Products of the gas-phase reactions of OH radicals with (C2H5O)2P(S)CH3 and (C2H5O)3PS

Products of the gas-phase reactions of OH radicals with O,O-diethyl methylphosphonothioate [(C2H5O)2P(S)CH3, DEMPT] and O,O,O-triethyl phosphorothioate [(C2H5O)3PS, TEPT] have been investigated at room temperature and atmospheric pressure of air using in situ atmospheric pressure ionization mass spectrometry (API-MS) and, for the TEPT reaction, gas chromatography and in situ Fourier transform infrared (FT-IR) spectroscopy. Combined with products quantified previously by gas chromatography, the products observed were: from the DEMPT reaction, (C2H5O)2P(O)CH3 (21+/-4% yield) and C2H5OP(S)(CH3)OH or C2H5OP(O)(CH3)SH (presumed to be C2H5OP(O)(CH3)SH by analogy with the TEPT reaction); and from the TEPT reaction, (C2H5O)3PO (54-62% yield), SO2 (67+/-10% yield), CH3CHO (22-40% yield) and, tentatively, (C2H5O)2P(O)SH. The FT-IR analyses showed that the formation yields of HCHO, CO, CO2, peroxyacetyl nitrate [CH3C(O)OONO2], organic nitrates, and acetates from the TEPT reaction were <5%, 3+/-1%, <7%, <2%, 5+/-3%, and 3+/-2%, respectively. Possible reaction mechanisms are discussed.     

Atmospheric chemistry of diethyl methylphosphonate, diethyl ethylphosphonate, and triethyl phosphate

Rate constants for the reactions of OH radicals and NO(3) radicals with diethyl methylphosphonate [DEMP, (C(2)H(5)O)(2)P(O)CH(3)], diethyl ethylphosphonate [DEEP, (C(2)H(5)O)(2)P(O)C(2)H(5)], and triethyl phosphate [TEP, (C(2)H(5)O)(3)PO] have been measured at 296 +/- 2 K and atmospheric pressure of air using relative rate methods. The rate constants obtained for the OH radical reactions (in units of 10(-11) cm(3) molecule(-1) s(-1)) were as follows: DEMP, 5.78 +/- 0.24; DEEP, 6.45 +/- 0.27; and TEP, 5.44 +/- 0.20. The rate constants obtained for the NO(3) radical reactions (in units of 10(-16) cm(3) molecule(-1) s(-1)) were the following: DEMP, 3.7 +/- 1.1; DEEP, 3.4 +/- 1.4; and TEP, 2.4 +/- 1.4. For the reactions of O(3) with DEMP, DEEP, and TEP, an upper limit to the rate constant of <6 x 10(-20) cm(3) molecule(-1) s(-1) was determined for each compound. Products of the reactions of OH radicals with DEMP, DEEP, and TEP were investigated using in situ atmospheric pressure ionization mass spectrometry (API-MS) and, for the TEP reaction, gas chromatography with flame ionization detection (GC-FID) and in situ Fourier transform infrared (FT-IR) spectroscopy. The API-MS analyses show that the reactions are analogous, with formation of one major product from each reaction: C(2)H(5)OP(O)(OH)CH(3) from DEMP, C(2)H(5)OP(O)(OH)C(2)H(5) from DEEP, and (C(2)H(5)O)(2)P(O)OH from TEP. The FT-IR and GC-FID analyses showed that the major products (and their molar yields) from the TEP reaction are (C(2)H(5)O)(2)P(O)OH (65-82%, initial), CO(2) (80 +/- 10%), and HCHO (55 +/- 5%), together with lesser yields of CH(3)CHO (11 +/- 2%), CO (11 +/- 3%), CH(3)C(O)OONO(2) (8%), organic nitrates (7%), and acetates (4%). The probable reaction mechanisms are discussed.     

A temperature-dependent relative-rate study of the OH initiated oxidation of n-butane: the kinetics of the reactions of the 1- and 2-butoxy radicals

The kinetics of the reactions of 1-and 2-butoxy radicals have been studied using a slow-flow photochemical reactor with GC-FID detection of reactants and products. Branching ratios between decomposition, CH3CH(O*)CH2CH3 --> CH3CHO + C2H5, reaction (7), and reaction with oxygen, CH3CH(O*)CH2CH3+ O2 --> CH3C(O)C2H5+ HO2, reaction (6), for the 2-butoxy radical and between isomerization, CH3CH2CH2CH2O* --> CH2CH2CH2CH2OH, reaction (9), and reaction with oxygen, CH3CH2CH2CH2O* + O2 --> C3H7CHO + HO2, reaction (8), for the 1-butoxy radical were measured as a function of oxygen concentration at atmospheric pressure over the temperature range 250-318 K. Evidence for the formation of a small fraction of chemically activated alkoxy radicals generated from the photolysis of alkyl nitrite precursors and from the exothermic reaction of 2-butyl peroxy radicals with NO was observed. The temperature dependence of the rate constant ratios for a thermalized system is given by k7/k6= 5.4 x 10(26) exp[(-47.4 +/- 2.8 kJ mol(-1))/RT] molecule cm(-3) and k9/k8= 1.98 x 10(23) exp[(-22.6 +/- 3.9 kJ mol(-1))/RT] molecule cm(-3). The results agree well with the available experimental literature data at ambient temperature but the temperature dependence of the rate constant ratios is weaker than in current recommendations.     

