Ascorbic Acid/Iodine and Triphenylphosphine/Iodine as Reducing Agents for the As(V)[dbnd]O Group

The scope of ascorbic acid/iodine and triphenylphosphine/iodine in methanol for the direct reduction of arsenic(V) compounds having the As[dbnd]O group has been investigated. Ascorbic acid/iodine reduces arsonic acids, diphenylarsinic acid (but not dimethylarsinic acid), and triphenylarsine oxide. The rates of reduction depend on the electronic effects of the ligands bound to arsenic and on the hydrogen-bonding strength of the species, when present. When the As(V) compound has an [sbnd]NH ₂ or an [sbnd]NH ₃ ⁺ group, the reduction product reacts with a ketonic form of dehydroascorbic acid, giving condensation product(s). Triphenylphosphine/iodine reduced slowly the zwitterionic o-aminophenylarsonic acid but reduced faster the hydrochloric acid salt of the same acid. It reduced dimethylarsinic acid as well because the powerful electron-withdrawing Ph ₃ P ⁺coordinated to As[dbnd]O seems to outweigh the electronic and hydrogen bonding effects.     

Synthesis of cationic gold(III) complexes using iodine(III)

Abstract

We report the synthesis and characterization of cationic Au(III) complexes supported by nitrogen-based ligands. The syntheses are achieved by reacting Au(I) complexes [Au(N-Me-imidazole)₂]⁺ and [Au(pyridine)(NHC)]⁺ with iodine(III) reagents PhI(OTf)(OAc) and [PhI(pyridine)₂]²⁺ yielding a series of cationic gold(III) complexes. In contrast, reactions of phosphine ligated gold(I) complexes with iodine(III) reagents results in the oxidation of the phosphine ligand.     

Maleanilic Acids as Highly Selective Reagents for the Amperometric Determination of Thorium (IV)

Abstract

Thorium has been determined amperometrically at an applied e. m. f. of -1.2V with fifteen maleanilic acids. Out of these o-tolyl, p-tolyl, 1-naphthyl, 2-naphthyland 4-amino maleanilic acid were found promising analyticalreagentsand most effective. Th(IV) in the range 6.60 to 2350.0 mg per 100 ml can be determined with an error of ± 0.2%. The interference of fifty-five ions were studied and only five ions Zn(II), Pb(II), Fe(III), UO₂ (II) and Zr(IV) interfered. which could be masked by the addition of S₂O² ₃ or SCN^?, Cl^? or SO^2- ₄, SCN^? or citrate, citrate or tartrate and P₂O^4- ₇ respectively.     

INTERACTION BETWEEN TRINUCLEAR OXOCENTRED COORDINATION COMPOUNDS OF TRANSITION METALS AND ORGANIC SOLVENTS1

Abstract

A number of oxo-centred trinuclear complexes have been obtained, of general formula [M₃O(OOCR)₆L₃]X (R?H, CH₃; M?Cr(III), Fe(III); L=pyridine, 4-picoline; X?NO^? ₃, ClO^? ₄). The behaviour of these compounds in absolute methanol and in dimethylsulphoxide was investigated by the conductometric method. Dissociation constants of the complexes were determined. Molar conductivities and solvodynamic radii of the cations were also evaluated. It has been shown that the cations do not undergo solvation to any measurable extent.     

Nicotinamide complex of silver(III) with expanded coordination number

Abstract

In strongly alkaline media ([OH^?]?≥?0.12 M), nicotinamide (nica) forms a complex with square-planar Ag(OH)₄^? [nica]?≥?0.05 M. The complex decomposes in seconds to nicotinamide N-oxide. The correlation of maximum absorbance of the complex with concentrations of nicotinamide and hydroxide requires that the complex is either the five-coordinate Ag(OH)₄(H_-1nica)^2? or the six-coordinate Ag(OH)₅(nica)^2?. Comparison with the reactions of Ag(OH)₄^? with nicotinate ion (nic^?) and acetamide under similar conditions indicates that nicotinamide coordinates with Ag(OH)₄^? by the amido group rather than the nitrogen on the pyridine ring or the amido oxygen. Kinetics of the Ag(III)-nica redox reaction are consistent with direct reaction between nicotinamide and uncoordinated Ag(OH₄)^?. Oxidation takes place at the pyridine ring, yielding nicotinamide N-oxide. Silver(III) is reduced to monovalent silver.     

