bluuebunny/crossref_metadata_2025 huggingface dataset:
Density-functional theory structures of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid complexes for ions across the lanthanide series
Authors: Smentek Lidia , Andes Hess B. , Cross Jason P. , Charles Manning H. , Bornhop Darryl J.
Published: December 2005

The use of organically chelated lanthanides in diagnosis and treatment is a rapidly growing field in medicine. In order to gain a deeper understanding into the properties of these chelates, particularly spectroscopic, density-functional calculations have been performed on a series of lanthanide ions chelated with 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid. Based on the results of these calculations, it has been concluded that the local symmetry experienced by the chelated lanthanide ion may be treated as being axial, which will make the interpretation of their spectroscopic properties greatly simplified. It has also been suggested that the so-called “capping” water molecule at the ninth coordination position of the lanthanide is hydrogen bonded to the acetate oxygens of the sidearms, rather than coordinated as the ninth ligand of the lanthanide.
Grating-induced plasmon mode in gold nanoparticle arrays
Authors: Félidj N. , Laurent G. , Aubard J. , Lévi G. , Hohenau A. , Krenn J. R. , Aussenegg F. R.
Published: December 2005

We study the dipolar coupling of gold nanoparticles arranged in regular two-dimensional arrays by extinction micro-spectroscopy. When the interparticle spacing approaches the plasmon resonance wavelength of the individual particles, an additional band of very narrow width emerges in the extinction spectrum. By systematically changing the particles dielectric environment, the particles shape, the grating constant and angle of incidence, we show how this band associated to a grating induced-resonance can be influenced in strength and spectral position. The spectral position can be qualitatively understood by considering the conditions for grazing grating orders whereas the strength can be related to the strength of dipolar scattering from the individual particles.
Geometries and excited-state dynamics of van der Waals dimers and higher clusters of 1-cyanonaphthalene
Authors: Fujiwara Takashige , Campos Ramos Ricardo , Zgierski Marek Z. , Lim Edward C.
Published: December 2005

Mass-selected resonant two-photon ionization and infrared-ultraviolet double-resonance spectroscopies are combined with correlated (second Møller-Plesset perturbation) quantum chemistry calculation to probe electronic spectra and ground-state geometries of the jet-cooled dimer and higher clusters of 1-cyanonaphthalene. The results indicate that the dimer and trimer have stacked geometries, consistent with the highly efficient, rapid excimer formation that follows photoexcitation of the ground-state clusters.
Nonlinear diffusion equation, Tsallis formalism and exact solutions
Authors: Assis P. C. , da Silva L. R. , Lenzi E. K. , Malacarne L. C. , Mendes R. S.
Published: December 2005

We address this work to analyze a nonlinear diffusion equation in the presence of an absorption term taking external forces and spatial time-dependent diffusion coefficient into account. The nonlinear terms present in this equation are due to a nonlinear generalization of the Darcy law and the presence of an absorbent (source) term. We obtain new exact solutions and investigate nonlinear effects produced on the solutions by these terms. We also connect the results found here within the Tsallis formalism.
Dynamic salt effect on intramolecular charge-transfer reactions
Authors: Zhu Jianjun , Ma Rong , Lu Yan , Stell George
Published: December 2005

The dynamic salt effect in charge-transfer reactions is investigated theoretically in this paper. Free-energy surfaces are derived based on a nonequilibrium free-energy functional. Reaction coordinates are clearly defined. The solution of the reaction-diffusion equation leads to a rate constant depending on the time correlation function of the reaction coordinates. The time correlation function of the ion-atmosphere coordinate is derived from the solution of the Debye-Falkenhagen equation. It is shown that the dynamic salt effect plays an important role in controlling the rate of charge-transfer reactions in the narrow-window limit but is balanced by the energetics and the dynamics of the polar-solvent coordinate. The simplest version of the theory is compared with an experiment, and the agreement is fairly good. The theory can also be extended to charge-transfer in the class of electrolytes that has come to be called “ionic fluids.”
Heterogeneous thermal excitation and relaxation in supercooled liquids
Authors: Weinstein Susan , Richert Ranko
Published: December 2005

We investigate a phenomenological model which rationalizes the effects of dielectric hole burning on the basis of heterogeneous dielectric and specific heat relaxation in supercooled liquids. The quantitative agreement between model predictions and dielectric hole-burning observations is lost if the assumption of correlated dielectric and thermal relaxation times is removed from the model. This suggests that dynamically distinct domains in real liquids are associated with a time constant which characterizes both the structural and thermal relaxation behaviors. The calculations demonstrate that the observed burn-induced modifications reflect the spectral selectivity and persistence time of the fictive temperatures within these domains, and that 100 or more cycles of the sinusoidal burn field can be required to saturate the heat accumulated in the slow degrees of freedom. It is also shown that the recovery of dielectric holes is entirely accounted for by the model, and that the persistence times do not provide direct insight into rate exchange processes. Additionally, the model predicts that the heating effects considered here are a significant source of nonlinear dielectric behavior, even in the absence of deliberate frequency selective hole burning.
Quantum wave-packet calculation of reaction probabilities, cross sections, and rate constants for Li+H2+ reaction
Authors: Gogtas Fahrettin
Published: December 2005

The Li+H2+(υ,j)→LiH(υ′,j′)+H+ reactive scattering has been studied by using quantum real wave-packet method. The state-to-state and state-to-all reaction probabilities for the entitled collision have been calculated. The probabilities show a smooth variation for all initial rotational quantum states. The J-shifting approximation has been employed to estimate the integral cross sections and thermal rate constants have been calculated.
Modification of the charge ordering in Pr1∕2Sr1∕2MnO3 nanoparticles
Authors: Biswas Anis , Das I. , Majumdar Chandan
Published: December 2005

Transport and magnetic properties have been studied in two sets of sol-gel prepared Pr1∕2Sr1∕2MnO3 nanoparticles having an average particle size of 30 and 45nm. Our measurements suggest that the formation of a charge-ordered state is largely affected due to lowering of the particle size, but the ferromagnetic transition temperature (TC) remains unaffected.
Numerical modeling of Hohlraum radiation conditions: Spatial and spectral variations due to sample position, beam pointing, and Hohlraum geometry
Authors: Cohen David H. , Landen Otto L. , MacFarlane Joseph J.
Published: December 2005

