Electron transfer versus energy transfer in the reactions of /sup 2/E Cr(bpy)/sub 3//sup 3 +/ with organochromium and organocobalt complexes

Journal Article · Wed May 25 04:00:00 EDT 1988 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00219a018· OSTI ID:7076961

Bakac, A; Espenson, J H

The pentaaquoorganochromium complexes, (H/sub 2/O)/sub 5/CrR/sup 2 +/, and a series of organocobalt complexes, (H/sub 2/O)((14)aneN/sub 4/)CoR/sup 2 +/ ((14)aneN/sub 4/ = 1,4,8,11-tetraazacyclotetradecane), quench the luminescence of /sup 3/E Cr(bpy)/sub 3//sup 3 +/. The kinetic trend in the reactions of (H/sub 2/O)/sub 5/CrR/sup 2 +/ at 25/sup 0/C (R, 10/sup -7/k/sub Cr//M/sup -1/ s/sup -1/: CH/sub 3/, approx. 0.15; C/sub 2/H/sub 5/, 1.9; 2-C/sub 3/H/sub 7/, 32; CH/sub 2/C/sub 6/H/sub 5/, 157; CH/sub 2/OCH/sub 3/, 8.5; CH/sub 2/Cl, approx. 0.1) is that expected for outer-sphere electron transfer to /sup 2/E Cr(bpy)/sub 3//sup 3 +/. The organocobalt complexes are generally more reactive, but the reactivity pattern (R, 10/sup -7/k/sub Co//M/sup -1/ s/sup -1/: CH/sub 3/, 9.4; C/sub 2/H/sub 5/, 13; 1-C/sub 2/H/sub 7/, 2.7; CH/sub 2/OCH/sub 3/, 5.2; CH/sub 2/Cl, 22; CH/sub 2/Br, 35) is clearly distinct from that observed in the organochromium series. The oxidation of the organocobalt complexes by Ru(bpy)/sub 3//sup 3 +/ shows a pattern that is typical of outer-sphere electron transfer (R, k/M/sup -1/: CH/sub 3/, 16.0; 1-C/sub 3/H/sub 7/, 442; CH/sub 2/OCH/sub 3/, 649; CH/sub 2/Cl, < 0.04; CH/sub 2/Br, < 0.4). The unusual reactivity trend in the reactions of the organocobalt complexes with Cr(bpy)/sub 3//sup 3 +/ thus signals a major change in mechanism. It is proposed that the cobalt complexes react by energy transfer to yield *(H/sub 2/O)Co((14)aneN/sub 4/)R/sup 2 +/ and Cr(bpy)/sub 3//sup 3 +/. The relaxation of *(H/sub 2/O)Co((14)aneN/sub 4/)R/sup 2 +/ to the ground state takes place in competition with the unimolecular homolysis to yield Co((14)aneN/sub 4/)(H/sub 2/O)/sub n//sup 2 +/ and R/sup ./.

• Research Organization: Iowa State Univ., Ames (USA)
• DOE Contract Number: W-7405-ENG-82
• OSTI ID: 7076961
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 110:11; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
140505 -- Solar Energy Conversion-- Photochemical
Photobiological
&amp; Thermochemical Conversion-- (1980-)
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical &amp; Physicochemical Properties
AZINES
BIPYRIDINES
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHROMIUM COMPLEXES
CHROMIUM COMPOUNDS
COBALT COMPLEXES
COMPLEXES
DATA
DE-EXCITATION
ELECTRON TRANSFER
ENERGY TRANSFER
ENERGY-LEVEL TRANSITIONS
EXPERIMENTAL DATA
HETEROCYCLIC COMPOUNDS
INFORMATION
KINETICS
LUMINESCENCE
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANOMETALLIC COMPOUNDS
PHOTOCHEMICAL REACTIONS
PYRIDINES
RADIATIONLESS DECAY
REACTION KINETICS
TRANSITION ELEMENT COMPLEXES
TRANSITION ELEMENT COMPOUNDS