Kinetics and mechanism of catalytic decomposition and oxidation of chlorine dioxide by the hypochlorite ion

The oxidation of ClO(2) by OCl(-)is first order with respect to both reactants in the neutral to alkaline pH range: -d[ClO(2)]/dt = 2k(OCl)[ClO(2)][OCl(-)]. The rate constant (T = 298 K, mu = 1.0 M NaClO(4)) and activation parameters are k(OCl) = 0.91 +/- 0.02 M(-1) s(-1), DeltaH = 66.5 +/- 0.9 kJ/mol, and DeltaS(++) = -22.3 +/- 2.9 J/(mol K). In alkaline solution, pH > 9, the primary products of the reaction are the chlorite and chlorate ions and consumption of the hypochlorite ion is not observed. The hypochlorite ion is consumed in increasing amounts, and the production of the chlorite ion ceases when the pH is decreased. The stoichiometry is kinetically controlled, and the reactants/products ratios are determined by the relative rates of the production and consumption of the chlorite ion in the ClO(2)/OCl(-) and HOCl/ClO(2)(-) reactions, respectively.     

Kinetics and mechanisms of S(IV) reductions of bromite and chlorite ions

The reaction of bromite with aqueous S(IV) is first order in both reactants and is general-acid catalyzed. The reaction half-lives vary from 5 ms (p[H+] 5.9) to 210 s (p[H+] 13.1) for 0.7 mM excess S(IV) at 25 degrees C. The proposed mechanism includes a rapid reaction (k(1) = 3.0 x 10(7) M(-1) s(-1)) between BrO(2)(-) and SO(3)(2-) to form a steady-state intermediate, (O(2)BrSO(3))(3-). General acids assist the removal of an oxide ion from (O(2)BrSO(3))(3-) to form OBrSO(3)(-), which hydrolyzes rapidly to give OBr(-) and SO(4)(2-). Subsequent fast reactions between HOBr/OBr(-) and SO(3)(2-) give Br(-) and SO(4)(2-) as final products. In contrast, the chlorite reactions with S(IV) are 5-6 orders of magnitude slower. These reactions are specific-acid, not general-acid, catalyzed. In the proposed mechanism, ClO(2)(-) and SO(3)H(-)/SO(2) react to form (OClOSO(3)H)(2)(-) and (OClOSO(2))(-) intermediates which decompose to form OCl(-) and SO(4)(2-). Subsequent fast reactions between HOCl/OCl(-) and S(IV) give Cl- and SO(4)(2-) as final products. SO(2) is 6 orders of magnitude more reactive than SO(3)H-, where k(5)(SO(2)/ClO(2)(-)) = 6.26 x 10(6) M(-1) s(-1) and k(6)(SO(3)H(-)/ClO(2)(-)) = 5.5 M(-1) s(-1). Direct reaction between ClO(2)(-) and SO(3)(2-) is not observed. The presence or absence of general-acid catalysis leads to the proposal of different connectivities for the initial reactive intermediates, where a Br-S bond forms with BrO(2)(-) and SO(3)(2-), while an O-S bond forms with ClO(2)(-) and SO(3)H-.     

Determination of chloride, chlorate and perchlorate by PDMS microchip electrophoresis with indirect amperometric detection

In this work, chloride, chlorate and perchlorate are fast separated on PDMS microchip and detected via in-channel indirect amperometric detection mode. With PDMS/PDMS microchip treated by oxygen plasma, anions chloride (Cl-), chlorate (ClO3-), and perchlorate (ClO4-) are separated within 35s. Some parameters including buffer salt concentration, buffer pH, separation voltage and detection potential are investigated in detail. The separation conditions using 15 mM (pH 6.12) of 2-(N-morpholino)ethanesulfonic acid (MES)+L-histidine (L-His) as running buffer, -2000 V as separation voltage and 0.7 V as detection potential are optimized. Under this condition, the detection limits of Cl-, ClO3-, and ClO4- are 1.9, 3.6, and 2.8 microM, respectively.     