View-factor simulations are presented of the spatially varying radiation conditions inside double-ended gold Hohlraums and single-ended gold Hohlraums (“halfraums”) used in inertial confinement fusion and high-energy density physics experiments [J. Lindl, Phys. Plasmas 11, 339 (2004); M. D. Rosen, Phys. Plasmas 3, 1803 (1996)]. It is shown that in many circumstances, the common assumption that the Hohlraum “drive” can be characterized by a single temperature is too simplistic. Specifically, the radiation conditions seen by an experimental package can differ significantly from the wall reemission measured through diagnostic holes or laser entrance holes (LEHs) by absolutely calibrated detectors. Furthermore, even in situations where the radiation temperature is roughly the same for diagnostics and experimental packages, or for packages at different locations, the spectral energy distributions can vary significantly, due to the differing fractions of reemitting wall, laser hot spots, and LEHs seen from different locations. We find that the spatial variation of temperature and especially the differences between what diagnostics looking in the LEH measure versus the radiation temperature on wall-mounted experimental packages are generally greater for double-ended Hohlraums than for halfraums. View-factor simulations can also be used to explore experimental variables (halfraum length and geometry, sample position, and beam pointing) that can be adjusted in order to, for example, maximize the radiation flux onto a sample, or other package. In this vein, simulations of Hohlraums and halfraums with LEH shields are also presented.
Confinement of Coulomb balls
Authors: Arp O. , Block D. , Klindworth M. , Piel A.
Published: December 2005

A model for the confinement of the recently discovered Coulomb balls is proposed. These spherical three-dimensional plasma crystals are trapped inside a rf discharge under gravity conditions and show an unusual structural order in complex plasmas. Measurements of the thermophoretic force acting on the trapped dust particles and simulations of the plasma properties of the discharge are presented. The proposed model of confinement considers thermophoretic, ion-drag, and electric field forces, and shows excellent agreement with the observations. The findings suggest that self-confinement does not significantly contribute to the structural properties of Coulomb balls.
Nuclear hyperfine interaction of rotating hydrogen: A spectroscopic investigation of hydrogen-OCS van der Waals complexes
Authors: Yu Zhenhong , Higgins Kelly J. , Klemperer William , McCarthy Michael C. , Thaddeus Patrick
Published: December 2005

The rotational spectra of five weakly bonded hydrogen-OCS complexes (paraH2,orthoH2, HD, orthoD2, and paraD2) are measured. Hyperfine structure is resolved and analyzed in all except the complex with paraH2, where I=0. For the two j=1 species, orthoH2-OCS and paraD2-OCS, nuclear hyperfine coupling constants are found to be da=21.2(2) and 8.4(2) kHz, respectively, indicative of nearly free uniaxial rotation of the hydrogen around the b-inertial axis. Similar analyses for HD-OCS and orthoD2-OCS yield the quadrupole coupling constants eqQa=16(2) and 30(2) kHz, respectively, showing that the internal rotational motions of HD and orthoD2 in the complex are slightly hindered producing a small nonspherical distribution. For orthoD2-OCS, the observed hyperfine structure indicates that the nuclear spin states I=0 and 2 are strongly coupled in the rotation of the complex.
Characteristics of HfO2–Al2O3 laminate films containing incorporated N as a function of stack structure and annealing temperature
Authors: Cho M.-H. , Chung K. B. , Whang C. N. , Ko D.-H. , Kim H. S.
Published: December 2005

The properties of Al2O3–HfO2 laminated films with incorporated N were investigated as a function of stack structure and annealing temperature by high-resolution x-ray photoelectron spectroscopy, and medium energy ion scattering (MEIS). The MEIS results indicate that the diffusion of Si from the Si substrate into film increased in the case where a film with a buffer layer of Al2O3 was present during the annealing at temperatures up to 800°C, while it led to a relative suppression in a film with a HfO2 buffer layer. The incorporation of N was gradually increased in the film with a buffer layer of Al2O3 on Si with annealing temperature, while the increase was abrupt in the film with a buffer layer of HfO2 on Si at an annealing temperature of 900°C. The N incorporated into the film was very unstable, resulting in out diffusion from the film after an additional annealing treatment.
Correlation of magnetic property with electrical transport property for ferromagnetic (Zn1−xMnx)O thin films
Authors: Lee Sejoon , Hwang Sun Jae , Lee Hye Sung , Shon Yoon , Yuldashev Shavkat U. , Kim Deuk Young
Published: December 2005

The correlation of electrical properties with magnetic properties for As+-implanted p-(Zn0.93Mn0.07)O thin films was investigated. For electrical transport measurements, it was clearly observed that the electrical mobility at the cryogenic temperature region is increased with decreasing temperatures. In Arrhenius plots of the carrier mobility, the critical point was observed at 65K. For Arrhenius plots of Mn2+-related emissions in photoluminescence measurements, the similar behavior was also observed at the same temperature region. The values of critical points are very closed to the value of the Curie temperature, thus it is expected that the increase of carrier mobility might be related to the activation of Mn2+ ions. Below the Curie temperature region, the activated Mn2+ ions will provide higher magnetic moments, and then the exchange interaction may increase in the material system. As a result, it will lead to enhance the spin-ordering effect and to reduce the probability of spin-disorder scattering. Therefore, the observation of gradual drop below the Curie temperature region in the temperature-dependent resistivity curve is expected to be a result from the spin-ordering effect due to the activation of Mn2+ ions.
Structural and magnetotransport properties of YBa2Cu3O7−δ∕Y2O3 quasimultilayers
Authors: Cai C. , Hänisch J. , Hühne R. , Stehr V. , Mickel C. , Gemming T. , Holzapfel B.
Published: December 2005

