A Spectrophotometric Study OE Zirconium Complexes of 4,5-Dihydroxyfluorescein

Zirconium (IV) ions form violet red complex with 4,5-dihydroxyfluorescein in fairly strong mineral acid medium. The reagent has been successfully applied as a metal indicator in the direct EDTA titration of zirconium. The complex formed by 4,5-dihydroxyfluorescein and zirconium ions has been studied spectrophotometrically in 0.1M HCl solution. It is found that when an excess of metal ion is present, a violet red colored complex with metal-ligand ratio of 1:1, (MR) is formed and when an excess of 4,5-dihydroxyfluorescein is present a 1:2 complex (MR₂) may be predominant. The 1:1 complex has maximum absorption at 510 mμ and the 1:2 complex has very low solubility and tends to precipitate out from the solution. Job's method, log-ratio method and gravimetric method were used to establish the composition of complexes. The apparent stability constant of the 1:1 complex is found to be log K_h = 4.46 or K_h = 2.9×10¹ at pH 1.2.     

Indirect Determination of Trace Tetraborate by Differential Pulse Polarography Using Its Copper Complex and Application to Waste and Drinking Water

A new differential pulse polarographic (DPP) method has been developed for the trace determination of boron. Its most stable copper complex is used in 0.5 M KNO₃ electrolyte since boron is not electroactive. By continuous addition of tetraborate to copper solution, the copper peak decreased first but then the peak became very small and nearly constant. This point was used for the boron determination. It was found that one mole of copper used two moles of tetraborate. Using this relationship, 1×10^?5 M tetraborate could be determined. The quantification limit was 2.5×10^?6 M and detection limit was 8×10^?7 M. In the presence of complex forming ions such as Pb, Zn, and Cd, the borate found in sample was somewhat smaller because of their reaction with borate. But since their complexes were not as strong as copper, only a few percent of borate were used. No interference was observed in the presence of calcium, chloride and sulfate. This method is applied for the determination of B in borax ore, waste water of borax industries and tap water of Ankara city.     

Study of the ionic conductivity of some fluorides of monovalent and tetravalent elements

Recently some interest has attached to ionic conductivity in the fluorides of metals with large cation radius because of the high fluorine mobility in these materials.A.c. conductivity measurements using the complex impedance method were carried out on sintered samples and showed that some binary fluorides of monovalent elements (M^I = K, Rb, Tl) and tetravalent elements (M^IV = Zr,Hf, Th, U) exhibit an appreciable ionic conductivity at moderate temperature : σ at 200°C (Ω^?1 cm^?1) Tl₃ZrF₇ 3.5 × 10^?3 Tl₂ZrF₆ 1.1 × 10^?2 Tl ZrF₅ 5 × 10^?4A single crystal study of Tl₃ZrF₇ shows that this compound crystallizes in the cubic system with space group Fm3m and cell parameter a = 9.34 Å. Therefore its crystal structure may be related to that of (NH₄)₃ZrF₇ [1 to 3] which is characterized by the presence of (ZrF₇)^3? ions with a pentagonal bipyramid as probable configuration. There are two crystallographically independent fluorine ions in position (96 j) of the space group Fm3m with a percentage of occupancy of 20.8 and 8.3 respectively. Thus Tl₃ZrF₇ is an example of fluoride where a three dimensional ionic conductivity occurs due to an incomplete occupation of a special symmetry position and where temperature increase might create rotation of (ZrF₇)^3? polyhedra giving rise to an important anionic disorder.In order to determine the origin of the ionic conductivity in TlZrF₅ we have undertaken the determination of the crystal structure of this fluoride from X-ray intensity measurements made with the aid of an automatic four circle diffractometer.TlZrF₅ cristallizes in the monoclinic system with unit-cell dimensions a = 8.112(1)Å, b = 7.927(3)Å, c = 7.929(1)Å, β = 123.99(1)° and space group P2 /c (No 14), Z = 4.In this structure, the Zr⁴⁺ ion is surrounded by eight F^? ions, the coordination polyhedron being a bicapped trigonal prism. This crystal structure consists of sheets (ZrF₅)^? that may be described as edge-shared and corner-shared bicapped trigonal prisms (ZrF₈). The sheets run parallel to the yOz plane and are bonded together by the Tl⁺ ions which are surrounded by twelve F^?ions. This arrangement produces relatively open tunnels in the b direction delimited by the cations. Of the five independent fluorine atoms, two of them, namely F(1) and F(4) are different from the other from the point of view of bonding and are located in these tunnels. Thus they are probably primarily responsible for the high conductivity of this material [4].With regard to Tl₂ZrF₆, it is the best as far as ionic conductivity is concerned. However its crystal structure is still unknown and its determination is actually under investigation in our laboratory.All this materials are good electronic insulators and their transport properties due to the high fluorine ion mobilities allow us to think that some of them hold considerable promise for use as solid electrolytes.     

