Mononuclear and binuclear 4-cyanopyridine complexes of bis(2,2′-bipyridine) (pyridine)ruthenium(II)

Abstract

New complexes derived from the Ru(bpy) 2(py) 2+ moiety (bpy= 2,2′-bipyridine, py = pyridine) were synthesized and characterized by spectroscopic techniques. The mononuclear complex [Ru(bpy) 2(py)(4-CNpy)] 2+ (4-CNpy = 4-eyanopyridine) seems to be the pyridine-bonded isomer of 4-CNpy, as disclosed by IR and UV-vis data (ν CN(nitrile) = 2240 cm −, λ max = 434 nm in CH 3CN). The binuclear complexes [Ru(bpy) 2(py)(4-CNpy) Ru(NH 3) 5] 4+ and [Ru(bpy) 2(py)(4-CNpy)Fe(CN) 5] − were also prepared; they showed new absorptions in the visible region at λ max ca 450 nm ascribable to MLCT (metal-to-ligand charge-transfer) transition from dπ orbitals of ruthenium or iron to π* orbitals of 4-CNpy. The former dimer was obtained as a PF 6 − salt, which presented ν CN(nitrile) = 2178 cm −1, as expected from an ammineruthenium(II) moiety bonded to 4-CNpy through the nitrile group. Oxidation of this species with cerium(IV) yielded the mixed-valence complex [Ru II(bpy) 2(py)(4-CNpy)Ru III(NH 3) 5 5+, with concomitant disappearance of the MLCT band of lowest energy.