A series of quasimultilayers of YBa2Cu3O7−δ(YBCO)∕Y2O3, namely, 70×[YBCO(m)∕Y2O3(n)] (m=40 pulse, and n=2, 5, 10, and 20 pulse) were prepared on single-crystal SrTiO3 using pulsed-laser deposition. X-ray diffraction measurements revealed that both in-plane and out-of-plane textures of YBCO in the present quasimultilayers are as good as in pure YBCO films. Nanoscale Y2O3 precipitates grow epitaxially inside YBCO. With increasing Y2O3 pulse number, Tc decreases slightly, while ΔTc remains less than 1.5K. As well, the YBCO lattice parameter c has an increasing trend with increasing n. This can be attributed to the effect of epitaxial strain induced by lattice mismatch. The flux pinning force density in films with lower Y2O3 content (such as n=2), is improved in large ranges of field and temperature. In contrast, films with high Y2O3 content show enhanced flux pinning only at low temperature, which is understandable from the temperature dependence of irreversibility fields.
Thermoelectric properties of the CoSi1−xGex alloys
Authors: Kuo Y. K. , Sivakumar K. M. , Huang S. J. , Lue C. S.
Published: December 2005

The effects of Ge partial substitution for Si on the thermoelectric properties of CoSi1−xGex alloys were investigated by means of thermal and electrical transport measurements. Electrical resistivity (ρ), Seebeck coefficient (S), and thermal conductivity (κ) measurements were performed on a series of CoSi1−xGex alloys with x varying from 0 to 0.15. A substantial decrease in electrical resistivity and lattice thermal conductivity was noticed with increasing substitution level, whereas the Seebeck coefficient shows a weak variation with respect to Ge concentration. The thermoelectric efficiency was found to be enhanced by an order of magnitude in CoSi with Ge substitution. These observations were interpreted on the basis of the changes in the electronic band structure induced by Ge substitution.
Conversion of solar heat into work: A supplement to the actual thermodynamic description
Authors: Laptev V. I.
Published: December 2005

The absorption of radiant energy in solar cells is divided into reversible and irreversible processes occurring in parallel. The paper proposes a method for calculating their relative contributions. We also show that photon reemission without work production plays a particular role in the conversion of solar heat into work and the attainment of higher solar cell efficiencies. The comparison of the well-known thermodynamic efficiency limitations of the solar energy conversion with and without entropy production makes it possible to formulate the notion “antenna states of the absorber particles.” The carriers of similar states are known as pigment molecules in the photosynthesis of plants. We show that it is impossible to attain very high efficiencies in the conversion of solar heat into work without the reversible antenna reemission of solar energy.
Implication of device functioning due to back reaction of electrons via the conducting glass substrate in dye sensitized solar cells
Authors: Hore Sarmimala , Kern Rainer
Published: December 2005

Enhanced efficiency of dye sensitized solar cells requires minimization of all electron losses in the device. In addition to the loss via the nanoparticles of TiO2, the loss via the surface of the conducting glass substrate (TCO) needs to be contained. This additional electron recombination pathway at the TCO becomes increasingly pronounced at low light intensities. Hence, the determination of the lifetime of electrons within the nanoparticles of TiO2 requires a resistive layer at the surface of the TCO. Lowering the electron loss at the TCO/electrolyte interface increases the shunt resistance, thereby increasing the fill factor by over 10%.
Acoustic streaming past a vibrating wall
Authors: Luchini Paolo , Charru François
Published: December 2005

The classic phenomenon of acoustic streaming is reconsidered for the case in which the boundary layers on the vibrating and the still walls are of comparable importance, in the small-gap configuration suitable for an ultrasonic motor. The effect of temperature oscillations is included in the analysis, as well as is the impedance matching with the elastic oscillations in the vibrating wall.
Magnetic dynamics of simple collective modes in a two-sphere plasma model
Authors: Essén Hanno
Published: December 2005

A plasma blob is modeled as consisting of two homogeneous spheres of equal radius and equal but opposite charge densities that can move relative to each other. Relative translational and rotational motion are considered separately. Magnetic effects from the current density caused by the relative motion are included. Magnetic interaction is seen to cause an inductive inertia. In the relative translation case the Coulomb attraction, approximately a linear force for small amplitudes, causes an oscillation. For a large number of particles, the corresponding oscillation frequency will not be the Langmuir plasma frequency, because of the large inductive inertia. For rotation an external magnetic field is included and the energy and diamagnetism of the plasma in the model is calculated. Finally, it is noted how the neglect of resistivity is motivated by the results.
Relationship between the physical and structural properties of NbzSiyNx thin films deposited by dc reactive magnetron sputtering
Authors: Sanjinés R. , Benkahoul M. , Sandu C. S. , Schmid P. E. , Lévy F.
Published: December 2005

The optical and electrical properties of NbzSiyNx thin films deposited by dc reactive magnetron sputtering have been investigated as a function of the Si content (CSi). Optical properties were studied by both specular reflectivity and spectroscopic ellipsometry. Electrical resistivity was measured by the van der Pauw method at room temperature and as a function of the temperature down to 10K. Both the optical and electrical properties of NbzSiyNx films are closely related with the chemical composition and microstructure evolution caused by Si addition. For CSi up to 4at.% the Si atoms are soluble in the lattice of the NbN crystallites. In this compositional regime, the optical and electrical properties show little dependence on the Si content. Between 4 and 7at.% the surplus of Si atoms segregates at the grain boundaries, builds an insulating SiNx layer, and originates important modifications in the optical and electrical properties of these films. Further increase of CSi leads to the formation of nanocomposite structures. The electrical properties of these films are well described by the grain-boundary scattering model with low probability for electrons to cross the grain boundary. The appearance of the intragranular-insulating SiNx layer and the reduction of the grain size are noticed in the dielectric function mainly as a strong damping of the plasma oscillation.
Elliptically polarized absorption spectroscopy and observation of spin coherence in intrinsic GaAs
Authors: Lai Tianshu , Liu Xiaodong , Xu Haihong , Jiao Zhongxing , Lei Liang , Wen Jinhui , Lin Weizhu
Published: December 2005

The elliptically polarized absorption spectroscopy is further developed to observe electron spin coherence dynamics in an intrinsic bulk GaAs in Voigt geometry. Absorption saturation quantum beats are observed and explained as spin-precession-dependent state filling. An analytical model is developed quantitatively to describe the quantum beats and used to fit experimental data to retrieve spin coherence lifetime. Comparing to the reported data reveals that the spin coherence dynamics of the real and imaginary of a complex refractive index is much different.
Chemical functionalization of GaN and AlN surfaces
Authors: Baur B. , Steinhoff G. , Hernando J. , Purrucker O. , Tanaka M. , Nickel B. , Stutzmann M. , Eickhoff M.
Published: December 2005

