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

Abstract

The preparations of multinuclear supramolecules assembled from 1‘,1‘ ‘‘-bis(terpyridyl)biferrocene redox-active subunits with Ru2+ metal centers are described. The electrochemical measurements of the series of Ru2+-coordinated 1‘,1‘ ‘‘-bis(terpyridyl)biferrocene complexes are dominated by the Ru2+/Ru3+ redox couple (E1/2 at ∼1.35 V), Fe2+/Fe3+ redox couples (E1/2 from ∼0.4 to ∼0.9 V), and terpy/terpy-/terpy2- redox couples (E1/2 at ∼−1.2 and ∼−1.4 V). The appreciable variations detected in the Fe2+/Fe3+ oxidation potentials indicate that there is an interaction between the spacer and the Ru2+ metal centers. On the coordination of Ru2+ 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*terpyRu)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 Ru2+ 1‘,1‘ ‘‘-bis(terpyridyl)biferrocene complexes reveals that there is a qualitative electronic coupling within the array. The coordination of Ru2+ transition-metal centers lowers the energy of the π*terpy orbitals, giving a more red-shifted transition.