17632-84-7Relevant articles and documents
Yields of Electron Transfer Reactions in the Quenching of the Phosphorescent States (2E) of Tris(2,2'-bipyridine)chromium(III) and Tris(4,7-diphenyl-1,10-phenanthroline)chromium(III) Compounds
Ohno, Takeshi,Kato, Shunji
, p. 1528 - 1533 (1984)
Molar absorption coefficients of the phosphorescent states (2E) of (3+) and (3+) were determined.The 2E state of (3+) was reduced to Cr(2,2'-bipyridin
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.
Oxidative homolysis of organochromium macrocycles
Steffan, Carl R.,Espenson, James H.,Bakac, Andreja
, p. 1134 - 1137 (2008/10/08)
The complexes RCrL(H2O)2+ (R = alkyl, aralkyl; L = 1,4,8,12-tetraazacyclopentadecane) are oxidized by Ru(bpy)33+ and 2E Cr(bpy)33+. The one-electron oxidized species RCrL(H2O)3+ undergoes subsequent homolysis; the R. radicals so produced may react with certain metal complexes, or they dimerize, depending on conditions. The rate constants for the rate-controlling step, electron transfer from RCrL(H2O)2+ to Ru(bpy)33+ or *Cr(bpy)33+, were measured by laser flash photolysis for an extensive range of R groups. For Ru(bpy)33+, the rate constants range from 14.2 L mol-1 s-1 (R = CH3) to 1.05 × 109 (R = 4-CH3C6H4CH2); for *Cr(bpy)33+, the corresponding values are 2.8 × 106 and 1.55 × 109 L mol-1 s-1. In both series, the order of rate constants is methyl . are linear, in accord with the rate-controlling step being electron transfer.
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.
Reactions of ferrocenes and ferrocenium ions with ground and excited states of tris(2,2′-bipyridine)chromium ions
Lee, Shaoyung,Bakac, Andreja,Espenson, James H.
, p. 1367 - 1369 (2008/10/08)
The kinetics of quenching of *Cr(bpy)33+ by d6 metallocenes and by ferrocenium ions were evaluated by laser flash photolysis. The quenching by ferrocenium ions proceeds by energy transfer and is dependent on the donor-acceptor distance, as expected for an electron-exchange mechanism. The rate constants for quenching with d6 metallocenes are at or near the diffusion-controlled limit. The reactions partition themselves between electron transfer and energy transfer. The Cr(bpy)32+ and the ferrocenium ions, formed by electron-transfer quenching, undergo rapid back electron transfer, k = (3-9) × 109 M-1 s-1.
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.
Electron-transfer reactions of uranium(V): Kinetics of the uranium(V)-uranium(VI) self-exchange reaction
Howes, Kevin R.,Bakac, Andreja,Espenson, James H.
, p. 791 - 794 (2008/10/08)
Uranium(V) has been prepared photochemically; its UV spectrum shows a peak at 255 nm with an extinction coefficient of 660 L mol-1 cm-1. Conventional UV/visible, stopped-flow, and laser flash photolysis techniques have been used to study the electron-transfer reactions of uranium(V) and uranium(VI) with a range of chromium, ruthenium, and cobalt complexes. Application of Marcus theory to these results suggests a uranium(VI)/uranium(V) self-exchange rate constant in the range 1-15 L mol-1 s-1. Some of the cross-reactions appear to be nonadiabatic, and these are slower than predicted.
REACTIONS OF CHROMIUM(III) COMPLEXES OF 1,10-PHENANTHROLINE, 2,2'-BIPYRIDYL, AND OXALATE WITH THE PULSE RADIOLYTICALLY GENERATED AQUATED ELECTRON, ZINC(I), AND CADMIUM(I)
Lawrance, Geoffrey A.,Sangster, David F.
, p. 1425 - 1430 (2007/10/02)
The chromium(II) ions (3+), (3+), (+), (+), (-), and(-)(phen = 1,10-phenanthroline, bipy = 2,2'-bipyridyl, ox = oxalate) react rapidly with the aquated electron to form the chromium(II) analogues.Rate constants for formation of the chromium(II) species are dependent on complex charge, increasing with increasing positive charge, but all greater than 1010 dm3 mol-1 s-1.Electronic spectra of the chromium(II) complexes prior to any dissociation were measured.While (2+) and (2+) decompose only slowly in aqueous solution, all complexes with oxalate ligands decompose rapidly with first-order rate constants > 8 x E3 s-1.This behaviour parallels the voltammetric behaviour at a glassy carbon electrode, where only (3+) and (3+) exhibit any reversible character for the CrIII-CrII couple.Electron-transfer reactions between the chromium(II) complexes and zinc(I) or cadmium(I), initiated radiolytically, have rate constants near 2 x E9 dm3 mol-1 s-1 in all cases, and are probably diffusion controlled.
Fe(H2O)6.
Guarr,Buhks,McLendon
, p. 3763 - 3767 (2007/10/02)
The deuterium isotope effect on the thermodynamic driving force is discussed. Theory correctly predicts a decrease in the kinetic isotope effect as the reaction driving force increases. The observed isotope effect for replacement of H//2O by D//2O is significantly larger than predicted even after correcting for the solvent dependence of the reaction driving force.