The covalent functionalization of GaN and AlN surfaces with organosilanes is demonstrated. Both octadecyltrimethoxysilane and aminopropyltriethoxysilane form self-assembled monolayers on hydroxylated GaN and AlN surfaces, confirmed by x-ray photoelectron spectroscopy and atomic force microscopy. The monolayer thickness on GaN was determined to 2.5±0.2nm by x-ray reflectivity. Temperature-programmed desorption measurements reveal a desorption enthalpy of 240kJ∕mol. The realization of micropatterned self-assembled monolayers and the hybridization of deoxyribonucleic acid molecules on biofunctionalized GaN surfaces are shown.
Structural and optical properties of InAs quantum dots regrown on atomic hydrogen-cleaned GaAs surface
Authors: Kim Jong Su , Kawabe Mitsuo , Koguchi Nobuyki , Lee Dong-Yul , Kim Jin Soo , Bae In-Ho
Published: December 2005

We report the structural and optical properties of InAs quantum dots (QDs) directly regrown on air-exposed and subsequent atomic hydrogen-cleaned (AHC) GaAs (001) surface. The average size of InAs QDs on the AHC GaAs surface is 29nm, which is larger than 22nm for the conventionally grown InAs QDs on GaAs. The integrated photoluminescence intensity of the InAs QDs on the AHC GaAs measured at room temperature is larger than that of the reference sample by two orders, even though the cleaned GaAs surface directly faced the base of the InAs QDs. The decrease in the interface states between the wetting layer and AHC GaAs was confirmed by Franz–Keldysh oscillations of the photoreflectance spectra.
Nonlinear viscosity and its role in drift-Alfvén modes
Authors: Tsypin V. S. , Mikhailovskii A. B. , Shirokov M. S. , Kovalishen E. A. , Konovalov S. V. , Galvão R. M. O.
Published: December 2005

The moment approach is used to analyze the part of the magnetized plasma viscosity related to the nonlinear character of the Landau collision integral in the Boltzmann kinetic equation (nonlinear viscosity), pointed out by Catto and Simakov [Phys. Plasmas 11, 90 (2004)]. It is shown that the results of these authors, who have used an alternative procedure based on a more detailed analysis of the kinetic equation, correspond to a 15-moment approach. In comparison with the 13-moment approach (density, temperature, velocity, heat flux, and the viscosity tensor) of Grad, the 15-moment approach takes into account two higher-order moments, one of which is the vector-type moment similar to the parallel heat flux and the second is the tensor-type moment similar to the parallel projection of the viscosity tensor. Both these higher-order moments enter into the Braginskii approximation. The nonlinear viscosity calculated in the scope of the 13-moment Grad approach is qualitatively the same as that found by Catto and Simakov. Its role is investigated for drift-Alfvén modes, driven by the combined effect of the dissipative part of perpendicular heat conductivity and the standard collisional viscosity, and it is shown to be essential for the radial transport of these modes. It is shown that the wave packet of drift-Alfvén modes, propagating in the diamagnetic drift direction and driven for reversed temperature gradient, is transported down the pressure gradient. In contrast to this, the wave packet propagating in the electron diamagnetic drift direction and driven for positive temperature gradient is transported up the pressure gradient.
A “standing-wave meter” to measure dispersion and loss of photonic-crystal waveguides
Authors: Wüest R. , Erni D. , Strasser P. , Robin F. , Jäckel H. , Buchler B. C. , Koenderink A. F. , Sandoghdar V. , Harbers R.
Published: December 2005

We demonstrate a “standing-wave meter” for measuring dispersion and loss along the length of a planar InP-based photonic-crystal waveguide. Light from a tunable cw laser was coupled into a single line-defect waveguide that terminated inside the crystal structure to form a retroreflector. This structure created a standing wave which was imaged using a scanning near-field optical microscope. By measuring the intensity distribution of the standing wave for a range of optical frequencies, waveguide dispersion and loss were measured with high accuracy. Comparisons of the measurement results with three-dimensional numerical simulations reveal that material dispersion effects as small as 0.8% affect the band structure measurably.
Highly efficient microcrystalline silicon solar cells deposited from a pure SiH4 flow
Authors: van den Donker M. N. , Rech B. , Finger F. , Kessels W. M. M. , van de Sanden M. C. M.
Published: December 2005

A time-resolved optical emission spectroscopic study identified transient behavior of the excited SiH emission in a parallel plate SiH4∕H2 plasma. The transient behavior could be prevented by filling the background gas with H2 prior to plasma ignition. Applying this condition, state-of-the-art microcrystalline silicon (μc-Si:H) could be deposited irrespective of the applied H2 flow, ultimately demonstrated by a 9.5% efficient solar cell deposited from pure SiH4. The results are discussed in terms of SiH4 back diffusion: an initial diffusion flux of SiH4 from the reactor’s dead volume back into the plasma.
Photorefractive properties of an unsensitized polymer composite based on a dicyanostyrene derivative as nonlinear optical chromophore
Authors: Quintana José A. , Boj Pedro G. , Villalvilla José M. , Ortíz Javier , Fernández-Lázaro Fernando , Sastre-Santos Ángela , Díaz-García María A.
Published: December 2005

We report on the photorefractive (PR) properties at the 633nm laser wavelength of a polymer composite based on the polymer poly(n-vinyl carbazole) (PVK), doped with the dicyanostyrene derivative 4-piperidinobenzylidene-malonitrile (PDCST) as nonlinear optical chromophore and the liquid plasticizer butyl benzyl phthalate (BBP), without the presence of sensitizer. The PR-effect is observed only when samples are previously subjected to an electric field (i.e., 20V∕μm for 10min). Photoconductivity and birefringence of the composite become significant when the electric field treatment is performed at temperatures higher than room temperature (24°C). Gain coefficient and PR speed, determined from two-beam coupling experiments, are compared to those obtained with the PVK∕PDSCT∕BBP∕C60 standard sensitized composite.
Atomistic analysis of the mechanism of hydrogen diffusion in plasma-deposited amorphous silicon thin films
Authors: Valipa Mayur S. , Maroudas Dimitrios
Published: December 2005

