title: Tuning through-bond Fe(III)/Fe(II) coupling by solvent manipulation of a central ruthenium redox couple.
abstract: The relationships between the intervalence energy (E(IT)) and the free energy difference (DeltaG) that exists between the minima of redox isomers (Fe(II)-Ru(III)/Fe(III)-Ru(II)) for various heterobimetallic complexes [(R-Fcpy)Ru(NH(3))(5)](2+/3+) (R = H, ethyl, Br, actyl; Fcpy = (4-pyridyl)ferrocenyl; Ru(NH(3))(5) = pentaam(m)ineruthenium) were examined. The changes in DeltaG for the complexes in various solvents were due to the effects of both solvent donicity and the substituents. The intervalence energy versus DeltaG, DeltaG approximately FDeltaE(1/2) (DeltaE(1/2) = E(1/2)(Fe(III/II)) - E(1/2)(Ru(III/II))), plots for the complexes in various solvents suggest a nuclear reorganization energy (lambda) of approximately 6000 cm(-1) (Chen et al. Inorg. Chem. 2000, 39, 189). For [(R-Fcpy)Ru(NH(3))(5)](2+) and [(et-Fcpy)Ru(NH(3))(4)(py)](2+) (Ru(NH(3))(4) = trans-tetraam(m)ineruthenium; py = pyridine) in various solvents, the E(1/2)(Ru(III/II)) of rutheniumam(m)ine typically was less than the E(1/2)(Fe(III/II)) of the ferrocenyl moiety. However, the low-donicity solvents resulted in relatively large values of E(1/2)(Ru(III/II)) for [(et-Fcpy)Ru(NH(3))(4)(py)](2+/3+/4+). Under our unique solvent conditions, a dramatic end-to-end interaction was observed for the trimetal cation, [(et-Fcpy)(2)Ru(NH(3))(4)](4+), in which the [(et-Fcpy)(2)Ru(NH(3))(4)](4+) included a central trans-tetraam(m)ineruthenium(III) and a terminal Fe(II)/Fe(III) pair. In general, results of electrochemical studies of [(et-Fcpy)(2)Ru(NH(3))(4)](2+) indicated both solvent-tunable E(1/2)(Ru(III/II)) (1 e(-)) and solvent-insensitive E(1/2)(Fe(III/II)) (2 e(-)) redox centers. However, in nitriles, two E(1/2)(Fe(III/II)) peaks were found with DeltaE(1/2)(Fe(III/II) - Fe(III/II)) ranging between 83 and 108 mV at a terminal metal-to-metal distance of up to 15.6 A. Furthermore, the bridging dpi orbital of the ruthenium center mediated efficient end-to-end interaction between the combinations of the terminal Fe(II)-Fe(III)/Fe(III)-Fe(II) pair. To our knowledge, this is the first example of solvent-tunable end-to-end interactions in multimetal complexes.
authors.affiliation: Department of Chemistry, Fu Jen Catholic University, Taipei Hsien 24205, Taiwan, Republic of China.
authors.forename: Yu-Chen
authors.initials: YC
authors.lastname: Lin
authors.forename: Wei-Tin
authors.initials: WT
authors.lastname: Chen
authors.forename: Joe
authors.initials: J
authors.lastname: Tai
authors.forename: Denny
authors.initials: D
authors.lastname: Su
authors.forename: Sheng-Yi
authors.initials: SY
authors.lastname: Huang
authors.forename: Ingrid
authors.initials: I
authors.lastname: Lin
authors.forename: Ju-Ling
authors.initials: JL
authors.lastname: Lin
authors.forename: Mandy M
authors.initials: MM
authors.lastname: Lee
authors.forename: Mong Feng
authors.initials: MF
authors.lastname: Chiou
authors.forename: Yen-Hsiang
authors.initials: YH
authors.lastname: Liu
authors.forename: Ken-Shin
authors.initials: KS
authors.lastname: Kwan
authors.forename: Yuan-Jang
authors.initials: YJ
authors.lastname: Chen
authors.forename: Hsing-Yin
authors.initials: HY
authors.lastname: Chen
mesh_terms: D000042:Absorption; D004563:Electrochemistry; D005290:Ferric Compounds / Q000737:chemistry*; D005296:Ferrous Compounds / Q000737:chemistry*; D000075163:Metallocenes; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010084:Oxidation-Reduction; D011725:Pyridines / Q000737:chemistry; D012428:Ruthenium / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet
chemical_list: D005290:Ferric Compounds; D005296:Ferrous Compounds; D000075163:Metallocenes; D009942:Organometallic Compounds; D011725:Pyridines; D012997:Solvents; D012428:Ruthenium; C023666:pyridine; C004998:ferrocene