Photophysical and theoretical studies of ruthenium(II)-acetylide and -cyanide complexes with aromatic diimine and trithiacyclononane

Ruthenium(II)-chloride, -cyanide, and -phenylacetylide complexes bearing aromatic diimine (2,2′-bipyridine (bpy), 4,4′-dimethyl-2,2′- bipyridine (Me₂bpy), or dipyrido-[3,2-f:2′,3′-h]- quinoxaline (dpq)) and cyclic tridentate thioether 1,4,7-trithiacyclononane ([9]aneS3) have been prepared. The crystal structures of [Ru([9]aneS3)(bpy) (C≡N)](PF₆) and [Ru([9]aneS3)(diimine)(C≡CPh)](PF ₆) (diimine = bpy and Me₂bpy) reveal Ru-C distances of 2.024(4) and 2.030(3)-2.038(2) Å, respectively. The oxidation waves for the complexes are attributed to the removal of an electron from a [d _π(Ru) + L] hybrid orbital (L = -Cl, -C≡N, and -C≡CPh), whereas the reduction waves are assigned as reduction of the aromatic diimine. The lowest-energy dipole-allowed absorptions for the complexes (λ_max = 403-475 nm, ε_max = (3-5) × 10³ dm³ mol^-1 cm^-1) are assigned as [d_π(Ru^II) + L] → π(diimine) charge transfer transitions. All the acetylide complexes weakly emit at λ_max = 663-680 nm in CH₃CN at 298 K with quantum yield = (5-8) × 10^-4 (λ_ex = 450 nm), and these emissions are described as [d_π(Ru) + L] → π(diimine) triplet charge transfer in nature. Density functional theory (DFT) and time-dependent-DFT (TD-DFT) calculations have been employed to examine the composition of the frontier molecular orbitals and the nature of the electronic transitions associated with the complexes. © 2010 American Chemical Society.