Tuning through-bond Fe(III)/Fe(II) coupling by solvent manipulation of a central ruthenium redox couple.
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.
Lin
Yu-Chen
YC
Department of Chemistry, Fu Jen Catholic University, Taipei Hsien 24205, Taiwan, Republic of China.
Chen
Wei-Tin
WT
Tai
Joe
J
Su
Denny
D
Huang
Sheng-Yi
SY
Lin
Ingrid
I
Lin
Ju-Ling
JL
Lee
Mandy M
MM
Chiou
Mong Feng
MF
Liu
Yen-Hsiang
YH
Kwan
Ken-Shin
KS
Chen
Yuan-Jang
YJ
Chen
Hsing-Yin
HY
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
D005290:Ferric Compounds; D005296:Ferrous Compounds; D000075163:Metallocenes; D009942:Organometallic Compounds; D011725:Pyridines; D012997:Solvents; D012428:Ruthenium; C023666:pyridine; C004998:ferrocene