Electromagnetic induction-assisted heating as a new method for on-line cloud point extraction of cadmium from water samples

We report on a novel method for on-line cloud point extraction (CPE) for preconcentration of cadmium ions. It is based on electromagnetic induction-assisted heating (EMIH) of iron particles in a packed bed contained in a quartz tube that acts as an on-line CPE enrichment column. The cadmium complex of 1-(2-pyridylazo)-2-naphthol is quantitatively retained by the column under the cloud point temperature with the help of EMIH. The column was then eluted with alcoholic borax buffer at room temperature and on-line coupled to FAAS. Under optimum conditions, the limit of detection (3 s_b/b) and limit of quantification (10 s_b/b) are 0.21 μg?L^?1 and 0.70 μg?L^?1 of Cd(II), respectively, and the relative standard deviation is 3.8 % (for n?=?8; at 20 ng?mL^?1). An enhancement factor of 76 is typically achieved. The correlation coefficient of the calibration graph using the present method was 0.9986. The method was successfully applied to determine Cd(II) in water samples

Electrical conductivity of potassium titanyl phosphate KTiOPO<Subscript>4</Subscript> pure crystals and those doped with Na<Superscript>+</Superscript>, Rb<Superscript>+</Superscript>, and F<Superscript>–</Superscript> ions

KTiOPO₄ crystals, both pure and doped with rubidium Rb⁺ and fluorine F^– ions, were grown in temperature range from 1060 to 846°С from salt solvent containing potassium metaphosphate КРО₃ and potassium orthophosphate К3РО₄ by using a Czochralski modified method. Potassium–sodium titanyl phosphate crystals were obtained from KTiOPO₄ crystals by the potassium isomorphic replacement with sodium; to this purpose, sodium chemical diffusion from NaNO₃ melt was used. Their ionic conductivity was studied by the electrochemical impedance spectroscopy method. The KTiOPO₄ crystal doping with rubidium and sodium ions was shown to lower the conductivity, whereas the doping with fluorine ions results in increased conductivity.     

Reentrant behavior of poly(vinyl alcohol)–borax semidilute aqueous solutions

 The reentrant behavior of Poly(vinyl alcohol) (PVA)–borax aqueous semidilute solutions with a PVA concentration of 20 g/l and borax concentrations varies from 0.0 to 0.20 M was investigated using dynamic light scattering (DLS) and dynamic viscoelastic measurements. Two (fast and slow modes) and three (fast, middle, and slow) relaxation modes of PVA semidilute aqueous solutions without and with the presence of borax, respectively, were observed from DLS measurements. The fast and middle relaxation modes were q ²-dependent (q is the scattering vector) characteristic of diffusive behavior; however, the slow modes were q ³-dependent, characteristic of intraparticle dynamics. The experimental results showed that the slow relaxation mode dominates the DLS relaxation. The DLS slow mode relaxation time, τ_s, and the viscoelastic modulus G′(ω) and G′′(ω) data had a similar trend and demonstrated reentrant behavior as the borax concentration was increased from 0.0 to 0.20 M, i.e. τ_s, G′(ω), and G′′(ω) fluctuated with increasing borax concentration. The excluded-volume effect of polymers, charge repulsion among borate ions bound on PVA molecules, and intermolecular cross-linking didiol–borate complexation caused an expansion of the polymer chain; however, the screening effect of free Na⁺ ions on the negative charge of the borate ions bound on PVA and intramolecular cross-linking didiol–borate complexation led to a shrinkage of the polymer chain. The reentrant behavior was the consequence of the balance between expansion and shrinkage of the PVA–borate complex. Received: 26 March 1999/Accepted in revised form: 3 September 1999     

Oxidations with potassium permanganate in the presence of fluoride

Summary The titration of ferrous iron in presence of fluoride ions in acid medium gives fleeting end points and erroneous results. A method is deviced to overcome this difficulty by oxidising the ferrous with an excess of KMnO₄ in alkaline medium. After mixing the reactants the excess of KMnO₄ is reduced by an excess of Hg₂ ²⁺ ions in presence of H₂SO₄ and fluoride. The remaining mercurous is then titrated with standard KMnO₄ solution.Part III: Issa, I. M., and M. Hamdy: Z. analyt. Chem. 174, 418 (1960).     