Kinetics and mechanisms of bromine chloride reactions with bromite and chlorite ions

Chloride ion catalyzes the reactions of HOBr with bromite and chlorite ions in phosphate buffer (p[H(+)] 5 to 7). Bromine chloride is generated in situ in small equilibrium concentrations by the addition of excess Cl(-) to HOBr. In the BrCl/ClO(2)(-) reaction, where ClO(2)(-) is in excess, a first-order rate of formation of ClO(2) is observed that depends on the HOBr concentration. The rate dependencies on ClO(2)(-), Cl(-), H(+), and buffer concentrations are determined. In the BrCl/BrO(2)(-) reaction where BrCl is in pre-equilibrium with the excess species, HOBr, the loss of absorbance due to BrO(2)(-) is followed. The dependencies on Cl(-), HOBr, H(+), and HPO(4)(2)(-) concentrations are determined for the BrCl/BrO(2)(-) reaction. In the proposed mechanisms, the BrCl/ClO(2)(-) and BrCl/BrO(2)(-) reactions proceed by Br(+) transfer to form steady-state levels of BrOClO and BrOBrO, respectively. The rate constant for the BrCl/ClO(2)(-) reaction [k(Cl)(2)]is 5.2 x 10(6) M(-1) s(-1) and for the BrCl/BrO(2)(-) reaction [k(Br)(2)]is 1.9 x 10(5) M(-1) s(-1). In the BrCl/ClO(2)(-) case, BrOClO reacts with ClO(2)(-) to form two ClO(2) radicals and Br(-). However, the hydrolysis of BrOBrO in the BrCl/BrO(2)(-) reaction leads to the formation of BrO(3)(-) and Br(-).     

Chemistry of a binuclear cadmium(II) hydroxide complex: formation from water,CO(2) reactivity,and comparison to a zinc analog

Treatment of the bmnpa (N,N-bis-2-(methylthio)ethyl-N-((6-neopentylamino-2-pyridyl)methyl)amine) ligand with equimolar amounts of Cd(ClO(4))(2).5H(2)O and Me(4)NOH.5H(2)O in CH(3)CN yielded the binuclear cadmium hydroxide complex [((bmnpa)Cd)(2)(mu-OH)(2)](ClO(4))(2).CH(3)CN (1). Complex 1 may also be prepared (a) by treatment of a CH(3)CN solution of (bmnpa)Cd(ClO(4))(2) (2) with 1 equiv of n-BuLi, followed by treatment with water or (b) from 2 in the presence of 1 equiv each of water and NEt(3). The hydroxide derivative 1 is not produced from 2 and water in the absence of an added base. Complex 1 possesses a binuclear structure in the solid state with hydrogen-bonding and CH/pi interactions involving the bmnpa ligand. The overall structural features of 1 differ from the halide derivative [((bmnpa)Cd)(2)(mu-Cl)(2)](ClO(4))(2) (3), particularly in that the Cd(2)(mu-OH)(2) core of 1 is symmetric whereas the Cd(2)(mu-Cl)(2) core of 3 is asymmetric. In acetonitrile solution, 1 behaves as a 1:2 electrolyte and retains a binuclear structure and secondary hydrogen-bonding and CH/pi interactions, whereas 3 is a 1:1 electrolyte, indicating formation of a mononuclear [(bmnpa)CdCl]ClO(4) species in solution. Treatment of 1 with CO(2) in anhydrous CH(3)CN yields the bridging carbonate complex [((bmnpa)Cd)(2)(mu-CO(3))](ClO(4))(2).CH(3)CN (4). Treatment of a chemically similar zinc hydroxide complex, [((benpa)Zn)(2)(mu-OH)(2)](ClO(4))(2) (benpa = N,N-bis-2-(ethylthio)ethyl-N-((6-neopentylamino-2-pyridyl)methyl)amine, with CO(2) also results in the formation of a carbonate derivative, [((benpa)Zn)(2)(mu-CO(3))](ClO(4))(2) (5), albeit the coordination mode of the bridging carbonate moiety is different. Treatment of 4 with added water results in no reaction, whereas 5 under identical conditions will undergo reaction to yield the zinc hydroxide complex [((benpa)Zn)(2)(mu-OH)(2)](ClO(4))(2).     

