bluuebunny/crossref_metadata_2025_split huggingface dataset:
Gold, Silver and Palladium Complexes with the 2,2′‐Dipyridylamine Ligand
Authors: Burgos Mercedes , Crespo Olga , Gimeno M. Concepción , Jones Peter G. , Laguna Antonio 
Published: May 2003

AbstractReaction of the 2,2′‐dipyridylamine (Py2NH) ligand with various gold and silver starting products leads to three‐ or four‐coordinate complexes. The structure of compound [Ag(NHPy2)(PPh3)]OTf shows weak interactions which produce bands of molecules parallel to the z axis. Other hydrogen bonds of the type C−H···O serve to link the ribbons. The derivative PPN[Au(Py2N)2] has also been obtained using PPN[Au(acac)2] [PPN = bis(triphenylphosphanyl)iminio, acac = acetylacetonate] as starting product to deprotonate the ligand. The palladium complex [PdCl2(Py2NH)2] is also reported. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Synthesis, Solid‐State Structure and Multinuclear NMR Studies of the New Polyhydrido Iridium Carbonyl Cluster Ir4H4(μ‐H)4(CO)4(PPh3)4
Authors: Garlaschelli Luigi , Greco Francesco , Peli Giulia , Manassero Mario , Sansoni Mirella , Gobetto Roberto , Salassa Luca , Della Pergola Roberto 
Published: May 2003

AbstractThe carbonyl hydride cluster Ir4H8(CO)4(PPh3)4 (1) has been formed in high yield and purity by heating a mixture of Ir4(CO)12 and PPh3 in toluene at 90 °C under hydrogen at atmospheric pressure. The product has been characterised by microanalysis, spectroscopy (IR, 1H and 31P NMR) and X‐ray diffraction. In the solid state one hydrogen, one CO and one triphenylphosphane ligand are terminally bonded to each iridium atom, whereas four hydride ligands are bridging. All the hydrogen atoms were directly located by X‐ray analysis at an average H−Ir distance of 1.55 Å (for the terminal H) and 1.75 Å (for the μ‐H). As shown by 1H and 31P NMR spectra, two isomeric forms (1A and 1B) of the cluster are present in CD2Cl2 solution at room temperature, and they do not interconvert in the explored temperature range. However, if a solid sample of the cluster is dissolved at 188 K, only 1A is detected by NMR spectroscopy. The structure of 1B could be proposed on the basis of the T1 relaxation times of the various hydrides: it results by localised exchange of H and CO around two vertices of the tetrahedral frame. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Bridged Aminotroponiminate Complexes of Zinc
Authors: Gamer Michael T. , Roesky Peter W. 
Published: May 2003

AbstractReactions of the n‐propyl‐bridged diaminotroponimine H2{(iPr)TP} with dialkylzinc compounds in toluene lead, depending on the stoichiometric ratio, either to dimetallic singly bridged products of composition [(RZn)2{(iPr)TP}] [R = Me (1), Et (2)] or to dimetallic doubly bridged helical products of composition [Zn{(iPr)TP}]2 (3). Compound 3, which was characterised by single‐crystal diffraction methods, is the first bridged aminotroponiminate complex in which a helical structure is observed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
The Use of Conductivity Measurements for the Characterization of Cationic Palladium(II) Complexes and for the Determination of Kinetic and Thermodynamic Data in Palladium‐Catalyzed Reactions
Authors: Jutand Anny 
Published: May 2003