Formation and decomposition of chemically activated cyclopentoxy radicals from the c-C5H9 + O reaction

The formation and the decomposition of chemically activated cyclopentoxy radicals from the c-C5H9 + O reaction have been studied in the gas phase at room temperature. Two different experimental arrangements have been used. Arrangement A consisted of a laser-flash photolysis set up combined with quantitative Fourier transform infrared spectroscopy and allowed the determination of the stable products at 4 mbar. The c-C5H9 radicals were produced via the reaction c-C5H10 + Cl with chlorine atoms from the photolysis of CFCl3; the O atoms were generated by photolysis of SO2. Arrangement B, a conventional discharge flow-reactor with molecular beam sampling, was used to determine the rate coefficient. Here, the hydrocarbon radicals (c-C5H9, C2H5, CH2OCH3) were produced via the reaction of atomic fluorine with c-C5H10, C2H6, and CH3OCH3, respectively, and detected by mass spectrometry after laser photoionization. For the c-C5H9 + O reaction, the relative contributions of intermediate formation (c-C5H9O) and direct abstraction (c-C5H8 + OH) were found to be 68 +/- 5 and 32 +/- 4%, respectively. The decomposition products of the chemically activated intermediate could be identified, and the following relative branching fractions were obtained: c-C5H8O + H (31 +/- 2%), CH2CH(CH2)2CHO + H (40 +/- 5%), 2 C2H4 + H + CO (17 +/- 5%), and C3H4O + C2H4 + H (12 +/- 5%). Additionally, the product formation of the c-C5H8 + O reaction was studied, and the following relative yields were obtained (mol %): C2H4, 24%; C3H4O, 18%; c-C5H8O, 30%; c-C5H8O, 23%; 4-pentenal, 5%. The rate coefficient of the c-C5H9 + O reaction was determined relative to the reactions C2H5 + O and CH3OCH2 + O leading to k = (1.73 +/- 0.05) x 10(14) cm3 mol(-1) s(-1). The experimental branching fractions are analyzed in terms of statistical rate theory with molecular and transition-state data from quantum chemical calculations, and high-pressure limiting Arrhenius parameters for the unimolecular decomposition reactions of C5H9O species are derived.     

Structural and kinetic studies on uranyl(V) carbonate complex using 13C NMR spectroscopy

We have measured 13C NMR spectra of uranyl(V) carbonate complex in D2O solution containing 1.003 M Na2(13)CO3 at various temperatures. Two singlet signals corresponding to free and coordinated CO3(2-) were observed at 169.13 and 106.70 ppm, respectively. From the peak area ratio, the structure of the uranyl(V) carbonate complex was determined as [U(V)O2(CO3)3]5-. Furthermore, kinetic analyses of the exchange reaction of free and coordinated CO3(2-) in [U(V)O2(CO3)3]5- were carried out using 13C NMR line-broadening. As a result, the first-order rate constant at 298 K and the activation parameters for CO3(2-) exchange reaction in [U(V)O2(CO3)3]5- were evaluated as 1.13 x 10(3) s(-1) and deltaH(double dagger) = 62.0 +/- 0.7 kJ x mol(-1), deltaS(double dagger) = 22 +/- 3 J x mol(-1) x K(-1), respectively. We suggest that the exchange follows a dissociative mechanism as in the corresponding [U(VI)O2(CO3)3]4- complex.     

Superoxide dismutase versus ferricytochrome C: determining rate constants for the spin trapping of superoxide by cyclic nitrones

