Electrochemical mediators for total oxidation of chlorinated hydrocarbons: formation kinetics of Ag(II), Co(III), and Ce(IV)

Mediated electrochemical oxidation (MEO) with Ag(n) and Co(iii) in 7 m HNO₃ and 3.5 M H₂SO₄ has been studied. High degradation rates were found for superchlorinated organic substances such as pentachlorophenol (PCP), Lindane and polychlorinated biphenyls (PCBs) using Ag(ii) in HNO₃ as mediator. An investigation on the formation kinetics of Ag(ii), Co(iii), and Ce(iv) by means of a rotating disc electrode (RDE) led to a quantitative determination of limiting currents at various mediator concentrations. Reaction rate constants of water oxidation by Ag(ii) were determined at various temperatures and compared to reaction rates of Co(iii).     

Electrical properties of macromolecular complexes of coordinated polymers with mixed valence of Co(II), Co(III) and Co(II–III)

Electrical properties of bis‐ethylenediamine Co(II), Co(III) and Co(II–III) mixed valence complexes and polyethylenediaminecarbosilazane (PEDCSZ) [Co(II), Co(III) and Co(II–III)] macromolecules were measured at room temperature in a frequency range between 1 Hz and 10⁶ Hz. Electrical modulus, permittivity and ac conductivity were calculated using ac impedance and phase‐angle measurements. It was found that the overall conductivity of PEDCSZ macromolecules with Co is much higher than that for Co monomers. In addition, the conductivity of PEDCSZ Co(III) and Co(II–III) mixed valence compounds are higher than those containing Co(II) where the electronic conduction is dominant. The relaxation time increases from about 2.7 × 10^?6 s for Co(II) chloride to a value of 2.9 × 10^?4 s for Co(II–III) chloride monomers. Copyright © 2003 Society of Chemical Industry     

Application of new unsymmetrical chiral Mn(III), Co(II,III) and Ti(IV) salen complexes in enantioselective catalytic reactions

New unsymmetrical chiral salen complexes were synthesized and the efficiency of Mn(III), Ti(IV), Co(II) and Co(III) type catalysts were examined in the enantioselective epoxidation of styrene and α‐methylstyrene, the trimethylsilylcyanation of benzaldehyde, the borohydride reduction of aromatic ketones and asymmetric hydrolysis of epoxides to diols, respectively. A very high level of enantioselectivity was attainable over the unsymmetrical chiral salen complexes prepared mainly from salicylaldehyde and 2‐formyl‐4,6‐di‐tert‐butylphenol derivatives. Enantiomeric excess of the corresponding reaction product obtained using unsymmetrical chiral salen catalysts was generally higher than that over conventional symmetric chiral salen catalysts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Electrochemical syntheses and structures of lead(II) and bismuth(III) complexes of 4-(trimethylammonio)benzenethiolate

Two main-group metal complexes of the zwitterionic ammonium thiolate complexes, [M(Tab)₃](ClO₄)_n (Tab = 4-(trimethylammonio)benzenethiolate) (1: M = Pb, n = 2; 2: M = Bi, n = 3), were prepared by electrochemical oxidation of Pb or Bi electrode in MeCN containing Tab and Et₄NClO₄. Each M atom in 1 and 2 is coordinated by three S atoms of three Tab ligands, forming a trigonal pyramidal coordination geometry. The resulting [M(Tab)₃]ⁿ⁺ cations are interconnected by secondary M⋯S interactions to form two different 1D cationic chains. The electrochemical properties of 1 and 2 were also investigated by cyclic voltammetry.     

Dinuclear,tetrakis(acetato)-bridged lanthanide(III) complexes from the use of 2-acetylpyridine hydrazone

The first employment of 2-acetylpyridine hydrazone in lanthanide(III) chemistry has led to dinuclear complexes with four bridging acetate groups of two different types and chelating 2-acetylpyridine hydrazone ligands.     

