H-atom transfer between metal complex ions in solution
The reaction between (Ru/sup IV/ (bpy)/sub 2/(py)(O))/sup 2 +/ and (Ru/sup II/(bpy)/sub 2/(py)(OH/sub 2/))/sup 2 +/ in H/sub 2/O to form 2 equiv of (Ru/sup III/-(bpy)/sub 2/(py)(OH))/sup 2 +/ occurs with a solvent isotope effect of (k/sub H/sub 2/O//k/sub D/sub 2/O/)/sup 25/sup 0/C/ = 16.1 +/- 0.2 both in neat solvent and at I = 0.10 M (Na/sub 2/SO/sub 4/). The rate of the reaction is independent of pH for 2 < pH < 9 but decreases at pH >9, where the Ru(II) aqua complex becomes deprotonated to form the hydroxo complex, (Ru/sup II/(bpy)/sub 2/(py)(OH))/sup +/ (pK/sub b/ = 3.20 +/- 0.05). The rate constants for the two pathways at T = 25 /sup 0/C and I = 0.10 M are k/sub H/sub 2/O/ = (2.174 +/- 0.028) x 10/sup 5/ M/sup -1/ s/sup -1/ and k/sub OH/ = (0.247 +/- 0.024) x 10/sup 5/ M/sup -1/ s/sup -1/. The solvent isotope effect is much smaller for the second pathway with (k/sub OH//k/sub OD/)/sup 25/sup 0/C/ = 1.5. Complementary kinetics studies on the cross reaction between (Ru/sup III/(trpy)(bpy)(OH))/sup 2 +/ and (Ru/sup II/(bpy)/sub 2/(py)(OH/sub 2/))/sup 2 +/ have revealed a significant kinetic isotope effect of (k/sub H/sub 2/O//k/sub D/sub 2/O/)/sup 25/sup 0/C/ = 5.8 +/- 0.4, which also displays a linear dependence on mole fraction of deuterium. The rate of the cross reaction in independent of pH for 3 < pH < 8 with k/sub H/sub 2/O/ = (4.1 +/- 0.2) x 10/sup 5/ M/sup -1/ s/sup -1/ (T = 25 /sup 0/C, I = 0.005 M). For pH > 9 a second pathway with (Ru/sup II/(bpy)/sub 2/(py)(OH))/sup +/ as the reductant dominates the kinetics and there is a dramatic increase in the observed rate, giving the extrapolated estimates, k/sub OH/ = (4.4 +/- 0.3) x 10/sup 7/ M/sup -1/ s/sup -1/ and k/sub OD/ approx. (2.9) x 10/sup 7/ M/sup -1/ s/sup -1/. In the pathway at the high pH there is no difference in H/sup +/ content between reactants and products and the reaction occurs by outer-sphere electron transfer.
- Research Organization:
- Univ. of North Carolina, Chapel Hill
- OSTI ID:
- 6421291
- Journal Information:
- J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 109:11; ISSN JACSA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400201* -- Chemical & Physicochemical Properties
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Isotope Exchange
& Isotope Separation
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AQUEOUS SOLUTIONS
AZINES
BIPYRIDINES
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
COMPLEXES
DATA
DEUTERIUM
DEUTERIUM COMPOUNDS
DISPERSIONS
EXPERIMENTAL DATA
HETEROCYCLIC COMPOUNDS
HYDROGEN COMPOUNDS
HYDROGEN ISOTOPES
HYDROGEN TRANSFER
INFORMATION
ISOTOPE EFFECTS
ISOTOPES
ISOTOPIC EXCHANGE
KINETICS
LIGHT NUCLEI
MIXTURES
NUCLEI
NUMERICAL DATA
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OXYGEN COMPOUNDS
PH VALUE
PYRIDINES
QUANTITY RATIO
REACTION KINETICS
RUTHENIUM COMPLEXES
SOLUTIONS
STABLE ISOTOPES
TRANSITION ELEMENT COMPLEXES
WATER