Given that spin trapping/electron paramagnetic resonance (EPR) spectroscopy has become the primary technique to identify important biologically generated free radicals, such as superoxide (O(2)(*-)), in vitro and in vivo models, evaluation of the efficiency of specific spin traps to identify this free radical is paramount. Recently, a family of ester-containing nitrones has been prepared, which appears to have distinct advantages for spin trapping O(2)(*-) compared to the well-studied spin traps 5,5-dimethyl-1-pyrroline N-oxide 1 and 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline N-oxide 2. An important determinant in the selection of a spin trap is the rate constant (k(app)) for its reaction with O(2)(*-), and several different methods have been employed in estimating this k(app). In this paper, the two most frequently used scavengers of O(2)(*-), ferricytochrome c and Cu/Zn-SOD, were evaluated as competitive inhibitors for spin trapping this free radical. Data presented herein demonstrate that SOD is the preferred compound when determining the k(app) for the reaction of O(2)(*-) with spin traps. Using this model, the k(app) for the reaction of nitrone 1, 5-tert-butoxycarbonyl-5-methyl-1-pyrroline N-oxide 3, and 5-methoxycarbonyl-5-methyl-1-pyrroline N-oxide 4 with O(2)(*)(-) was estimated to be 24.6 +/- 3.1, 73.0 +/- 12, and 89.4 +/- 1.0 M(-1) s(-1) at pH 7.0, respectively. Several other comparative studies between known spin traps were also undertaken.     

Mixed transition metal-lanthanide complexes at high oxidation states: heteronuclear CeIVMnIV clusters

The syntheses of the first mixed-metal CeIVMnIV complexes are reported. [CeMn2O3(O2CMe)(NO3)4(H2O)2(bpy)2](NO3) (1; bpy=2,2'-bipyridine) was obtained from the reaction of Mn(NO3)2.xH2O and bpy with (NH4)2Ce(NO3)6 in a 1:1:2 molar ratio in 25% aqueous acetic acid. The complexes [CeMn6O9(O2CR)9(X)(H2O)2]y+ (R=Me, X=NO3-, y=0 (2); R=Me, X=MeOH, y=+1 (3); R=Et, X=NO3-, y=0 (7)) were obtained from reactions involving a [Mn(O2CR)2].4H2O/CeIV ratio of approximately 1:1.5 in concentrated aqueous carboxylic acid. A related reaction in less-concentrated aqueous acetic acid and in the presence of L (where L=2-hydroxy-6-methylpyridine (mhpH), 2-pyrrolidinone (pyroH), or pyridine (py)) gave [Ce3Mn2O6(O2CMe)6(NO3)2(L)a(H2O)b] (L=mhpH, a=4, b=0 (4); L=pyroH, a=2, b=3 (5)) and {{(pyH)3[Ce3Mn2O6(O2CMe)7.5(NO3)3].(HO2CMe)0.5.(H2O)2}2(NO3)}n (6), respectively. Solid-state magnetic susceptibility (chiM) data for compounds 1, 4, and 5 were fit to the theoretical chiMT versus T expression for a MnIV2 complex derived using the isotropic Heisenberg spin Hamiltonian (H=-2J?1? 2) and the Van Vleck equation. The obtained fit parameters were (in the format J, g) 1, -45.7(3) cm(-1), 1.95(5); 4, -0.40(10) cm(-1), 2.0(1); and 5, -0.34(10) cm(-1), 2.0(1), where J is the exchange interaction constant between the two MnIV ions. The data for compound 3 were fit by a matrix diagonalization method that gave J1=-5.8 cm(-1), J2=-0.63 cm(-1), J3 approximately 0, and g=2.0(1), where J1 and J2 are the exchange interactions for the [MnIV2O2(Omicron2CMe)] and [MnIV2O(Omicron2CMe)2] units, respectively, and J3 for a uniform next-nearest-neighbor interaction. Theoretical estimates of the exchange constants in compounds 1 and 3 obtained with the ZILSH method were in excellent and good agreement, respectively, with the values obtained from fits of the magnetization data. The difference for 3 is assigned to the presence of the Ce4+ ion, and atomic bond indices obtained from the ZILSH calculations were used to rationalize the values of the various exchange constants based on metal-ligand bond strengths.     

Kinetic analysis of one-step solid-state reaction for Li4Ti5O12/C

The kinetics of one-step solid-state reaction of Li(4)Ti(5)O(12)/C in a dynamic nitrogen atmosphere was first studied by means of thermogravimetric-differential thermal analysis technique at five different heating rates. According to the double equal-double steps method, the Li(4)Ti(5)O(12)/C solid-state reaction mechanism could be properly described as the Jander equation, which was a three-dimensional diffusion with spherical symmetry, and the reaction mechanism functions were listed as follows: f(α) = (3)/(2)(1 - α)(2/3)[1 - (1 - α)(1/3)](-1), G(α) = [1 - (1 - α)(1/3)](2). In FWO method, average activation energy, frequency factor, and reaction order were 284.40 kJ mol(-1), 2.51 × 10(18) min(-1), and 1.01, respectively. However, the corresponding values in FRL method were 271.70 kJ mol(-1), 1.00 × 10(17) min(-1), and 0.96, respectively. Moreover, the values of enthalpy of activation, Gibbs free energy of activation, and entropy of activation at the peak temperature were 272.06 kJ mol(-1), 240.16 kJ mol(-1), and 44.24 J mol(-1) K(-1), respectively.     