Hydrothermal syntheses and crystal structures of four novel lanthanide(III) complexes based on two mixed N,O-donor ligands

Four novel polymeric lanthanide(III) complexes [Pr(NCP)(2,5-pydc)]_n·1.5nH₂O (1), [La(NCP)(2,5-pydc)]_n (2), [Nd(NCP)(2,5-pydc)]_n (3) and [Sm(NCP)(2,5-pydc)]_n (4) (HNCP = 2-(4-carboxyphenyl)imidazo(4,5-f)(1,10)phenanthroline, 2,5-H₂pydc = pyridine-2,5-dicarboxylic acid) have been hydrothermally synthesized and characterized via elemental analysis and single crystal X-ray diffraction. Structural analyses revealed that all of these four complexes possess similar two-dimensional sheet structures, which are further linked by the hydrogen bonds to furnish three-dimensional supramolecular structures. Meanwhile, the thermogravimetric analysis and photoluminescent property of complexes 1–4 have also been investigated.     

Destruction of aniline by mediated electrochemical oxidation with Ce(IV) and Co(III) as mediators

Mediated electrochemical oxidation has been employed to test the feasibility of treating soluble organic wastes. We report Ce(IV)- and Co(III)-mediated electrochemical oxidation of aniline at various electrodes in acidic media as an example of organic waste. Aniline was oxidized by an electrogenerated electron transfer mediator, Ce⁴⁺ or Co³⁺, in the anolyte and carbon dioxide was produced as a final oxidation product. Carbon dioxide was collected by bubbling through a barium hydroxide solution. When a powerful oxidizing agent, Ce(IV) or Co(III), was used as an electron shuttling mediator, parameters affecting the coulombic efficiency for aniline oxidation were the standard oxidation potentials of the mediators, their concentrations and the reaction temperature. Intermediate species produced during the oxidation of aniline were identified by cyclic voltammetric and absorption spectroscopic measurements.     

Nanostructured catalysts for oxygen electroreduction based on bimetallic monoethanolamine complexes of Co(III) and Ni(II)

Oxygen reduction electrocatalysts based on the monoethanolmine complexes {[CoEtm]₂(μ-Etm)₄Ni(NO₃)₂} and {[CoEtm]₂(μ-Etm)₄Ni(NO₃)₂} + activated carbon AG-3 have been obtained by high-temperature synthesis. The nature of active centers on the synthesized electrocatalysts was described. Using potentiostatic and cyclic potentiodynamic voltammetry, the kinetic characteristics of catalysts in the oxygen electroreduction reaction were determined. Thermal decomposition of the thermally unstable complexes was described and character of the active centers formed was discussed. The optimal synthesis temperature of electrocatalysts is 600 °C in an inert atmosphere. The calculated exchange current densities for the oxygen electroreduction reaction at the catalysts in 1 M KOH at 20 °C was j ₀  = 1.01 × 10^?3 A g^?1–3.3 × 10^?3 A g^?1. The Tafel slopes of stationary polarization curves are 0.054–0.063 V for b ₁ and 0.106–0.125 V for b ₂ . The prepared electrocatalysts can be recommended only for electrochemical systems with alkaline electrolyte.     

Gallium(III) and indium(III) complexes of cross-bridged tetraamine ligands

Gallium(III) and indium(III) complexes of cross-bridged cyclam and cyclen tetraaza macrocyclic ligands have been prepared and structurally characterized. In the crystalline state, both the GaCl₃ (cross-bridged cyclam) and InBr₃ (cross-bridged cyclen) complexes feature hexacoordinate cations in cis-folded tetradentate ligand clefts with ancillary cis-dihalides. These represent the first well-characterized gallium and indium halide complexes of tetraazamacrocycles.     

Monometallic and bimetallic europium(III) and terbium(III) complexes: Synthesis and luminescent properties

Eight new lanthanide complexes of the form Ln(L)₃bipy and [Ln(L)₃]₂bpm were synthesized (where L = 2,2,6,6-tetramethyl-3,5-heptanedione (tmh) and 1,1,1-trifluoro-5,5-dimethyl-2,4-hexanedione (tdh), bipy = 2,2′-bipyridine, bpm = 2,2′-bipyrimidine and Ln = Tb(III) or Eu(III)). The luminescent spectra are typical of Tb(III) and Eu(III) complexes with intense transitions at 545 nm for Tb(III) and 612 nm for the Eu(III) complexes. Energy gaps between the tmh 1 orbitals and the ⁰D_J manifold of Eu(III) are too large to give efficient energy transfer therefore emission spectra for Eu(tmh)₃bipy and [Eu(tmh)₃]₂bpm were not detected. Lifetimes are greatest for the Tb(III) complexes containing tmh terminal ligands while the longest lifetimes for the Eu(III) complexes occur with the tdh terminal ligands.     