Chemical composition and crystal structure of β-alumina type R+-gallate (R+ = K+, NH+4)

The crystal structures of β-alumina type K⁺-gallate (K⁺-β-gallate), Mg²⁺-doped K⁺-β-gallate, and NH⁺₄-β-gallate were refined by the single crystal X-ray diffraction method. The positive charges of excess K⁺ ions in K⁺-β-gallate were compensated by O^2? ions in the mO site which coordinated with interstitial Ga³⁺ ions. The charge compensation mechanism mentioned above was changed by doping with Mg²⁺ ions. The excess charges in Mg²⁺-doped K⁺-β-gallate were compensated by the replacement of Mg²⁺ ions for Ga³⁺ ions at the middle of spinel block. No defects were found in NH⁺₄-β-gallate for the charge compensation, which was completely consistent with the result of thermal analysis that indicated a stoichiometric composition of NH⁺₄-β-gallate.     

NMR and DFT study of chemical bonding of the titanyl ion in pentafluoro complexes (NH4)3TiOF5 and Rb2KTiOF5

19F NMR and DFT methods are used to study the electronic structure and chemical bonding of titanyl ions in pentafluoro titanyl complexes (NH₄)₃TiOF₅ and Rb₂KTiOF₅. The experimental values of the anisotropy of ¹⁹F NMR chemical shifts (CSs) are shown to be consistent with the calculated parameters within the DFT method. At normal temperatures orientational disordering of octahedral [TiOF₅]^3- anions occurs, fluorine atoms steadily occupying cis- and trans-positions with respect to the O^2- ion. In both complexes, trans-position is not fully occupied; the occupation ratio does not exceed ~4:0.9. When the temperature is decreased to 150 K, the value of the CS anisotropy of the fluorine atom resonance line in trans-position is found to be smaller than the dipole-dipole broadening, whereas the line from fluorine atoms in cis-positions transforms into an asymmetric broad line characterized by the triaxial anisotropy of the CS tensor. It is shown that the found anisotropy corresponds to violation of the axial symmetry of Ti—F cis bonds because of strong delocalization of the electron density of Ti—O bonds in the titanyl ion.     

Ferric Chloride Complexes in Aqueous Solution: An EXAFS Study

A series of concentrated aqueous solutions of ferric chloride with different chloride:iron(III) ratios has been studied by means of EXAFS to determine the structure around the iron(III) ion of the dominating species in such solutions. The dominating species in dilute acidic aqueous solution of ferric chloride, at less than 1 mmol·dm^?3, are the hydrated iron(III) and chloride ions, while in concentrated aqueous solution and in solutions with an excess of chloride ions, up to 1.0 mol·dm^?3, it is the trans-[FeCl₂(H₂O)₄]⁺ complex. Possible higher chloroferrate(III) or dimeric [Fe₂Cl₆] complexes at room temperature, as proposed in the literature, were not observed in any of the studied solutions in spite of an excess of chloride ions of 1 mol·dm^?3.     

Loss of CO from the molecular ions of o-, m- and p-anisoyl fluorides,CH3OC6H4COF,with fluorine atom migration

Loss of CO from the molecular ions ([CH₃OC₆H₄COF]⁺˙) of o-, m- and p-anisoyl fluorides has been investigated by mass-analysed ion kinetic energy (MIKE) spectrometry. This reaction involves fluorine atom migration from the carbonyl group to the benzene ring. In the cases of o- and p-anisoyl fluorides, the fluorine atom migrates via a three-membered transition state to form the molecular ions ([CH₃OC₆H₄F]⁺˙) of o- and p-fluoroanisoles, respectively. On the other hand, in the case of m-anisoyl fluoride, the fluorine atom migrates from the carbonyl group to the benzene ring via a three- or four-membered transition state.     

