Generation of a Hydroperoxidochromium Complex from Nitratochromium(III) Ions and Hydrogen Peroxide

Cheng, Mingming; Song, Wenjing; Bakač, Andreja

doi:10.1002/ejic.200800829

Cited by 5 publications

(12 citation statements)

References 19 publications

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“…The labilization of one or more positions at the metal, most likely the four cis sites, 75,76 allows H 2 O 2 to coordinate and form the mixed nitrato/peroxo intermediate I followed by the release of nitrate. If this mechanism is correct, then it follows that the hydroperoxo group must have even stronger cis-labilizing properties than nitrate does or else the proportion of coordinated hydroperoxide could not be much greater than its proportion in solution, i.e., e0.2%, in stark contrast to the experimental yield of >50%.…”

Section: Reactivity Of Organic Versus Metal-based Intermediatesmentioning

confidence: 99%

“…Even if the substitution could be accelerated, as in complexes with cis-labilizing ligands, the yields of the peroxo/hydroperoxo product in aqueous solutions would be expected to be negligibly small, given that H 2 O 2 and H 2 O compete for the labile position(s), and water is a better Lewis base and is present at much higher concentrations. Despite these arguments, it was recently discovered that Cr aq OOH 2+ can be generated in 50−60% yield from Cr aq ONO 2 2+ or Cr aq O 2 CCH 3 2+ and 10−100 mM H 2 O 2 in acidic water, as shown in eq . A few percent of Cr aq OO 2+ was also generated.…”

Section: Alternative Sources Of Metal-activated Oxygenmentioning

confidence: 99%

“…The reaction in eq has a rate constant k = 0.043 M −1 s −1 , independent of [H + ] in the range 0.10 M ≤ [H + ] ≤ 0.50 M. A mechanism proposed to account for these results is shown in eq . Cr aq ONO 2 2 + + normalH 2 normalO 2 .4em → .4em Cr aq OOH 2 + + NO 3 − ( + Cr aq OO 2 + + Cr aq 3 + ) The labilization of one or more positions at the metal, most likely the four cis sites, , allows H 2 O 2 to coordinate and form the mixed nitrato/peroxo intermediate I followed by the release of nitrate. If this mechanism is correct, then it follows that the hydroperoxo group must have even stronger cis-labilizing properties than nitrate does or else the proportion of coordinated hydroperoxide could not be much greater than its proportion in solution, i.e., ≤0.2%, in stark contrast to the experimental yield of >50%.…”

Section: Alternative Sources Of Metal-activated Oxygenmentioning

confidence: 99%

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Oxygen Activation with Transition-Metal Complexes in Aqueous Solution

Bakač

2010

Inorg. Chem.

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Coordination to transition-metal complexes changes both the thermodynamics and kinetics of oxygen reduction. Some of the intermediates (superoxo, hydroperoxo, and oxo species) are close analogues of organic oxygen-centered radicals and peroxides (ROO(*), ROOH, and RO(*)). Metal-based intermediates are typically less reactive, but more persistent, than organic radicals, which makes the two types of intermediates similarly effective in their reactions with various substrates. The self-exchange rate constant for hydrogen-atom transfer for the couples Cr(aq)OO(2+)/Cr(aq)OOH(2+) and L(1)(H(2)O)RhOO(2+)/L(1)(H(2)O)RhOOH(2+) was estimated to be 10(1+/-1) M(-1) s(-1). The use of this value in the simplified Marcus equation for the Cr(aq)O(2+)/Cr(aq)OOH(2+) cross reaction provided an upper limit k(CrO,CrOH)

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Section: Reactivity Of Organic Versus Metal-based Intermediatesmentioning

confidence: 99%

Section: Alternative Sources Of Metal-activated Oxygenmentioning

confidence: 99%

Section: Alternative Sources Of Metal-activated Oxygenmentioning

confidence: 99%

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Oxygen Activation with Transition-Metal Complexes in Aqueous Solution

Bakač

2010

Inorg. Chem.

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“…Since both CrOOH 2þ (aq) and CrOO 2þ (aq) can act as precursors of genotoxic Cr V , these results may have implications for the toxicology of ostensibly benign Cr III in the presence of physiological peroxide and environmental nitrate or other potentially bidentate ligands. 129 A corollary of the proposed nitrato cis activation mechanism is that other potentially bidentate ligands such as RCO 2 À , SO 4 2À , SO 3 2À (if O-bonded), and CO 3 2À should activate cis ligands in Cr III complexes, which are predisposed to associative processes, though probably not in Co III analogues, which are not. Indeed, attempts to make Cr III analogues of the familiar Co(NH 3 ) 5 OCO 2 þ and Co(NH 3 ) 4 (O 2 CO) þ salts yield only Cr(OH) 3 , and efforts in the writer's laboratory to make Cr(NH 3 ) 5 SO 4 þ have been unsuccessful.…”