On-line separation and preconcentration of inorganic arsenic and selenium species in natural water samples with CTAB-modified alkyl silica microcolumn and determination by inductively coupled plasma-optical emission spectrometry

A new, simple, and selective method has been presented for the separation and preconcentration of inorganic arsenic (As(III)/As(V)) and selenium (Se(IV)/Se(VI)) species by a microcolumn on-line coupled with inductively coupled plasma-optical emission spectrometry (ICP-OES). Trace amounts of As(V) and Se(VI) species were separated and preconcentrated from total As and Se at desired pH values by a conical microcolumn packed with cetyltrimethylammonium bromide (CTAB)-modified alkyl silica sorbent in the absence of chelating reagent. The species adsorbed by CTAB-modified alkyl silica sorbent were quantitatively desorbed with 0.10 ml of 1.0 mol l⁻¹ HNO₃. Total inorganic arsenic and selenium were similarly extracted after oxidation of As(III) and Se(IV) to As(V) and Se(VI) with KMnO₄ (50.0 μmol l⁻¹). The assay of As(III) and Se(IV) were based on subtracting As(V) and Se(VI) from total As and total Se, respectively. All parameters affecting the separation/preconcentration of As(V) and Se(VI) including pH, sample flow rate and volume, eluent solution and volume have been studied. With a sample volume of 3.0 ml, the sample throughput was 24 h⁻¹ and the enrichment factors for As(V) and Se(VI) were 26.7 and 27.6, respectively. The limits of detection (LODs) were 0.15 μg l⁻¹ for As(V) and 0.10 μg l⁻¹ for Se(VI). The relative standard deviations (RSDs) for nine replicate determinations at 5.0 μg l⁻¹ level of As(V) and Se(VI) were 4.0% and 3.6%, respectively. The calibration graphs of the method for As(V) and Se(VI) were linear in the range of 0.5–1000.0 μg l⁻¹ with a correlation coefficient of 0.9936 and 0.9992, respectively. The developed method was successfully applied to the speciation analysis of inorganic arsenic and selenium in natural water samples with satisfactory results.     

Determinations Coulometriques De Quinones Et De Chloronaphtoquinones A L'Aide Du Titane (III) Electrogenere

Abstract

Small quantities of chloronaphtoquinones derivatives, quinhydrone and traces of benzoquinone are titrated using titanium (III) electrogenerated at a platinum electrode. The most suitable electrogenerating media used are discussed in details. As low as 5μg of benzoquinone were determined with a good precision.     

A New Hybrid Cmpo/Nopopo Ligand: Synthesis and Selected Lanthanide Coordination Chemistry

Abstract

A two-step synthesis for 2,6-bis[(diphenyl)-N,N-diethylcarbamoylmethylphosphine oxide]pyridine N-oxide (3) from 2,6-bis[(diphenylphosphinoyl)methyl]pyridine is reported along with coordination chemistry with Dy(III) and Yb(III). Crystal structure determinations for the ligand 3_S,S and 1:1 complexes [Dy(3_R,S )(NO₃)₃]·(Me₂CO) and [Yb(3_R,S )(NO₃)₃]·(Me₂CO) are described. In these complexes, the pentafunctional ligand 3 coordinates in a tridentate NOPOPO chelate mode.     

Synthesis and properties of new polyamides derived from 1,4-bis(4-aminophenoxy)-2,5-di-tert-butylbenzene and aromatic dicarboxylic acids

The diamine 1,4-bis(4-aminophenoxy)-2,5-di-tert-butylbenzene, containing symmetric, bulky di-tert-butyl substituents and a flexible ether unit, was synthesized and used to prepare a series of polyamides by the direct polycondensation with various aromatic dicarboxylic acids in N-methyl-2-pyrrolidinone (NMP) using triphenyl phosphite and pyridine as condensing agents. All the polymers were obtained in quantitative yields with inherent viscosities of 0.32–1.27 dL g⁻¹. Most of these polyamides, except II _a , II _d , and II _e , showed an amorphous nature and dissolved in polar solvents and less polar solvents. Polyamides derived from 4,4′-sulfonyldibenzoic acid, 4,4′-(hexafluoro-isopropylidene)dibenzoic acid, and 5-nitroisophthalic acid were even soluble in a common organic solvent such as THF. Most polyamide films could be obtained by casting from their N,N-dimethylacetamide (DMAc) solutions. The polyamide films had a tensile strength range of 49–78 MPa, an elongation range at break of 3–5%, and a tensile modulus range of 1.57–2.01 GPa. These polyamides had glass transition temperatures ranging between 253 and 276°C, and 10% mass loss temperatures were recorded in the range 402–466°C in nitrogen atmosphere. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1069–1074, 1998     