Generation and reactivity of rhodium(IV) complexes in aqueous solutions

At pH = 1 and 25 degrees C, the Fenton-like reactions of Fe(aq)(2+) with hydroperoxorhodium complexes LRh(III)OOH(2+) (L = (H(2)O)(NH(3))(4), k = 30 M(-1) s(-1), and L = L(2) = (H(2)O)(meso-Me(6)-[14]aneN(4)), k = 31 M(-1) s(-1)) generate short-lived, reactive intermediates, believed to be the rhodium(IV) species LRh(IV)O(2+). In the rapid follow-up steps, these transients oxidize Fe(aq)(2+), and the overall reaction has the standard 2:1 [Fe(aq)(2+)]/[LRhOOH(2+)] stoichiometry. Added substrates, such as alcohols, aldehydes, and (NH(3))(4)(H(2)O)RhH(2+), compete with Fe(aq)(2+) for LRh(IV)O(2+), causing the stoichiometry to change to <2:1. Such competition data were used to determine relative reactivities of (NH(3))(4)RhO(2+) toward CH(3)OH (1), CD(3)OH (0.2), C(2)H(5)OH (2.7), 2-C(3)H(7)OH (3.4), 2-C(3)D(7)OH (1.0), CH(2)O (12.5), C(2)H(5)CHO (45), and (NH(3))(4)RhH(2+) (125). The kinetics and products suggest hydrogen atom abstraction for (NH(3))(4)RhO(2+)/alcohol reactions. A short chain reaction observed with C(2)H(5)CHO is consistent with both hydrogen atom and hydride transfer. The rate constant for the reaction between Tl(aq)(III) and L(2)Rh(2+) is 2.25 x 10(5) M(-1) s(-1).     

Unusual structural types in polynuclear iron chemistry from the use of N,N,N',N'-tetrakis(2-hydroxyethyl)ethylenediamine (edteH4): Fe5, Fe6, and Fe12 clusters

The syntheses, crystal structures, and magnetochemical characterization of five new iron clusters [Fe5O2(O2CPh)7(edte)(H2O)] (1), [Fe6O2(O2CBut)8(edteH)2] (2), [Fe12O4(OH)2(O2CMe)6(edte)4(H2O)2](ClO4)4 (3), [Fe12O4(OH)8(edte)4(H2O)2](ClO4)4 (4), and [Fe12O4(OH)8(edte)4(H2O)2](NO3)4 (5) (edteH4= N,N,N',N'-tetrakis(2-hydroxyethyl) ethylenediamine) are reported. The reaction of edteH4 with [Fe3O(O2CPh)6(H2O)3](NO3) and [Fe3O(O2CBut)6(H2O)3](OH) gave 1 and 2, respectively. Complex 3 was obtained from the reaction of edteH4 and NaO2CMe with Fe(ClO4)3, whereas 4 and 5 were obtained from the reaction of edteH4 with Fe(ClO4)3 and Fe(NO3)3, respectively. The core of 1 consists of a [Fe4(mu3-O)2]8+ butterfly unit to which is attached a fifth Fe atom by four bridging O atoms. The core of 2 consists of two triangular [Fe3(mu3-O)]7+ units linked together by six bridging O atoms. Finally, the cores of 3-5 consist of an [Fe12(mu4-O)4(mu-OH)2]26+ unit. Variable-temperature (T) and -field (H) solid-state direct and alternating current magnetization (M) studies were carried out on complexes 1-3 in the 1.8-300 K range. Analysis of the obtained data revealed that 1, 2, and 3-5 possess an S = 5/2, 5, and 0 ground-state spin, respectively. The fitting of the obtained M/N(muB) vs H/T data was carried out by matrix diagonalization, and this gave values for the axial zero-field splitting (ZFS) parameter D of -0.50 cm-1 for 1 and -0.28 cm-1 for 2.     

Novel 3D, 2D, and 0D first-row coordination compounds with 4,4'-bipyridine-N,N'-dioxide incorporating sulfur-containing anions

The reaction of M(S2O6) (M = Cu(II), Ni(II), and Co(II)) with 4,4'-bipyridine-N,N'-dioxide (bpdo) results in the formation of novel 3D, 2D, and mononuclear complexes. Complex 1, {[Cu(H2O)(bpdo)2](S2O6)(H2O)}n, is a 2-D wavelike polymer with the Cu(II) ion located on a 2-fold axis and having a distorted square-pyramidal coordination sphere. With Co(II) and Ni(II), 3-D complexes, {[M(bpdo)3](S2O6)(C2H5OH)7}n [M = Co(II) (2), Ni(II) (3)], were obtained. The metal atoms are situated on centers of symmetry and have octahedral environments coordinated to six bpdo molecules. The same reaction in aqueous solution with a metal/ligand ratio of 1:1 results in the formation of mononuclear complexes, {[M(bpdo)(H2O)5](SO4)(H2O)2} [M = Co(II) (4), Ni(II) (5)], accompanied by the decomposition of the dithionate anions S2O6(2-) to sulfate anions SO4(2-).     