Oxidation of toluidine blue by chlorite in acid and mechanisms of the uncatalyzed and Ru(III)-catalyzed reactions: a kinetic approach

The complex mechanism of the uncatalyzed and Ru(III)-catalyzed oxidation of toluidine blue [(7-amino-8-methylphenothiazin-3-ylidene)dimethyl ammonium chloride, TB(+)Cl(-)] (λ(max) = 626 nm) by acidic chlorite is elucidated by a kinetic approach. Both the uncatalyzed and catalyzed reactions had a first-order dependence on the initial ClO(2)(-) and H(+) concentrations ([ClO(2)(-)](0) and [H(+)](0), respectively). The catalyzed reaction had a first-order dependence on the initial Ru(III) concentration ([Ru(III)](0)). The overall reaction of toluidine blue and chlorite ion was as follows: TB(+) + 5ClO(2)(-) + H(+) = P + 2ClO(2) + 2HCOOH + 3Cl(-) + H(2)O, where P is (7-amino-8-methyl-5-sulfoxophenothiazin-3-ylidene)amine. Consistent with the experimental results, the pertinent reaction mechanisms are proposed.     

Nucleophile assistance of electron-transfer reactions between nitrogen dioxide and chlorine dioxide concurrent with the nitrogen dioxide disproportionation

The reaction of chlorine dioxide with excess NO(2)(-) to form ClO(2)(-) and NO(3)(-) in the presence of a large concentration of ClO(2)(-) is followed via stopped-flow spectroscopy. Concentrations are set to establish a preequilibrium among ClO(2), NO(2)(-), ClO(2)(-), and an intermediate, NO(2). Studies are conducted at pH 12.0 to avoid complications due to the ClO(2)(-)/NO(2)(-) reaction. These conditions enable the kinetic study of the ClO(2) reaction with nitrogen dioxide as well as the NO(2) disproportionation reaction. The rate of the NO(2)/ClO(2) electron-transfer reaction is accelerated by different nucleophiles (NO(2)(-) > Br(-) > OH(-) > CO(3)(2-) > PO(4)(3-) > ClO(2)(-) > H(2)O). The third-order rate constants for the nucleophile-assisted reactions between NO(2) and ClO(2) (k(Nu), M(-2) s(-1)) at 25.0 degrees C vary from 4.4 x 10(6) for NO(2-) to 2.0 x 10(3) when H(2)O is the nucleophile. The nucleophile is found to associate with NO(2) and not with ClO(2) in the rate-determining step to give NuNO(2)(+) + ClO(2)(-). The concurrent NO(2) disproportionation reaction exhibits no nucleophilic effect and has a rate constant of 4.8 x 10(7) M(-1) s(-1). The ClO(2)/NO(2)/nucleophile reaction is another example of a system that exhibits general nucleophilic acceleration of electron transfer. This system also represents an alternative way to study the rate of NO(2) disproportionation.     

New pathways for chlorine dioxide decomposition in basic solution

The product distribution from the decay of chlorine dioxide in basic solution changes as the ClO(2) concentration decreases. While disproportionation reactions that give equal amounts of ClO(2)(-) and ClO(3)(-) dominate the stoichiometry at millimolar or higher levels of ClO(2), the ratio of ClO(2)(-) to ClO(3)(-) formed increases significantly at micromolar ClO(2) levels. Kinetic evidence shows three concurrent pathways that all exhibit a first-order dependence in [OH(-)] but have variable order in [ClO(2)]. Pathway 1 is a disproportionation reaction that is first order in [ClO(2)]. Pathway 2, a previously unknown reaction, is also first order in [ClO(2)] but forms ClO(2)(-) as the only chlorine-containing product. Pathway 3 is second order in [ClO(2)] and generates equal amounts of ClO(2)(-) and ClO(3)(-). A Cl(2)O(4) intermediate is proposed for this path. At high concentrations of ClO(2), pathway 3 causes the overall ClO(3)(-) yield to approach the overall yield of ClO(2)(-). Pathway 2 is attributed to OH(-) attack on an oxygen atom of ClO(2) that leads to peroxide intermediates and yields ClO(2)(-) and O(2) as products. This pathway is important at low levels of ClO(2).     