Synthesis,characterization and dynamic stereochemistry of thermochromic tris(dithiocarbamato)vanadium(III) complexes stereochemistry of thermochromic tris(dithiocarbamato)vanadium(III) complexes

The vanadium(III) complexes, V(S₂CNMe₂)₃ (1) and V(S₂CN ⁱ Pr₂)₃ (2) were prepared and characterized by analysis, IR, electronic and ¹H NMR spectra. The complexes show reversible thermochromic behaviour. MM2 calculations were used to simulate the molecular structure of 1. For 2, variable temperature ¹H NMR revealed hindered rotation about C–N bonds. The rotational energy barrier (38?kJ?mol^?1) was obtained by molecular mechanics force-field calculations.     

Crystal Structure and Triboluminescence Spectrum of A μ2-(ONC5H5) Bridging Dinuclear Europium(III) Complex

The crystal structure and triboluminescence spectrum of a _μ2-(ONC₅H₅) bridging dinuclear europium(III) complex, Eu₂(TTA)₆(PyO)₂ where HTTA=2-thenoyltrifluoroacetone, PyO=pyridine N-oxide, are reported. It is centrosymmetric and two Eu(III) atoms are bridged by two pyridine oxide oxygen atoms. The Eu……Eu distance is 4.2137(9) Å. The triboluminescence maximum is similar to that of the photoluminescence and the disorder of the thienyl rings and CF₃ groups may be responsible for its triboluminescent activity. The complex crystallizes in the triclinic space group P&1macron; with cell parameters a = 12.239(1), b = 12.614(2), c = 14.048(2) Å, α = 110.31(1), β = 112.05(1), γ = 99.23(1)°, V = 1776.6(4) Å ³ and Z = 2. The strcutre was refined by full-matrix least squares methods to R = 0.0451 and R _w = 0.01170.     

VANADIUM(III) AND VANADIUM(IV) COMPLEXES WITH PYRAZINE IN ALCOHOL SOLUTION

Abstract

The V(III)-pyrazine system was examined spectroscopically in the isoamyl alcohol solution. An unstable, violet-red, binuclear vanadium(III) complex [V₂(pyraz)Cl₄]²⁺ was found to be formed. On exposure to air it was slowly converted into a sparingly soluble green vanadium(IV) compound, [VO(pyraz)OH]Cl.H₂O. This compound was examined by the analytical, spectroscopic (electronic and infra-red spectra) and magnetic methods.     

SOME METAL COMPLEXES OF α, β, γ, δ-TETRA-(4-PYRIDYL) PORPHINE

Abstract

The zinc (II), copper (II), nickel (II), cobalt (II), chloromanganese (III), and chloroiron (III) complexes of α, β, γ, δ-tetra-(4-pyridyl)-porphine (4-TPyP) were prepared. The magnetic susceptibilities from near 0° to 90° K and at room temperature were measured for solid Cu(4-TPyp), Ni(4-TPyP), Co-(4-TPyP), ClMn(4-TPyP) · H₂ O and ClFe(4-TPyP). The Mössbauer spectra of ClFe(4-TPyP) were obtained at several temperatures. The infrared spectra and d-spacings were obtained for all of the solids. Electronic spectra of the complexes in pyridine and, where possible, in 0.1 N HCl solution were recorded. Evidence of intermolecular interaction was found for Co(4-TPyP), Ni(4-TPyP), and ClFe(4-TPyP).     

STUDIES OF THE STRUCTURE OF VANADIUM(III) COMPLEXES WITH NITROGEN CONTAINING LIGANDS IN ALCOHOLIC SOLUTIONS. I. COMPLEXES OF V(III) WITH AZOLES

Abstract

Anhydrous vanadium trichloride reacts with azoles in low concentrated ethyl alcohol solution of V(III) to produce 1:1 electrolytic complexes of the type [V (azole)₄Cl₂]⁺. Studies of the visible spectra of all the above complexes demonstrate that the vanadium(III) is octahedrally co-ordinated. The room temperature magnetic moments of the complexes (～ 2.8 B.M.) are consistant with the presence of two unpaired electrons per vanadium atom. At higher concn. of V(III) the polynuclear violet-red complexes probably are formed.     

