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), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 101:4; ISSN JACSA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400201* -- Chemical & Physicochemical Properties
AMMINES
AZINES
BIPYRIDINES
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
COMPARATIVE EVALUATIONS
COMPLEXES
DATA
DATA FORMS
ELECTRON EXCHANGE
ELECTRON TRANSFER
ENTHALPY
ENTROPY
EXPERIMENTAL DATA
FLUORINE COMPOUNDS
HALOGEN COMPOUNDS
HETEROCYCLIC COMPOUNDS
HYDROGEN COMPOUNDS
INFORMATION
INORGANIC ACIDS
ISOLATED VALUES
KINETICS
LEAST SQUARE FIT
MAXIMUM-LIKELIHOOD FIT
MEDIUM TEMPERATURE
NUMERICAL DATA
NUMERICAL SOLUTION
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANIC SULFUR COMPOUNDS
PERCHLORIC ACID
PH VALUE
PHENANTHROLINES
PHYSICAL PROPERTIES
PRECURSOR
PYRIDINES
REACTION KINETICS
RUTHENIUM COMPLEXES
SPECTRA
SULFONIC ACIDS
TEMPERATURE DEPENDENCE
THEORETICAL DATA
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENT COMPLEXES
ULTRAVIOLET SPECTRA