title: Effect of axial ligands on the spectroscopic and electrochemical properties of diruthenium compounds.
abstract: Three related diruthenium complexes containing four symmetrical anionic bridging ligands were synthesized and characterized as to their electrochemical and spectroscopic properties. The examined compounds are represented as Ru2(dpb)4Cl, Ru2(dpb)4(CO), and Ru2(dpb)4(NO) in the solid state, where dpb = diphenylbenzamidinate anion. Different forms of Ru2(dpb)4Cl are observed in solution depending on the utilized solvent and the counteranion added to solution. Each Ru2(5+) form of the compound undergoes multiple redox processes involving the dimetal unit. The reversibility as well as potentials of these diruthenium-centered electrode reactions depends upon the solvent and the bound axial ligand. The Ru2(5+/4+) and Ru2(5+/6+) processes of Ru2(dpb)4Cl were monitored by UV-vis spectroscopy in both CH2Cl2 and PhCN. A conversion of Ru2(dpb)4Cl to [Ru2(dpb)4(CO)](+) was also carried out by simply bubbling CO gas through a CH2Cl2 solution of Ru2(dpb)4Cl at room temperature. The chemically generated [Ru2(dpb)4(CO)](+) complex undergoes several electron transfer processes in CH2Cl2 containing 0.1 M TBAClO4 under a CO atmosphere, and the same reactions were seen for a chemically synthesized sample of Ru2(dpf)4(CO) in CH2Cl2, 0.1 M TBAClO4 under a N2 atmosphere, where dpf = N,N'-diphenylformamidinate anion. Ru2(dpb)4(NO) undergoes two successive one-electron reductions and a single one-electron oxidation, all of which involve the diruthenium unit. The CO and NO adducts of Ru2(dpb)4 were further characterized by FTIR spectroelectrochemistry, and the IR spectral data of these compounds are discussed in light of results for previously characterized Ru2(dpf)4(CO) and Ru2(dpf)4(NO) derivatives under similar solution conditions.
authors.affiliation: Department of Chemistry, University of Houston , 112 Fleming Building, Houston, Texas 77204-5003, United States.
authors.forename: Machima
authors.initials: M
authors.lastname: Manowong
authors.forename: Baocheng
authors.initials: B
authors.lastname: Han
authors.forename: Thomas R
authors.initials: TR
authors.lastname: McAloon
authors.forename: Jianguo
authors.initials: J
authors.lastname: Shao
authors.forename: Ilia A
authors.initials: IA
authors.lastname: Guzei
authors.forename: Siyabonga
authors.initials: S
authors.lastname: Ngubane
authors.forename: Eric
authors.initials: E
authors.lastname: Van Caemelbecke
authors.forename: John L
authors.initials: JL
authors.lastname: Bear
authors.forename: Karl M
authors.initials: KM
authors.lastname: Kadish