Influence de certains ions inorganiques, de l'éthanol et du peroxyde d'hydrogène sur la photominéralisation du β-naphtol en présence de TiO2

TiO₂ photocatalytic mineralization of β-naphthol: influence of some inorganic ions, ethanol, and hydrogen peroxide. In this work, the photocatalytic oxidation of β-naphthol in aqueous suspensions of TiO₂ was investigated at room temperature, by following the formation of CO₂. The disappearance of β-naphthol fits a Langmuir-Hinshelwood kinetic model. The activation energy for the degradation reaction of β-naphthol is estimated at 10.2 kJ/mol. The effects of some additives such as ethanol, H₂O₂, and inorganic ions (Cl⁻, SO₄²⁻, HCO₃⁻, NO₃⁻, Fe³⁺, Cu^2+, and Cr³⁺) on the photomineralization of β-naphthol were examined. The inhibition of the anions for this reaction was in the order : NO₃⁻ < HCO₃⁻ < SO₄²⁻ < Cl⁻. This can be due to a partial blockage of catalyst active sites by these ions or their reaction with an oxidizing radical such as OH. The most photoactive systems for β-naphthol degradation were found in the presence of ferric ions, while the addition of Cr³⁺ strongly inhibited the photocatalytic decomposition of β-naphthol.     

Synthèse et propriétés magnétiques de solutions solides entre l'oxyde de chrome CrO2 et l'oxyhydroxyde de cobalt CoOOH

Solid solutions of general formula (1 ? x)CrO₂, xCoOOH have been prepared by hydrothermal synthesis under very high pressure conditions (80 kb). Cr⁶⁺O₃ and CoCr⁶⁺O₄ were used as starting materials. Homogeneous ferromagnetic phases were obtained when 0 ? x ? 0.5. X ray powder patterns clearly demonstrate the isotype with InOOH, an orthorhombic distorted rutile type structure. The results of the magnetic measures performed on samples with different compositions indicate that part of the Cr⁴⁺ cation have been reduced to Cr³⁺ and that the general formula of the solid solutions should be written Cr⁴⁺_1?(x+y)Cr³⁺_yCo²⁺_xO₂H_x+y.     

Environnement tetraedrique de l'ion Cu et structure fine du seuil d'absorption K dans quelques chromites: application à l'étude d'oxydes à valence mixte

Copper zinc and copper manganese spinel chromites are studied using neutron diffraction. Cr³⁺ ions in tetrahedral environments are observed in CuCr₂O₄ and Cu_0.25Zn_0.75Cr₂O₄. These results leads to a new interpretation of the optical spectra (drs). The measurement of X-ray absorption fine structure of copper in the near edge rayon (Xanes) have been obtained using the Lure synchrotron radiation sources (Orsay, France). The spectra of Cu²⁺ in the tetrahedral environment of a quadratic or cubic matrix are characterized by the splitting of the main peak in the range 18–23 eV above the 1s → 3d transition. The X-ray absorption spectroscopy reveals the two oxidation states of copper in mixed oxides such as CuCrMnO₄. The copper(I) 1s → 4s transition is observed as a shoulder located at 10 eV on the slope of the main peak. A finer structure appears in the derivative spectrum.     

Etude de composés d'addition d'acides de Lewis. XXXVI [1] Composés d'addition de l'anthraquinone-9, 10 et de l'anthrone avec divers acides de Lewis

Solid stoichiometric adducts of 9, 10-anthraquinone with SbCl₅, ZrCl₄, TiCl₄ SnCl₄, AlCl₃, have been prepared. The very important lowering Δω of the IR. carbonyl frequency, ranging from ?175 cm^?1 for SbCl₅ to ?117 cm^?1 for SnCl₄, shows that the acceptor is linked by a dative bond to the carbonyl oxygen atom acting as a donor; an assignment of most of the fundamental IR. frequencies is proposed for anthraquinone and the mentioned adducts. Similar assignments and interpretation have been made for anthrone and its solid adduct with SbCl₅, ZrCl₄, TiCl₄, SnCl₄, AlCl₃ and ZnCl₂, where the C?O lowerings range from ?164 cm^?1 for SbCl₅ to ?97 cm^?1 for ZnCl₂.     