Luminescent Ag i-Cu i heterometallic hexa-, octa-, and hexadecanuclear alkynyl complexes

A series of Ag(I)-Cu(I) heteronuclear alkynyl complexes were prepared by reaction of polymeric (MCCC(6)H(4)R-4)(n)() (M = Cu(I) or Ag(I); R = H, CH(3), OCH(3), NO(2), COCH(3)) with [M'(2)(mu-Ph(2)PXPPh(2))(2)(MeCN)(2)](ClO(4))(2) (M' = Ag(I) or Cu(I); X = NH or CH(2)). Heterohexanuclear complexes [Ag(4)Cu(2)(mu-Ph(2)PNHPPh(2))(4)(CCC(6)H(4)R-4)(4)](ClO(4))(2) (R = H, 1; CH(3), 2) were afforded when X = NH, and heterooctanuclear complexes [Ag(6)Cu(2)(micro-Ph(2)PCH(2)PPh(2))(3)(CCC(6)H(4)R-4)(6)(MeCN)](ClO(4))(2) (R = H, 3; CH(3), 4; OCH(3), 5; NO(2), 6) were isolated when X = CH(2). Self-assembly reaction between (MCCC(6)H(4)COCH(3)-4)(n) and [M'(2)(mu-Ph(2)PCH(2)PPh(2))(2)(MeCN)(2)](ClO(4))(2), however, gave heterohexadecanuclear complex [Ag(6)Cu(2)(micro-Ph(2)PCH(2)PPh(2))(3)(CCC(6)H(4)COCH(3)-4)(6)](2)(ClO(4))(4) (7). The heterohexanuclear complexes 1 and 2 show a bicapped cubic skeleton (Ag(4)Cu(2)C(4)) consisting of four Ag(I) and two Cu(I) atoms and four acetylide C donors. The heterooctanuclear complexes 3-6 exhibit a waterwheel-like structure that can be regarded as two Ag(3)Cu(CCC(6)H(5))(3) components put together by three bridging Ph(2)PCH(2)PPh(2) ligands. The heterohexadecanuclear complex 7 can be viewed as a dimer of heterooctanuclear complex [Ag(6)Cu(2)(micro-Ph(2)PCH(2)PPh(2))(3)(CCC(6)H(4)COCH(3)-4)(6)](ClO(4))(2) through the silver and acetyl oxygen (Ag-O = 2.534 (4) A) linkage between two waterwheel-like Ag(6)Cu(2) units. All of the complexes show intense luminescence in the solid states and in fluid solutions. The microsecond scale of lifetimes in the solid state at 298 K reveals that the emission is phosphorescent in nature. The emissive state in compounds 1-5 is likely derived from a (3)LMCT (CCC(6)H(4)R-4 --> Ag(4)Cu(2) or Ag(6)Cu(2)) transition, mixed with a metal cluster-centered (d --> s) excited state. The lowest lying excited state in compounds 6 and 7 containing electron-deficient 4-nitrophenylacetylide and 4-acetylphenylacetylide, respectively, however, is likely dominated by an intraligand (3)[pi --> pi] character.     

Ab initio/density functional theory and multichannel RRKM study for the ClO + CH2O reaction

The potential energy surface for the CH(2)O + ClO reaction was calculated at the QCISD(T)/6-311G(2d,2p)//B3LYP/6-311G(d,p) level of theory. The rate constants for the lower barrier reaction channels producing HOCl + HCO, H atom, OCH(2)OCl, cis-HC(O)OCl and trans-HC(O)OCl have been calculated by TST and multichannel RRKM theory. Over the temperature range of 200-2000 K, the overall rate constants were k(200-2000K) = 1.19 x 10(-13)T(0.79) exp(-3000.00/T). At 250 K, the calculated overall rate constant was 5.80 x 10(-17) cm(3) molecule(-1) s(-1), which was in good agreement with the experimental upper limit data. The calculated results demonstrated that the formation of HOCl + HCO was the dominant reaction channel and was exothermic by 9.7 kcal/mol with a barrier of 5.0 kcal/mol. When it retrograded to the reactants CH(2)O + ClO, an energy barrier of 14.7 kcal/mol is required. Furthermore, when HOCl decomposed into H + ClO, the energy required was 93.3 kcal/mol. These results suggest that the decomposition in both the forward and backward directions for HOCl would be difficult in the ground electronic state.     

