Alkynyl-Bridged Ruthenium(II) 4′-Diferrocenyl-2,2′:6′,2′′-terpyridine Electron Transfer Complexes: Synthesis, Structures, and Electrochemical and Spectroscopic Studies

Abstract

The novel ligand 4′-diferrocenylalkyne-2,2′:6′,2′′-terpyridine ( 7; Fc-C≡C-Fc-tpy; tpy = terpyridyl; Fc = ferrocenyl) and its Ru 2+ complexes 8 – 10 have been synthesized and characterized by single-crystal X-ray diffraction, cyclic voltammetry, and UV–vis and luminescence spectroscopy. Electrochemical data and UV absorption and emission spectra indicate that the insertion of an ethynyl group causes delocalization of electrons in the extended π* orbitals. Cyclic voltammetric measurements of 7 show two successive reversible one-electron-oxidation processes with half-wave potentials of 0.53 and 0.78 V. The small variations of the E 1/2 values for the Fe 2+ /Fe 3+ redox couples after the coordination of the Ru 2+ ion suggest a weak interaction between the Ru 2+ and Fe 2+ centers. After insertion of an ethynyl group, UV–vis absorption spectra show a red shift of the absorption peak of the 1 [(d(π) Fe ) 6 ] → 1 [(d(π) Fe ) 5 (π* tpy Ru ) 1 ] MMLCT of the Ru 2+ complexes. The Ru 2+ complex 8 exhibits the strongest luminescence intensity (λ max em 712 nm, Φ em = 2.63 × 10 –4, τ = 323 ns) relative to analogous ferrocene-based terpyridine Ru(II) complexes in H 2 O/CH 3 CN (4/1 v/v) solution.