Stabilité dans le méthanol et propriétés thermodynamiques de transfert des cryptates de certains cations de transition et de métaux lourds

Stability in Methanol and Thermodynamic Transfer Properties of the Cryptates of some Transition Cations and Heavy Metals The nature and stability of the macrocyclic and macrobicyclic complexes of Ag⁺, Cd²⁺, and Pb²⁺ (Mⁿ⁺) with 21, 22, 211, 221 and 222 in anhydrous methanol 0.05M in Et₄N⁺ClO^?₄, at 25° (see Scheme) have been determined by potentiometry and spectrophotometry. Binuclear complexes M₂L²ⁿ⁺ have been observed in all cases, besides the mononuclear MLⁿ⁺ complexes. The macrobicyclic 1:1 complexes MLⁿ⁺ exhibit an important ‘cryptate effect’ with Mⁿ⁺=Ag⁺, Pb²⁺ and Cd²⁺, but not with Cu²⁺ and Zn²⁺; their stability is in all cases maximum with 221. The applicability to our results of the recent extrathermodynamic hypothesis involving MLⁿ⁺ cryptates is examined.     

Controlling Cr3+/Cr4+ concentration in single-phase host toward tailored super-broad near-infrared luminescence for multifunctional applications

Full control on the valence of the active ions in solids to improve properties is the central topic of chemistry and materials. Cr³⁺ and Cr⁴⁺ ions generally emit wavelength-different near-infrared (NIR) light. Here, we have developed a chromium valence-controllable single-phase phosphor, Mg₂GeO₄:Cr³⁺,Cr⁴⁺ to achieve super-broad NIR luminescence. High Li ⁺ content charge compensators can stabilize Cr³⁺, whereas high-temperature sintering tends to facilitate the formation of Cr⁴⁺. Through fine adjusting the synthesis conditions, pure Cr³⁺ or Cr⁴⁺ luminescence can be obtained with peak emission locating at 935 nm and 1190 nm, respectively. Super broad band dual emission spanning from 650 nm to 1600 nm is realized via fully controlling the concentration ratio of Cr³⁺ to Cr⁴⁺ in a single host. By measuring the transmission spectra of several foodstuff illuminated by our phosphors, non-destructive analysis in food safety areas can be realized. This study provides a new strategy for exploiting super broad band NIR luminescent materials.     

The mercury chromates Hg6Cr2O9 and Hg6Cr2O10—Preparation and crystal structures, and thermal behaviour of Hg6Cr2O9

The basic mercury(I) chromate(VI), Hg₆Cr₂O₉ (=2Hg₂CrO₄·Hg₂O), has been obtained under hydrothermal conditions (200 °C, 5 days) in the form of orange needles as a by-product from reacting elemental mercury and K₂Cr₂O₇. Hydrothermal treatment of microcrystalline Hg₆Cr₂O₉ in demineralised water at 200 °C for 3 days led to crystal growth of red crystals of the basic mercury(I, II) chromate(VI), Hg₆Cr₂O₁₀ (=2Hg₂CrO₄·2HgO). The crystal structures were solved and refined from single crystal X-ray data sets. Hg₆Cr₂O₉: space group P2₁2₁2₁, Z=4, a=7.3573(12), b=8.0336(13), , 3492 structure factors, 109 parameters, R[F²>2σ(F²)]=0.0371, wR(F² all)=0.0517; Hg₆Cr₂O₁₀: space group Pca2₁, Z=4, a=11.4745(15), b=9.4359(12), , 3249 structure factors, 114 parameters, R[F²>2σ(F²)]=0.0398, wR(F² all)=0.0625. Both crystal structures are made up of an intricate mercury-oxygen network, subdivided into single building blocks [O-Hg-Hg-O] for the mercurous compound, and [O-Hg-Hg-O] and [O-Hg-O] for the mixed-valent compound. Hg₆Cr₂O₉ contains three different Hg₂²⁺ dumbbells, whereas Hg₆Cr₂O₁₀ contains two different Hg₂²⁺ dumbbells and two Hg²⁺ cations. The Hg^I-Hg^I distances are characteristic and range between 2.5031(15) and 2.5286(9) Å. All Hg₂²⁺ groups exhibit an unsymmetrical oxygen environment. The oxygen coordination of the Hg²⁺ cations is nearly linear with two tightly bonded O atoms at distances around 2.07 Å. For both structures, the chromate(VI) anions reside in the vacancies of the Hg-O network and deviate only slightly from the ideal tetrahedral geometry with average Cr-O distances of ca. 1.66 Å. Upon heating at temperatures above 385 °C, Hg₆Cr₂O₉ decomposes in a four-step mechanism with Cr₂O₃ as the end-product at temperatures above 620 °C.     