Analytical Utility of the Unique Colour Reaction Between Uranyl Ions and Alizarin Fluorine Blue

Abstract

The uranyl-alizarin fluorine blue chelate complex shows an absorption peak at 560 nm, 30 nm higher than that of any other single metal complex of the reagent. The complex shows, at pH 4.5, a conditional stability constant of 2.3 × 10⁶ litres mole^?1 and molar absorptivity of 4100 litres mole^?1 cm^?1. Study of the feasibility of using this reaction for the photometric determination of Uo₂ ⁺² in both one and two liquid phase systems reveals serious interference from other metal ions.     

Ab-initio study of localization of an excess electron in sodium halide clusters

The equilibrium geometries of Na _n F _n and Na _n F _n?1 are optimized forn=2, 3, 4 at the SCF level. The Na _n F _n molecules appear as formed by Na⁺ and F^? ions. The paper studies the localization of the excess electron in the Na _n F _n?1 molecules. Na _n F _n?1 is obtained by removing from Na _n F _n a fluorine atom, and the excess electron takes the place of this lacking center, and allows a weak bond between the neighbouring Na atoms. Secondary minimum geometries, for which the excess electron has no defined place, are also studied.     

Cu(II) Ion Complexation by Excess of β-cyclodextrin in Aqueous Alkaline Solutions

Polarographic investigations of Cu(II) complexation in aqueous alkaline solutions containing an excess of β-cyclodextrin (β-CD) show that the complex formation begins at pH > 11, the concentration of free (uncomplexed) Cu(II) ions being in the range from ca. 10^-12 to ca. 10^-19 M, depending on β-CD concentration and pH. The formation of copper(II) 1:1 hydroxy-complex with β-cyclodextrin anion (CD^2-) was observed at pH 11–14. The logarithm of the stability constant of CuCD(OH)^2- ₂ complex is 19.7 ± 0.2 (20 °C, ionic strength 1.0), the values of the molar extinction coefficient and of the diffusion coefficient of this complex are 50 M^-1 cm^-1 (λ_max = 660 nm) and 1.0 × 10^-6 cm² s^-1, respectively.     

Diethyl (biscyclohexano)BODIPY dicarboxylates. Chelation of alkaline-earth metal ions and sensor properties

meso-Aryl-substituted (biscyclohexano)bis(ethoxycarbonyl)BODIPY [aryl = phenyl, 3,4-dimethoxyphenyl, and 2,3,5,6,8,9,11,12-octahydro-1,4,7,10,13-benzopentaoxacyclopentadecin-15-yl-(m-{benzo-15-crown-5}-yl)] were synthesized. The effect of alkaline-earth metals on the absorption and fluorescence spectra of these compounds was investigated. In all compounds along with the mechanism of the photoinduced electron transfer (PET), well-known for the crown-containing BODIPY-based sensors, one more response pattern is observed. The large excess of Ca²⁺ and Ba²⁺ ions in the system leads to the changes both in the UV-Vis and emission spectra. The complex formation results in the decrease of emission intensity and in its red shift. Besides, a new longwave absorption band appears in the UV-Vis spectrum of the BODIPY-metal ion complex. The formation constants of the complexes corresponding to this response pattern is about 100 times less than the formation constant of Ca²⁺-crown ether complex. ¹H, ¹³C, ¹¹B, and ¹⁹F NMR spectra, the results of quantum-chemical calculations, and their comparison with the literature data of X-ray diffraction study suggest that the binding of Ca²⁺ and Ba²⁺ ions occurs in the cavity formed by the fluorine atoms and the carbonyl oxygen atoms of the ester groups.     

Gas-phase C-F bond cleavage in perfluorohexane using W-, Si-, P-, Br-, and I-containing ions: Comparisons with reactions at fluorocarbon surfaces

Gas-phase reactions of W-, Si-, P-, Br-, and I-containing ions with the target molecule perfluorohexane at low collision energies (<15 eV) parallel known ion/surface reactions of the same projectile ions at fluorinated self-assembled monolayer surfaces. Charge exchange, dissociative charge exchange, and fluorine atom abstraction are observed and the majority of the projectile ions also undergo reactive charge exchange to produce specific fluorocarbon fragment ions of the target molecule in distinctive relative abundances. Abstraction of up to five fluorine atoms is observed upon collision of W⁺ with gaseous perfluorohexane, while similar experiments with CI⁺, SiCl⁺, and PCl^+· show abstraction of one or two fluorine atoms. Other projectiles, including Si^+·, PCl ₂ ⁺ , Br⁺, CBr⁺, and I⁺, abstract only a single fluorine atom. These patterns of fluorine atom abstraction are similar to those observed in ion/surface collisions. Also paralleling the ion/surface reactions, halogen exchange (Cl-for-F) reactions occur between the Cl-containing projectile ions and perfluorohexane to produce C₆F₁₂Cl⁺, a product of chemical modification of the target. Collisions of PCl^+· and PCl ₂ ⁺ also result in production of C₆F ₁₂ ^+· , indicating that the corresponding surface modification reaction involving molecular defluorination should be sought. Implications for previously proposed mechanisms, new ion/surface reactions, and for the use of gas-phase studies to guide investigations of the ion/surface reactions are discussed.     

