Comparison of the rates of electron exchange reactions of ammine complexes of ruthenium(II) and -(III) with the predictions of adiabatic, outer-sphere electron transfer models
The rate constants for the Ru(NH/sub 3/)/sub 6//sup 3+/2+/, Ru(NH/sub 3/)/sub 4/(bpy)/sup 3+2+/, and Ru(NH/sub 3/)/sub 2/(bpy)/sub 2//sup 3+/2+/ electron exchange reactions have been measured by a technique involving subtle modifications of the ligands. The rate constants (M/sup -1/s/sup -1/, medium) at 25/sup 0/C are 3.2 x 10/sup 3/, 0.1 M CF/sub 3/SO/sub 3/H, for the Ru(NH/sub 3/)/sub 6//sup 3+/2+/ exchange; 7.7 x 10/sup 5/, 0.1 M CF/sub 3/SO/sub 3/H, and 2.2 x 10/sup 6/, 0.1 M HClO/sub 4/, for the Ru(NH/sub 3/)/sub 4/(bpy)/sup 3+/2+/ exchange; 8.4 x 10/sup 7/, 0.1 M HClO/sub 4/, for the Ru(NH/sub 3/)/sub 2/(bpy)/sup 3+/2+/ exchange. The rate constants and activation parameters for the Ru(NH/sub 3/)/sub 4/(bpy)/sup 3+/2+/ exchange reaction were determined as a function of ionic strength (k = 4.1 x 10/sup 4/ M/sup -1/s/sup -1/, ..delta..H is not equal to 4.0 kcal mol/sup -1/, and ..delta..S is not equal to -24 cal deg/sup -1/ mol/sup -1/ at zero ionic strength and 25/sup 0/C). The rate constants determined in this work together with those for the analogous Ru(NH/sub 3/)/sub 5/py/sup 3+/2+/ and Ru(bpy)/sub 3//sup 3+/2+/ exchange reactions are compared with the predictions of theoretical models. Good linearity was found for a plot of log k/sub ex/ vs. 1/anti r, where anti r is the mean separation of the ruthenium centers in the activated complex. The Marcus model derived on the basis of a reactive collision formulation gives better agreement with the observed rate constants and activation parameters at zero ionic strength than the conventional ion-pair preequilibrium model. Contrary to prediction, the increase in exchange rate with increasing ionic strength is reflected primarily in a decreased enthalpy of activation. 6 figures, 5 tables.
- Research Organization:
- Brookhaven National Lab., Upton, NY
- OSTI ID:
- 6296138
- Journal Information:
- J. Am. Chem. Soc.; (United States), Vol. 101:4
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
RUTHENIUM COMPLEXES
CHEMICAL REACTIONS
AMMINES
BIPYRIDINES
CHEMICAL REACTION KINETICS
COMPARATIVE EVALUATIONS
ELECTRON EXCHANGE
ENTHALPY
ENTROPY
EXPERIMENTAL DATA
FLUORINE COMPOUNDS
ISOLATED VALUES
LEAST SQUARE FIT
MEDIUM TEMPERATURE
PERCHLORIC ACID
PH VALUE
PHENANTHROLINES
PRECURSOR
SULFONIC ACIDS
TEMPERATURE DEPENDENCE
THEORETICAL DATA
ULTRAVIOLET SPECTRA
AZINES
COMPLEXES
DATA
DATA FORMS
ELECTRON TRANSFER
HALOGEN COMPOUNDS
HETEROCYCLIC COMPOUNDS
HYDROGEN COMPOUNDS
INFORMATION
INORGANIC ACIDS
KINETICS
MAXIMUM-LIKELIHOOD FIT
NUMERICAL DATA
NUMERICAL SOLUTION
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANIC SULFUR COMPOUNDS
PHYSICAL PROPERTIES
PYRIDINES
REACTION KINETICS
SPECTRA
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENT COMPLEXES
400201* - Chemical & Physicochemical Properties