We report the mechanism and activation barrier of H diffusion on the surface and in the bulk of plasma-deposited hydrogenated amorphous silicon (a-Si:H) films during postdeposition exposure of the films to H atoms from a H2 plasma. Our study is based on molecular-dynamics simulations of repeated impingement of H atoms on surfaces of smooth a-Si:H films over the temperature range 475–800K. The H diffusion mechanism is identical both on the a-Si:H surface and in the bulk a-Si:H film. Specifically, the H atom diffuses rapidly through a floating-bond-mediated migration process; this floating bond accompanies the H atom as it hops from one Si atom to another. The Si atoms between which the H hops during its diffusion are typically either very weakly bonded or not bonded to each other. The calculated activation barrier for H diffusion is only 0.10eV.
Magnetic, Spectral and Structural Aspects of Spin Transitions in Iron(II) Complexes of 2-(Pyrazol-3-yl)pyridine and 3-(Thiazol-2-yl)pyrazole
Authors: Harimanow Lucia S. , Sugiyarto Kristian H. , Craig Donald C. , Scudder Marcia L. , Goodwin Harold A.
Published: December 2005

Tris(ligand)iron(II) complexes of 2-(pyrazol-3-yl)pyridine (3ppH) and
3-(thiazol-2-yl)pyrazole (3tpH) undergo temperature-induced singlet
(1A1) ⇔ quintet
(5T2) transitions. The transition
in [Fe(3ppH)3]
[CF3SO3]2.2H2O
is continuous and centred above room temperature while that in the anhydrous
triflate salt is discontinuous and is centred below room temperature. The
latter transition occurs via a thermal hysteresis loop of width 12 K,
Tc↓ and Tc↑ being 229
and 241 K, respectively. The displacement of the transition to lower
temperature in the anhydrous salt is believed to be associated with the loss
of hydrogen bonding involving the uncoordinated pyrazole >NH group and
solvate water. In [Fe(3tpH)2(3tp)]
[ClO4].2H2O and
[Fe(3tpH)2(3tp)]
[BF4].2H2O (3tp is the
deprotonated ligand) continuous transitions are observed, centred below room
temperature. In these instances the displacement is consistent with the
intrinsically weaker field of the bidentate system containing two
five-membered heterocycles. Structural data were obtained for
[Fe(3ppH)3][CF3SO3]2.2H2O,
[Fe(3tpH)3]
[BF4]2.1·5H2O
and [Ni(3tpH)3]
[BF4]2.2(3tpH). The
average metal–nitrogen distances in the complexes are 1·97,
2·18 and 2·09 Å, severally. The large difference in the
distances for the two iron complexes arises from the different ground states:
a singlet for the 3ppH complex and a quintet for the 3tpH complex. In all
three salts there is extensive hydrogen bonding involving the pyrazole >NH
groups, the anions and the solvate molecules.
[Fe(3ppH)3]
[CF3SO3]2.2H2O:
monoclinic, space group
P21/c,
a 12·33(1), b
24·44(1), c 12·55(1) Å, β
115·27(4)°, Z 4. [Fe(3tpH)3]
[BF4]2.1·5H2O:
monoclinic, space group C 2/c,
a 41·56(2), b
16·418(3), c 18·154(7) Å, β
106·94(2)°, Z 8. [Ni(3tpH)3]
[BF4]2.2(3tpH):P
bcn, a 14·928(2),
b 15·310 (3), c
17·882 (3) Å, Z 4.
Experiments Directed Towards the Synthesis of Anthracyclinones. XXXIII. Hetero-Diels-Alder Reactions Using Togni's Catalyst
Authors: Bercich Mark D. , Cambie Richard C. , Rutledge Peter S.
Published: December 2005

(+)-Bis[3-(heptafluorobutyryl)camphorato]oxovanadium(IV)
[(+)-VO(hfc)2] (2) is an effective
catalyst for the hetero-Diels-Alder reaction of a variety of anthraquinone
aldehydes and silyloxy dienes giving high yields of cycloadducts. The
reactions all proceed with strict endo topology giving
rise to cis products; this indicates that they follow a
similar mechanistic pathway to that proposed by Danishefsky for reactions
catalysed by the europium complexes Eu(fod)3 and
Eu(hfc)3. Reactions employing the dimethoxy aldehydes
(3) and (4) and the phenolic aldehydes (5) and (6) proceed with only modest
degrees of enantioselection. Reaction with the benzyloxy aldehyde (7) proceeds
with significantly reduced enantioselectivity indicating that the nature of a
substituent at C1 can have a significant effect. Enantioselectivity is
generally higher for reactions at low temperature and when toluene rather than
dichloromethane is used as solvent. The cycloadduct (24) has been elaborated
to the anthracene C-glycoside (28) of known
configuration, thereby establishing that the hetero-Diels-Alder reaction
favours formation of the
2′R,6′R enantiomer of
(24). This enantiofacial selectivity has been correlated with the sense of
anisochrony observed in the 1H n.m.r. spectrum of the
ketone (17), a derivative of (24), in the presence of the solvating agent
(S)-(+)-trifluoroanthrylethanol
[(S)-(+)-TFAE]. The enone (21) has been
elaborated to the anthraquinone olivose C-glycoside
(33), a synthesis demonstrating the utility of hetero-Diels-Alder reactions
involving silyloxy dienes with terminal silyloxy or methyl substituents for
such syntheses.
The Crystal Structures of the 4-Bromocamphorenic Acids: a Unique Isomorphous Series Among Isomeric Carboxylic Acids
Authors: Smith Graham , Venzke Brian N. , Kennard Colin H. L. , Carman Raymond M.
Published: December 2005

The crystal structure determinations of the isomeric 4-bromocamphorenic acids
[(1R)-4-bromo-1,2,2-trimethylcyclohex-3-ene-1-carboxylic
acid and
(1R)-4-bromo-1,6,6-trimethylcyclohex-3-ene-1-carboxylic
acid], and that of crystals of the normal isomeric mixture of the two
from the synthetic preparation, have been completed. This set provides an
example of an unusual isomorphous organic crystal series that shows little
variation in melting points between pure isomeric end-members and the
‘isomeric mixture’, which is typically 70 : 30%. This ratio
is consistent with the observed occurrence of two conformational modifications
of the acid found among the three independent molecules in the
crystallographic asymmetric unit; this gives two different but typically
cyclic hydrogen-bonded carboxylic acid associations. In the ‘isomeric
mixture’, random associations of both isomers, consistent with the
reaction ratio, result in the isomorphous crystalline structure in which the
double bond is statistically distributed over the two adjacent ring sites.
This phenomenon also provides an explanation of the physical anomalies that
have been associated with these compounds since their first reported synthesis
in 1896.
A New Sideroxylonal from Eucalyptus melliodora
Authors: Eschler Bart M. , Foley William J.
Published: December 2005