Direct potentiometric titration of chlorite in presence of chlorate, chlorine dioxide and chloride

A direct potentiometric titration of chlorite in the presence of chlorate, chlorine dioxide and chloride is described. Chlorite is determined in 0.01-0.0005 M sodium chlorite at pH 2.0-3.5 using hypochlorite solution. The course of the reaction is followed potentiometrically using saturated calomel and platinum electrodes; the end-point is indicated by a potential jump of about 230 mV. Under these conditions no reaction takes place with chlorate, chlorine dioxide or chloride. Previously, the determination of chlorite in such mixtures was only possible by difference from several oxidimetric titrations.     

First example of a 2:1 cocrystal of mixed Cu(I)/Cu(II) complexes and a novel ferromagnetic bis(mu-hydroxo)dicopper(II) complex with a bis(pyrazol-1-yl)methane bidentate ligand

A unique 2:1 cocrystal of mixed Cu(I)/Cu(II) complexes [Cu(I)(H2CPz2)(MeCN)2](ClO4) (1) and [Cu(II)(H2CPz2)2(ClO4)2] (4), a novel ferromagnetic ClO(4-)-bridged bis(mu-hydroxo)dicopper(II) complex, [Cu2(H2CPz2)2(OH)2(ClO4)](ClO4)(CH3CN)(0.5) (5), and a bischelated copper(I) complex, [Cu(H2CPz2)2](ClO4) (2), prepared from a one-pot reaction of [Cu(MeCN)4](ClO4) and H2CPz2, are described. The structures of these complexes have been determined by X-ray crystallographic methods. The Cu(I)-N(acetonitrile) bond distances in complex 1 are nonequivalent (1.907(8) and 2.034(9) A), leading to the dissociation of one MeCN to form a Y-shaped complex, [Cu(I)(H2CPz2)(MeCN)](ClO4) (3), which is oxidized readily in air to form complex 5 with a butterfly Cu2O2 core.     

Kinetics and mechanisms of the ozone/bromite and ozone/chlorite reactions

Ozone reactions with XO(2)(-) (X = Cl or Br) are studied by stopped-flow spectroscopy under pseudo-first-order conditions with excess XO(2)(-). The O(3)/XO(2)(-) reactions are first-order in [O(3)] and [XO(2)(-)], with rate constants k(1)(Cl) = 8.2(4) x 10(6) M(-1) s(-1) and k(1)(Br) = 8.9(3) x 10(4) M(-1) s(-1) at 25.0 degrees C and mu = 1.0 M. The proposed rate-determining step is an electron transfer from XO(2)(-) to O(3) to form XO(2) and O(3)(-). Subsequent rapid reactions of O(3)(-) with general acids produce O(2) and OH. The OH radical reacts rapidly with XO(2)(-) to form a second XO(2) and OH(-). In the O(3)/ClO(2)(-) reaction, ClO(2) and ClO(3)(-) are the final products due to competition between the OH/ClO(2)(-) reaction to form ClO(2) and the OH/ClO(2) reaction to form ClO(3)(-). Unlike ClO(2), BrO(2) is not a stable product due to its rapid disproportionation to form BrO(2)(-) and BrO(3)(-). However, kinetic spectra show that small but observable concentrations of BrO(2) form within the dead time of the stopped-flow instrument. Bromine dioxide is a transitory intermediate, and its observed rate of decay is equal to half the rate of the O(3)/BrO(2)(-) reaction. Ion chromatographic analysis shows that O(3) and BrO(2)(-) react in a 1/1 ratio to form BrO(3)(-) as the final product. Variation of k(1)(X) values with temperature gives Delta H(++)(Cl) = 29(2) kJ mol(-1), DeltaS(++)(Cl) = -14.6(7) J mol(-1) K(-1), Delta H(++)(Br) = 54.9(8) kJ mol(-1), and Delta S(++)(Br) = 34(3) J mol(-1) K(-1). The positive Delta S(++)(Br) value is attributed to the loss of coordinated H(2)O from BrO(2)(-) upon formation of an [O(3)BrO(2)(-)](++) activated complex.     