AbstractThis review illustrates how conductivity measurements are used to characterize the cationic character of aryl‐, vinyl‐, hydrido‐, and (η3‐allyl)palladium(II) complexes generated by oxidative addition of aryl and vinyl triflates, acetic/formic acid, and allylic carboxylates/carbonates, respectively, with palladium(0) complexes in DMF. These cationic palladium(II) complexes have been postulated as key intermediates in Stille, Heck, Tsuji−Trost, and Trost reactions, but most of them have never been characterized in the context of real oxidative additions, i.e., with the counteranion delivered by the reagent (triflates, carboxylates, and carbonates). The role of chloride ions has been examined and the mechanistic consequences are reported. Conductivity measurements are also used to obtain thermodynamic and kinetic data on the formation of cationic palladium(II) complexes and, consequently, to gain a deeper insight into the mechanism of palladium‐catalyzed reactions. The reversibility of oxidative additions of acetic/formic acid and allylic carboxylates/carbonates with Pd0 complexes has been established and equilibrium constants have been determined. The isomerization of cyclic trans/cis cationic (η3‐allyl)palladium(II) complexes is evidenced by a rate constant that depends on the Pd0 precursor: kinetic evidence for an SN2 mechanism that is responsible for the loss of stereoselectivity observed in catalytic reactions. Under conditions in which the oxidative additions are irreversible, the kinetics of the formation of cationic (η3‐allyl)palladium(II) complexes has been monitored by conductivity measurements for the determination of the rate constants. By comparing the rate of disappearance of Pd0, it has been shown that oxidative additions of allylic carboxylates proceed in two steps with the detection of intermediate neutral, kinetic Pd0 complexes ligated to the allylic carboxylate unit. As an example of its application, the mechanism of a Stille reaction has been investigated by conductivity measurements of an ionic by‐product in DMF. © Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003
P−B Adducts of 3,4‐Dimethyl‐1‐phosphaferrocene with Bromoboranes
Authors: Scheibitz Matthias , Bats Jan W. , Bolte Michael , Wagner Matthias 
Published: May 2003

AbstractThe crystalline adducts FcP−BBr3 (2) and FcP−BBr2Fc (3), which are very rare examples of P‐bonded complexes between phosphaferrocene and a main‐group metal atom, were obtained by the reaction of 3,4‐dimethyl‐1‐phosphaferrocene (FcP) with BBr3 and FcBBr2 (Fc: ferrocenyl). According to X‐ray crystallography, the Fe−P bond length in 2 is 0.085 Å shorter than in the parent phosphaferrocene. All structural changes resulting from P−B acid−base pairing follow the same qualitative trend, but are significantly larger than those occurring from the formation of transition metal complexes of phosphaferrocene. In contrast to 2, NMR spectroscopy reveals 3 to be almost completely dissociated in CDCl3 solution at room temperature. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Tungsten(VI) Complexes Derived from Calix[6]‐ and ‐[8]arenes: Oxo and Oxychloride Species
Authors: Redshaw Carl , Elsegood Mark R. J. 
Published: May 2003

AbstractTreatment of p‐tert‐butylcalix[6]areneH6 (H6L) or p‐tert‐butylcalix[8]areneH8 (H8L1) with 2 equiv. of [WOCl4] in refluxing toluene affords, after workup, the complexes [(WOCl2)2LH2] (1) and [{WO(NCMe)}2L1] (2), respectively. The molecular structures of 1 and 2 have been determined and reveal conformationally constrained macrocyclic rings. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Electrochemical Study of PW12O$\rm{_{40}^{3-}}$ in Poly(ethylene glycol) Electrolyte
Authors: Zhao Feng , Gu Ningyu , Liu Shaoqin , Wang Zhenxin , Dong Shaojun 
Published: May 2003

AbstractThe electrochemical properties of PW12O$\rm{_{40}^{3-}}$ (abbreviated as PW12) anion in poly(ethylene glycol) (PEG) have been studied by cyclic voltammetry, complex impedance and FT‐IR spectroscopy. The PW12 anion in PEG‐LiClO4 electrolyte shows reasonable facile electrochemistry, and the diffusion coefficients of PW12 were measured with microelectrode. It is shown that ionic conductivity of polymer electrolytes based on low molecular weight PEG can be improved by the addition of PW12. The increase of conductivity is coupled with decrease of transient cross‐links density of polymer chains which is evidenced by the downshift of COC stretching mode. The phenomena are explained in view of ion‐ion and ion‐polymer interactions.
Cyclic Voltammetry and Structural Studies of Nitric Oxide Monolayers Adsorbed on Pt(111)
Authors: Casero E. , Martin‐Gago J. A. , Alonso C. 
Published: May 2003

