17632-84-7Relevant articles and documents
Ferrandi,Endicott
, p. 219 (1979)
Electron Transfer versus Energy Transfer in the Reactions of 2E Cr(bpy)33+ with Organochromium and Organocobalt Complexes
Bakac, Andreja,Espenson, James H.
, p. 3453 - 3457 (1988)
The pentaaquoorganochromium complexes, (H2O)5CrR2+, and a series of organocobalt complexes, (H2O)(aneN4)CoR2+ (aneN4=1,4,8,11-tetraazacyclotetradecane), quench the luminescence of 2E Cr(bpy)33+.The kinetic trend in the reactions of (H2O)5CrR2+ at 25 deg C (R, 10-7 kCr/M-1 s-1: CH3, ca. 0.15; C2H5, 1.9; 2-C3H7, 32; CH2C6H5, 157; CH2OCH3, 8.5; CH2Cl, ca. 0.1) is that expected for outer-sphere electron transfer to 2E Cr(bpy)33+.The organocobalt complexes are generally more reactive, but the reactivity pattern (R, 10-7 kCo/M-1 s-1: CH3, 9.4; C2H5 13; 1-C3H7 2.7; CH2OCH3 5.2; CH2Cl 22; CH2Br 35) is clearly distinct from that observed in the organochromium series.The oxidation of the organocobalt complexes by Ru(bpy)33+ shows a pattern that is typical of outer-sphere electron transfer (R k/M-1: CH3 16.0; 1-C3H7, 442; CH2OCH3 649; CH2Cl, 3+ thus signals a major change in mechanism.It is proposed that the cobalt complexes react by energy transfer to yield and Cr(bpy)33+.The relaxation of to the ground state takes place in competition with the unimolecular homolysis to yield Co(aneN4)(H2O)n2+ and R..The semiquantitatively measured yields of Cr(bpy)32+ are consistent with these assignments, as are literature data that show efficient energy transfer quenching of by inorganic cobalt(III) macrocycles but not by (H2O)5CrIIIX complexes.
Oxidation of cobalt(II) macrocycles by tris(bipyridyl)ruthenium(III) ions
Lee, Shaoyung,Bakac, Andreja,Espenson, James H.
, p. 2480 - 2482 (2008/10/08)
The kinetics of the electron-transfer reactions between Ru(bpy)33+ and selected Co(II) complexes were evaluated by laser flash photolysis. The cobalt(II) complexes investigated were (H2O)2Co(N4mac)2+, with N4mac = [14]aneN4, C-meso-Me6[14]aneN4, tim ([14]tetraeneN4), [15]aneN4, and tmc (1,4,8,11-tetramethylcyclam). The respective second-order rate constants at 25°C, μ = 0.10 M, are 3.2 × 107, 7.8 × 106, 2.1 × 107, 1.7 × 107, and 6 × 105 M-1 s-1. The results have been evaluated for their agreement with the Marcus theory. The complex Co(tmc)2+ also reacts with Ru(phen)33+ (k = 1.0 × 106 M-1 s-1) and with Ru(4,7-Me2Phen)33+ (k = 3.2 × 104 M-1 s-1). These cobalt(II) complexes also quench the emission of the excited-state complex *Cr(bpy)33+. Quenching occurs by electron transfer, except for Co(tmc)2+, which appears to react by energy transfer.
Reductive quenching of 2E Cr(bpy)33+ by Fe2+ and Cr(bpy)32+
Bakac, Andreja,Zahir, Khurram,Espenson, James H.
, p. 315 - 318 (2008/10/08)
The reductive quenching of the doublet excited state of Cr(bpy)33+ by Fe(H2O)62+ at pH 1 in aqueous perchlorate solutions produces Cr(bpy)32+; k = (5.3 ± 0.3) × 106 M-1 s-1 at 25°C and 1 M ionic strength. Concurrent reduction of 2E Cr(bpy)33+ by Cr(bpy)32+, unrecognized in previous studies, provides a catalytic route for the deactivation of the excited state. This reaction can be eliminated by the addition of Fe(H2O)63+, which rapidly oxidizes the chromium(II) complex; k = 9.2 × 108 M-1 s-1. The quenching of 2E Cr(bpy)33+ by Cr(bpy)32+ was demonstrated by the effect of Fe2+ on the excited state lifetimes and yields of Cr(bpy)32+ in experiments with Fe2+ as quencher. This required solution of the differential rate equations by numerical integration; the program KINSIM was used and gave the value kCr = (5 ± 3) × 109 M-1 s-1. The indicated quenching reaction was also observed directly.