Experimental and theoretical study of the reactions between small neutral iron oxide clusters and carbon monoxide

Reactions of small neutral iron oxide clusters (FeO(1-3) and Fe(2)O(4,5)) with carbon monoxide (CO) are investigated by experiments and first-principle calculations. The iron oxide clusters are generated by reaction of laser-ablation-generated iron plasma with O(2) in a supersonic expansion and are reacted with carbon monoxide in a fast flow reactor. Detection of the neutral clusters is through ionization with vacuum UV laser (118 nm) radiation and time-of-flight mass spectrometry. The FeO(2) and FeO(3) neutral clusters are reactive toward CO, whereas Fe(2)O(4), Fe(2)O(5), and possibly FeO are not reactive. A higher reactivity for FeO(2) [sigma(FeO(2) + CO) > 3 x 10(-17) cm(2)] than for FeO(3) [sigma(FeO(3) + CO) approximately 1 x 10(-17) cm(2)] is observed. Density functional theory (DFT) calculations are carried out to interpret the experimental observations and to generate the reaction mechanisms. The reaction pathways with negative or very small overall barriers are identified for CO oxidation by FeO(2) and FeO(3). The lower reactivity of FeO(3) with respect to FeO(2) may be related to a spin inversion process present in the reaction of FeO(3) with CO. Significant reaction barriers are calculated for the reactions of FeO and Fe(2)O(4-5) with CO. The DFT results are in good agreement with experimental observations. Molecular-level reaction mechanisms for CO oxidation by O(2), facilitated by condensed phase iron oxides as catalysts, are suggested.     

Polyoxomolybdodiphosphonates: examples incorporating ethylidenepyridines

We have synthesized and structurally characterized three pyridylethylidene-functionalized diphosphonate-containing polyoxomolybdates, [{Mo(VI)O(3)}(2){Mo(V)(2)O(4)}{HO(3)PC(O)(CH(2)-3-C(5)NH(4))PO(3)}(2)](6-) (1), [{Mo(VI)(2)O(6)}(2){Mo(V)(2)O(4)}{O(3)PC(O)(CH(2)-3-C(5)NH(4))PO(3)}(2)](8-) (2), and [{Mo(V)(2)O(4)(H(2)O)}(4){O(3)PC(O)(CH(2)-3-C(5)NH(4))PO(3)}(4)](12-) (3). Polyanions 1-3 were prepared in a one-pot reaction of the dinuclear, dicationic {Mo(V)(2)O(4)(H(2)O)(6)}(2+) with 1-hydroxo-2-(3-pyridyl)ethylidenediphosphonate (Risedronic acid) in aqueous solution. Polyanions 1 and 2 are mixed-valent Mo(VI/V) species with open tetranuclear and hexanuclear structures, respectively, containing two diphosphonate groups. Polyanion 3 is a cyclic octanuclear structure based on four {Mo(V)(2)O(4)(H(2)O)} units and four diphosphonates. Polyanions 1 and 2 crystallized as guanidinium salts [C(NH(2))(3)](5)H[{Mo(VI)O(3)}(2){Mo(V)(2)O(4)}{HO(3)PC(O)(CH(2)-3-C(5)NH(4))PO(3)}(2)]·13H(2)O (1a) and [C(NH(2))(3)](6)H(2)[{Mo(VI)(2)O(6)}(2){Mo(V)(2)O(4)}{O(3)PC(O)(CH(2)-3-C(5)NH(4))PO(3)}(2)]·10H(2)O (2a), whereas polyanion 3 crystallized as a mixed sodium-guanidinium salt, Na(8)[C(NH(2))(3)](4)[{Mo(V)(2)O(4)(H(2)O)}(4){O(3)PC(O)(CH(2)-3-C(5)NH(4))PO(3)}(4)]·8H(2)O (3a). The compounds were characterized in the solid state by single-crystal X-ray diffraction, IR spectroscopy, and thermogravimetric and elemental analyses. The formation of polyanions 1 and 3 is very sensitive to the pH value of the reaction solution, with exclusive formation of 1 above pH 7.4 and 3 below pH 6.6. Detailed solution studies by multinuclear NMR spectrometry were performed to study the equilibrium between these two compounds. Polyanion 2 was insoluble in all common solvents. Detailed computational studies on the solution phases of 1 and 3 indicated the stability of these polyanions in solution, in complete agreement with the experimental findings.     