AbstractThe structural analysis of the adsorption of NO monolayers on Pt(111) from solution has been explored by cyclic voltammetry (CV) and X‐ray photoelectron spectroscopy (XPS) techniques. The monolayers were formed from acid solutions saturated with NO gas as well and from nitrite solutions in sulfuric acid. Results by both techniques indicate a maximum coverage of 0.2 monolayers as well as the presence of NO molecularly adsorbed on the surface with different orientations. The voltammetric oxidation of NO gives rise to two peaks separated in the voltammogram by 50 mV. This value is in agreement with the theoretical value of 9 kJ corresponding to the difference between different adsorption sites. A mechanism for the surface mediated oxidation process from adsorbed NO to NO2 under potential control is proposed.
Natural Bioactive Material: A Preparation of Soluble Eggshell Membrane Protein
Authors: Yi Feng , Yu Jian , Guo Zhao‐Xia , Zhang Li‐Xia , Li Qiang 
Published: May 2003

AbstractThe proteins of eggshell membranes, an industrial waste product, are dissolved by reductive cleavage with aqueous 3‐mercaptopropionic acid and acetic acid. The soluble protein preparation is cast into a thin film, and its bioactivity is investigated by cell culture.Photomicrograph of NIH3T3 fibroblasts cultured on SEP film for 3 days.magnified imagePhotomicrograph of NIH3T3 fibroblasts cultured on SEP film for 3 days.
Gels at Extremely Low Weight Fractions Formed by Irreversible Self‐Assembly of Proteins
Authors: Veerman Cecile , Sagis Leonard M. C. , van der Linden Erik 
Published: May 2003

AbstractFood‐grade biomaterials, like β‐lactoglobulin, bovine serum albumin, and ovalbumin, can assemble into fibrils. Using the irreversible fibril formation for β‐lactoglobulin, gels can be formed even at protein concentrations of 0.07%. These fibrillar mesostructures form new structuring materials for food and pharmaceutical applications.TEM micrograph of β‐lg at pH 2, after heating at 80 °C for 10 h and then the pH was adjusted to pH 8.magnified imageTEM micrograph of β‐lg at pH 2, after heating at 80 °C for 10 h and then the pH was adjusted to pH 8.
Synthesis of a Polyphenol with a Mesoionic 6‐Oxo‐1,6‐dihydropyrimidin‐3‐ium‐4‐olate as Pendant Group and Its Photochemical Behavior
Authors: Tonami Hiroyuki , Uyama Hiroshi , Kobayashi Shiro , Menges Bernhard , Mittler Silvia , Theis Alexander , Ritter Helmut 
Published: May 2003

AbstractThis study deals with the synthesis of a polyphenol bearing photosensitive groups, and its photochemical behavior upon UV irradiation. Mesoionic 5‐(4‐hydroxybenzyl)‐6‐oxo‐1,2,3‐triphenyl‐1,6‐dihydropyrimidin‐3‐ium‐4‐olate was prepared by condensation of 4‐benzyloxybenzylmalonic acid with N,N′‐diphenylbenzamidine using dicyclohexylcarbodiimide as condensing agent, followed by deprotection of the benzyl group. The monomer was polymerized by an iron‐salen complex to give a polymer with a mesoionic 6‐oxo‐1,6‐dihydropyrimidin‐3‐ium‐4‐olate moiety as the pendant group. Spin coated polymer films were prepared and characterized. It was shown by IR spectroscopy that irradiation with UV light converted the mesoionic structure to a bis(β‐lactam) structure. Waveguide spectroscopy showed a large decrease in the film thickness without refractive index changes during irradiation.Time development of the refractive index and the film thickness measured with p‐polarized light.magnified imageTime development of the refractive index and the film thickness measured with p‐polarized light.
Synthesis and Characterization of Conducting Copolymers of (S)‐2‐Methylbutyl‐2‐(3‐thienyl)acetate with Pyrrole and Thiophene
Authors: Levent Anil , Toppare Levent , Cianga Ioan , Yağci Yusuf 
Published: May 2003