Substitution behaviour of novel dinuclear Pt(II) complexes with bio-relevant nucleophiles

The novel dinuclear Pt(II) complexes [{trans-Pt(NH(3))(2)Cl}(2)(μ-pyrazine)](ClO(4))(2) (Pt1), [{trans-Pt(NH(3))(2)Cl}(2)(μ-4,4'-bipyridyl)](ClO(4))(2)·DMF (Pt2), and [{trans-Pt(NH(3))(2)Cl}(2)(μ-1,2-bis(4-pyridyl)ethane)](ClO(4))(2) (Pt3), were synthesized. Acid-base titrations, and temperature and concentration dependent kinetic measurements of the reactions with biologically relevant ligands such as thiourea (Tu), glutathione (GSH) and guanosine-5'-monophosphate (5'-GMP) were studied at pH 2.5 and 7.2. The reactions were followed under pseudo-first-order conditions by stopped-flow and UV-vis spectrophotometry. (1)H NMR spectroscopy was used to follow the substitution of chloride in the complex [{trans-Pt(NH(3))(2)Cl}(2)(μ-4,4'-bipyridyl)](ClO(4))(2)·DMF by guanosine-5'-monophosphate (5'-GMP) under second-order conditions. The results indicate that the bridging ligand has an influence on the reactivity of the complexes towards nucleophiles. The order of reactivity of the investigated complexes is Pt1 > Pt2 > Pt3.     

Dinuclear zinc(II) complexes of tetraiminodiphenol macrocycles and their interactions with carboxylate anions and amino acids. Photoluminescence, equilibria, and structure

The reaction equilibria [H(4)L](2+) + Zn(OAc)(2) right harpoon over left harpoon [Zn(H(2)L)](2+) + 2HOAc (K(1)) and [Zn(H(2)L)](2+) + Zn(OAc)(2) right harpoon over left harpoon [Zn(2)L](2+) + 2HOAc (K(2)), involving zinc acetate and the perchlorate salts of the tetraiminodiphenol macrocycles [H(4)L(1)(-)(3)](ClO(4))(2), the lateral (CH(2))(n)() chains of which vary between n = 2 and n = 4, have been studied by spectrophotometric and spectrofluorimetric titrations in acetonitrile. The photoluminescence behavior of the complexes [Zn(2)L(1)](ClO(4))(2), [Zn(2)L(2)(H(2)O)(2)](ClO(4))(2), [Zn(2)L(2)(mu-O(2)CR)](ClO(4)) (R = CH(3), C(6)H(5), p-CH(3)C(6)H(4), p-OCH(3)C(6)H(4), p-ClC(6)H(4), p-NO(2)C(6)H(4)), and [Zn(2)L(3)(mu-OAc)](ClO(4)) have been investigated. The X-ray crystal structures of the complexes [Zn(2)L(2)(H(2)O)(2)](ClO(4))(2), [Zn(2)L(3)(mu-OAc)](ClO(4)), and [Zn(2)L(2)(mu-OBz)(OBz)(H(3)O)](ClO(4)) have been determined. The complex [Zn(2)L(2)(mu-OBz)(OBz)(H(3)O)](ClO(4)) in which the coordinated water molecule is present as the hydronium ion (H(3)O(+)) on deprotonation gives rise to the neutral dibenzoate-bridged compound [Zn(2)L(2)(mu-OBz)(2)].H(2)O. The equilibrium constants (K) for the reaction [Zn(2)L(2)(H(2)O)(2)](2+) + A(-) right harpoon over left harpoon [Zn(2)L(2)A](+) + 2H(2)O (K), where A(-) = acetate, benzoate, or the carboxylate moiety of the amino acids glycine, l-alanine, l-histidine, l-valine, and l-proline, have been determined spectrofluorimetrically in aqueous solution (pH 6-7) at room temperature. The binding constants (K) evaluated for these systems vary in the range (1-8) x 10(5).     

Catalytic oxidation of 3,5-Di-tert-butylcatechol by a series of mononuclear manganese complexes: synthesis, structure, and kinetic investigation