Fenton chemistry of 1,3-dimethyluracil

Hydroxyl radicals were generated in the Fenton reaction at pH 4 (Fe(2+) + H(2)O(2) --> Fe(3+) + .OH + OH-, k approximately equal to 60 L mol(-1) s(-1)) and by pulse radiolysis (for the determination of kinetic data). They react rapidly with 1,3-dimethyluracil, 1,3-DMU (k = 6 x 10(9) L mol(-1) s(-1)). With H(2)O(2) in excess and in the absence of O(2), 1,3-DMU consumption is 3.3 mol per mol Fe(2+). 1,3-DMUglycol is the major product (2.95 mol per mol Fe(2+)). Dimers, prominent products of .OH-induced reactions in the absence of Fe(2+)/Fe(3+) (Al-Sheikhly, M.; von Sonntag, C. Z. Naturforsch. 1983, 31b, 1622) are not formed. Addition of .OH to the C(5)-C(6) double bond of 1,3-DMU yields reducing C(6)-yl 1 and oxidizing C(5)-yl radicals 2 in a 4:1 ratio. The yield of reducing radicals was determined with tetranitromethane by following the buildup of nitroform anion. Reaction of 1 with Fe(3+) that builds up during the reaction or with H(2)O(2) gives rise to a short-chain reaction that is terminated by the reaction of Fe(2+) with 2, which re-forms 1,3-DMU. In the presence of O(2), 1.1 mol of 1,3-DMU and 0.6 mol of O(2) are consumed per mol Fe(2+) while 0.16 mol of 1,3-DMU-glycol and 0.17 mol of organic hydroperoxides (besides further unidentified products) are formed. In the presence of O(2), 1 and 2 are rapidly converted into the corresponding peroxyl radicals (k = 9.1 x 10(8) L mol(-1) s(-1)). Their bimolecular decay (2k = 1.1 x 10(9) L mol(-1) s(-1)) yields approximately 22% HO(2)./O(2).(-) in the course of fragmentation reactions involving the C(5)-C(6) bond. Reduction of Fe(3+) by O(2).(-) leads to an increase in .OH production that is partially offset by a consumption of Fe(2+) in its reaction with the peroxyl radicals (formation of organic hydroperoxides, k approximately 3 x 10(5) L mol(-1) s(-1); value derived by computer simulation).     

Removal of the potent greenhouse gas NF3 by reactions with the atmospheric oxidants O(1D), OH and O3

Nitrogen trifluoride, NF(3), a trace gas of purely anthropogenic origin with a large global warming potential is accumulating in the Earth's atmosphere. Large uncertainties are however associated with its atmospheric removal rate. In this work, experimental and theoretical kinetic tools were used to study the reactions of NF(3) with three of the principal gas-phase atmospheric oxidants: O((1)D), OH and O(3). For reaction (R2) with O((1)D), rate coefficients of k(2)(212-356 K) = (2.0 ± 0.3) × 10(-11) cm(3) molecule(-1) s(-1) were obtained in direct competitive kinetics experiments, and experimental and theoretical evidence was obtained for F-atom product formation. These results indicate that whilst photolysis in the stratosphere remains the principal fate of NF(3), reaction with O((1)D) is significant and was previously underestimated in atmospheric lifetime calculations. Experimental evidence of F-atom production from 248 nm photolysis of NF(3) was also obtained, indicating that quantum yields for NF(3) destruction remain significant throughout the UV. No evidence was found for reaction (R3) of NF(3) with OH indicating that this process makes little or no contribution to NF(3) removal from the atmosphere. An upper-limit of k(3)(298 K) < 4 × 10(-16) cm(3) molecule(-1) s(-1) was obtained experimentally; theoretical analysis suggests that the true rate coefficient is more than ten orders of magnitude smaller. An upper-limit of k(4)(296 K) < 3 × 10(-25) cm(3) molecule(-1) s(-1) was obtained in experiments to investigate O(3) + NF(3) (R4). Altogether these results underpin calculations of a long (several hundred year) lifetime for NF(3). In the course of this work rate coefficients (in units of 10(-11) cm(3) molecule(-1) s(-1)) for removal of O((1)D) by n-C(5)H(12), k(6) = (50 ± 5) and by N(2), k(7) = (3.1 ± 0.2) were obtained. Uncertainties quoted throughout are 2σ precision only.     