Sideroxylonal C (3),
(2RS,3RS,4RS)-2-(3,5-diformyl-2,4,6-trihydroxyphenyl)-5,7-dihydroxy-3-(1-methyl-
ethyl)-4-(2-methylpropyl)chroman-6,8-dicarbaldehyde, was isolated from
Eucalyptus melliodora leaf, and its structure determined
by spectroscopic methods.
Crystal structure and lattice energetics of 10-methylacridinium halides
Authors: Storoniak Piotr , Krzyminski Karol , Dokurno Pawel , Konitz Antoni , Blazejowski Jerzy
Published: December 2005

The crystal structures of 10-methylacridinium chloride monohydrate, bromide
monohydrate and iodide were determined by X-ray analysis. The compounds
crystallize in the triclinic space group, P¯1, with
2 molecules in the unit cell. The molecular arrangement in the crystals
revealed that hydrogen bonds (in hydrates) and van der Waals contacts play a
significant part in intermolecular interactions. To discover their nature,
contributions to the crystal lattice energy arising from electrostatic (the
most important since the compounds form ionic crystals), dispersive and
repulsive interactions were calculated. Enthalpies of formation of the salts,
their stability and susceptibility to decomposition could be predicted from a
combination of crystal lattice energies with values of other thermochemical
characteristics obtained theoretically or taken from the literature. The role
of water in the stabilization of the crystal lattice of the hydrates is also
explained. The information gathered has given an insight into the features and
behaviour of compounds which can be regarded as models of a large group of
aromatic quaternary nitrogen salts.
Cyclic Voltammetry as an Indicator of Antioxidant Activity
Authors: Papanikos A. , Eklund J. , Jackson W. R. , Kenche V. B. , Campi E. M. , Robertson A. D. , Jarrott B. , Beart P. M. , Munro F. E. , Callaway J. K.
Published: December 2005

A series of compounds based around combining the neuroprotective properties of non-competitive N-methyl D-aspartic acid (NMDA) receptor antagonists with antioxidant functionalities have been prepared. The redox chemistry of these compounds has been evaluated using cyclic voltammetry, and the results have been compared with their radical-scavenging properties obtained from two standard biological assays, the inhibition of lipid peroxidation (thiobarbituric acid reacting substances assay) and the Sapphire colorimetric assay. Results from these different methods show general concordance. The most effective antioxidants were substituted phenols, e.g. Trolox�. The antioxidant activity of a series of pyrimidines was shown to be dependent on the presence of three amino substituents.
Synthesis of [Cu2(Me2[9]aneN2S)2(OH)2](PF6)2, a Hydroxo-Bridged Copper(II) Complex of N,N′-Dimethyl-1-thia-4,7-diazacyclononane (Me2[9]aneN2S). X-Ray Structural Analysis, Magnetic Susceptibility, E.P.R. and Visible Spectroscopy
Authors: Grillo Vincent A. , Hambley Trevor W. , Gahan Lawrence R. , Hanson Graeme R. , Stranger Robert , Moubaraki Boujemaa , Murray Keith S.
Published: December 2005

The bis(µ-hydroxo) complex [Cu 2 (Me
2 [9]aneN 2 S)
2 (OH) 2 ] (PF
6 ) 2 (Me 2
[9]aneN 2 S =
N,N′-dimethyl-1-thia-4,7-
diazacyclononane) results after reaction of [Cu(Me
2 [9]aneN 2
S)(MeCN)] (PF 6 ) with dioxygen at −78°C
in acetonitrile. The complex has been characterized by X-ray crystallography:
orthorhombic, space group Pnma, with
a 18.710(3), b 16.758(2),
c 9.593(2) Å, and Z =
4. The structure refined to a final R value of 0.051.
The complex contains two copper(II) ions bridged by two hydroxo groups with
Cu···Cu 2.866(1) Å. The solid-state magnetic
susceptibility study reveals ferromagnetic coupling, the fitting parameters
being J = +46±5 cm
−1 , g =
2.01±0.01 and ? = −0.58±0.03 K. The
frozen-solution e.p.r. spectrum in dimethyl sulfoxide is characteristic of a
monomeric copper(II) ion (g
‖ 2.300, g
⊥ 2.063; A
‖156.2 × 10 −4
cm −1 , A
⊥ 9.0 × 10 −4
cm −1 ) with an N 2 O
2 donor set. Thioether coordination to the copper(II) in
solution is supported by the presence of an intense absorption assigned to a
σ(S)→Cu II LMCT transition at
c. 34000 cm −1 . The
single-crystal spectrum of [Cu 2 (Me
2 [9]aneN 2 S)
2 (OH) 2 ] (PF
6 ) 2 (273 K) reveals d→d
transitions at 14500 and 18300 cm −1 and a weak
π(S)→Cu II charge-transfer band at approximately
25000 cm −1.
Structural Systematics of Rare Earth Complexes. XVIII (Hydrated) Mononuclear 1 : 1 Adducts of Lanthanoid(III) Chlorides with 2,2′-Bipyridine
Authors: Semenova Lioubov I. , Skelton Brian W. , White Allan H.
Published: December 2005