AbstractPolymerization of methylbutyl‐2‐(3‐thienyl)acetate (MBTA) was achieved by constant current electrolysis at low temperature. Subsequently, the syntheses of block copolymers of polyMBTA were accomplished in the presence of either pyrrole or thiophene by constant potential electrolysis. Moreover, the copolymer of MBTA with thiophene was obtained with constant potential electrolysis.The synthesis of monomer MBTA.magnified imageThe synthesis of monomer MBTA.
Synthesis and Characterization of Amphiphilic Poly(ethylene oxide)‐block‐poly(hexyl methacrylate) Copolymers
Authors: Mahajan Surbhi , Renker Sabine , Simon Peter F. W. , Gutmann Jochen S. , Jain Anurag , Gruner Sol M. , Fetters Lewis J. , Coates Geoffrey W. , Wiesner Ulrich 
Published: May 2003

AbstractWe describe the preparation of amphiphilic diblock copolymers made of poly(ethylene oxide) (PEO) and poly(hexyl methacrylate) (PHMA) synthesized by anionic polymerization of ethylene oxide and subsequent atom transfer radical polymerization (ATRP) of hexyl methacrylate (HMA). The first block, PEO, is prepared by anionic polymerization of ethylene oxide in tetrahydrofuran. End capping is achieved by treatment of living PEO chain ends with 2‐bromoisobutyryl bromide to yield a macroinitiator for ATRP. The second block is added by polymerization of HMA, using the PEO macroinitiator in the presence of dibromobis(triphenylphosphine) nickel(II), NiBr2(PPh3)2, as the catalyst. Kinetics studies reveal absence of termination consistent with controlled polymerization of HMA. GPC data show low polydispersities of the corresponding diblock copolymers. The microdomain structure of selected PEO‐block‐PHMA block copolymers is investigated by small angle X‐ray scattering experiments, revealing behavior expected from known diblock copolymer phase diagrams.SAXS diffractograms of PEO‐block‐PHMA diblock copolymers with 16, 44, 68 wt.‐% PEO showing spherical (A), cylindrical (B), and lamellae (C) morphologies, respectively.magnified imageSAXS diffractograms of PEO‐block‐PHMA diblock copolymers with 16, 44, 68 wt.‐% PEO showing spherical (A), cylindrical (B), and lamellae (C) morphologies, respectively.
Free Energy of a Non‐Gaussian Polymer Brush
Authors: Amoskov Victor M. , Pryamitsyn Victor A. 
Published: May 2003

AbstractAn analytical theory describing layers of polymer chains grafted to a planar surface (i.e. polymer brush) is developed. We consider a brush of chains with finite extensibility (or non‐Gaussian brush) within the framework of molecular field theory. An analytical solution for free energy of the brush and a few other brush characteristics are obtained and studied. Comparison with other known models of a brush is also made.Chain extensibility E(x, y) for Gaussian model (dashed lines) and BCC model (solid lines) for a few chain end positions y (numbers near curves).imageChain extensibility E(x, y) for Gaussian model (dashed lines) and BCC model (solid lines) for a few chain end positions y (numbers near curves).
Chemical Composition Distribution of Multicomponent Copolymers
Authors: Anantawaraskul Siripon , Soares João B. P. , Wood‐Adams Paula M. 
Published: May 2003

