Generation of rhodium(II) and rhodium(I) from the one-electron reduction of tris(2,2'-bipyridine)rhodium(III) ion in aqueous solution
- Istituto F.R.A.E., Bologna, Italy
The reaction of Rh(bpy)/sub 3//sup 3 +/ with radiation-generated reducing radicals (e/sub aq//sup -/,. CO/sub 2//sup -/, and (CH/sub 3/)/sub 2/COH) in aqueous solution quantitatively and rapidly (k = 10/sup 9/-10/sup 10/ M/sup -1/ s /sup -1/) yields Rh(bpy)/sub 3//sup 2 +/ (lambda/sub max/ 485 nm, epsilon/sub max/ 1.0 x 10/sup 3/ M/sup -1/ cm/sup -1/) which undergoes slow (k = 0.45 +- 0.05 s/sup -1/ at pH 3-10) loss of bpy at room temperature. Rh(bpy)/sub 3//sup 2 +/ reacts with O/sub 2/ (k = 4.9 x 10/sup 8/ M/sup -1/ s/sup -1/) via electron transfer. In alkaline solution, Rh(bpy)/sub 3//sup 2 +/ undergoes disproportionation with ligand-labilized Rh(II) to form Rh(bpy)/sub 3//sup 3 +/ and red-violet Rh(bpy)/sub 2//sup +/. At pH > 10, ligand-labilized Rh(II) reduces Rh(bpy)/sub 3//sup 3 +/ resulting in a redox-catalyzed ligand-labilization chain reaction; at pH 14, G(bpy) approx. = G(-Rh(bpy)/sub 3//sup 3 +/) > 300. The nature of O/sub 2/-sensitive Rh(bpy)/sub 2//sup +/, its spectrum, and state of aggregation is highly dependent upon the pH of the solution, (Rh(I)), and the nature and concentration of the counteranion. At least four forms of Rh(bpy)/sub 2//sup +/ are clearly identified: (a) a red-violet soluble form (lambda/sub max/ 518 nm, epsilon/sub max/ 9500 M/sup -1/ cm/sup -1/) which is formulated as Rh(bpy)/sub 2/(OH)/sub n//sup (1-n)/ and may be dimeric via hydroxide bridging (in neutral solution, very small changes in pH have a large effect on the spectrum which shows a main band at approx. 415 nm and a well-defined shoulder in the 470-nm region); (b) a violet insoluble form represented as Rh(bpy)/sub 2/X where X = Cl/sup -/, ClO/sub 4//sup -/, etc.; (c) a transient green form observed when the red-violet form is acidified which is formulated as Rh(bpy)/sub 2/(OH/sub 2/)/sub n//sup +/; (d) a colorless form in acidic solution which is assigned as a hydride in which the metal center is formally Rh(III), e.g., RhH(bpy)/sub 2//sup 2 +/. At natural pH, H/sub 2/ is produced with an efficiency of approx. 25% in the absence of any catalyst. The relevance of these results to solar energy conversion schemes is examined. 11 figures.
- OSTI ID:
- 6454834
- Journal Information:
- J. Am. Chem. Soc.; (United States), Vol. 103:12
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
RHODIUM COMPLEXES
RADIOLYSIS
ABSORPTION SPECTRA
BIPYRIDINES
CHEMICAL REACTION KINETICS
EXPERIMENTAL DATA
GAMMA RADIATION
OXYGEN
PH VALUE
PULSES
REDUCTION
ULTRAVIOLET RADIATION
AZINES
CHEMICAL RADIATION EFFECTS
CHEMICAL REACTIONS
CHEMISTRY
COMPLEXES
DATA
DECOMPOSITION
ELECTROMAGNETIC RADIATION
ELEMENTS
HETEROCYCLIC COMPOUNDS
INFORMATION
IONIZING RADIATIONS
KINETICS
NONMETALS
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PYRIDINES
RADIATION CHEMISTRY
RADIATION EFFECTS
RADIATIONS
REACTION KINETICS
SPECTRA
TRANSITION ELEMENT COMPLEXES
400600* - Radiation Chemistry