The mechanism of Pu<Superscript>VI</Superscript> oxidation with ozone and other reagents in alkaline solutions

The analysis of reported data on the interaction of ozone with alkaline solutions of Pu^VI leads to the conclusion that the process of ozonation involves reactions O₃ + OH^– → HO ₂ ^- + O₂, O₃ + + HO ₂ ^- + OH^– → O ₃ ^- + O ₂ ^- + H₂O and O₃ + O ₂ ^- → O ₃ ^- + O₂. The O ₃ ^- radical ion oxidizes Pu^VI, the HO ₂ ^- and O ₂ ^- anions reduce Pu^VII and Pu^VI and react with O ₃ ^- . Using persulfate instead of O₃ in aerated solution at 80—95 °C results in thermal decomposition of the S₂O ₈ ^2- anion into radical ions of SO ₄ ^- , oxidizing OH^– to the O^– ion, which in reaction with O₂ forms O ₃ ^- . The oxidation of PuVI proceeds via the formation of an activated complex with O ₃ ^- . where charge transfer occurs with the simultaneous elimination of two H⁺ ions. A similar mechanism is operating in reactions of Pu^VI with BrO^–, Fe(CN) ₆ ^3– , Am^VI, and Am^VII. Upon the γ-radiolysis of alkaline solutions of Pu^VI saturated with N₂O or containing S₂O ₈ ^2– , e _aq ^– is converted into O^– and then into O ₃ ^- ; F₂ and XeF₂ in alkaline solutions are decomposed with the formation of H₂O₂, which prevents producing Pu^VII.     

Synthesis and crystal structure of 18-crown-6 <Emphasis Type="Italic">E</Emphasis>-2-phenylethenylphosphonic acid diaqua(18-crown-6)sodium <Emphasis Type="Italic">E</Emphasis>-2-phenylethenylphosphonate

New complex compound, diaqua(18-crown-6)sodium E-2-phenylethenylphosphonate 18-crown-6 E-2-phenylethenylphosphonic acid, [Na(18-crown-6)(H₂O)₂]⁺·HO ₃ ^? PCH=CHPh·18-crown-6·H₂O₃PCH=CHPh, was obtained and its crystal and molecular structures were studied by the X-ray structural analysis. In this structure the complex cation [Na(18-crown-6)(H₂O)₂]⁺ is of guest-host type. The coordination polyhedron of its Na⁺ cation is a slightly screwed hexagonal bipyramid with the base consisting of all 6 O atoms of 18-crown-6 ligand and with two opposite apexes at two O atoms of two ligand water molecules. In the studied crystal structure the alternating complex cations and 18-crown-6 molecules as well as the molecules of acid and its anion HO ₃ ^? PCH=CHPh form by means of hydrogen bonds the infinite chains of two different types.     

Reactions of alkoxy and peroxy radicals with carbon monoxide

Experimental rate constants of the reactions HO^· + CO → H^· + CO₂, RO^· + CO → R^· + CO₂, HO ₂ ^· + CO → HO^· + CO₂, and RO ₂ ^· + CO → RO^· + CO₂ are analyzed in the framework of the intersecting-parabolas model. The transition states of the additions of the methoxy and methylperoxy radicals to carbon monoxide were calculated by quantum-chemical methods. The reactions occur in two consecutive steps: first the HO^· (RO^·, RO ₂ ^· ) radical adds to CO and then the resulting unstable intermediate radical decomposes to evolve CO₂. The kinetic parameters of these reactions are calculated by two methods (using the intersecting-parabolas model and the quantum-chemical method). The activation energies and rate constants of a series of R _i O^· + CO and R _i O ₂ ^· + CO reactions are calculated. A comparison of the kinetic parameters suggests close similarity between the transition states in the additions of the O-centered radicals to CO and olefins.     