The syntheses,characterization and fluorescence spectra of novel,octakis(alkylthiophthalocyanato) nickel(II) and palladium(II) complexes

The syntheses, characterization and fluorescence studies of several {octakis(alkylthio)phthalocyanato} palladium(II) and nickel(II) complexes are presented. The absorption spectra of some of the complexes showed extra peaks which are attributable to non-planar distortion, the extent of which, was found to dependent on alkyl chain length. The fluorescence excitation spectra of the nickel(II) derivatives were not in agreement with their absorption spectra, owing to structural changes upon excitation. Fluorescence quantum yields were very low (<1%) for all complexes as a consequence of the open-shell electronic structures of nickel(II) and palladium(II).     

Cadmium(II) chloride complexes of imidazole-based ligands: Solvothermal syntheses,crystal structures and luminescent properties

Presented are the solvothermal syntheses, structures, characterizations, and luminescent properties of four novel organic-modified cadmium chloride complexes constructed from CdCl₂ and imidazole (or its derivatives), namely [CdCl₂(Im)₄] (1, Im = imidazole), [CdCl₄(HAPI)₂] (2, API = N-(3-Aminopropyl)-imidazole), [Cd(μ-Cl)₂(1-Mim)₂]_∞ (3, 1-Mim = 1-methyl imidazole) and [CdCl₃(HAPI)]_∞ (4). 1 and 2 feature a zero dimensional (0D) mononuclear structure with different mole ratios of Cd: Cl: ligand, while compound 3 and 4 bear infinite chains constructed from different subunits and connection modes. Worthy of note is that 4 represents a new structural type in the family of organic modified cadmium halides. The fluorescence spectra showed that compounds 1–4 exhibited emission peaks around 450 nm with the quantum yields of 23.01%, 5.84%, 27.31%, 5.71%, respectively.     

Zeolite encapsulated Ru(III), Cu(II) and Zn(II) complexes as effective catalysts for the oxidation of ethylbenzene

Ru(III), Cu(II) and Zn(II) complexes of imidazole (ImzlH) have been synthesized in the supercages of zeolite-Y by flexible ligand method and characterized by spectroscopic (IR and UV?CVis) studies, XRD and thermogravimetric analysis, surface area, and pore volume measurements. These complexes were screened for their catalytic study towards the oxidation of ethylbenzene to a mixture of acetophenone, benzaldehyde and styrene using tert-butylhydroperoxide (TBHP) as an oxidant. A best-suited reaction condition has been optimized for these catalysts by varying the amount of the oxidant and catalyst, reaction time and volume of solvent for maximum transformation of ethylbenzene. Under the optimized reaction conditions, [Cu(ImzlH)]-Y gave 79.3% conversion after 1?h of reaction time. All these catalysts were more selective towards acetophenone formation. Among the prepared catalysts, zeolite encapsulated Cu(II) complex was found to be more active than the corresponding Ru(III) and Zn(II) complexes and all the complexes were stable enough to be reused. The catalytic activities of the neat complexes and metal exchanged zeolites were also compared with the zeolite encapsulated metal complexes.     

Electrometric study of La(III), Ce(III), Pr(III) and Sm(III) complexes of n-glycylglycine

Saxena and co-workers have made extensive study on the complexing tendencies of several thiols and some of the aminoacids with various metals[1–4]. This paper reports the determination of composition and stabilities of La(III), Ce(III), Pr(III) and Sm(III) complexes of N-Glycylglycine at 30° C and 40° C by applying potentiometric and conductometric titration techniques and also the values of ΔG, ΔH and ΔS at 30° C accompanying the complexation reactions. There is however, no reference in the literature on the study of the present system.     