The manganese compounds [Mn(bpia)(OAc)(OCH(3))](PF(6)) (1), [Mn(bipa)(OAc)(OCH(3))](PF(6)) (2), [Mn(bpia)(Cl)(2)](ClO(4)) (3), [Mn(bipa)(Cl)(2)](ClO(4)) (4), [Mn(Hmimppa)(Cl)(2)] x CH(3)OH (5), and [Mn(mimppa)(TCC)] x 2CHCl(3) (6) (bpia = bis(picolyl)(N-methylimidazole-2-yl)amine; bipa = bis(N-methylimidazole-2-yl)(picolyl)amine; Hmimppa = ((1-methylimidazole-2-yl)methyl)((2-pyridyl)methyl)(2-hydroxyphenyl)amine; TCC = tetrachlorocatechol) were synthesized and characterized by various techniques such as X-ray crystallography, mass spectrometry, IR, EPR, and UV/vis spectroscopy, cyclic voltammetry, and elemental analysis. 1 and 2 crystallize in the triclinic space group Ponemacr; (No. 2), 4 and 6 crystallize in the monoclinic space group P2(1)/n (No. 14), and 5 crystallizes in the orthorhombic space group Pna2(1). Complexes 1-4 are structurally related to the proposed active site of the manganese-dependent extradiol-cleaving catechol dioxygenase exhibiting an N(4)O(2) donor set (1 and 2) or N(4)Cl(2) donor set (3 and 4). Cyclic voltammetric data show that the substitution of oxygen donor atoms with chloride causes a shift of redox potentials to more positive values. These compounds show high catalytic activity regarding the oxidation of 3,5-di-tert-butylcatechol to 3,5-di-tert-butylquinone exhibiting saturation kinetics at high substrate concentrations. The turnover numbers k(cat) = (86 +/- 7) h(-1) (1), k(cat) = (101 +/- 4) h(-1) (2), k(cat) = (230 +/- 4) h(-1) (3), and k(cat) = (130 +/- 4) h(-1) (4) were determined from the double reciprocal Lineweaver-Burk plot. Compounds 5 and 6 can be regarded as structural and electronic Mn analogues for substituted forms of Fe-containing intradiol-cleaving catechol dioxygenases. To our knowledge 5 is the first mononuclear Mn(II) compound featuring an N(3)OCl(2) donor set.     

Kinetics and mechanism of the oxidation of amaranth with hypochlorite

The reaction mechanism of the oxidation of Amaranth dye (2-hydroxy-1-(4-sulfonato-1-naphthylazo) naphthalene-3,6-disulfonate) with hypochlorite under varied pH conditions was elucidated by a kinetic approach. Under excess concentration of oxidant, the reaction followed pseudo-first-order kinetics with respect to Amaranth, and the oxidation was found to occur through two competitive reactions, initiated by hypochlorite and hypochlorous acid. The reaction order with respect to both OCl(-) ion and HOCl was unity. While the latter reaction was fast, the significance of the oxidation paths depended on the relative concentration of the two oxidizing species, which was dictated by the reaction pH. The role of the H(+) ion in the reaction was established. For the hypochlorite ion and hypochlorous acid facilitated reactions, the second-order rate coefficients were 1.9 and 23.2 M(-1) s(-1), respectively. The energy parameters were E(a) = 33.7 kJ mol(-1), ΔH(?) = 31.2 kJ mol(-1) and ΔS(?) = -190.6 J K(-1) mol(-1) for the OCl(-) ion-driven oxidation, and E(a) = 26.9 kJ mol(-1), ΔH(?) = 24.3 kJ mol(-1) and ΔS(?) = -222.8 J K(-1) mol(-1) for the reaction with HOCl-initiated oxidation. The major oxidation products for both the pathways were 3,4-dihydroxy naphthalene-2,7-disulfonic sodium salt (P(1)), dichloro-1,4-naphthoquione (P(2)) and naphtha(2,3)oxirene-2, 3-dione (P(3)). On the basis of the primary salt effect and other kinetic data, the rate law for the overall reaction and probable reaction mechanism was elucidated. The proposed mechanism was validated by simulations using Simkine-2.     

Conversion of phenyl-substituted cyclopentadienes to pyrylium cations

Phenyl-substituted cyclopentadienes are proved to form phenylated pyrylium cations in the presence of silver(I) perchlorate by insertion of an oxygen atom into the cyclopentadiene-ring. Three phenylated pyrylium compounds, [(Ph(5)C(5)O(+))(ClO(4)(-))](2)(CH(2)Cl(2)) (1), Ag(ClO(4))(H(2)O)(Ph(4)HC(5)O(+)) (ClO(4)(-)) (2), and (Ph(3)H(2)C(5)O(+))(ClO(4)(-)) (3) have been synthesized and characterized. A possible reaction pathway and formation mechanism of the pyrylium cation are proposed and discussed.     

