Efficient energy transfer via the cyanide bridge in dinuclear complexes containing Ru(ii) polypyridine moieties

Abstract

We report the synthesis, structure and properties of the cyanide-bridged dinuclear complex ions [Ru(L)(bpy)(μ-NC)M(CN)₅]^2−/− (L = tpy, 2,2′;6′,2′′-terpyridine, or tpm, tris(1-pyrazolyl)methane, bpy = 2,2′-bipyridine, M = Fe(II), Fe(III), Cr(III)) and the related monomers [Ru(L)(bpy)X]²⁺ (X = CN⁻ and NCS⁻). All the monomeric compounds are weak MLCT emitters (λ = 650–715 nm, ϕ ≈ 10⁻⁴). In the Fe(II) and Cr(III) dinuclear systems, the cyanide bridge promotes efficient energy transfer between the Ru-centered MLCT state and a Fe(II)- or Cr(III)-centered d–d state, which results either in a complete quenching of luminescence or in a narrow red emission (λ ≈ 820 nm, ϕ ≈ 10⁻³) respectively. In the case of Fe(III) dinuclear systems, an electron transfer quenching process is also likely to occur.