Room-temperature single-crystal X-ray structure determinations are recorded for a number of adducts of hydrated lanthanoid(III) chlorides with 2,2′-bipyridine, ‘bpy’, crystallized from water/ethanol solutions, which contain mononuclear arrays with 1 : 1 Ln/bpy stoichiometry. Extended isomorphous series have been defined pertinent to the heavy end of the Ln series: crystals of LnCl3/bpy/H2O (1 : 1 : 6) ([(bpy)Ln(OH2)6]Cl3), seemingly inclusive of (at least) the range Ln = Ho(-)Lu and Y, are monoclinic, P 21/n, a ≈ 14·2, b ≈ 7·7, c ≈ 17·4 Å, β ≈ 91°, Z = 4, with an eight-coordinate LnN2O6 array; conventional R values on |F| were 0·043, 0·029, 0·057 for No 2435, 3120, 1846 independent ‘observed’ (I > 3σ(I)) diffractometer reflections (Ln = Ho, Lu, Y). Crystals of LnCl3/bpy/H2O (1 : 1·5 : 8) ([(bpy)Ln(OH2)6]Cl3.½bpy.2H2O), seemingly encompassing (at least) the range Ln = Er(-)Lu and Y, are triclinic, P 1, a ≈ 11·7, b ≈ 11·0, c ≈ 10·1 Å, α ≈ 85·8, β ≈ 74·7, γ ≈ 79·5°, Z = 2, R 0·038, 0·033, 0·048 for No 3897, 4377, 3130, and contain similar [(bpy)Ln(OH2)6]3+ cations as does HoCl3/bpy/H2O (1 : 2 : 7), [(bpy)Ho(OH2)6]Cl3.bpy.H2O, orthorhombic, Pbca, a 18·02(2), b 20·06(2), c 15·051(9) Å, Z = 8, R 0·057 for No 3009. By contrast, only sporadic, diverse and unrelated forms are thus far defined among the lighter Ln: EuCl3/bpy/H2O(1 : 1 : 5) ([(bpy)Eu(OH2)4Cl2]Cl.H2O), triclinic, P 1, a 11·506(7), b 11·098(5), c 6·974(8) Å, α 77·35(7), b 85·1(1), γ 89·54(4)°, Z = 2, R 0·063 for No 4633, also contains a mononuclear [(N,N′-bidentate)Ln(unidentate)6] array. PrCl3/bpy/H2O(1 : 1 : 3)(× 4) is a remarkable compound, being 2[(bpy)Pr(OH2)3Cl3] [(bpy)(H2O)2Cl2Pr(µ-Cl)2PrCl2(OH2)2(bpy)].2H2O, triclinic, P 1, a 13·490(4), b 11·121(2), c 10·162(1) Å, α 96·06(1), β 90·08(2), γ 96·43(2)°, Z = 2 f.u., R 0·045 for No 4127, with a mononuclear species of PrCl3/bpy/H2O (1 : 1 : 3) stoichiometry and a binuclear species of 1 : 1 : 2 stoichiometry. A binuclear ethanol solvated array has been characterized for LaCl3/bpy/EtOH (1 : 1 : 2) [(bpy)(EtOH)2Cl2La(µ-Cl)2LaCl2(HOEt)2(bpy)], with eight-coordinate lanthanum; this complex is triclinic, P 1, a 11·426(8), b 10·673(7), c 10·453(7) Å, α 109·60(5), β 113·10(5), γ 105·80(5)°, Z = 1 dimer, R 0·046 for No 2786.
Structural Systematics of Rare Earth Complexes. XIX (Hydrated) 1 : 2 Mononuclear Adducts of Lanthanoid(III) Chlorides with 2,2′-Bipyridine and 1,10-Phenanthroline
Authors: Semenova Lioubov I. , White Allan H.
Published: December 2005

Room-temperature single-crystal X-ray structure determinations are recorded for a number of adducts of hydrated lanthanoid(III) trichlorides with 2,2′-bipyridine (‘bpy’) and 1,10-phenanthroline (‘phen’), crystallized from water, methanol or ethanol solutions, containing mononuclear arrays with 1 : 2 Ln/bpy or phen stoichiometry. LaCl3/phen/H2O(1 : 3 : 9), [(phen)2La(OH2)5]Cl3.phen.4H2O, although of overall 1 : 3 LaCl3/phen stoichiometry, has a lattice phen; it is orthorhombic, Pnna, a 19·947(7), b 16·457(5), c 12·213(2) Å, Z = 4; conventional R on |F| was 0·030 for No 2567 ‘observed’ (I >3σ(I)) diffractometer reflections. LaCl3/phen/H2O/MeOH (1 : 2 : 6 : 1), [(phen)2La(OH2)5]Cl3.H2O.MeOH, is triclinic, P 1, a 19·060(3), b 9·252(3), c 8·994(3) Å, α 69·33(3), β 86·81(2), γ 89·66(2)°, Z = 2, R 0·037 for No 5452. LaCl3/bpy/H2O (1 : 2 : 6), [(bpy)2La(OH2)4Cl]Cl2.2H2O, is monoclinic, P 21/c, a 19·389(3), b 9·071(1), c 16·873(2) Å, β 114·10(1)°, Z = 4, R 0·029 for No 4699. All three of these complexes have a nine-coordinate [(N,N′-bidentate)2La(unidentate)5] coordination environment with quasi-2 symmetry; that of the remaining compounds following is eight-coordinate [(N,N′-bidentate)2Ln(unidentate)4]. LuCl3/phen/H2O (1 : 2 : 6), [(phen)2Lu(OH2)4]Cl3.2H2O, is monoclinic, C 2/c, a 11·045(7), b 17·660(6), c 14·474(9) Å, β 92·82(5)°, Z = 4, R 0·042 for No 1695, the Lu lying on a crystallographic 2 -axis. Crystals of LnCl3/phen/H2O(1 : 2 : 4), [(phen)2Ln(OH2)3Cl]Cl2.H2O (Ln = Dy, Er, Y), are triclinic, P 1, a≈ 12·6, b ≈ 10·5, c ≈ 10·4 Å, α ≈ 93·3, β ≈ 109·3, γ ≈ 96·8°, Z = 2, R 0·030, 0·040, 0·052 for No 4221, 5100, 2690 respectively. PrCl3/bpy/H2O/EtOH (1 : 2 : 1 : 0·5), [(bpy)2Pr(OH2)Cl3].½EtOH, is triclinic, P 1, a 13·331(3), b 10·734(2), c 9·758(2) Å, α 63·67(2), β 78·99(2), γ 71·24(2)°, Z = 2, R 0·033 for No 4596, while [(bpy)2Pr(OH2)2Cl2]Cl is monoclinic, C 2/c, a 15·921(15), b 11·314(8), c 14·114(8) Å, β 116·70(6)°, Z = 4, R 0·041 for No 2269. ErCl3/bpy/H2O(1 : 2 : 2 (also)), [(bpy)2Er(OH2)2Cl2]Cl, is cubic, I 23, a 26·032(4) Å, Z = 24, R 0·066 for No 1644. Crystals of LnCl3/phen/H2O/MeOH (1 : 2 : 1 : 1), [(phen)2Ln(OH2)Cl3].MeOH (Ln = La, Pr, Nd, Eu), are monoclinic, P 21/a, a ≈ 13·2, b ≈ 10·7, c ≈ 18·5 Å, β ≈ 102·1°, Z = 4, R 0·054, 0·032, 0·040, 0·054 for No 2872, 4792, 3179, 2847 respectively. LnCl3/bpy/H2O/EtOH (1 : 2 : 1 : 1), [(bpy)2Ln(OH2)Cl3].EtOH (Ln = Nd, Eu), are triclinic, P 1, a ≈ 11·3, b ≈ 10·9, c ≈ 10·4 Å, α ≈ 75·5, β ≈ 89·8, γ ≈ 78·0°, Z = 2, R 0·044, 0·056 for No 4979, 3596 respectively. LaCl3/bpy/EtOH (1 : 2 : 0·5) is binuclear [(bpy)2Cl2La(µ-Cl)2LaCl2(bpy)2].EtOH, monoclinic, P 21/c, a 9·6878(2), b 17·5696(3), c 16·1341(2) Å, β 123·10(1)°, Z = 2, R 0·033 for No 4256. A totally unsolvated array is found for YbCl3/bpy (1 : 2), [(bpy)2YbCl3], monoclinic, P 21/c, a 15·065(8), b 8·598(4), c 16·92(1) Å, β 112·46(5)°, Z = 4, R 0·032 for No 3548, in which, alone, the metal atom is seven-coordinate.
Synthesis of Precursors for the Pyrolytic Formation of Pentatetraenones
Authors: Arena Phillip , Brown Roger F. C. , Eastwood Frank W. , McNaughton Don
Published: December 2005