Etude par spectrométrie de masse de l'ionisation de benzonitriles,de phénylacétonitriles et de N,N-diméthylanilines substitués

Molecular ionization potentials for series of compounds of the type X? C₆H₄? CN, X? C₆H₄CH₂? CN and X? C₆H₄? N(CH₃)₂ have been measured using the retarding potential difference technique (RPD. technique). The effect of the various substituents X is better correlated through the electrophilic Brown σ_p⁺ constants than through Hammett's σ_p values. No meta-para orientation effect is observed. For all the disubstituted phenyl compounds studied, the effect of the second substituent is affected by the electron-releasing power of the original substituent. Ionization potentials calculated by using the semi-empirical method of equivalent orbitals are in good agreement with the experimental values.     

Etude de composés d'addition d'acides de Lewis,XXXIV [1] Composés d'addition de benzoquinone-1, 4 avec TiCl4

The adduct 1,4-benzoquine · TiCl₄ has been prepared in CH₂Cl₂ solution at about ?60°. Its IR. spectrum has been recorded at the same temperature. The experimental study of the vibrational frequencies has been completed by the calculation of the fundamental vibrations in the molecular plane, using Wilson's FG method, with slightly simplified models of 1,4-benzoquinone · TiCl₄ (13 masses) and 1,4-benzoquinone · 2 TiCl₄ (14 masses); analysis by use of internal and symmetry coordinates. An assignment of most of the observed bands is proposed and the conclusion is reached that the complex, when solid, is (1,4-benzoquinone · TiCl₄)_n. The force constants F(C? O) are 9,85 · 10⁵ dyne/cm for the quinone and 8,8 · 10⁵ dyne/cm for the disturbed carbonyl bond of the polymerized complex in the model proposed. At ordinary temperature in benzene solution of the components the adduct 1,4-benzoquinone. TiCl₄ · benzene precipitated; with the help of the models, the fundamental vibrations of its IR. spectrum have been assigned.     

Kinetics and Mechanism of Oxidation of Chromium(III)‐guanosine 5‐Monophosphate Complex by Periodate

The kinetics of oxidation of the chromium(III)‐guanosine 5‐monophosphate complex, [Cr^III(L)(H₂O)₄]³⁺(L = guanosine 5‐monophosphate) by periodate in aqueous solution to Cr^VI have been studied spectrophotometrically over the 25–45 °C range. The reaction is first order with respect to both [IO₄^?] and [Cr^III], and increases with pH over the 2.38–3.68 range. Thermodynamic activation parameters have been calculated. It is proposed that electron transfer proceeds through an inner‐sphere mechanism via coordination of IO₄^? to chromium(III).     

Zur Kenntnis eines gemischtvalenten Oxochromats(III,IV): Sr4Cr3O9

About a Mixed-Valence-Oxochromate(III, IV): Sr₄Cr₃O₉ Single crystals of the hitherto unknown compound Sr₄Cr₃O₉ were prepared and examined by four circle diffractometer technique (space group C–P3, a = 9.6182; c = 7.8736 Å, Z = 3). The point positions of chromium are occupied statistically by Cr³⁺ and Cr⁴⁺. The Cr³⁺/Cr⁴⁺-coordination is partly unusual, there are one dimensional chains of CrO₆-polyhedra incorporated in a [Sr₄O₉]^10?-network.     