Synthesis,spectral and antimicrobial studies of chloroantimony(III)di[3(2′-hydroxyphenyl)-5-(4-substitutedphenyl)pyrazolinates]

Dichloroantimony(III) pyrazolinates and chloroantimony(III) dipyrazolinates of the type SbCl₂(C₁₅H₁₂N₂OX) and SbCl(C₁₅H₁₂N₂OX)₂ [where C₁₅H₁₂N₂OX = 3(2′-hydroxyphenyl)-5-(4-X-phenyl)pyrazoline, X=H in1 and5;–CH₃ in2 and6;–OCH₃ in3 and7 and–Cl in4 and8] have been synthesized by reaction of SbCl₃ and sodium salt of pyrazolines in 1 : 1 and 1 : 2 molar ratio in anhydrous benzene at elevated temperature. These newly synthesized derivatives have been characterized by elemental analysis (C, H, N, Cl and Sb), molecular weight measurement and spectral studies [IR and¹H and¹³C NMR]. The free pyrazoline and some dichloroantimony(III) pyrazolinates and chloroantimony(III) dipyrazolinates have been screened for antibacterial and antifungal activities, with some dichloroantimony(III) pyrazolinates and chloroantimony(III) dipyrazolinates exhibiting higher antibacterial and antifungal effects than free pyrazoline and some antibiotics.     

An Adaptable N-Heterocyclic Carbene Macrocycle Hosting Copper in Three Oxidation States

A neutral hybrid macrocycle with two trans-positioned N-heterocyclic carbenes (NHCs) and two pyridine donors hosts copper in three oxidation states (+I–+III) in a series of structurally characterized complexes ( 1 – 3 ). Redox interconversion of [LCu]^+/2+/3+ is electrochemically (quasi)reversible and occurs at moderate potentials (E_1/2=−0.45 V and +0.82 V (vs. Fc/Fc⁺)). A linear C^NHC-Cu-C^NHC arrangement and hemilability of the two pyridine donors allows the ligand to adapt to the different stereoelectronic and coordination requirements of Cu^I versus Cu^II/Cu^III. Analytical methods such as NMR, UV/Vis, IR, electron paramagnetic resonance, and Cu Kβ high-energy-resolution fluorescence detection X-ray absorption spectroscopies, as well as DFT calculations, give insight into the geometric and electronic structures of the complexes. The XAS signatures of 1 – 3 are textbook examples for Cu^I, Cu^II, and Cu^III species. Facile 2-electron interconversion combined with the exposure of two basic pyridine N sites in the reduced Cu^I form suggest that [LCu]^+/2+/3+ may operate in catalysis via coupled 2 e⁻/2 H⁺ transfer.     

The first three‐dimensional FeIII–SrII heterometallic coordination polymer: poly[[diaquatetrakis(μ3‐pyridine‐2,3‐dicarboxylato)diiron(III)strontium(II)] dihydrate]

The title compound, poly[[diaqua‐1κ²O‐tetrakis(μ₃‐pyridine‐2,3‐dicarboxylato)‐2:1:2′κ¹⁰N,O²:O^2′,O³:O^3′;2:1:2′κ⁸O³:O^3′:N,O²‐diiron(III)strontium(II)] dihydrate], {[Fe₂Sr(C₇H₃O₄)₄(H₂O)₂]·2H₂O}_n, which has triclinic (P) symmetry, was prepared by the reaction of pyridine‐2,3‐dicarboxylic acid, SrCl₂·6H₂O and Fe(OAc)₂(OH) (OAc is acetate) in the presence of imidazole in water at 363 K. In the crystal structure, the pyridine‐2,3‐dicarboxylate (pydc²⁻) ligand exhibits μ₃‐η¹,η¹:η¹:η¹ and μ₃‐η¹,η¹:η¹,η¹:η¹ coordination modes, bridging two Fe^III cations and one Sr^II cation. The Sr^II cation, which is located on an inversion centre, is eight‐coordinated by six O atoms of four pydc²⁻ ligands and two water molecules. The coordination geometry of the Sr^II cation can be best described as distorted dodecahedral. The Fe^III cation is six‐coordinated by O and N atoms of four pydc²⁻ ligands in a slightly distorted octahedral geometry. Each Fe^III cation bridges two neighbouring Fe^III cations to form a one‐dimensional [Fe₂(pydc)₄]_n chain. The chains are connected by Sr^II cations to form a three‐dimensional framework. The topology type of this framework is tfj . The structure displays O—H...O and C—H...O hydrogen bonding.     

