Dinuclear bis(terpyridine)ruthenium(II) complexes by amide coupling of ruthenium amino acids: Synthesis and properties

Two redox-asymmetric amide-bridged bis(terpyridine) ruthenium(II) complexes (3a, 3b) have been prepared by amide coupling of a carboxylic acid functionalized complex with an amine substituted complex and they were fully characterized by spectroscopic analyses. They emit at 692 and 750 nm at room temperature in fluid solution with quantum yields larger than 10(-3) and (MLCT)-M-3 lifetimes of 22 ns. Ru center dot center dot center dot Ru distances were estimated from DFT models as 17.7 and 13.4 angstrom for 3a and 3b, respectively. Cyclic voltammetry gives two oxidation potentials for the differently substituted ruthenium sites with splittings of 0.10 and 0.23 V for 3a and 3b, respectively. Oxidation of 3b with Ce-IV ions gives the corresponding mixed-valent Ru-II-Ru-III system which is valence-localized according to NIR spectroscopic and theoretical analyses. (C) 2011 Elsevier B.V. All rights reserved.