Reactivity study of a hydroperoxodicopper(II) complex: hydroxylation, dehydrogenation, and ligand cross-link reactions

Employing a binucleating phenol-containing ligand PD'OH, a mu-phenoxo-mu-hydroperoxo dicopper(II) complex [Cu(II)2(PD'O-)(-OOH)(RCN)2](ClO4)2 (1, R = CH3, CH3CH2 or C6H5CH2; lambda(max) = 407 nm; nu(O-O) = 870 cm(-1); J. Am. Chem. Soc. 2005, 127, 15360) is generated by reacting a precursor dicopper(I) complex [Cu(I)2(PD'OH)(CH3CN)2](ClO4)2 (2) with O2 in nitrile solvents at -80 degrees C. Species 1 is unable to oxidize externally added substrates, for instance, PPh3, 2,4-tert-butylphenol, or 9,10-dihydroanthracene. However, upon thermal decay, it hydroxylates copper-bound organocyanides (e.g., benzylcyanide), leading to the corresponding aldehyde while releasing cyanide. This chemistry mimics that known for the copper enzyme dopamine-beta-monooxygenase. The thermal decay of 1 also leads to a product [Cu(II)3(L")2(Cl-)2](PF6)2 (6); its X-ray structure reveals that L" is a Schiff base-containing ligand which apparently derives from both oxidative N-dealkylation and then oxidative dehydrogenation of PD'OH; the chloride presumably derives from the CH2Cl2 solvent. With an excess of PPh3 added to 1, a binuclear Cu(I) complex [Cu(I)2(L')(PPh3)2](ClO4)2 (5) with a cross-linked PD'OH ligand L' has also been identified and crystallographically and chemically characterized. The newly formed C-O bond and an apparent k(H)/k(D) = 2.9 +/- 0.2 isotope effect in the benzylcyanide oxidation reaction suggest a common ligand-based radical forms during compound 1 thermal decay reactions. A di-mu-hydroxide-bridged tetranuclear copper(II) cluster compound [{Cu(II)2(PD'O-)(OH-)}2](ClO4)4 (8) has also been isolated following warming of 1. Its formation is consistent with the generation of [Cu(II)2(PD'O-)(OH-)]2+, with dimerization a reflection of the large Cu...Cu distance and thus the preference for not having a second bridging ligand atom (in addition to the phenolate O) for dicopper(II) ligation within the PD'O- ligand framework.     

Mononuclear and dinuclear copper(I) complexes of bis(3,5-dimethylpyrazol-1-yl)methane: synthesis, structure, and reactivity

The synthesis and structures of a mononuclear copper(I) carbonyl complex [Cu(OClO3)(CO)(H2CPz2')] (3) and a dinuclear copper(I) carbonyl complex [{Cu(CO)(H2CPz2')}2(mu-pyrazine)](ClO4)2 (4), where H2CPz2' = bis(3,5-dimethylpyrazol-1-yl)methane, are described. These two compounds were generated by the carbonylation of the corresponding copper(I)-acetonitrile complexes, [Cu(H2CPz2')(MeCN)](ClO4) (1) and [{Cu(H2CPz2')(MeCN)}2(mu-pyrazine)](ClO4)2 (2). Alternatively, treatment of mononuclear 1 and 3, respectively, with pyrazine in a molar ratio of 2:1 produces the pyrazine-bridged dinuclear Cu(I) complexes 2 and 4. Each of the complexes 1-4 can react with PPh3 to generate a common three-coordinated copper(I) complex [Cu(PPh3)(H2CPz2')](ClO4) (5). The structures of complexes 1-5 were all confirmed by X-ray crystallography. Comparison of the Cu(I)-C(CO) bond distances and the CO stretching frequencies of 3 and 4 indicates the back-donating properties of d pi(Cu)-pi*(pyrazine) bonds in 4, and accordingly, stabilizes the mixed-valence species generated from 2. Complex 3, stabilized by the strong interaction between copper(I) ion and perchlorate counteranion (Cu(I)-O(ClO4) = 2.240(3) A), is a potential precursor for polynuclear copper(I) carbonyl complexes.