Spectrophotometry Determination of Arsenic(III) and Antimony(III) by Means of Isonicotinoylhydrazones of 4-Dimethylaminobezaldehyde (4-Dbih) and 2-Hydroxynaphthaldehyde (2-Hnih)

Abstract

4-DBIH and 2-HNIH react with As(III) and Sb(III) respectively, in CH₃COOH medium to form colored complexes stable in presence of EDTA. As(III) and Sb(III) do not react with 2-HNIH and 4-DBIH respectively, and the Sb(III)-2-HNIH complex is extractable into isoamyl alcohol. These behaviours were used for the spectrophotometry determination of As (III) and Sb(III) in presence of several cations.     

Characterization of [ReO(Tetramethylthiourea)4](PF6)3 in Solution: Electrochemical,NMR and Ligand Substitution Studies

The complex [ReO(Me₄tu)₄]³⁺, with Me₄tu = tetramethylthiourea, is characterized in nonaqueous media. Its structure is studied in acetonitrile solution by ¹H and ¹³C NMR and its electrochemical behavior in the same solvent is analyzed by means of cyclic voltamperometric measurements. Heteronuclear correlation and variable temperature NMR experiments suggest that the complex ion shows a similar structure in solution and in the solid state. At low temperatures (below 0°C) free rotation of the dimethylamine groups around the thiocarbonyl carbon-nitrogen bond is restricted and the dissolved complex adopts the rigid structure observed in the solid state. Cyclic voltamperometric results suggest that the redox behavior of this compound can be explained through an E_rC_iE_r mechanism (a chemical reaction coupled between two electron-transfer reactions). An initial one electron reduction of the complex from Re(V) to Re(IV) followed by an irreversible chemical reaction, leads to a new electroactive species of Re(IV)*, which is reduced to Re(III). The ability of [ReO(Me₄tu)₄](PF₆)₃ to serve as a precursor for other Re(V) complexes by ligand substitution is established, in acetone solution, with different kinds of incoming ligands: diethyldithiocarbamate (Et₂dtc), ethylenediamine (en) and pyridine (py). The previously known complexes [Re^v ₂O₃(Et₂dtc)₄], [Re^VO₂(en)₂](PF₆) and [Re^VO₂(py)₄](PF₆) are easily synthesized under mild conditions with high yields.     

Dual‐column capillary microextraction (CME) combined with electrothermal vaporization inductively coupled plasma mass spectrometry (ETV‐ICP‐MS) for the speciation of arsenic in human hair extracts

In this work, dual‐column capillary microextraction (CME) system consisting of N‐(2‐aminoethyl)‐3‐aminopropyltrimethoxysilane (AAPTS)‐silica coated capillary (C1) and 3‐mercaptopropyl trimethoxysilane (MPTS)‐silica coated capillary (C2) was developed for sequential separation/preconcentration of arsenite [As(III)], arsenate [As(V)], monomethylarsonic acid [MMA(V)] and dimethylarsinic acid [DMA(V)] in the extracts of human hair followed by electrothermal vaporization inductively coupled plasma mass spectrometry (ETV‐ICP‐MS) detection with iridium as permanent modifier. Various experimental parameters affecting the dual‐column microextraction of different As species had been investigated in detail. It was found that at pH 9, As(V) and MMA could be quantitatively retained by C1 and only As(III) could be quantitatively retained by C2. With the aid of valve switching, As(V)/MMA(V) retained on C1 and As(III) retained on C2 could be sequentially desorbed by 10 µl of 0.01 mol l^?1 HNO₃ [for As(V)], 0.1 mol l^?1 HNO₃ [for MMA(V)] and 0.2 mol l^?1 HNO₃‐3% thiourea (m/v) [for As(III)], respectively, the eluents were immediately introduced into the Ir‐coated graphite tubes for further ETV‐ICP‐MS detection. With two‐step ETV pyrolysis program, Cl^? in the sample matrix could be in situ removed, and the total As in the human hair extracts or digested solution could be interference‐free, determined by ETV‐ICP‐MS. DMA(V) in the human hair extracts was obtained by subtraction of total As in the human hair extracts from other three As species. Under the optimized conditions, the detection limits (3 σ) of the method were 3.9 pg ml^?1 for As(III), 2.7 pg ml^?1 for As(V), 2.6 pg ml^?1 for MMA(V) and 124 pg ml^?1 for total As with the relative standard deviations less than 7.0% (C = 0.1 ng ml^?1, n = 7), and the enrichment factor was 286, 262 and 260 for As(III), As(V) and MMA(V), respectively. The developed method was successfully applied for the speciation of arsenic in the extracts of human hair. Copyright © 2009 John Wiley & Sons, Ltd.