β‐K2Cr2O7

The monoclinic modification of dipotassium dichromate, β‐K₂Cr₂O₇, has been synthesized in the K₂Cr₂O₇–H₂O system. The structure consists of K⁺ cations and Cr₂O₇^2? dimers. In contrast with triclinic α‐K₂Cr₂O₇ [Kuz'min, Ilyukhin, Kharitonov & Belov (1969). Krist.Tech. 4 , 441–461], the Cr₂O₇^2? groups in β‐K₂Cr₂O₇ have twofold crystallographic symmetry and are parallel to each other.     

Propriétés électriques du trioxyde de tungstène a proximité de sa composition stoechiométrique. Influence des conditions thermodynamiques de préparation et phénomènes de trempe

The experimental study of variations in electrical conductivity of WO_3−x vs oxygen partial pressure and temperature shows evidence of interstitial W⁶_i· as being the major defect. Under certain conditions, point defects can order themselves in extended defects. The behavior of electrical conductivity can be interpreted in terms of thermodynamic equilibrium between point defects and extended defects, the latter leading to structural modifications beyond a certain departure from stoichiometry. Moreover, WO_3−x shows evidence of quenching phenomena allowing it to keep electrical features characteristic of high temperatures down to room temperature. These properties may explain discrepancies between previous data.     

Formal chromium–chromium triple bonds and bent rings in the binuclear cycloheptatrienylchromium carbonyls (C7H7)2Cr2(CO)n (n = 6, 5, 4, 3, 2, 1, 0): A density functional theory study

Binuclear cycloheptatrienylchromium carbonyls of the type (C₇H₇)₂Cr₂(CO)_n (n = 6, 5, 4, 3, 2, 1, 0) have been investigated by density functional theory. Energetically competitive structures with fully bonded heptahapto η⁷-C₇H₇ rings are not found for (C₇H₇)₂Cr₂(CO)_n structures having two or more carbonyl groups. This result stands in contrast to the related (C_nH_n)₂M₂(CO)_n (M = Mn, n = 6; M = Fe, n = 5; M = Co, n = 4) systems. Most of the predicted (C₇H₇)₂Cr₂(CO)_n structures have bent trihapto or pentahapto C₇H₇ rings and CrCr distances in the range 2.4–2.5 Å suggesting formal triple bonds. In some cases rearrangement of the heptagonal C₇H₇ ring to a tridentate cyclopropyldivinyl or tridentate bis(carbene)alkyl ligand is observed. In addition structures with CO insertion into the C₇H₇–Cr bond are predicted for (C₇H₇)₂Cr₂(CO)_n (n = 6, 4, 2). The global minima found for the (C₇H₇)₂Cr₂(CO)_n derivatives for n = 6, 5, and 4 are (η⁵-C₇H₇)(OC)₂CrCr(CO)₄(η¹-C₇H₇), (η³-C₇H₇)(OC)₂CrCr(CO)₃(η^2,1- C₇H₇), and (η⁵-C₇H₇)₂Cr₂(CO)₄, respectively. The global minima for (C₇H₇)₂Cr₂(CO)_n (n = 3, 2) have rearranged C₇H₇ groups. Singlet and triplet structures with heptahapto η⁷-C₇H₇ rings are found for the dimetallocenes (η⁷-C₇H₇)₂Cr₂(CO) and (η⁷-C₇H₇)₂Cr₂, with the singlet structures being of much lower energies in both cases.     

Etude par Résonance Magnétique Nucléaire de dérivés phosphores. Etude de dithiaphospholanes-1,3,2

The proton NMR spectral analysis of eight different 1,3,2-dithiaphospholanes with various groups attached to the phosphorus atom has been performed. The AA′BB′X (X phosphorus atom) system shows that the two ³J(P? S? C? H) coupling constants have a small magnitude and opposite signs. Using the ³J(HH) values, the torsion about the C₄—C₅ bond has been evaluated. The conformational requirements in the two isomers of the 2 phenyl-4-methyl-1,3,2-dithiaphospholane are also discussed.     