AbstractThe number and weight chemical composition distributions in random terpolymers were derived using a statistical approach. The solution was then generalized to comprise higher multicomponent copolymers. The analytical solution was verified with Monte Carlo simulations and by considering limiting cases. Chemical composition distributions for fractions of random terpolymers of various kinetic chain lengths were also investigated. In a similar way to the results for binary copolymers described by Stockmayer's distribution, broadening of the distribution is observed for low‐molecular‐weight chains.Comparison of chemical composition distributions from Stockmayer (Equation (3)) and statistical approach (Equation (4)).imageComparison of chemical composition distributions from Stockmayer (Equation (3)) and statistical approach (Equation (4)).
Free‐Radical Frontal Copolymerization: The Dependence of the Front Velocity on the Monomer Feed Composition and Reactivity Ratios
Authors: Perry Michael F. , Volpert Vladimir A. , Lewis Lydia L. , Nichols Homer A. , Pojman John A. 
Published: May 2003

AbstractFrontal copolymerization is a process in which a spatially localized reaction zone propagates into a mixture of two monomers, converting them into a copolymer. In the simplest case of free‐radical copolymerization, a mixture of monomers and initiator is placed into a test tube. Reaction is initiated at one end of the tube, and a self‐sustained thermal wave, in which chemical conversion occurs, develops and propagates through the tube. We develop a mathematical model of the frontal copolymerization process and analytically determine the structure of the polymerization wave, the propagation velocity, maximum temperature, and degree of conversion of the monomers. Specifically, we examine their dependence on reactivity ratios as well as other kinetic parameters, monomer feed composition, and exothermicity of the reactions. Our analytic results are in good quantitative agreement with both direct numerical simulations of the model and experimental data, which are also presented in the paper.Dependence of front velocity on monomer feed composition for different heat release parameters.imageDependence of front velocity on monomer feed composition for different heat release parameters.
Polaron states and associated optical absorption in an emeraldine‐base polymer with 4n ± 1 nitrogen sites
Authors: Zhang Y. , Liu J. , Yu W. L. 
Published: May 2003

AbstractBond length and ring angle configurations of the (4n ± 1)‐polarons and the associated optical absorption coefficient α(ω) in an emeraldine‐base polymer were calculated on the basis of the Baranowski–Büttner–Voit (BBV) model. The numerical calculations show some obvious differences between the four types of polarons (P+4n+1, P–4n+1, P+4n–1, P–4n–1). The solutions of P+4n±1 (∼1.5 eV) and P–4n±1 (∼0.8 eV) match the 1.4 eV and 0.9 eV PA peaks very well. The theory also shows that through the optical absorption spectrum only one cannot distinguish the P+4n+1 and P+4n–1 (or P–4n+1 and P–4n–1) in detail.
On the mobility of delocalized and self‐trapped positronium states in ionic crystals
Authors: Bondarev I. V. 
Published: May 2003

AbstractThe temperature dependence of the diffusivity is studied for delocalized and self‐trapped positronium (Ps) atoms in ionic crystals. Detailed calculations taking into account low‐temperature and inelastic scattering corrections and a Ps scattering form‐factor have been performed for delocalized Ps. Low‐temperature and inelastic corrections to the delocalized Ps diffusivity are shown to be essential below several tens of K, while the form‐factor contribution is negligibly small up to thousand K. The mobility of self‐trapped Ps is analyzed within the framework of a small polaron approach. The hopping contribution to the self‐trapped Ps diffusivity is shown to be adiabatic in its physical nature. The tunnel contribution is in general not small and may turn out to be dominating even at very high temperatures.
The effects of bulk and surface fields on the phase diagram of a transverse Ising thin film
Authors: Kaneyoshi T. 
Published: May 2003

AbstractThe phase diagram of a transverse Ising thin film is investigated by the use of two theoretical frameworks, namely the standard mean field theory and the effective field theory. The effects of the ratio p between the bulk and surface transverse fields on the critical temperature are discussed by including the modification of surface exchange interaction. Some characteristic features are found in the phase diagrams when the ratio p increases from p = 1.0. They are enhanced for the film with thickness L smaller than 5.0. In particular, the critical ratio at which the critical temperature of the film with a finite transverse field reduces to zero, being independent of L, exhibits a linear relation when it is plotted against the modification of surface exchange interaction.
Anisotropy of optical absorption spectra of rare‐earth orthoaluminate DyAlO3
Authors: Valiev U. V. , Gruber J. B. , Rakhimov Sh. A. , Nabelkin O. A. 
Published: May 2003

