Cobalt(I) polypyridine complexes. Redox and substitutional kinetics and thermodynamics in the aqueous 2,2'-bipyridine and 4,4'-dimethyl-2,2'-bipyridine series studied by the pulse-radiolysis technique
Pulse radiolysis was used to study Co(I) produced by e/sub aq//sup -/ reduction of Co(II) in aqueous solutions containing 2,2'-bipyridine (bpy) or 4,4'-dimethyl-2,2'-bipyridine (dmb) and a hydroxyl radical scavenger. Six equilibria between CoL/sub n//sup +/ and CoL/sub n//sup 2 +/ pairs were characterized. The absorption maxima and stability constants (log K) of the CoL/sub n//sup +/ species are as follows: Co(bpy)/sub 3//sup +/, 610 nm, 6.9; Co(bpy)/sub 2//sup +/, 570 nm, 7.6; Co(bpy)/sup +/, 670 nm, greater than or equal to 12; Co(dmb)/sub 3//sup +/, 610 nm, 7.3; Co(dmb)/sub 2//sup +/, 500 nm, 8.0; Co(dmb)/sup +/, 660 nm, greater than or equal to 12. The reduction potentials vs. NHE, based on E/sup 0/ (Co(bpy)/sub 3//sup 2+/+/) = -0.95 V and E/sup 0/(Co(dmb)/sub 3//sup 2+/+/) = -1.07 V, were as follows: Co(bpy)/sub 2//sup 2+/+/, -1.09 V; Co(bpy)/sup 2+/+/, -1.23 V; Co(dmb)/sub 2//sup 2+/+/, -1.17 V; Co(dmb)/sup 2+/+, -1.29 V; Co/sup 2+/+/, less than or equal to -1.6 V. Stability constants were also measured for the Co(II) species in 0.1 M chloride. The log K values are 5.95, 5.27, and 4.60 for Co(bpy)/sup 2 +/, Co(bpy)/sub 2//sup 2 +/, and Co(bpy)/sub 3//sup 2 +/, respectively, and 6.38, 5.92, and 5.25 for Co(dmb)/sup 2 +/, Co(dmb)/sub 2//sup 2 +/, and Co(dmb)/sub 3//sup 2 +/, respectively. The (CH/sub 3/)/sub 2/COH and CO/sub 2//sup -/ radicals, produced by OH oxidation of 2-propanol and formate, react slowly (k approx. 10/sup 6/ to 4 x 10/sup 7/ M/sup -1/ s/sup -1/) with the Co(II) complexes to yield Co(I) and radical-addition products in parallel. 40 references, 8 tables, 3 figures.
- Research Organization:
- Brookhaven National Lab., Upton, NY
- DOE Contract Number:
- AC02-76CH00016
- OSTI ID:
- 5616545
- Journal Information:
- Inorg. Chem.; (United States), Vol. 24:3
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
BIPYRIDINES
RADIOLYSIS
COBALT COMPLEXES
ABSORPTION SPECTRA
AQUEOUS SOLUTIONS
CHEMICAL REACTION KINETICS
EXPERIMENTAL DATA
HYDRATION
HYDROXYL RADICALS
ORGANOMETALLIC COMPOUNDS
PULSED IRRADIATION
PULSES
REDOX POTENTIAL
REDUCTION
SOLVATED ELECTRONS
THERMODYNAMIC PROPERTIES
VALENCE
AZINES
CHEMICAL RADIATION EFFECTS
CHEMICAL REACTIONS
CHEMISTRY
COMPLEXES
DATA
DECOMPOSITION
DISPERSIONS
ELECTRONS
ELEMENTARY PARTICLES
FERMIONS
HETEROCYCLIC COMPOUNDS
INFORMATION
IRRADIATION
KINETICS
LEPTONS
MIXTURES
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PHYSICAL PROPERTIES
PYRIDINES
RADIATION CHEMISTRY
RADIATION EFFECTS
RADICALS
REACTION KINETICS
SOLUTIONS
SOLVATION
SPECTRA
TRANSITION ELEMENT COMPLEXES
400600* - Radiation Chemistry