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Synthesis and properties of the Ru(tacn)/sub 2//sup 3+/2+/ couple and NMR study of the electron self-exchange (tacn = 1,4,7-triazacyclononane)

Journal Article · · Inorg. Chem.; (United States)
DOI:https://doi.org/10.1021/ic00288a006· OSTI ID:5826296
;
The tridentate ligand tacn (1,4,7-triazacyclononane) reacted at room temperature with the Ru(DMF)/sub 6//sup 2+/ (DMF = N,N'-dimethylformamide) complex to form the complex Ru(tacn)/sub 2//sup 2+/, from which Ru(tacn)/sub 2//sup 3+/ was obtained by chemical or electrochemical oxidation. The couple exhibited a reversible formal potential of 0.37 V (vs NHE) and a large electron-self-exchange rate constant (k/sub ex/ = 5 /times/ 10/sub 4/ M/sup /minus/1/ s/sup /minus/1/, /mu/ = 0.1 M, T = 23/degree/C) as measured directly by the broadening, in the presence of Ru(tacn)/sub 2//sup 3+/, of (a) the single /sup 13/C NMR signal and (b) the /sup 1/H multiplet of Ru(tacn)/sub 2//sup 2+/. The large rate constant fits well into the series of Ru amine complexes and, allowing for the effect of strain in the ligand on electron exchange reactions, also compares well with those for the corresponding cobalt and nickel couples, supportive of adiabatic behavior in all cases. Due to their high stability and inertness, both Ru(tacn)/sub 2//sup 2+/ and Ru(tacn)/sub 2//sup 3+/ are useful outer-sphere electron-transfer agents. Interestingly, Ru(tacn)/sub 2//sup 3+/ is rather unreactive toward dehydrogenation of the coordinated amine ligand, in contrast to other Ru(III) complexes. The uv-vis spectra of both complexes are dominated by charge-transfer bands. For the Ru(II) complex a weak band at 355 nm (60 M/sup /minus/1/ cm/sup /minus/1/) is assigned to the spin-allowed transition of /sup 1/A/sub 1g/-/sup 1/T/sub 1g/ parentage, confirming the observation made in other tacn complexes that the ligand exerts a substantially stronger ligand field on the metal than ammonia and ethylenediamine. Assignments for the absorption spectrum of Ru(tacn)/sub 2//sup 3+/, which exhibits a surprising low-energy band at 375 nm (300 M/sup /minus/1/ cm/sup /minus/1/), are discussed. 50 refs., 4 figs., 3 tabs.
Research Organization:
Australian National Univ., Canberra
OSTI ID:
5826296
Journal Information:
Inorg. Chem.; (United States), Journal Name: Inorg. Chem.; (United States) Vol. 27:15; ISSN INOCA
Country of Publication:
United States
Language:
English

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Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
400202 -- Isotope Effects
Isotope Exchange
& Isotope Separation
ALKANES
AMIDES
CARBON 13
CARBON ISOTOPES
CHEMICAL REACTIONS
CYCLOALKANES
DATA
EVEN-ODD NUCLEI
EXPERIMENTAL DATA
FORMAMIDE
HYDROCARBONS
INFORMATION
ISOTOPES
LIGHT NUCLEI
NMR SPECTRA
NUCLEI
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
REFRACTORY METAL COMPOUNDS
RUTHENIUM COMPOUNDS
SPECTRA
STABLE ISOTOPES
TRANSITION ELEMENT COMPOUNDS