A new N,N,O chelate for transition metal chemistry: Fe5 and Fe6 clusters from the use of 6-hydroxymethyl-2,2'-bipyridine (hmbpH)

The initial use of the anion of 6-hydroxymethyl-2,2'-bipyridine (hmbpH) as a chelate in coordination chemistry is described. The syntheses, crystal structures, and magnetochemical characterization are reported of four new iron(III) clusters [Fe5O2(OH)(O2CMe)5(hmbp)3](ClO4)2 (1) and [Fe6O2(OH)2(O2CR)6(hmbp)4](NO3)2 (R=Ph (2), Me (3), But (4); hmbpH=6-hydroxymethyl-2,2'-bipyridine). The reaction of Fe(ClO4)3, hmbpH, and sodium acetate in a 1:1: approximately 4 ratio in EtOH gave 1, and the reaction between [Fe3O(O2CR)6(H2O)3](NO3) (R=Ph, Me, But) and hmbpH in a 1:1 ratio in MeCN gave 2-4, respectively. The core of 1 consists of a [Fe4(mu3-O)2]8+ butterfly unit to which is attached a fifth Fe atom by bridging O atoms. The core of 2-4 also consists of a [Fe4(mu3-O)2]8+ butterfly unit to which are attached an Fe atom on either side by bridging O atoms. Variable-temperature (T) and -field (H) solid-state DC and AC magnetization (M) studies were carried out on complexes 1-4 in the 5.0-300 K range. Fitting of the data revealed that 1 has an S=5/2 ground state spin whereas 2-4 possess an S=5 ground state. Fitting of the M/NmicroB vs H/T data by matrix diagonalization and including only axial zero-field splitting (ZFS) gave values of the axial ZFS parameter |D| of 0.75, 0.36, 0.46, and 0.36 cm(-1) for 1-4, respectively.     

Synthesis and characterization of a family of penta- and tetra-manganese(III) complexes derived from an assembly system containing tert-butylphosphonic acid

A family of manganese complexes, [Mn 5O 3( t-BuPO 3) 2(MeCOO) 5(H 2O)(phen) 2] ( 1), [Mn 5O 3( t-BuPO 3) 2(PhCOO) 5(phen) 2] ( 2), [Mn 4O 2( t-BuPO 3) 2(RCOO) 4(bpy) 2] (R = Me, ( 3); R = Ph, ( 4)), NBu (n) 4[Mn 4O 2(EtCOO) 3(MeCOO) 4(pic) 2] ( 5), NR' 4[Mn 4O 2( i-PrCOO) 7(pic) 2] (R' = Bu (n) , ( 6); R' = Et, ( 7)), were synthesized and characterized. The seven manganese clusters were all prepared from a reaction system containing tert-butylphosphonic acid, Mn(O 2CR) 2 (R = Me, Ph) and NR' 4MnO 4 (R' = Bu (n) , Et) with similar procedures except for using different N-containing ligands (1,10-phenanthroline (phen), 2,2'-bipyridine (bpy) and picolinic acid (picH)) as coligands. The structures of these complexes vary with the N-containing donors. Both the cores of complexes 1 and 2 feature three mu 3-O and two capping t-BuPO 3 (2-) groups bridging five Mn (III) atoms to form a basket-like cage structure. Complexes 3 and 4 both have one [Mn 4(mu 3-O) 2] (8+) core with four coplanar Mn (III) atoms disposed in an extended "butterfly-like" arrangement and two capping mu 3- t-BuPO 3 (2-) binding to three manganese centers above and below the Mn 4 plane. Complexes 5, 6, and 7 all possess one [Mn 4(mu 3-O) 2] (8+) core just as complexes 3 and 4, but they display a folded "butterfly-like" conformation with the four Mn (III) atoms nonplanar. Thus, the seven compounds are classified into three types, and three representative compounds 1.2H 2O.MeOH.MeCN , 3.6H 2O.2MeCOOH , and 5.0.5H 2O have been characterized by IR spectroscopy, ESI-MS spectroscopy, magnetic measurements and in situ UV-vis-NIR spectroelectrochemical analysis. Magnetic susceptibility measurements reveal the existence of both ferromagnetic and antiferromagnetic interactions between the adjacent Mn (III) ions in compound 1.2H 2O.MeOH.MeCN , and antiferromagnetic interactions in 3.6H 2O.2MeCOOH and 5.0.5H 2O. Fitting the experimental data led to the following parameters: J 1 = -2.18 cm (-1), J 2 = 6.93 cm (-1), J 3 = -13.94 cm (-1), J 4 = -9.62 cm (-1), J 5 = -11.17 cm (-1), g = 2.00 ( 1.2H 2O.MeOH.MeCN ), J 1 = -5.41 cm (-1), J 2 = -35.44 cm (-1), g = 2.13, zJ' = -1.55 cm (-1) ( 3.6H 2O.2MeCOOH ) and J 1 = -2.29 cm (-1), J 2 = -35.21 cm (-1), g = 2.02, zJ' = -0.86 cm (-1) ( 5.0.5H 2O ).     