Nucleophilic activity of peroxyhydrocarbonate and peroxocarbonate ions relative to 4-nitrophenyl diethyl phosphonate

Peroxocarbonate ions HCO ₄ ^? and CO ₄ ^2? , which are formed in the H₂O₂/NH₄HCO₃/HO^? system, react with 4-nitrophenyl diethyl phosphonate (I) through a nucleophilic mechanism with rate constants \(k_{HCO_4^ - } = 0.008\) and \(k_{CO_4^{2 - } } = 0.13 L/mol \cdot s\). Comparison of these constants with the corresponding constants of other inorganic anions in their reaction with I in the framework of the Brönsted equation indicates that HCO ₄ ^? and CO ₄ ^2? are typical α-nucleophiles.     

Crystal structure of 4,7,13,16,21,24-hexaoxa-1,10-diazoniabicyclo [8.8.8]hexacosane nitrate-hydrogen nitrate perchlorate semihydrate

An adduct of 2.2.2-cryptand with nitric and perchloric acids of the [H₂(Crypt-222)· 0.52H₂O]²⁺·ClO ₄ ^? ·NO ₃ ^? ·HNO₃ composition (I) is prepared and characterized by single crystal X-ray diffraction. The triclinic structure of I (space group \(P\overline 1 \), a = 10.176 Å, b = 11.272 Å, c = 12.870 Å, α = 78.61°, β = 76.62°, γ = 79.88°, Z = 2) is solved by a direct method and refined in the full-matrix anisotropic approximation to R = 0.062 for all 3642 measured independent reflections (CAD-4 automated diffractometer, λMoK _α). The structure of I contains a dication of 2.2.2-cryptand in the endo-endo conformation, two hydrogen atoms at the protonated N atoms are directed inside the cavity which also includes a water molecule with a site occupation factor of 0.52. Tetrahedral ClO ₄ ^? anion in I is disordered. In I, the H atom of the NO ₃ ^? ·HNO₃ dimer is split over two close positions with occupation factors of 0.33 and 0.67; this dimer is joined by a very strong single disordered hydrogen bond N-O-H?O = N between the molecule of nitric acid and its anion.     

Photosensitized formation of peroxyl radicals in aqueous solutions of adenine at 77 K

Conditions for the formation of peroxyl radicals photosensitized by near-UV irradiation in frozen aqueous solutions of adenine containing 0.1 M NaCl (pH 4–7) are studied. Analysis of the EPR spectra shows that the systems under study contain two types of peroxyl radicals presumably classified earlier as O ₂ ^?· and HO _2· ^· . The effect of freezing methods on the production of the radicals is shown. The signal from O ₂ ^?· predominates in the spectra of samples with open surfaces and is likely due to the reduction of adsorbed O₂ molecules with photoejected electrons. The signal from HO ₂ ^· could be due to photoinduced interaction between the sensitizer and solvent. Possible mechanisms of these processes are considered.     

Crystal Structure and Properties of Levofloxacinium 2-Thiobarbiturate Trihydrate

The structure of levofloxacinium 2-thiobarbiturate trihydrate LevoH ₂ ⁺ Htba^–·3H₂O (I) (LevoH is levofloxacin, H₂tba is 2-thiobarbituric acid) is determined (CIF file CCDC No. 1547466); its thermal decomposition and IR spectrum are studied. The crystals of I are triclinic: a = 8.670(1) Å, b = 9.605(1) Å, c = 15.786(2) Å, α = 89.144(5)°, β = 88.279(5)°, γ = 76.068(5)°, V = 1275.4(3) ų, space group P1, Z = 2. The unit cell of I contains two LevoH ₂ ⁺ ions, two Htba^– ions, and six H₂O molecules. The absolute structure of the crystal and the configuration of the chiral center in a levofloxacin molecule S are determined. Experiments for generating the second optical harmonics gave a positive result. Intermolecular hydrogen bonds (HBs) N–H···O and O–H···O in I form a bilayer system along the ab diagonal with hydrophilic moieties within a layer and hydrophobic moieties directed outward. The structure is stabilized by multiple HBs and the π–π interaction between the Htba–and LevoH ₂ ⁺ ions and between the LevoH ₂ ⁺ ions.     

