Development of Polynuclear Molecular Wires Containing Ruthenium(II) Terpyridine Complexes

The preparations of multinuclear supramolecules assembled from 1‘,1‘ ‘‘-bis(terpyridyl)biferrocene redox-active subunits with Ru 2+ metal centers are described. The electrochemical measurements of the series of Ru 2+ -coordinated 1‘,1‘ ‘‘-bis(terpyridyl)biferrocene complexes are dominated by the Ru 2+ /Ru 3+ redox couple ( E 1/2 at ∼1.35 V), Fe 2+ /Fe 3+ redox couples ( E 1/2 from ∼0.4 to ∼0.9 V), and terpy/terpy - /terpy 2 - redox couples ( E 1/2 at ∼−1.2 and ∼−1.4 V). The appreciable variations detected in the Fe 2+ /Fe 3+ oxidation potentials indicate that there is an interaction between the spacer and the Ru 2+ metal centers. On the coordination of Ru 2+ metal centers with 1‘,1‘ ‘‘-bis(terpyridyl)biferrocene, there is a rise to a red-shifted and more intense 1 [(d(π) Fe ) 6 ] → 1 [d(π) Fe ) 5 (π* terpy Ru ) 1 ] transition in the visible region. The observed red-shifted absorption from ∼510 nm in monomeric [Ru(terpy) 2 ] 2+ and [Ru(terpy)(fcterpy)] 2+ complexes to ∼570 nm in polynuclear Ru 2+ 1‘,1‘ ‘‘-bis(terpyridyl)biferrocene complexes reveals that there is a qualitative electronic coupling within the array. The coordination of Ru 2+ transition-metal centers lowers the energy of the π* terpy orbitals, giving a more red-shifted transition.