Novel Ag(I) complexes with propeller-like structure of tripodal ligand: syntheses and structures of two- and three-coordinate silver (I) complexes

Two mononuclear Ag(I) complexes, [Ag(tbsb)](NO₃)·DMF (1) and [Ag(tbsb)](NO₃)·4.5H₂O (2) {tbsb=1,3,5-tris(2-benzimidazol)sulfanylmethyl)-2,4,6-trimethylbenzene}, have been synthesized by self-assembly reaction of AgNO₃ with tbsb and characterized structurally. The silver atoms of both the complexes are coordinated by the imine nitrogen atoms from a tripodal ligand (tbsb) to form two- and three-coordinate structures, respectively. Complex 1 presents the first example of silver (I) compound of the tripodal ligand possessing propeller-like structure.     

Two novel Co(II)-based coordination polymers with hms and pcu nets: syntheses,structures and properties

Two new Co(II)-based coordination polymers, [Co(HL)(H₂O)₂] (1) and [Co(HL)(bpy)]·H₂O (2) (H₃L = 5-((4-carboxyphenoxy)methyl)benzene-1,3-dioic acid, bpy = 4,4′-bipyridine), have been synthesized under hydrothermal conditions. The two compounds have been characterized by single crystal and powder X-ray diffraction analyses, infrared analyses, elemental analyses and thermogravimetric analyses. Compound 1 shows a 3D 2-fold interpenetrating hms framework, whereas compound 2 reveals a typical 3D pcu net. The UV–vis diffuse reflectance spectra of compounds 1 and 2 have been investigated. Moreover, the magnetic susceptibilities of compounds 1 and 2 have been studied.     

Optical properties of PMMA doped with erbium(III) and ytterbium(III) complexes

In this article, we report the fabrication and optical/spectroscopic properties of polymethylmethacrylate (PMMA) doped with rare earth (RE) (Er³⁺ and Er³⁺/Yb³⁺) ions. Infrared spectroscopy revealed only very weak O? H stretching vibration peaks in the samples, which is important if satisfactory photoluminescence is to be observed at 1530 nm. Measurement of transmission spectra in the wavelength ranges from 300 to 700 nm for Er³⁺‐doped samples and from 900 to 1050 nm for Yb³⁺‐doped samples enabled us to observe the ⁴G_11/2 (377 nm) and ²H_11/2 (519 nm) transmission bands typical for Er³⁺‐doped samples, as well as the ²F_5/2 (975 nm) band typical for Yb³⁺‐doped samples. Under excitation at 980 nm, at room temperature, the characteristic Er³⁺ emission at 1530 nm was also observed with improving trend when the higher RE concentrations were applied. The results indicate that the PMMA reveals very low tendency to the RE clustering, which together with low cost and easy fabrication make it a material with a great potential in the active photonics devices. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Cytotoxicity of Co(III) Complexes of Arginine

The cytotoxicity of four Co(III) complexes of arginine on nontumour MDBK cells and on two cell lines derived from transplantable tumors, LSCC-SF(Mc29) and LSR-SF (SR), was evaluated comparative!y. Based on the cytotoxic concentration required to inhibit cell surveillance by 50% cc(nabla') it was found that: (i) the cytotoxicity of complexes tested increases when the concentration decreased; (ii) the cell surveillance depends on both complex and cell specificities. The complex specificity was illustrated by the order 1 > 4 > 2 >/= 3 . The cell specific response was demonstrated by the fact that LSCC-SG (Mc29) cells were up to 60 times more sensitive to 1 while LSR-SF (SR) cells were up to 1000 times more sensitive to 2 as compared to MDBK cells. Furthermore, with the prolongation of action on nontumour cells the cytotoxicity of 4 decreased up to 300 times while for both tumour cells it was independent on the duration of action.     

A novel nitronyl nitroxide radical and its Gd(III), Tb(III), Dy(III) complexes: Synthesis,structure and magnetic properties

Three new lanthanide complexes based on a novel nitronyl nitroxide radical [Ln(hfac)₃(NITPhiPr)₂] (Ln = Gd(1), Tb(2), Dy(3); hfac = hexafluoroacetylacetonate, NITPhiPr = 4′-isopropyl-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) have been successfully synthesized, characterized structurally and magnetically, which all display radical-Ln(III)-radical tri-spin structures. The magnetic studies reveal the ferromagnetic interactions between the Gd(III) ion and radicals and the antiferromagnetic interaction between two radicals in the complex 1. And both Ln(III)–radical ferromagnetic interactions exist in complexes 2 and 3.