AbstractThe polarization spectra of optical absorption for the 4f–4f transition 6H15/2 → 6F3/2 and 6H15/2 → 6F5/2 in the rare‐earth orthoaluminate DyAlO3 have been studied experimentally at the temperature T = 78 K. It has been shown that the non‐trivial character of the polarization absorption spectra anisotropy for low temperatures can be explained by a contribution of the J–J “mixing” mechanism for the excited multiplets of the ground 4f(n) configuration of the Dy3+ ion in the low‐symmetry crystalline field in the orthoaluminate structure. The results of numerical calculations of energies and wave functions of the Stark sublevels of the excited multiplets 6F3/2 and 6F5/2 are presented for the ground 4f9 configuration of the rare‐earth Dy3+ ion in the crystalline field of Cs symmetry.
Dynamics of Ising spins with antiferromagnetic bonds on a triangular lattice
Authors: Ismail G. , Salem A. 
Published: May 2003

AbstractSix‐coupled Ising spins on a triangular lattice with antiferromagnetic (AF) nearest neighbour and ferromagnetic (F) next‐nearest neighbour interactions are investigated by Glauber dynamics. The system is fully frustrated and has seven non‐trivial local energy minima in both clusters. The ground state has four degenerate states with energy –6. These states are separated by the energy barrier ΔE = 4.0 to invert spins in the ground state. The dynamics of AF‐F and F‐AF coupling clusters are solved exactly. Each cluster contributes as many long relaxation times as it has non‐trivial local energy minima. The barriers against inversion of the clusters take only two values, 0 and 4|J|. In the paramagnetic case (PM), there is no diverging relaxation time. In the ferromagnetic case (FM), there is only one long‐lived mode. The longest relaxation times follow an Arrhenius law. Both AF‐F and F‐AF clusters undergo a zero‐temperature phase transition. The real and imaginary parts of the dynamic susceptibility display maxima if plotted versus temperature. The frequency dependence of the susceptibilities explain the effect of frustration. The real part reveals two plateaus and the imaginary part displays two corresponding maxima if they are plotted as functions of the logarithm of frequency. The Argand plots show two overlapping semicircles for fixed frequency at low temperature, indicating the time separation of the modes.
Importance of effective two‐body interaction extracted from third‐order pseudopotential energy and a realistic evaluation of non‐pairwise forces in simple metals
Authors: Haldar S. , Sen D. 
Published: May 2003

AbstractCalculation of metallic pair interaction, extracted from higher order pseudopotential energy in the case of Al shows excellent agreement with recent ab initio calculation based on large set of experimental data. The calculation performed with ab initio pseudopotential has provided comprehensive unified study of various metallic properties of a number of simple metals. Analysis of the perturbation calculation beyond second order is shown to yield a reasonable estimate for the non‐pairwise interaction in these metals.
Nonlinear optical properties of a new substituted cluster: C48N12
Authors: Liu Hong , Chen Jiangwei 
Published: May 2003

AbstractWe attempted to investigate the doping effect on the nonlinear optical properties of heavier substituted fullerenes by using the extended Su–Schrieffer–Heeger (SSH) model. It is found that heavier substituted doping of C60 does not necessarily lead to a higher nonlinear optical polarizability value, because the delocalized character of π electrons in this system disappears with heavier substituting.
Volume and pressure dependence of the Grüneisen parameterγat high temperature
Authors: Cui Guang‐lei , Chen Li‐rong 
Published: May 2003

AbstractIn this paper, starting from the relation between the Anderson–Grüneisen parameterδ(T, P) and the second Grüneisen parameterq, we obtain a new computing formula for the volume and pressure dependence of the Grüneisen parameterγat high temperature. Applying this formula to sodium chloride, lithium, sodium, and potassium in different pressure ranges, we find that the calculated values of the Grüneisen parameterγare in good agreement with the experimental values.