Wastewater treatment with ionizing radiation

In water treatment by ionizing radiation ^·OH is suggested to initiate the degradation of organics. In these reactions mostly carbon centred radicals form. Here we show that other inorganic radicals also highly contribute to the initiation of degradation. Cl^? and HCO₃ ^? in the treated water reacting with ^·OH transform to Cl ₂ ^·? and CO ₃ ^·? . In their reactions C-centred radicals form, too. The reactions of e _aq ^? and H^· water radiolysis intermediates may also produce carbon centred radicals. The C-centred radicals react readily with dissolved O₂, this is the starting step of the gradual oxidation.     

Hydration of CBr<Subscript>3</Subscript>COOH molecules and CBr<Subscript>3</Subscript>CO<Stack><Subscript>2</Subscript><Superscript>–</Superscript></Stack> anions in aqueous solutions

The optimal structures and the vibrational frequencies of H-bonded complexes formed from one-two CBr₃COOH molecules or the CBr₃CO ₂ ^– anion with water molecules are calculated by density functional theory (B3LYP/6-31++G(d,p)). The comparison of the obtained results with the known Raman spectra of the CBr₃COOH–H₂O and NaCBr₃CO ₂ ^– ·H₂O solutions (with component molar ratios of ≤1:16) shows that they include stable hydrates: CBr₃COOH·H₂O and CBr₃CO ₂ ^– ·(H₂O)₆. The first one has a cyclic form, and the second has a cubic globular form. The vibrational band frequencies of the CBr₃COOH molecule and the CBr₃CO ₂ ^– anion in the spectra of both solutions are almost completely determined by the mutual arrangement of units in these hydrates.     

Theoretical study of oxoborate complexes with MO<Stack><Subscript>4</Subscript><Superscript><Emphasis Type="Italic">n</Emphasis>−</Superscript></Stack> tetraoxo anions in the inner and outer spheres of the B<Subscript>20</Subscript>O<Subscript>30</Subscript> cluster

The energies and structural and spectroscopic characteristics of endohedral (MO₄©B₂₀O ₃₀ ^n? ) and exohedral (MO₄ · B₂₀O ₃₀ ^n? ) isomers of oxoborate complexes with MO ₄ ^n? tetraoxo anions with 32 valence electrons located in the inner and outer spheres of the B₂₀O₃₀ cluster have been calculated by the density functional theory method (B3LYP). It has been demonstrated that, among the endohedral MO₄©B₂₀O ₃₀ ^n? clusters with strong multiply charged anions (VO ₄ ^3? , CrO ₄ ^2? , PO ₄ ^3? , SO ₄ ^2? , AsO ₄ ^3? , SeO ₄ ^2? , etc.), the isomer in which a “guest” tetrahedron MO₄ is located at the center of the B₂₀O₃₀ cage and bonded to it through internal oxygen bridges M-O*-B is the most favorable one. Among the exohedral analogues MO₄ · B₂₀O ₃₀ ^n? , two most favorable isomers contain the “capping” MO₄ tetrahedron bonded to the B₂₀O₃₀ cage through two and three external M-O-B bridges. For the complexes with doubly charged SO ₄ ^2? and SeO ₄ ^2? anions, the third exohedral isomer in which the sulfite or selenite group MO₃ is bidentately coordinated to the oxidized B₂₀O₂₉(OO) cage with one peroxide bridge turns out to be close in energy to the above two isomers. For the systems with high negative charge n, the exohedral isomers are much more favorable than the endohedral isomer; however, with decreasing charge, the difference in energy between them decreases to ~10–18 kcal/mol, so that the exo–endo transition between them can require moderate energy inputs. For the endohedral complexes with singly charged ClO ₄ ^? and BrO ₄ ^? anions, two isomers with close energies are preferable in which the central atoms of the guest tetrahedra are reduced to the state of singly charged ions, while the oxoborate cage is oxidized to B₂₀O₂₆(OO)₄ with four peroxide groups B-O-O-B and retains its closed (closo) structure. In the most favorable isomer of the complexes with multicharged ortho-anions BO ₄ ^5? , CO ₄ ^4? , and NO ₄ ^3? , the outersphere anion is reduced to, respectively, borate, carbonate, and nitrate bidentately coordinated to the oxidized B₂₀O₂₉(O)₂ cage with an open structure and two strongly elongated terminal B-O bonds. The results are compared with the data of previous calculations of endohedral and exohedral vanadate complexes MO₄©V₂₀O ₅₀ ^n? and MO₄ · V₂₀O ₅₀ ^n? with the same guest anions MO ₄ ^n? .     

