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Reactions of tris- and bis(2,2'-bipyridine)rhodium(II) complexes in aqueous solution

Journal Article · · Inorg. Chem.; (United States)
DOI:https://doi.org/10.1021/ic00147a002· OSTI ID:5862207
;
Pulse-radiolytic methods have been used to characterize Rh(bpy)/sub 3//sup 2 +/ and Rh/sup II/(bpy)/sub 2/(aq). The rhodium(II) complexes are produced by one-electron reduction of Rh(bpy)/sub 3//sup 3 +/ and Rh(bpy)/sub 2/(OH)/sub 2//sup +/, respectively, by either e/sub aq//sup -/ or R.=(CH/sub 3/)/sub 2/COH (the radical produced predominantly by the reaction of 2-propanol with the hydroxyl radical). For reduction by R., rate constants of 2.3 x 10/sup 9/ M/sup -1/ s/sup -1/ for Rh(bpy)/sub 3//sup 3 +/ and 2.4 x 10/sup 8/ M/sup -1/ s/sup -1/ for Rh(bpy)/sub 2/(OH)/sub 2//sup +/ at 25/sup 0/C were found. Small amounts of ''double reduction'' give Rh(bpy)/sub 3//sup +/, which undergoes bipyridine dissociation with k = 5 x 10/sup 4/ s/sup -1/ at 25/sup 0/C. The bis complex Rh/sup II/(bpy)/sub 2/(aq) exhibits two dissociable protons implicating pK/sub a/ (Rh(bpy)/sub 2/(H/sub 2/O)/sub 2//sup 2 +/-Rh(bpy)/sub 2/(H/sub 2/O)(OH)/sup +/) = 8.6 and pK/sup a/ (Rh(bpy)/sub 2/(H/sub 2/O)(OH)/sup +/-Rh(bpy)/sub 2/(OH)/sub 2//sup 0/ = 11.1. In the absence of added bpy or Rh(bpy)/sub 3//sup 3 +/, Rh/sup II/(bpy)/sub 2/ undergoes rapid dimerization (k = (2.3 x 10/sup 11/) exp(-4.3 kcal mol/sup -1//RT) at pH 8.9), and the dimer ultimately converts to Rh(bpy)/sub 2//sup +/ and Rh(bpy)/sub 2/(OH)/sub 2//sup +/ (k = 0.9 x 10/sup -2/ s/sup -1/ at 25/sup 0/C, 0.8 x 10/sup -1/ s/sup -1/ at 60/sup 0/C). Reaction of bipyridine with Rh(bpy)/sub 2/(H/sub 2/O)/sub 2//sup 2 +/ to give Rh(bpy)/sub 3//sup 2 +/ proceeds with k = 0.3 x 10/sup 9/ M/sup -1/ s/sup -1/, while for the reverse reaction k = 0.6 s/sup -1/ at 25/sup 0/C and 4.3 s/sup -1/ at 50/sup 0/C. Disproportionation of Rh(bpy)/sub 3//sup 2 +/ to Rh(bpy)/sub 2//sup +/ and Rh(bpy)/sub 3//sup 3 +/ proceeds via reduction of Rh/sup II/(bpy)/sub 2/ by Rh(bpy)/sub 3//sup 2 +/ (k = 3.0 x 10/sup 8/ M/sup -1/ s/sup -1/ at pH 8.9 and 25/sup 0/C).
Research Organization:
Brookhaven National Lab., Upton, NY
OSTI ID:
5862207
Journal Information:
Inorg. Chem.; (United States), Journal Name: Inorg. Chem.; (United States) Vol. 22:5; ISSN INOCA
Country of Publication:
United States
Language:
English

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Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
400301 -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
400600* -- Radiation Chemistry
AQUEOUS SOLUTIONS
AZINES
BARYONS
CHEMICAL RADIATION EFFECTS
CHEMICAL REACTIONS
CHEMISTRY
COMPLEXES
DECOMPOSITION
DIMERIZATION
DISPERSIONS
ELEMENTARY PARTICLES
ELEMENTS
FERMIONS
HADRONS
HETEROCYCLIC COMPOUNDS
METALS
MIXTURES
NUCLEONS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PLATINUM METALS
POLYMERIZATION
PROTONS
PYRIDINE
PYRIDINES
RADIATION CHEMISTRY
RADIATION EFFECTS
RADIOLYSIS
REDUCTION
RHODIUM
RHODIUM COMPLEXES
RHODIUM COMPOUNDS
SOLUTIONS
TRANSITION ELEMENT COMPLEXES
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS