bluuebunny/crossref_metadata_2025 huggingface dataset:
Single‐AtomO‐Bridged Urea in a Dinickel(II) Complex together with NiII4, CuII2and CuII4Complexes of a Pentadentate Phenol‐Containing Schiff Base with (O,N,O,N,O)‐Donor Atoms
Authors: Mukherjee Soumen , Weyhermüller Thomas , Bothe Eberhard , Wieghardt Karl , Chaudhuri Phalguni
Published: February 2003

A pentadentate phenol‐containing ligand (H3L) with N2O3donor atoms yields NiII2(1), NiII4(2), CuII2(3) and CuII4(4) complexes, which have been structurally characterized by X‐ray diffraction. Complex1contains a single‐atomO‐bridged urea. The compounds were characterized by IR, UV/Vis, mass spectrometry, electrochemistry and variable‐temperature (2−295 K) magnetic susceptibility measurements. Analysis of the susceptibility data shows antiferromagnetic interactions between the metal centers indicating a diamagnetic ground state for complexes1,3and4, whereas complex2, a tetranuclear NiIIcubane, has a complicated low‐lying magnetic structure with a non‐diamagnetic ground state. A plot ofJvs. Ni−O−Ni angles for all structurally characterized Ni4O4cubane cores, including2, irrespective of their symmetry exhibits a large variation ofJvalues within a small range of Ni−O−Ni angles. The electrochemistry of all complexes was investigated in detail and the ligand‐centered oxidation to a radical‐ligand is inferred from the occurrence of oxidation processes at potentials which are similar. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
(Allenylidene)ruthenium Complexes with Redox‐Active Substituents and Ligands
Authors: Hartmann Stephan , Winter Rainer F. , Brunner Birgit M. , Sarkar Biprajit , Knödler Axel , Hartenbach Ingo
Published: February 2003

We describe the allenylidene complexes [TpL2Ru=C=C=CPhR]+ SbF6− [Tp = HB(pz)3−, L2 = 2 PPh3 or 1,1′‐bis(diphenylphosphanyl)ferrocene (dppf), R = Ph or ferrocenyl] and their spectroscopic and electrochemical characteristics. Three of these compounds possess redox‐active, ferrocene‐based substituents or ligands − that are oxidized at lower potentials than the ruthenium center itself − attached either to the terminal carbon atom of the allenylidene ligand or to the ruthenium atom. The Fc/Ph‐substituted complexes 3a and 3b provide unique examples of hindered rotation of the allenylidene substituent around the M=C bond. For 3a (L2 = 2 PPh3), two isomers differing in the orientation of the vertically aligned, unsymmetrically substituted allenylidene ligand are discernible even at 388 K. The dppf‐substituted congener 3b has the allenylidene ligand in a horizontal orientation and exhibits a rotational barrier, as determined by dynamic 31P NMR spectroscopy, of ΔG≠ = 47 kJ/mol at TC = 238 K. The changes in the spectroscopic and electrochemical properties upon replacement of the PPh3 by a dppf ligand and the Ph by an Fc moiety can be explained in terms of the bonding within these systems. These effects are attenuated when the ferrocene‐based redox tags are oxidized, as shown by IR and UV/Vis spectroelectrochemistry. Thus, infrared spectroelectrochemistry reveals a blue shift of the allenylidene stretch upon oxidation of the dppf ligand, while oxidation of the ferrocene covalently linked to the unsaturated C3 ligand has the opposite effect. Oxidation of the ruthenium atom influences the bonding within the unsaturated ligand more profoundly. Results from IR spectroelectrochemistry point to a vinylidene structure in the RuIII state. Reduction enhances the contribution of alkynyl‐type resonance forms to the overall bonding description, as also shown by IR spectroelectrochemistry. For the ferrocenyl‐substituted allenylidene complexes, oxidation and reduction result in bleaching of the intense optical low‐energy absorption band attributed to a ferrocenyl‐to‐allenylidene charge‐transfer process. The EPR spectra of the paramagnetic reduced forms of these complexes also indicate spin delocalization into the aryl substituents attached to the allenylidene ligand. The complexes Tp(dppf)RuCl and [Tp(dppf)Ru=C=C=CPh2]+ SbF6− were also characterized by X‐ray crystallography. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Manganese‐Salen Complexes as Oxygen‐Transfer Agents in Catalytic Epoxidations − A Density Functional Study of Mechanistic Aspects
Authors: Cavallo Luigi , Jacobsen Heiko
Published: February 2003

The mechanism of the Jacobsen−Katsuki epoxidation has been investigated by application of density functional theory; the results of a series of calculations for simplified model systems of different spin states are presented. In the chosen computational approach, the epoxidation of ethylene with a cationic five‐coordinate model catalyst is predicted to occur through a radical intermediate, similarly to the reaction mechanism calculated for the corresponding neutral six‐coordinate species. Although the radical intermediate shows a small energetic preference for the quintet state over the triplet state, the computed reaction profile does not suggest that two‐state reactivity involving spin change plays a major role during the oxygen‐transfer step. Comparative orbital analysis of the cationic and the neutral complexes elucidates the role of a ligand trans to the oxo group. A π‐donor trans to the forming OR− ligand in the radical intermediate causes a relative destabilization of a possible quintet occupation, thus conferring spin rigidity to the six‐coordinate species derived from the neutral catalyst. A reaction pathway resulting in rotational collapse might involve a spin‐crossing process. The ligand framework of the tetra‐chelating N,O ligand in the radical intermediate exhibits a considerable amount of ligand folding. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
A Dinuclear Iron Complex with Two Cofacial [FeS4] Cores Linked by Covalent Ligand Periphery Clamps and Dissociable Thiolate Bridges
Authors: Sellmann Dieter , Peters Kai P. , Molina Raquel Montón , Heinemann Frank W.
Published: February 2003

As part of a long‐term study of dinuclear iron complexes with sulfur‐rich coordination spheres and cofacial, sterically variable binding sites for molecules relevant to nitrogenase, the complex (AsPh4)2 [{Fe(‘apS4’)}2] (5) was synthesized and completely characterized [‘apS4’4− = 1,3‐bis(2,3‐dimercaptobenzamido)propane(4−)]. Complex 5 contains two cofacial [FeIII(S2C6H4R)2]− units linked by [Fe−S−Fe] thiolate bridges and two peripheral propanediamide ligand backbones that are located on opposite sides of the molecular anion and prevent the complete separation of the two [FeS4] cores of 5 if the Fe−S−Fe bridges dissociate. No marked differences were found in the molecular parameters, spectroscopic, magnetic and electrochemical properties of the [Fe2S8] cores in the anion of 5 and the parent complex [{Fe(S2C6H4)2}2]2−. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Vanadium‐Catalysed Aerobic Cleavage of C−C Bonds in Substituted Cyclohexanones To Afford Carboxylic Acids: Two Model Complexes with Tetrahedral Geometry around Vanadium(V)
Authors: Vennat Maxence , Herson Patrick , Brégeault Jean‐Marie , Shul'pin Georgiy B.
Published: February 2003

Two monosilanol/disilanol derivatives were synthesised by treatment of Ph3SiOH or Ph2Si(OH)2 with [nBu4N]VO3 (3) in ethanol solution. The mononuclear anionic dioxo vanadium(V) species [{Ph3SiO}2VO2]− (4) and the dinuclear complex anion [{Ph2SiO2VO2}2]2− (5) thus obtained are unusual and novel model compounds with ≡Si−O−V(O)2O linkages characterised by single‐crystal X‐ray diffraction. The catalytic activities of these tert‐butylammonium complexes, together with those of the simple vanadium derivatives 3 and 5, of the vanadyl precursors VOSO4·5H2O (1) and [VO(acac)2] (2), and also of “H6[PMo9V3O40]·aq”, were tested for aerobic C−C bond cleavage in 2‐hydroxycyclohexanone and 2‐methylcyclohexanone. Monomeric vanadium species show the same chemistry as the polyoxometalate but with lower yields of acids or keto acids, and so the redox and acid properties of HPA‐n (n = 3, 4) are better tuned. Mechanisms for these oxidation reaction, including electron transfer from a substrate coordinated to vanadium, are proposed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Template Synthesis of Chiral Vicinal Diphosphinites as Their PtII and PdII Complexes
Authors: Bergamini Paola , Bertolasi Valerio , Cattabriga Michela , Ferretti Valeria , Loprieno Urania , Mantovani Nicoletta , Marvelli Lorenza
Published: February 2003

The metal‐templated synthesis of a few examples of vicinal diphenylphosphinites is accomplished when the corresponding vicinal diols react with the diphenylchlorophosphane complexes cis‐[MCl2(PPh2Cl)2] (M = Pt, Pd) in anhydrous THF. This process is proposed as a new synthetic route for PtII and PdII complexes of the new ligands 1,2‐bis(diphenylphosphinito)butane, 2,3‐bis(diphenylphosphinito)butane, and 2,3‐bis(diphenylphosphinito)diisopropyl‐L‐tartrate, containing seven‐membered chelate rings including stereogenic carbons. The new chiral phosphane‐phosphinite (R)‐3‐(diphenylphosphanyl)‐2‐(diphenylphosphinito)propanol has also been obtained as a PtII six‐membered chelate. The X‐ray crystal structure of some of the described complexes and NMR evidence of the possibility of removing the ligands from the metal are reported. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Di‐ and Trivalent Ytterbium Complexes Containing Linked Amino‐ and Amidocyclopentadienyl Ligands
Authors: Trifonov Alexander T. , Spaniol Thomas P. , Okuda Jun
Published: February 2003

Reactions of the aminocyclopentadienes (C5Me4H)SiMe2NHR (R = Et, allyl, nPr, tBu) with [YbI2(THF)2] in the presence of two equivalents of potassium 1,2‐diphenylethenide in THF at room temperature gave the diamagnetic half‐sandwich complexes [Yb(η5‐C5Me4SiMe2NHR)Ln(μ‐I)]2 (L = THF, n = 2, L = DME, n = 1). The tert‐butylamido derivative [Yb(η5‐C5Me4SiMe2NHtBu)(THF)2(μ‐I)]2 was characterized by X‐ray structural analysis as a dinuclear complex containing a nonchelating aminocyclopentadienyl ligand. Deprotonation of the aminocyclopentadiene (C5H4tBu)SiMe2NHtBu with two equivalents of potassium 1,2‐diphenylethenide in THF, followed by reaction with [YbI2(THF)2] at 60 °C, gave the trivalent ytterbium ate complex [K(DME)][Yb{(η5:η1‐C5H3tBu‐3)SiMe2NtBu}2]. A single crystal X‐ray diffraction study of this complex shows polymeric chains consisting of trivalent ytterbocene units with two chelating amidocyclopentadienyl ligands coordinated to potassium ions. Metalation of the aminoindene (C9H7)SiMe2NHtBu under the same conditions and treatment with [YbI2(THF)2] in THF at ambient temperature resulted in the formation of the divalent ytterbocene complex [Yb{η5‐(1‐C9H6)SiMe2NHtBu}2(THF)2]. The reaction of ytterbium naphthalenide [Yb(C10H8)(THF)2] with one equivalent of (C9H7)SiMe2NHtBu afforded the bis(indenyl) compound which was isolated as its 2,2′‐bipyridyl adduct [Yb{η5‐(1‐C9H6)SiMe2NHtBu}2(bipy)]. It was shown by single‐crystal structural analysis to exhibit a bent metallocene structure with noncoordinating amino side‐chains. The reaction of (C5Me4H)CH2SiMe2NHtBu, which contains a longer CH2SiMe2 bridge, with [Yb(C10H8)(THF)2] gave the complex [Li0.5][Yb(μ‐η5:η1‐C5Me4CH2SiMe2NtBu)(THF)2(μ‐I)0.5]. Single crystal X‐ray structure analysis revealed the presence of polymeric chains consisting of dinuclear iodo‐bridged [Yb(η5:η1‐C5Me4CH2SiMe2NtBu)] units with a chelating linked amidocyclopentadienyl ligand, intermolecularly bridged by lithium ions. The lithium ions are bonded in an η5‐manner to both units, forming a lithocene structure. When YbCl3 was reacted with Li2[(C5H3tBu‐3)SiMe2NCH2CH2X] (X = NMe2, OMe), heterobimetallic complexes Li[Yb{(η5:η1‐C5H3tBu‐3)SiMe2NCH2CH2X}2] with a helical metallocene structure were isolated. The single crystal structure analysis of one of the three possible diastereomers of Li{Yb[(η5:η1‐C5H3tBu‐3)SiMe2NCH2CH2NMe2]2}, viz. the thermodynamically stable (R,R)/(S,S) epimer was performed. When YbCl3 was reacted with one equivalent of Li2[(C5H3tBu‐3)SiMe2NCH2CH2NMe2] and reduced “in situ” with one equivalent of sodium 1,2‐diphenylethenide in THF, the ytterbium(II) metallocene complex [Li(THF)]2[Yb{(η5‐C5H3tBu‐3)SiMe2NH(CH2CH2NMe2)}2(μ‐Cl)2] was isolated, which exhibits a structure with the two amino functions coordinating to the lithium ions and the chloro ligands bridging both the lithium and ytterbium centers. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Synthesis, Crystal Structure and Magneto‐Structural Correlation of an Unusual Thiocyanato‐Bridged Nickel(II) Compound, [Ni(μ‐NCS)(dpt)(NCS)]2[Ni(μ‐NCS)(dpt)(NCS)]4 [dpt = bis(3‐aminopropyl)amine]
Authors: Kumar Maji Tapas , Mostafa Golam , Clemente‐Juan Juan M. , Ribas Joan , Lloret Francesc , Okamoto Ken‐ichi , Chaudhuri Nirmalendu Ray
Published: February 2003

Reaction of Ni(ClO4)2·6H2O with bis(3‐aminopropyl)amine (dpt) and ammonium thiocyanate produces the novel thiocyanato‐bridged nickel(II) compound [Ni(μ‐NCS)(dpt)(NCS)]2[Ni(μ‐NCS)(dpt)(NCS)]4, which has been structurally characterised. The structure determination reveals that there are two different molecules in the crystal lattice; one is dinuclear and other is tetranuclear. Low‐temperature magnetic measurements show that there are ferro‐ as well as antiferromagnetic interactions. The ferromagnetic interaction arises from the dinuclear part and the doubly bridged part of the tetranuclear unit; the antiferromagnetic interaction occurs between singly bridged nickel centres in the tetranuclear unit. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Cover Picture
Authors: Fleischer Holger , Mitzel Norbert W. , Schollmeyer Dieter
Published: February 2003

The cover picture shows yellow crystals and red melt of tellurium(II) dimethanethiolate, Te(SCH3)2, together with its molecular structure in the solid state and the lightinduced deposition of elemental tellurium on glass, from a solution of Te(SCH3)2. In the solid state, Te(SCH3)2 exhibits a cis conformation of the methyl groups with respect to the TeS2 plane, an unprecedented case for nonfunctionalized organotrichalcogenides. For Te(SR)2 (R = Me, Et, iPr, tBu) Te−S bonding and Te···S intermolecular distances are correlated, as are 125Te NMR chemical shifts and the ionization energies of the corresponding thiols. Results are rationalized in terms of σ‐ and π‐type np(S)‐σ*(Te−S) orbital interactions. Details are presented in the article by H. Fleischer et al. on p. 815 ff.
Vinylogue Mono‐ and Bimetallic Cationic Sesquifulvalene and Monohydro Sesquifulvalene Complexes for Second Harmonic Generation
Authors: Meyer‐Friedrichsen Timo , Wong Hans , Prosenc Marc H. , Heck Jürgen
Published: February 2003

The donor‐acceptor complexes with a vinylogue monohydro sesquifulvalene and sesquifulvalene backbone of the type [(η5‐C5H5)Ru{µ‐(η5‐C5H4)C2H2(η6‐C7H7)}ML](PF6)n [n = 0: ML = none (1), Cr(CO)3 (2); n = 1: ML = Ru(η5‐C5H5) (3a), Ru(η5‐C5Me5) (3b)] and [(η5‐C5H5)Ru{µ‐(η5‐C5H4)C2H2(η7‐C7H6)}ML](PF6)n [n = 1: ML = none (4), Cr(CO)3 (5); n = 2: ML = Ru(η5‐C5H5) (6a), Ru(η5‐C5Me5) (6b)], respectively, have been synthesised, and spectroscopically and structurally characterised. A charge‐shift correlation was carried out by means of 1H NMR spectroscopic studies and an increased ground‐state donor‐acceptor interaction in the order 5 < 6b < 4 < 6a was found. The corresponding donor‐acceptor interaction in 3a and 3b varies by an insignificant amount. Hyper‐Rayleigh scattering (HRS) was applied to determine the first hyperpolarisability β of the mono‐ and dicationic complexes 3a−6b. The β values obtained for the cationic sesquifulvalene complexes 4−6b are among the largest ever measured for ruthenocenyl containing complexes due to a strong resonance enhancement: the sesquifulvalene complexes 4−6a, 6b show first hyperpolarisabilities which range between 360 and 700 × 10−30 esu, whereas β for the monohydrosesquifulvalene complexes are considerably lower (75 and 162 × 10−30 esu). For the latter complexes the first hyperpolarisability doubles on going from Ru(η5‐C5Me5) (3b) to Ru(η5‐C5H5) (3a) in the acceptor unit. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Macrocyclic, Dinuclear Zinc(II)‐Directed Self‐Assembly with Pyridine, 2,2′‐Bipyridine and 2‐Methylquinoline: μ2‐OH Bridging Bi‐Macrocyclic Complexes and Hydrogen‐Bond‐Supported Donor‐Acceptor Complexes
Authors: Huang Wei , Gou Shaohua , Qian Huifen , Hu Dahua , Chantrapromma Suchada , Fun Hoong‐Kun , Meng Qingjin
Published: February 2003

Two macrocyclic dinuclear zinc(II) complexes (1a and 1b) have been self‐assembled in the presence of pyridine and 2,2′‐bipyridine, respectively, to form μ2‐OH‐bridged bimacrocycles with a Zn4O4 cavity through coordination bonding. The X‐ray structural analysis reveals that both compounds {2a: [Zn4La2(OH)2]2(ClO4)2; 2b: [Zn4Lb2(OH)2]2(ClO4)2} have an open‐mouthed sandwich‐like structure with π−π interactions between parts of two phenyl rings to strengthen two hydroxyl groups connecting the metal atoms in the same direction of the macrocycle. Furthermore, nonclassical C−H···Cl intermolecular interactions have been observed in the crystal of 2b. In addition, the reaction of 1a with quinoline derivatives has yielded novel hydrogen‐bond‐supported donoracceptor complexes {3a: [Zn2La(H2O)2(C10H9N)2](ClO4)2}. The crystallographic study of the complex containing 2‐methylquinoline indicates that two 2‐methylquinoline molecules are linked to two coordinating water molecules above and below the macrocyclic framework through O−H···N hydrogen bonds. The 2‐methylquinoline plane interacts in a face‐to‐face fashion with the phenyl ring of adjacent macrocyclic frameworks, forming an ordered arrangement where one macrocycle and two 2‐methylquinolines are arrayed alternately with almost the same separation. The interplanar distance mentioned before is ca. 3.6 Å. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
The Photophysical Properties of Hybrid Metal Complexes Containing both 2,2′‐Bipyridine and 2,2′:6′,2′′‐Terpyridine Units
Authors: Harriman Anthony , Hissler Muriel , Khatyr Abderrahim , Ziessel Raymond
Published: February 2003

Stepwise cross‐coupling reactions between functionalized metallo synthons and bipyridine‐ or terpyridine‐based building blocks afford novel photoactive, hybrid complexes bearing multiple chromophores that function separately or cooperatively according to the nature of the coordinated metal cations. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Dynamic Behavior of an N‐Metalated β‐Enaminoimine Complex − Preparation of N‐Phosphanylenamine and β‐Enaminoimine Derivatives
Authors: Maraval Alexandrine , Owsianik Krzysztof , Arquier Damien , Igau Alain , Coppel Yannick , Donnadieu Bruno , Zablocka Maria , Majoral Jean‐Pierre
Published: February 2003

Variable‐temperature NMR spectroscopy of the β‐enaminoimine complex 2 showed a dynamic process which was attributed to an internal fluxional aldimido N‐zirconated π‐linear/σ‐bent structure. Such an internal rearrangement has been previously proposed to occur in these systems but never observed. We have prepared a variety of (N‐phosphanyl‐β‐enamino)imine ligands using the hydrozirconation/transmetalation reaction of malonodinitrile compounds RCH(CN)2 (R = H, PPh2). In addition to their potential uses in coordination chemistry, these systems are good tools for the study of intramolecular hydrogen bonding. The X‐ray crystal structure of 14 at 180 K shows an unsymmetrical system with the N(H) proton localized on one of the two chelating nitrogen atoms, consistent with the existence in solution of a low barrier proton transfer process with a double‐well potential. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Syntheses and Crystal Structures of Copper and Silver Complexes with New Imine Ligands − Air‐Stable, Photoluminescent CuIN4 Chromophores
Authors: Patra Goutam Kumar , Goldberg Israel
Published: February 2003

A series of new imine ligands [1 (C12H12N2S2), 2 (C12H12N2S2), 3 (C24H18N4S2), and 5 (C30H27N7)] have been synthesized (1 and 2 are structural isomers). CuI and AgI complexes of the nonconjugated dithiophene‐diimine ligands 1, 2 and the tripodal imine‐amine ligand 5 have also been prepared and thoroughly characterized by spectroscopic techniques as well as by X‐ray diffraction. In cyclic voltammetry at a glassy carbon milli electrode in anhydrous dichloromethane under dry N2, the corresponding CuI complexes [6 (2C12H12N2S2·CuClO4), 7 (2C12H12N2S2·CuClO4), and 12 (C30H27N7·CuClO4)] show quasi‐reversible CuII/I couples with high redox potentials (1.001 V for 6, 0.958 V for 7, and 0.692 V for 12, vs. Ag/AgCl). This indicates that the π‐acid ligands 1, 2, and 5 preferentially stabilize copper(I) over copper(II). The CuIN4 chromophores in the complexes 6, 7, and 12 display photoluminescence in dichloromethane at room temperature. The related silver complexes of the same three ligands 10 (2C12H12N2S2·AgClO4), 11 (2C12H12N2S2·AgClO4), and 13 [C30H27N7·Ag(CH3CN)ClO4] reveal similar structural features but lack specific photophysical properties. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
The Reactivity of an Iron(II)/Iron(III) System with Polyamine Ligands in Ethanol: An Electrochemical Study
Authors: Ugalde‐Saldivar Víctor M. , Sosa‐Torres Martha E. , González Ignacio
Published: February 2003

The pentadentate ligand picdien [LA; 1,9‐bis(2′‐pyridyl)‐2,5,8‐triazanonane)] and [Fe(DMSO)6](NO3)3 produce the hexacoordinate coordination compound [FeL′B]2+ after reaction in ethanol. This compound shows a change in the oxidation state of FeIII to FeII as well as an increase in the denticity of the starting ligand LA. The new ligand L′B {1,9‐bis(2′‐pyridyl)‐5‐[(ethoxy‐2′‐pyridyl)methyl]‐2,5,8‐triazanon‐1‐ene} has an imine carbon−nitrogen double bond. This study provides evidence for the nature of the intermediate species during the formation of [FeL′B](BPh4)2. A systematic study was performed based on the evolution of the voltammograms observed after the addition of ligand (LA, LB) or base (LiOEt) to FeIII, FeII solutions or stoichiometric metal‐ligand mixtures (LB is L′B without the imine group). The stability of FeLA3+ and FeLA2+ species in acidic media and under nitrogen atmosphere was confirmed. The reactivity of FeLB3+ and FeLA3+ systems was found to be very similar, and the reduction products were found to be FeII species with simultaneous ligand oxidation, which, in both cases, produces an imine double bond, giving rise to an intramolecular redox reaction. The following disproportionation equation describes the general form of this process: 2 FeL3+ ⇄ FeL2+ + FeL′2+ + 2 H+. The oxidation was verified by the double bond formation in LA and LB giving rise to L′A and L′B as can be seen in the general equation: R1−CH2−NH−R2 ⇄ R1−CH=N−R2 + 2 H+ + 2e−. The disproportionation reaction for FeLA3+ and FeLB3+ species depends on the acidity level of the media: this reaction cannot be verified in acidic media, while neutral and slightly basic media favour formation of the FeII species with L′A and L′B. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Synthesis, X‐ray Studies and Magnetic Properties of Dinuclear NiII and CuII Complexes Bridged by the Azo‐2,2′‐bipyridine Ligand
Authors: Campos‐Fernández Cristian S. , Galán‐Mascarós José R. , Smucker Bradley W. , Dunbar Kim R.
Published: February 2003

Two new paramagnetic transition metal complexes that contain the bridging ligand azo‐2,2′‐bipyridine (abpy) have been prepared and characterized by X‐ray crystallography and magnetic susceptibility measurements. The compound [Ni2(μ‐abpy)(CH3CN)2(NO3)4]·2CH3CN (1·2CH3CN) crystallizes in the triclinic space group P$\bar 1$
with a = 8.290(5) Å, b = 8.343(5) Å, c = 11.180(5) Å, α = 105.36(3)°, β = 94.39(3)°, γ = 107.56(3)°, V = 700.5(7) Å3 and Z = 1. The related salt [Cu2(μ‐abpy)(CH3CN)8][BF4]4 (2) crystallizes in the triclinic space group P$\bar 1$
with a = 10.240(2) Å, b = 10.597(2) Å, c = 10.712(2) Å, α = 64.23(3)°, β = 78.21(3)°, γ = 78.57(3)°, V = 1026.7(3) Å3 and Z = 1. Solutions of 2 eventually produce the polymeric CuI compound {[Cu(μ‐abpy)][BF4]}∞ (3) which was also crystallographically characterized: monoclinic space group P21/n, with a = 9.295(2) Å, b = 9.541(2) Å, c = 13.486(3) Å, β = 91.58(3)°, V = 1195.5(4) Å3 and Z = 4. The magnetic properties of these dinuclear paramagnetic complexes have been studied in detail, and have provided an opportunity for probing the ability of this ligand to mediate magnetic exchange interactions between paramagnetic metal centers. Compound 1 exhibits antiferromagnetic exchange interactions (J = −7.5 cm−1) whereas the magnetic interactions in compound 2 were found to be negligible. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Synthesis of (η3‐Allyl)bromodicarbonylbis(pyrazole)molybdenum(II) and Reactivity towards [Au(acac)PPh3]: Structure and Dynamic Behavior of the Monometallic Pyrazole and Heterometallic Pyrazolate Complexes
Authors: Paredes Paloma , Miguel Daniel , Villafañe Fernando
Published: February 2003

The reactions of [Mo(η3‐allyl)Br(CO)2(NCMe)2] and two equivalents of Hpz (pyrazole) or Hdmpz (3,5‐dimethylpyrazole) lead to [Mo(η3‐allyl)Br(CO)2(Hpz)2] or [Mo(η3‐allyl)Br(CO)2(Hdmpz)2]. The Hpz and Hdmpz ligands are coordinated cis and trans with respect to the allyl group in the solid state, whereas in their solutions a slow trigonal twist process is detected. These complexes react with Tl(acac) giving [Mo(acac)(η3‐allyl)(CO)2(Hpz)] and [Mo(acac)(η3‐allyl)(CO)2(Hdmpz)], which also undergo a slow trigonal twist process in solution. The latter complex may also be obtained by the reaction of equimolar amounts of [Mo(η3‐allyl)Br(CO)2(Hdmpz)2] and [Au(acac)PPh3], giving [AuBrPPh3] as a by product. The reaction of these molybdenum acac complexes with [Au(acac)PPh3] give rise to the heterobimetallic bridging pyrazolate complexes [Mo(acac)(η3‐allyl)(CO)2(μ‐pz)AuPPh3] and [Mo(acac)(η3‐allyl)(CO)2(μ‐dmpz)AuPPh3]. The solid state structure of the latter, which is also obtained from [Mo(η3‐allyl)Br(CO)2(Hdmpz)2] and two equivalents of [Au(acac)PPh3], with [AuBrPPh3] as a by product, reveals the coordination of the bridging dimethylpyrazolate ligand trans to the allyl group. Two different dynamic processes which are slowed down at low temperatures are detected in solution for each heterobimetallic complex: trigonal twist for the pyrazolate bridging complex, and hindered rotation of the Mo−N bond for the more hindered dimethylpyrazolate complex. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Electro‐oxidation of Carbon Monoxide and Methanol on Carbon‐Supported Pt–Sn Nanoparticles: a DEMS Study
Authors: Manzo‐Robledo A. , Boucher A.‐C. , Pastor E. , Alonso‐Vante N.
Published: February 2003

A comparative study between carbon supported Platinum–Tin (Pt–Snsyn), synthesized via the carbonyl route, and the commercial (Pt3Sn) from E–TEK is reported. The electro‐oxidation of methanol and adsorbed CO, in sulphuric acid medium, were used as probes to evaluate the performance of these electrocatalysts. In‐line differential mass spectrometry (DEMS) was used for this purpose. Both nanoparticulate materials had a mean particle size of  = 1.68 ± 0.72 nm, and  = 3.58 ± 1.94 nm, respectively. It is demonstrated that, under the same experimental conditions, our homemade Pt–Snsynis less sensitive to poisoning by CO. This observation was again verified during the oxidation of methanol. These results are discussed in terms of the local disorder of the particles surface atoms, favourably induced by size effect and the preparation route employed.
Fuel Cell Operation with Oxygen Enrichment
Authors: Fournier M. , Hamelin J. , Agbossou K. , Bose T.K.
Published: February 2003

Experimental results on the performance of a Ballard 5 kW proton exchange membrane fuel cell stack for different oxygen contents in the oxidant are presented. A description of the experimental setup is given. Polarization, power, and efficiency curves as a function of the current density, for different oxygen concentrations are presented. This detailed characterization of the fuel cell stack behavior is required in order to evaluate the effects of oxygen enrichment on the net power output of the stack. This investigation is done in the framework of a project on stand‐alone power generation systems using renewable energy sources, and based on hydrogen production and storage. An electrolyzer, powered by the excess electrical energy from renewable energy sources, produces hydrogen. The stored hydrogen could then be used to feed an energy conversion device, such as a fuel cell stack, which acts as a secondary power source in periods of high demand. Therefore, a second objective is to evaluate the possibility of using the oxygen produced by the electrolyzer for the enrichment. Other oxygen enrichment techniques such as membrane gas separation and pressure swing adsorption are also discussed. Net available power and system efficiency are used as comparison factors.
Mathematical Modelling and Simulation of Polymer Electrolyte Membrane Fuel Cells. Part I: Model Structures and Solving an Isothermal One‐Cell Model
Authors: Hertwig K. , Martens L. , Karwoth R.
Published: February 2003

Amongst the various types of fuel cells, the polymer electrolyte membrane fuel cell (PEM‐FC) can be used favourably in vehicles and for in house energy supply. The focus of the development of these cells is not only to provide cost‐effective membranes and electrodes, but also to optimise the process engineering for single cells and to design multi‐cell systems (cell stacks). This is a field in which we have successfully applied the methods of mathematical modelling and simulation. Initially, in this work, a partial model of a single membrane‐electrode unit was developed in which the normal reaction technology fields (concentration, temperature, and flow‐speed distributions) were calculated, but also the electrical potential and current density distribution in order to develop model structures for technically interesting PEM‐FC. This allows the simulation of the effects that the geometric parameters (electrode and membrane data and the dimensions of the material feed and outlet channels) and the educt and coolant intake data have on the electrical and thermal output data of the cell. When complete, cell stacks consisting of a number of single cells, most of which have bipolar switching, are modelled the distribution of the gas flows over the single cells and the specific conditions of heat dissipation must also be taken into consideration. In addition to the distributions mentioned above, this simulation also produces characteristic current‐voltage and power‐voltage curves for each application that can be compared with the individual process variations and cell types, thus making it possible to evaluate them both technically and economically. The results of the simulation of characteristic process conditions of a PEM‐FC operated on a semi‐technical scale are presented, which have been determined by means of a three‐dimensional model. The distributions of the electrical current density and all component voltage drops that are important for optimising the conditions of the process are determined and also the water concentration in the membrane as an important factor that influences the cell’s momentary output and the PEM‐FC’s long‐term stability.
Empirical Model Equations for the Direct Methanol Fuel Cell DMFCs
Authors: Argyropoulos P. , Scott K. , Shukla A.K. , Jackson C.
Published: February 2003

Empirical model equations, proposed for polymer electrolyte fuel cells, are used to predict the cell voltage vs. current density response of a liquid feed direct methanol fuel cell. The model equations are validated against experimental data for a small‐scale fuel cell over a wide range of methanol concentration and temperatures. A new empirical equation is presented which is able to predict the voltage response of liquid feed direct methanol fuel cells over a wide range of operating conditions and even in the case of very low current densities caused by, for example, the use of dilute methanol solutions or low cell temperatures.
Reliable Fuel Cell Simulation Using an Experimentally Driven Numerical Model
Authors: Lunghi Piero , Bove Roberto
Published: February 2003

The necessity of a simulation tool for integrated power plant with MCFCs has led to the development of a numerical model by which it is possible to evaluate the performances of the cell and the plant the cell is embedded in. Many mathematic models can be found in the literature that evaluate electrochemical fuel cell performance [1–9]; however the model must be developed according to a specific target. In other words, if the main purpose of the study is, for example, shape optimization, the model must be very accurate concerning internal conditions, such as current density, temperature distribution, etc. The models found in the literature [1–3, 5, 9] seem to produce excellent results. However, the aim here is to create a mathematical model for fuel cell stacks, which can be integrated into a simulation modular code for the Balance of the Plant (BoP) optimization. Plant modelling can be performed using commercially available software. Often, since fuel cells are innovative devices, numerical codes that simulate their behaviour must be implemented by using a proprietary code. Previous papers can be found in the literature [4, 10, 11], where fuel cell stacks are inserted in an entire power plant, but very often the fuel cell block is zero‐dimensional and it is not affected by the variation in input parameters. The authors, for this purpose, have developed a module to be integrated into commercial software for plants simulation, Aspen Plus. The model adopted is simple, but at the same time, it calculates with good accuracy fuel cell performance under any conditions. Another important element taken into account during the code development is the validation through experimental data. In the present work, the authors have adopted an analytic model for evaluating the electrochemical performance [6] of a fuel cell and results obtained are compared with those found out during the tests on a Molten Carbonate Fuel Cell. Some phenomena not described in the original model are considered and an enhanced model for the cell performance is developed. The model obtained is therefore used to analyse fuel cell behaviour under several operating conditions. These results seem to fit very well with experimental analyses conducted in the test rig of the University of Perugia.
In Situ Investigation of Two‐Phase Flow Patterns in Flow Fields of PEFC’s Using Neutron Radiography
Authors: Geiger A.B. , Tsukada A. , Lehmann E. , Vontobel P. , Wokaun A. , Scherer G.G.
Published: February 2003

A novel in situ method for the investigation of the two‐phase flow patterns occurring in the flow fields of polymer electrolyte fuel cells (PEFC’s) has been developed. In these experiments, the gas / liquid two‐phase flow in hydrogen fuel cells as well as in direct methanol fuel cells (DMFC’s) has been studied. Unique results and the promising use of neutron radiography for PEFC research are shown. Its current limitations but also future developments and opportunities are discussed.
Kinetics of Methanol Oxidation on Supported and Unsupported Pt/Ru Catalysts Bonded to PEM
Authors: Khazova O.A. , Mikhailova A.A. , Skundin A.M. , Tuseeva E.K. , Havránek A. , Wippermann K.
Published: February 2003

The kinetics and mechanism of methanol adsorption and oxidation on real Pt/Ru (1:1) electrodes were investigated. In model electrode systems, the addition of supporting proton‐conducting electrolyte is necessary. Therefore, the influence of sulphuric acid on the kinetics of methanol adsorption and oxidation was also investigated. It turns out that the steady state adsorption is not significantly affected by the addition of sulphuric acid. However, if sulphuric acid is used as an additional electrolyte, the rate of methanol adsorption and steady state oxidation decreases, whereas the active surface of the catalyst increases. The mechanism of methanol oxidation is not affected by the addition of sulphuric acid. At low potentials, the adsorption of methanol is found to be much faster than its oxidation. Hence, the oxidation of the methanol intermediate species is believed to be the rate‐determining step under these conditions. This result is confirmed by apparent orders of reaction of about 0.5. At potentials in the range of 0.3–0.5 V, a mixed activation‐adsorption control is supposed, whereas at potentials more positive than 0.5 V, the adsorption of methanol is probably the rds. This is supported by the apparent reaction orders and apparent activation energies of methanol oxidation.
Genotypic and phenotypic characteristics of antibiotic‐producing soil Streptomyces investigated by RAPD‐PCR
Authors: Gharaibeh Raad , Saadoun Ismail , Mahasneh Amjad
Published: February 2003

Random amplified polymorphic DNA (RAPD) analysis has been used to determine the relatedness of 73 antibiotic‐producing soil Streptomyces isolates that were recovered from different soil habitats in Jordan based on their RAPD‐PCR fingerprints. Genetic polymorphisms between these isolates showed three common bands of 2777, 800 and 250 bp shared by approximately (95%) of them. Some specific bands were also observed. Further analysis of RAPD patterns with the UPGMA resulted in clustering the tested isolates into two main super clusters. Super cluster I was more homogenous than super cluster II and contained all the reference strains. However, super cluster II consists of unrelated isolates within five small groups. As RAPD fingerprints of the tested isolates linked to their phenotypes, differentiation between isolates with different cultural properties was observed.
A novel membrane glycoprotein of Escherichia coli
Authors: Kumar Manoj , Mishra Nivedita , Upreti R. K.
Published: February 2003

A novel glycoprotein (Gp45) has been isolated and purified from Escherichia coli. To our knowledge, Gp45 is the third glycoprotein isolated from E. coli membrane and it is the second in the non‐pathogenic strain of the organism. For the isolation of Gp45, cell extract or membrane fraction was treated with sodium deoxycholate for 4 h and precipitated with trichloroacetic acid (TCA). The supernatant fraction of TCA containing the Gp45 was further purified on DEAE‐Sephadex A‐25. SDS‐PAGE showed a single band at 45 kDa position that stained with periodic‐Schiff reagent. It contained 60% carbohydrate and 40% protein content. The monosaccharide composition also substantiated the characteristics of the glycoprotein. The E. coli grown in presence of 14C‐glucosamine further confirmed the localization and biosynthesis of this glycoprotein on the membrane during the growth phase. Bacitracin, a general inhibitor of the glycosylation, inhibited its biosynthesis.
Identification of a major protein upon phosphate starvation of Pseudomonas aeruginosa PAO1
Authors: Madhusudhan Kunapuli T. , McLaughlin Robert , Komori Naoka , Matsumoto Hiroyuki
Published: February 2003

To understand the physiology of non‐differentiating bacteria exposed to nutrient deprivation and stress, various approaches have been employed in combination with detailed analysis of protein synthesis pattern. In this study, separation of proteins from clarified cell extracts of Pseudomonas aeruginosa PAO1 grown under phosphorus limiting conditions was achieved by high resolution two‐dimensional gel electrophoresis (2‐DE). Limitation of phosphate in the growth medium revealed significant differences in the 2‐DE pattern of proteins between phosphate starved cells and an unstarved control. A major protein identified as PstS, a phosphate binding protein of the pts operon was exclusively found on 2‐DE gels of phosphate starved bacteria. The identity of protein was established based on the results of Edman degradation, amino acid analysis and mass spectrometry. PstS was also found in other pseudomonads, and therefore, it can be used as a landmark protein in proteomic studies. Additionally, we propose utilizing pstS of pseudomonads for testing bioavailable phosphate from soils and water streams.
Entomopathogenic effect of Aspergillus giganteus and Penicillium corylophilum on two triatomine vectors of Chagas disease
Authors: da Costa Gisela Lara , de Moraes Aurea Maria Lage , Galvão Cleber
Published: February 2003

Two strains, Penicillium corylophilum and Aspergillus giganteus, of the most frequent species found in a survey of triatomines, were used for bioassays in the second and fourth nymphs stage of Triatoma infestans and Panstrongylus megistus. Two procedures, bite and pulverization, were used and compared. A. giganteus was most effective, causing mortality in at least 50% of the nymphs of the two species tested with exception of the nymphs of the fourth stage of P. megistus. Variation in entomopathogenic capacity of the fungal species were observed in the experiments. The two procedures used proved effective.
Survival and accumulation of microorganisms in soils irrigated with secondary treated wastewater
Authors: Malkawi Hanan I. , Mohammad Munir J.
Published: February 2003

Secondary‐treated wastewater was used to irrigate forage crops during two years (1994 and 1995). The bacteriological quality of the soil irrigated with both secondary treated wastewater (without chlorination) and with potable water was evaluated. The following three treatments were investigated in this study: i) irrigation with potable water in amount equivalent to 100% of the class A Pan evaporation reading (as taken from the nearest Meteorological Weather Station); ii) irrigation with treated wastewater in amount equivalent to 100% of the A Pan reading and iii) irrigation with treated wastewater in amount equivalent to 125% of the A Pan reading. At the end of the last growing season, soil samples were collected at two soil depths and subjected to microbiological analysis. The bacteriological analysis showed that the total aerobic bacterial counts of surface soil were similar in all irrigated plots, suggesting that the use of this wastewater did not stimulate or inhibit these microflora. Surface soil was found to have higher bacterial counts than deeper soil suggesting bacterial removal from irrigation water by the first few centimeters of soil due to natural infiltration of soil. The total coliforms ranged from 2.1 × 103CFU/g to 4.2 × 103CFU/g while fecal coliforms were less, ranging from 1.2 × 102CFU/g to 4.2 × 102CFU/g. No detectable helminth eggs were recorded in the treated wastewater used for irrigation. The results strongly suggest the necessity to treat wastewater effluents to an extent to which no or very few residual bacterial contaminants will be detected.
Induction of phenol utilization in Pseudomonas CF600 grown under varying nitrogen levels
Authors: Moharikar Aditi , Purohit Hemant J.
Published: February 2003

This study demonstrates the effect of various nitrogen levels in the medium along with different carbon sources in the media on the utilization of phenol by Pseudomonas CF600. Experiments were carried out using cultures derived from minimal media containing the carbon sources phenol and citrate, followed by varying nitrogen levels in the medium. Respirometric analysis under different conditions was carried out with cells using phenol and catechol as substrates. When nitrogen was limiting in the medium, phenol induced higher oxygen uptake rates, whereas catechol was independent of the nitrogen levels. These observations were also supported by the residual phenol levels in the medium with different levels of nitrogen as NH4 ion. Results show that nitrogen‐limiting conditions favor the phenol utilization by Pseudomonas CF600.
The activities of the two thioredoxins from Streptomyces aureofaciens are not interchangeable
Authors: Horecká Tatiana , Perečko Dušan , Kutejová Eva , Mikulášová Darina , Kollárová Marta
Published: February 2003

The physico‐chemical features of the NADPH‐thioredoxin reductase (TRR) and two thioredoxins from Streptomyces aureofaciens (A14) are reported. The activity of pure S. aureofaciens thioredoxin reductase decreased drastically in the presence of NADPH or NADH while NADP+, NAD+, as well as S. aureofaciens thioredoxin‐1 (TR1) activated the enzyme activity significantly. TR1 fully protected the enzyme from inactivation and also promoted its complete reactivation. S. aureofaciens thioredoxin‐2 (TR2) did not protect thioredoxin reductase from NADPH inactivation. The results indicate that although the two thioredoxins from S. aureofaciens have similar biochemical properties, their essential oxidoreductase activities are not interchangeable.
The influence of co‐cultivation on expression of the antifungal protein in Aspergillus giganteus
Authors: Meyer Vera , Stahl Ulf
Published: February 2003

The afp gene of Aspergillus giganteus encodes a small, highly basic polypeptide with antifungal activity, named Antifungal Protein (AFP). The protein is secreted by the mould and inhibits the growth of various filamentous fungi. In this paper we report that co‐cultivation of A. giganteus with various microorganisms alters afp expression. It was found that co‐cultivation modulates afp expression on the level of transcription, using a reporter system based on the β‐glucuronidase gene. The presence of Fusarium oxysporum triggered afp transcription whereas dual cultures of A. giganteus and A. niger resulted in suppression of afp transcription. Growth tests performed with several carbon and nitrogen sources, revealed that the influence of co‐cultivation is strongly dependent on the medium composition.
Comparison of aspartate transcarbamoylase regulation in Pseudomonas alcaligenes and Pseudomonas mendocina
Authors: Santiago Manuel F. , West Thomas P.
Published: February 2003

The regulation of aspartate transcarbamoylase activity in cell extracts of Pseudomonas alcaligenes ATCC 14909 and Pseudomonas mendocina ATCC 25411 was compared. Under saturating substrate concentrations, pyrophosphate, CTP, UDP and ADP were highly inhibitory of the P. alcaligenes transcarbamoylase activity while pyrophosphate, UDP, ADP, ATP and GTP were the most effective inhibitors of the P. mendocina transcarbamoylase. By examining transcarbamoylase inhibition by ribonucleotide triphosphates, it was possible to differentiate these species assigned to different DNA homology groups and such an analysis might prove useful in the reclassification of Pseudomonas species.
Screening for soluble methane monooxygenase in methanotrophic bacteria using combined molecular and biochemical methods for hydroxylase detection
Authors: Grosse Stephan , Mueller Claudia , Rogge Gerlind , Wendlandt Karin‐Dagmar , Miguez Carlos B. , Kleber Hans‐Peter
Published: February 2003

Three well known methanotrophic bacteria (Methylosinus trichosporium OB3b, Methylocystis sp. WI 14, and Methylocystis sp. GB 25) and three newly isolated methanotrophic bacteria (Methylocystis sp. WI 11, Methylocystis sp. X, and FI‐9) were screened for sMMO considering the existence of hydroxylase (component A) genes as well as its gene expression. For these purposes monoclonal antibodies that specifically recognize each subunit of the hydroxylase of Methylocystis sp. WI 14 (α‐subunit [9E5/F2], β‐subunit [4E2/G11], γ‐subunit [10G3/D7]) were produced. PCR amplification using well known primers showed that the hydroxylase encoding genes appear to be only present in M. trichosporium OB3b, Methylocystis sp. WI 11 and WI 14, and in the isolate FI‐9. Western and ELISA analysis using the monoclonal antibodies revealed that all subunits of hydroxylase were present. However, in FI‐9, only the α‐subunit of the hydroxylase might be expressed. Surprisingly, in Methylocystis sp. GB 25, where no sMMO activity and no amplification with sMMO specific primers was obtained, the antibody 4E2/G11 recognized a protein band with exactly the same molecular mass as the β‐subunit of the hydroxylase. Methylocystis sp. X showed no positive reaction in any of the tests. In combination with the detection methods currently used, the described antibodies provide a powerful tool for detecting even partially expressed hydroxylase genes.