Defects and characteristics of the structure and properties of aluminum oxides

Based on IR spectroscopy data, it was established that nonstoichiometry defects in the structure of aluminum oxides were components of the Wannier-Mott exciton states and included the Al-O, Al-Al, O₂, O ₂ ⁺ , O ₂ ^? , O ₂ ^2? , O₃, and O_2n isolated oscillators in the ground and electronically excited states. It was shown that their presence manifested itself by thermoemission of molecular oxygen singlet forms, excess heat capacity, and anomalous diamagnetism at elevated temperatures.     

4,7,13,16,21,24-Hexaoxa-1,10-diazoniabicyclo[8.8.8]-hexacosane Bis(nitrate-hydrogennitrate): Synthesis and crystal structure

A crystalline adduct of 2.2.2-cryptand and nitric acid, [H₂(Crypt-222)]²⁺·2(NO ₃ ^? ·HNO₃) (I), is synthesized and studied using X-ray diffraction analysis. The monoclinic structure of compound I (space group C2/c, a = 13.326 Å, b = 15.262 Å, c = 15.020 Å, β = 98.96°, Z = 4) is solved by a direct method and refined by the full-matrix least-squares method in the anisotropic approximation to R = 0.067 for 2647 independent reflections (CAD4 automated diffractometer, λMoK _α radiation). In the structure of compound I, the 2.2.2-cryptand dication lies on an axis 2 and has an endo-endo conformation, for which two H atoms at two protonated N atoms are directed inside the cavity. One of the NO ₃ ^? ·HNO₃ dimers is situated in the inversion center, and the other dimer lies on another axis 2 and is disordered over three orientations. All H atoms in the NO ₃ ^? ·HNO₃ dimers are equiprobably disordered over two close sites. Each of the two NO ₃ ^? ·HNO₃ dimers is formed by the very strong disordered N-O-H···O=N hydrogen bond between the nitric acid molecule and nitrate anion.     

Degradation of trichloroethylene in aqueous solution by persulfate activated with Fe(III)–EDDS complex

In this study, an environmentally friendly complexing agent, S,S′-ethylenediamine-N,N′-disuccinic acid (EDDS), was applied in Fe(III)-mediated activation of persulfate (PS), and the degradation performance of trichloroethylene (TCE) was investigated. The effects of PS concentration, Fe(III)/EDDS molar ratio, and inorganic anions on TCE degradation were evaluated, and the generated reactive oxygen species responsible for TCE removal were identified. The results showed that nearly complete TCE degradation was achieved with PS of 15.0 mM and a molar ratio of Fe(III)/EDDS of 4:1. An increase in PS concentration or Fe(III)/EDDS molar ratio to a certain value resulted in enhanced TCE degradation. All of the anions (Cl^?, HCO₃ ^?, SO₄ ^2?, and NO ₃ ^? ) at tested concentrations had negative effects on TCE removal. In addition, investigations using radical probe compounds and radical scavengers revealed that sulfate radicals (SO ₄ ^·? ), hydroxyl radicals (^·OH), and superoxide radical anions (O ₂ ^·? ) were all generated in the Fe(III)–EDDS/PS system, and ^·OH was the primary radical responsible for TCE degradation. In conclusion, the Fe(III)–EDDS-activated PS process is a promising technique for TCE-contaminated groundwater remediation.     

Effect of ascorbic acid and its derivatives on the radiation-chemical transformations of hydroxyl-containing organic compounds

The effect of ascorbic acid, 5,6-O-isopropylidyl-2,3-O-dimethylascorbic acid, and 2-O-glucopyranosylascorbic acid on the formation of main radiolysis products of ethanol and aqueous ethanol, ethylene glycol, α-methylglucopyranoside, and maltose solutions was studied by means of continuous radiolysis. The obtained results indicate that ascorbic acid effectively reacts with the carbon-centered hydroxyl-containing radicals derived from the substrates, thus decreasing the yield of their recombination and fragmentation products. It was found that the interaction of ascorbic acid and its derivatives with the carbon-centered radicals during the radiolysis of deaerated ethanol and its aqueous solutions may occur via both reducing and oxidizing mechanisms and that ascorbic acid in the aerated solutions acts as a hydrogen donor, reducing mainly the HO ₂ ^· radical to hydrogen peroxide.     

Thermal behavior analysis of halloysite selected from Inner Mongolia Autonomous Region in China

Thermal behavior of halloysite selected from Erdos, Inner Mongolia Autonomous Region in China, was investigated by thermogravimetry and differential thermal gravity (TG–DTG), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and scanning electron microscope (SEM). The XRD results indicated that the mineralogical composition of halloysite sample was determined as 7 Å halloysite with the d ₍₀₀₁₎ value of 0.734 nm, a small amount of 10 Å halloysite with the d ₍₀₀₁₎ value of 0.998 nm, quartz, calcite, anhydrite, siderite, and analcite. The crystal chemical formula of halloysite specimen is (Ca_0.007Na_0.039K_0.048)(Al_1.935Fe _0.032 ³⁺ Mn _0.003 ²⁺ Ti _0.002 ⁴⁺ Mg _0.015 ²⁺ Ca _0.021 ²⁺ )₂ [(Si_1.935Al _0.065 ³⁺ )₂](OH)₄·2H₂O according to the oxygen atom method. The TG–DTG–DSC data showed that a small amount of water molecule layer in the interlayer and the dehydroxylation was observed at 493.6 °C. The XRD, FT-IR, and SEM data clearly show that the structure changes and dehydroxylation of the halloysite with the temperature increased from 200 to 1200 °C. The dehydration of the halloysite is followed by the loss of intensity and evolution of the OH vibration bands and the change in microstructure. Dehydroxylation is followed by the decrease in the intensity of the bands at 3696 and 3620 cm^?1, which is completely disappeared at 700 °C. The thermal behavior of halloysite was influenced by the mineralogy composition and impurities.     

Long-lived excited electronic states of the dichloroethylene cation isomers probed by charge exchange ionization

Charge exchange technique has been used to detect the presence of long-lived excited electronic states of trans-, cis-, and 1,1-C₂H₂Cl ₂ ^+· . The \(\tilde B\) states of the three cations which are formed by removal of an electron from an in-plane chlorine nonbonding orbital of the corresponding neutrals have been found to have long lifetimes (tens of microseconds or longer). Whether the à states formed by removal of an electron from the other in-plane chlorine nonbonding orbitals are long-lived also can not be determined by the present experiments. Cations in the excited electronic states above the \(\tilde B\) states were not detected because of their prompt dissociation following intramolecular relaxation or radiative decay.     

Structure of Aqueous Lithium Tetraborate Solution

The structure of aqueous lithium tetraborate solutions was investigated by species distribution calculation and synchrotron X-ray scattering. It shows that the dominant species in supersaturated solution at 298.15 K is B₄O₅(OH) ₄ ^2? and the minor species are B₃O₃(OH) ₅ ^2? , B₃O₃(OH) ₄ ^? and B(OH)₃. The ‘intramolecular’ structural parameters of B₄O₅(OH) ₄ ^2? , such as bond length and coordination number, were gives out using density function theory calculation. X-ray scattering study shows that the distance Li–O(H₂O)_I of [Li(H₂O)₄]⁺ is about 0.1983 nm with the coordination number(CN) 4 in tetrahedral configuration. The B–O(H₂O) distance in hydrated anion B₄O₅(OH)₄(OH₂) ₈ ^2? is 0.3662 nm with the CN 12. The Li⁺–B distance is about 0.3364 nm with a coordination number ~1.0. The temperature effect on solution structure was also discussed.     

Crystal structure of Ba<Subscript>3</Subscript>[UO<Subscript>2</Subscript>(C<Subscript>2</Subscript>O<Subscript>4</Subscript>)<Subscript>2</Subscript>(NCS)]<Subscript>2</Subscript> · 9H<Subscript>2</Subscript>O

Single crystals of Ba₃[UO₂(C₂O₄)₂(NCS)]₂ · 9H₂O are synthesized and studied by X-ray diffraction. The crystals are orthorhombic, space group Fddd, Z = 16, and the unit cell parameters are a = 16.253(3) Å, b = 22.245(3) Å, c = 39.031(6) Å. The main crystal structural units are mononuclear complex groups [UO₂(C₂O₄)₂NCS]^3? of the crystal-chemical family (AB ₂ ⁰¹ M¹ (A = UO ₂ ²⁺ , B⁰¹ = C₂O ₄ ^2? , M¹ = NCS^?) of the uranyl complexes linked into a three-dimensional framework by electrostatic interactions and hydrogen bonds involving oxalate ions and water molecules.     

Synthesis and crystal structure of Rb<Subscript>2</Subscript>[(UO<Subscript>2</Subscript>)<Subscript>2</Subscript>(C<Subscript>2</Subscript>O<Subscript>4</Subscript>)<Subscript>2</Subscript>(SeO<Subscript>4</Subscript>)] · 1.33H<Subscript>2</Subscript>O

The single crystals of Rb₂[(UO₂)₂(C₂O₄)₂(SeO₄)] · 1.33H₂O were synthesized and studied by X-ray diffraction. The crystals are monoclinic, space group P2₁/m, Z= 2, the unit cell parameters: a = 5.6537(8), b = 18.736(3), c = 9.4535(15) Å, β = 98.440(5)°, V = 990.6(3) ų, R ₁ = 0.0506. The main structural units of the crystal are infinite layers of [(UO₂)₂(C₂O₄)₂(SeO₄)]^2?, corresponding to the crystal chemical group A₂K ₂ ⁰² B² (A = UO ₂ ²⁺ , K⁰² = C₂O ₄ ^2? , B² = SeO ₄ ^2? ) of uranyl complexes. The uranium-containing layers are united into a three-dimensional framework through the electrostatic interactions with the outer-sphere rubidium ions and the hydrogen bonding system involving the outer-sphere water molecules.     

Crystal structure of Cs[(UO<Subscript>2</Subscript>)<Subscript>2</Subscript>(C<Subscript>2</Subscript>O<Subscript>4</Subscript>)<Subscript>2</Subscript>(OH)] · H<Subscript>2</Subscript>O

Single crystals of Cs[(UO₂)₂(C₂O₄)₂(OH)] · H₂O were synthesized and structurally studied using X-ray diffraction. The compound crystallizes in monoclinic space group P2₁/m, Z = 2, with the unit cell parameters a = 5.5032(4) Å, b = 13.5577(8) Å, c = 9.5859(8) Å, β = 97.012(3)°, V = 709.86(9) ų, R = 0.0444. The main building units of crystals are [(UO₂)₂(C₂O₄)₂(OH)]^? layers of the A₂K ₂ ⁰² M² (A = UO ₂ ²⁺ , K⁰² = C₂O ₄ ^2? , and M² = OH^?) crystal-chemical family. Uranium-containing layers are linked into a three-dimensional framework via electrostatic interactions with outer-sphere cations and hydrogen bonds with water molecules.