Fluorine Bonding Enhances the Energetics of Protein-Lipid Binding in the Gas Phase

This paper reports on the first experimental study of the energies of noncovalent fluorine bonding in a protein-ligand complex in the absence of solvent. Arrhenius parameters were measured for the dissociation of gaseous deprotonated ions of complexes of bovine β-lactoglobulin (Lg), a model lipid-binding protein, and four fluorinated analogs of stearic acid (SA), which contained (X =) 13, 15, 17, or 21 fluorine atoms. In all cases, the activation energies (E_a) measured for the loss of neutral XF-SA from the (Lg + XF-SA)^7– ions are larger than for SA. From the kinetic data, the average contribution of each?>?CF₂ group to E_a was found to be ~1.1 kcal mol^–1, which is larger than the ~0.8 kcal mol^–1 value reported for?>?CH₂ groups. Based on these results, it is proposed that fluorocarbon–protein interactions are inherently stronger (enthalpically) than the corresponding hydrocarbon interactions.

Luminescence and nonradiative relaxation of Pb2+, Sn2+, Sb3+, and Bi3+ in oxide glasses

Absorption and fluorescence spectra of Sn²⁺ and Sb³⁺ in borax, phosphate, and germanate glasses were measured in the temperature range 87–295°K. Fluorescence decay times of these ions in borax glass at 87°K was a single exponent with τ ≈ 6–11 μsec. At 293°K, two decay times were resolved in the range of 50–2000 nsec. The nonexponential behavior is interpreted by the repopulation of the ³P₁ level from the ³P₀ level. The temperature dependence of fluorescence and the low values of quantum efficiencies of fluorescence are explained by means of the configurational coordinate diagram model.     

Photochemical and Electrochemical Reduction of Carbon Dioxide to Carbon Monoxide Mediated by (2,2′-Bipyridine)tricarbonylchlororhenium(I) and Related Complexes as Homogeneous Catalysts

[fac-Re(bpy) (CO)₃Cl] (bpy = 2,2′-bipyridine) is an efficient homogeneous catalyst for the selective and sustained photochemical or electrochemical reduction of CO₂ to CO. A quantum yield of 14% and a faradic efficiency of 98% were measured in the presence of excess Cl^? ions. The photochemical process took place under visible-light irradiation and consumed a tertiary amine as electron donor. A formato-rhenium complex was isolated in the absence of excess Cl^? ions. Substitution by Cl^? ion generated free formate, but no CO was detected. Luminescence measurements showed that the tertiary amine quenches the metal-to-ligand charge-transfer excited state of the rhenium complex via a reductive mechanism, with a rate constant of 3.4 × 10⁷M^?1S^?1. The 19e-complex [Re(bpy) (CO)₃X]^? produced either photochemically or electrochemically appears to be the active precursor in the CO-generation process. Detailed spectroscopic studies on ¹³C-enriched carbonyl-rhenium and formato-rhenium complexes derived from ¹³C-enriched CO₂ were performed in order to confirm the origin of the products and to study the exchange of the ligands. A mechanism for the present CO₂ photoreduction process is presented; it involves separate pathways for CO and formate generation, in which the [Re(bpy) (CO)₃X] complex plays the role of both the photoactive and the catalytic center.     

模拟水中铜镍合金B10耐蚀性的光电化学研究

采用循环伏安、光电化学和电化学阻抗谱技术对模拟水中铜镍合金B10的腐蚀行为进行了研究.在电位从正往负向扫描中 B10表面膜显示p-型光响应,光响应来自电极表面的Cu2O层,但最大光电流比硼砂-硼酸中的要低。B10电极的耐蚀性能随着溶液中Cl-、SO42-和S2-浓度及pH的增加而降低。温度的升高会导致光电流由p-型转为n-型,耐蚀性能急剧下降。电化学阻抗谱测量结果与光电化学方法得到的结果相一致。