Section: Spectator Ligands and Stereochemical Changementioning

confidence: 99%

Ligand Substitution Dynamics in Metal Complexes

Swaddle

2010

Physical Inorganic Chemistry

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On the base of our previous studies due to the presence of halides in our complexes there is strong probability for obtaining coordination polymers. Crystal engineering well-defined as the understanding of intermolecular interactions in the context of crystal packing and the utilization of such understanding in the design of new solids with desired physical and chemical properties. Owing to the fact that the small changes in the ligands may play a significant role in the complexes, the organic ligand (1-naphtyl pyridine-2-carboxylate) (L), was synthesized. In order make more steric repulsion around of the complexes resulted in the substitution effect around of the naphtyl moiety was hired in the design. Relocation in the position of functional group was fulfilled our expectations. Three new mercury (II) halide complexes, [Hg(L)2Cl2] (1), [Hg(L)2Br2] (2) and [Hg(L)2I2] (3) were synthesized. All of the compounds were fully characterized using FT-IR, TGA, DSC, mass spectrometry, CHNOS elemental analyses, PXRD, NMR and SCXRD. The results indicate that metal-ligand polymerization controlled by substitution effect. The coordination geometry around the Hg (II) ion is seesaw shape in distorted tetrahedral geometry for compounds (1), (2) and (3) with τ4 of 0.74, 0.76 and 0.78, respectively. Due to the replacement of the functional group (mentioned substitution effect), flexibility of coodinated ligand was decreased. In the previously reported structures, the angle between two planes of aromatic rings in the analogous ligand was 78.37o which changed to the 59.47o, 50.75o and 64.90o for mercury halide series complexes. In present study these angles are 89.09, 89.73 and 88.90 for titled complexes based on new designed ligand. Consequently, this study emphasize that the substitution effect can play the significant role through the flexibility of designed ligand to control the metal-ligand polymerization.

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“…In our earlier studies , of the reactivity of Cr aq OOH 2+ , we have focused on reactions with oxygen-atom acceptors , 1-e reductants , and coordinating anions , . In every instance, the self-decomposition of Cr aq OOH 2+ was much slower than the reaction of interest, but several observations suggested that high-valent chromium species were involved as intermediates in the slow background decay.…”

Section: Introductionmentioning

confidence: 99%

Intramolecular Conversion of Pentaaquahydroperoxidochromium(III) Ion to Aqueous Chromium(V): Potential Source of Carcinogenic Forms of Chromium in Aerobic Organisms

Carraher

Bakač

2010

Chem. Res. Toxicol.

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The decomposition of the title compound (H(2)O)(5)CrOOH(2+) (hereafter Cr(aq)OOH(2+)) in acidic aqueous solutions is kinetically complex and generates mixtures of products (Cr(aq)(3+), HCrO(4)(-), H(2)O(2), and O(2)). Relative yields of individual products vary greatly with reaction conditions and initial concentrations of Cr(aq)OOH(2+). At pH 5.5 in the presence of O(2), the reaction was complete in less than a minute and generated chromate in about 70% yield. These findings, in addition to poor reproducibility of kinetic data, are indicative of the involvement of one or more reactive intermediates that consume additional amounts of Cr(aq)OOH(2+) in post-rate-determining steps. The kinetics were simplified in the presence of H(2)O(2) or ABTS(2-), both of which are capable of scavenging strongly oxidizing intermediates. The measured rate constant in 0.10 M HClO(4) at low O(2) concentrations (≤0.03 mM) was independent of the concentration of the scavengers and was, within error, the same for ABTS(2-), k = 4.9 (±0.2) × 10(-4) s(-1), and H(2)O(2), k = 5.3 (±0.7) × 10(-4) s(-1). At a constant ionic strength of 1.0 M, the reaction in the presence of either H(2)O(2) or ABTS(2-) obeyed a two-term rate law, k(obs)/s(-1) = 6.7 (±0.7) × 10(-4) + 7.6 (±1.1) × 10(-4) [H(+)]. Both in the presence and absence of ABTS(2-) as the scavenger, the yields of H(2)O(2) increased with increasing [H(+)]. These results are discussed in terms of a dual-pathway mechanism for the decay of Cr(aq)OOH(2+). The H(+)-catalyzed path leads to the dissociation of H(2)O(2) from Cr(III), while in the H(+)-independent reaction, Cr(aq)OOH(2+) is transformed to Cr(V). Both scavengers rapidly remove Cr(V) and simplify both the kinetics and products.

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Generation of a Hydroperoxidochromium Complex from Nitratochromium(III) Ions and Hydrogen Peroxide

Cited by 5 publications

References 19 publications

Oxygen Activation with Transition-Metal Complexes in Aqueous Solution

Oxygen Activation with Transition-Metal Complexes in Aqueous Solution

Ligand Substitution Dynamics in Metal Complexes

Intramolecular Conversion of Pentaaquahydroperoxidochromium(III) Ion to Aqueous Chromium(V): Potential Source of Carcinogenic Forms of Chromium in Aerobic Organisms

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