One-step synthesis of stoichiometrically defined metal oxide nanoparticles at room temperature

A great variety of metal oxide nanoparticles have been readily synthesized by using alkali metal oxides, M(2)O (M is Na or Li) and soluble metal salts (metal chlorides) in polar organic solutions, for example, methanol and ethanol, at room temperature. The oxidation states of the metals in the resulting metal oxides (Cu(2)O, CuO, ZnO, Al(2)O(3), Fe(2)O(3), Bi(2)O(3), TiO(2), SnO(2), CeO(2), Nb(2)O(5), WO(3), and CoFe(2)O(4)) range from 1 to 6 and remain invariable through the reactions where good control of stoichiometry is achieved. Metal oxide nanoparticles are 1-30 nm and have good monodispersivity and displayed comparable optical spectra. These syntheses are based on a general ion reaction pathway during which the precipitate occurs when O(2-) ions meet metal cations (M(n+)) in anhydrous solution and the reaction equation is M(n+) + n/2 O(2-) --> MO(n/2) (n=1-6).     

Cationic Rh complexes with novel spiro tetraarylpentaborate anions prepared from arylboronic acids and aryloxorhodium complexes

Ar-B(OH)2 (1a: Ar = C6H4OMe-4, 1b: Ar = C6H3Me2-2,6) react immediately with Rh(OC6H4Me-4)(PMe3)3 (2) in 5 : 1 molar ratio at room temperature to generate [Rh(PMe3)4]+[B5O6Ar4]- (3a: Ar = C6H4OMe-4, 3b: Ar = C6H3Me2-2,6). p-Cresol (92%/Rh), anisole (80%/Rh) and H2O (364%/Rh) are formed from 1a and 2. The reaction of 1a with 2 for 24 h produces [Rh(PMe3)4]+[B5O6(OH)4]- (4) as a yellow solid. This is attributed to hydrolytic dearylation of once formed 3a because the direct reaction of 3a with excess H2O forms 4. An equimolar reaction of 2 with phenylboroxine (PhBO)3 causes transfer of the 4-methylphenoxo ligand from rhodium to boron to produce [Rh(PMe3)4]+[B3O3Ph3(OC6H4Me-4)]- (5). Arylboronic acids 1a and 1b react with Rh(OC6H4Me-4)(PR3)3 (6: R = Et, 8: R = Ph) and with Rh(OC6H4Me-4)(cod)(PR3) (11: R = iPr, 12: R = Ph) to form [Rh(PR3)4]+[B5O6Ar4]- (7a: R = Et, Ar = C6H4OMe-4, 7b: R = Et, Ar = C6H3Me2-2,6, 9a: R = Ph, Ar = C6H3Me2-2,6) and [Rh(cod)(PR3)(L)]+[B5O6Ar4]- (13b: R = iPr, L = acetone, Ar = C6H3Me2-2,6, 14a: R = Ph, L = PPh3, Ar = C6H4OMe-4, 14b: R = Ph, L = PPh3, Ar = C6H3Me2-2,6), respectively. Hydrolysis of 14a yields [Rh(cod)(PPh3)2]+[B5O6(OH)4]- (15) quantitatively.     

Zinc(II) ortho-hydroxyphenylhydrazo-β-diketonate complexes and their catalytic ability towards diastereoselective nitroaldol (Henry) reaction

The zinc(II) complexes with ortho-hydroxy substituted arylhydrazo-β-diketonates [Zn(2)(CH(3)OH)(2)(μ-L(1))(2)] (5), [Zn{(CH(3))(2)SO}(H(2)O)(L(2))] (6), [Zn(2)(H(2)O)(2)(μ-L(3))(2)] (7) and [Zn(H(2)O)(2)(L(4))]·H(2)O (8) were synthesized by reaction of a zinc(II) salt with the appropriate hydrazo-β-diketone, HO-2-C(6)H(4)-NHN=C{C(=O)CH(3)}(2) (H(2)L(1), 1), HO-2-O(2)N-4-C(6)H(3)-NHN=C{C(=O)CH(3)}(2) (H(2)L(2), 2), HO-2-C(6)H(4)-NHN=CC(=O)CH(2)C(CH(3))(2)CH(2)C(=O) (H(2)L(3), 3) or HO-2-O(2)N-4-C(6)H(3)-NHN=[CC(=O)CH(2)C(CH(3))(2)CH(2)C(=O) (H(2)L(4), 4). They were fully characterized, namely by X-ray diffraction analysis that disclosed the formation of extensive H-bonds leading to 1D chains (5 and 6), 2D layers (7) or 3D networks (8). The thermodynamic parameters of the Zn(II) reaction with H(2)L(2) in solution, as well as of the thermal decomposition of 1-8 were determined. Complexes 5-8 act as diastereoselective catalysts for the nitroaldol (Henry) reaction. The threo/erythro diastereoselectivity of the β-nitroalkanol products ranges from 8:1 to 1:10 with typical yields of 80-99%, depending on the catalyst and substrate used.