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 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 (E-1/2 at similar to1.35 V), Fe2+/Fe3+ redox couples (E(1/)2 from similar to0.4 to similar to0.9 V), and terpy/terpy(-)herpy(2-) redox couples (E-1/2 at similar to-1.2 and similar to-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(pi)(Fe))(6)] --> (1)[d(pi)(Fe))(5)(pi*(Ru)(terp))(1)] transition in the visible region. The observed red-shifted absorption from similar to510 nm in monomeric [Ru(terpy)(2)](2+) and [Ru(terpy)(fcterpy)](2+) complexes to similar to570 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 pi*(terpy) orbitals, giving a more red-shifted transition.