the solvent donor number. This feature can be attributed to two separate metal-to-ligand charge-transfer transitions, in agreement with the theoretical predictions obtained by extensive configuration interaction calculations, which take into account the solvent effects. The calculation of the potential energy curves of the ground and excited states along the Ru-tetrazine coordinate allows the interpretation of the relative intensities of the observed bands, as well as the interpretation of their line-shape profiles.
ABSTRACT
A study of absorption spectra in the near-infrared (NIR) and visible (vis) regions of trinuclear Ru complexes containing pyrazine (pyz) as bridging ligand, trans-[(Ru(NH(3))(5)pyz)(2)Ru(NH(3))(4)](m+)(m = 6-9), is reported. The spectra were recorded on aqueous solutions containing the described species formed in situ by stoichiometric additions of a standard solution of Ce(SO(4))(2). They were interpreted in terms of a simple 5-orbital-3-parameter model which includes the effects of d-pi interaction and electronic correlation. The model is shown to account for the observed NIR-vis spectra of the complex ions. The 6+ parent species was synthesized by an improved literature method and fully characterized. The novel 8+ complex was also prepared and characterized. The 9+ ion was established to be slowly reduced by water, with dioxygen formation. Electrochemical (CV and DPV) studies were performed on the trinuclear 6+ complex, as well as on its constituent fragments [Ru(NH(3))(5)(pyz)](2+) and trans-[Ru(NH(3))(4)(pyz)(2)](2+).
ABSTRACT
The first luminescent and redox active multinuclear Ru(II) compound containing both electron-poor (2,3-bis(2-pyridyl)pyrazine, 2,3-dpp) and electron-rich (3,5-bis(pyridyn-2-yl)-1,2,4-triazole, Hbpt) polypyridine bridging ligands has been synthesized. The novel compound is [(bpy)(2)Ru(&mgr;-bpt)Ru{(&mgr;-2,3-dpp)Ru(bpy)(2)}(2)](7+) (1; bpy = 2,2'-bipyridine). Its absorption spectrum, luminescence properties, and redox behavior have been studied and are compared with the properties of the parent complexes [Ru{(&mgr;-2,3-dpp)Ru(bpy)(2)}(3)](8+) (2) and [(bpy)(2)Ru(&mgr;-bpt)Ru(bpy)(2)](3+) (3). The absorption spectrum of 1 is dominated by ligand-centered bands in the UV region and by metal-to-ligand charge transfer bands in the visible region. Excited states and oxidation and reduction processes are localized in specific sites of the multicomponent structure. However, perturbations of each component on the redox and excited states of the others, as well as electronic interactions between the chromophores, can be observed. Intercomponent energy transfer from the upper-lying (&mgr;-bpt)(bpy)Ru-->bpy CT excited state of the Ru(bpy)(2)(&mgr;-bpt)(+) component to the lower-lying (bpy)(2)Ru-->&mgr;-2,3-dpp CT excited state of the Ru(bpy)(2)(&mgr;-2,3-dpp)(2+) subunit(s) is efficient in 1 in fluid solution at room temperature, whereas this process is not observed in a rigid matrix at 77 K. A two-step energy transfer mechanism is proposed to explain the photophysical properties of the new compound.
