Journal of the American Chemical Society, Vol.133, No.45, 18433-18446, 2011
Simultaneous Bridge-Localized and Mixed-Valence Character in Diruthenium Radical Cations Featuring Diethynylaromatic Bridging Ligands
A series of bimetallic ruthenium complexes [{Ru(dppe)Cp*}(2)(mu-C CArC C)] featuring diethynylaromatic bridging ligands (Ar = 1,4-phenylene, 1,4-naphthylene, 9,10-anthrylene) have been prepared and some representative molecular structures determined. A combination of UV-vis-NIR and IR spectroelectrochemical methods and density functional theory (DFT) have been used to demonstrate that one-electron oxidation of compounds [{Ru(dppe)Cp*}(2) (mu-C CArC C)](HC CArCE CH = 1,4-diethynylbenzene; 1,4-diethynyl-2,5-dimethoxybenzene; 1,4-diethynylnaphthalene; 9,10-diethynylanthracene) yields solutions containing radical cations that exhibit characteristics of both oxidation of the diethynylaromatic portion of the bridge, and a mixed-valence state. The simultaneous population of bridge-oxidized and mixed-valence states is likely related to a number of factors, including orientation of the plane of the aromatic portion of the bridging ligand with respect to the metal d-orbitals of appropriate pi-symmetry.