Reactions anodiques et cathodiques des composes de Cr(VI) en milieu de nitrates alcalins fondus

The electrochemical behavior of chromate and dichromate, ions in molten NaNO₃-KNO₃ at 250°C has been studied by single-sweep voltammetry and cyclic voltammetry. The anodic dimerization of CrO₄^2- ions has been shown to proceed in three steps, the reaction: CrO₄^2-→CrO_4ad^?+e^? being rate-determining. The cathodic reduction of Cr₂O₇^2- ions includes the coupled acid-base reactions; it forms solid chromium oxide Cr₂O₃ and the soluble chromate and chromite ions.     

Un nouvel exemple de transposition: l'épimérisation en C(3) d'hydroxy-3-δ1-pyrazolines dérivées de sucres

A Novel Example of Reversible Ring Opening: The Epimerization at C(3) of Sugar 3-Hydroxy-Δ¹-pyrazolines Reaction of 1 (either geometrical isomer) with hydrazine followed by in situ Ag₂O oxidation led to two pairs of interconverting isomers 4 ? 5 and 6 ? 7 . By the same treatment, (Z)- 10 and (or) (E)- 10 gave the pair 11 ? 12 . Acetylation of 4 ? 5 led to a non interconverting mixture of 8 and 9 . This fact, and the lack of incorporation of ¹⁸O when the epimerization took place in the presence of H₂¹⁸O indicated that the most probable mechanism consisted in a reversible ring opening ( D ? E ? F ). The kinetic parameters of these reactions are given and structural assignments proposed for the new compounds.     

Inner-sphere oxidation of cis-diaquabis(oxalato)chromate(III) by periodate in aqueous weakly acidic solutions

The kinetics of oxidation of cis-[Cr^III(ox)₂(H₂O)₂]^– (ox = C₂O₄ ^2–) by IO₄ ^– showed a first-order dependence on the initial Cr^III complex concentration in the presence of a vast excess of [IO₄ ^–]. The dependence of the pseudo-first-order rate constant on [IO₄ ^–] is complex and is consistent with the formation of a precursor complex. It is proposed that this complex is formed through the coordination of the two carbonyl oxygens of the ox ligand with the IO₄ ^– ion, forming a cyclic intermediate. The kinetics are consistent with the hydroxo form of the Cr^III complex being the reactive species, whereas the aqua species forms an unreactive complex.     

Déplacements Chimiques du Carbone 13, Constantes de Couplage 1J(CH) et 3J(CH) dans une série de dérivés trisubstitués du benzène

¹³C chemical shifts, 1-bond and 3-bond (meta) ¹³C? H coupling constants have been determined in a series of trisubstituted benzene; the substituents are Cl, NH₂, N(C₂H₅)₂, N(iC₃H₇)₂, N(C₂H₄)₂O. Chemical shifts are only in moderate agreement with the usual additivity rules. Additivity rules relative to the above mentioned coupling constants are proposed. With few exceptions, the difference between predicted and observed values is less than 10%.     

Kinetics and mechanism of the oxidation of nitrilotris(methylenephosphonato)chromium(III) by periodate

The kinetics of oxidation of nitrilotris(methylenephosphonato)chromium(III), Cr^IIINTMP, by periodate to yield Cr^VI have been studied spectrophotometrically over the 5.80–6.85 pH range at 22–33 °C. The reaction rate, which is first-order with respect to [Cr^IIINTMP] and [IO^– ₄] and inversely dependent on [H⁺], obeys the rate law:-d[Cr^IIINTMP/dt=kKK_h[IO^- ₄] [Cr^III]_T/K_h+ [H⁺] +KK_h[IO^- ₄] The values of the intramolecular electron transfer, k, and the formation constant of the intermediate complex, K, were determined at various temperatures. The hydrolysis constant for Cr^IIINTMP, K _h , was determined spectrophotometrically and is in agreement with the value estimated from the kinetic data. The activation parameters were calculated from the temperature dependence of the specific rate constants. A mechanism is proposed in which the hydroxo complex, [CrHNTMP(OH)]^3–, is the reactive species. The results support a mechanism where intramolecular electron transfer is the rate-determining step.