3-(9′,10′-Dihydro-9′,10′-ethanoanthracen-11′-ylidene)prop-2-enoyl
chloride and its [12′,12′- 2 H2]
and [1- 13 C] isotopomers have been prepared
and pyrolysed. Argon matrix infrared spectroscopy showed
ν2 bands at 2207 . 7, 2207 . 0, and 2168
. 5 cm−1 respectively for the three
pentatetraenone isotopomers. The pyrolysate of the 12′-methyl
substituted precursor showed a band at 2205 cm−1
which was tentatively assigned to methylpentatetraenone. The 12′-ethenyl
substituted precursor gave a pyrolysate showing ketene bands but also yielded
9,10-dihydro-9,10[1′,2′]-benzenoanthracene.
Preparation and Structure of Ru2(µ−O2CCF3)2(CO)4(NCMe)2
Authors: Bruce Michael I. , Skelton Brian W. , White Allan H. , Zaitseva Natasha N.
Published: December 2005

The molecular structure of
Ru2(µ-O2CCF3)2(CO)4(NCMe)2,
obtained from
Ru3(CO)10(NCMe)2
and CF3CO2H, or from
Ru3(CO)12 and
CF3CO2H in a
CH2Cl2/MeCN mixture, is
presented. The central Ru–Ru bond [2·683(1) Å] is
bridged by the two carboxylato ligands [Ru–O (average)
2·133 Å]. Each ruthenium carries
mutually cis CO ligands approximately
trans to the Ru–O vectors and an MeCN ligand in
the axial position [Ru–N (average) 2·18 Å].
Conformational Comparisons Between Phenoxyacetic Acid Derivatives in Adducts and in the Free Form
Authors: Smith Graham , Cooper Catherine J. , Chauhan Veena , Lynch Daniel E. , Parsons Simon , Healy Peter
Published: December 2005

Six molecular complexes containing the herbicidally active
(2,4-dichlorophenoxy)acetic acid (2,4-d) and (2,4,5-trichlorophenoxy)acetic
acid (2,4,5-t) have been prepared and studied by using single-crystal X-ray
diffraction techniques. These adduct structures are 2,4-d with
4,4′-dipyridine (2 : 1 complex), and 2,4,5-t with respectively
5-nitroquinoline (1 : 1), 4,4′-dipyridine (2 : 1), 2-amino-2-thiazoline
(1 : 1), 2-aminobenzothiazole (1 : 1) and 2-amino-5-ethyl-1,3,4-thiadiazole (1
: 1). The conformations of the phenoxyacetic acid molecules were found to be
either synclinal (in three cases) or antiperiplanar (in the other three
cases). A general review is also made about the conformational aspects of
previously reported adducts of phenoxyacetic acid derivatives and how they
compare to their free acid structures.
Two New Withanolides from the Aerial Parts of Datura innoxia
Authors: Siddiqui Bina S. , Afreen Shamsul , Begum Sabira
Published: December 2005

Two new steroidal lactones of the withanolide group named as withametelinol
(1a) and withametelinone (2) have been isolated from the aerial parts of
Datura innoxia along with withametelin. The structures
of the new constituents have been established as
(20R,22R)-21,24-epoxy-12α-hydroxy-1-oxowitha-2,5,25(27)-trienolide
and
(20R,22R)-21,24-epoxy-1,12-dioxowitha-2,5,25(27)-trienolide
through spectroscopic studies including one- and two-dimensional (COSY-45,
NOESY, HMQC, HMBC) n.m.r. spectroscopy and chemical
transformations.
A New Class of Herbicides that are Derivatives of 8-Oxabicyclo[3.2.1]oct-6-en-3-one
Authors: Barbosa Luiz Cláudio de A. , Conceição Gelson J. A. , Demuner Antônio J. , Silva Antônio A. , Mann John , Piló-Veloso Dorila
Published: December 2005

Treatment of 8-oxabicyclo[3.2.1]oct-6-en-3-one with a catalytic
amount of osmium tetraoxide and excess hydrogen peroxide resulted in the
formation of the acetonide
exo-6,exo-7-isopropylidenedioxy-8-oxabicyclo[3.2.1]oct-3-one
(2), in 96% yield. This acetonide was converted into several aromatic
alcohols (4a–k) through a Grignard reaction. The alcohols were treated
with aqueous HCl in acetone, and the corresponding alkenes
(5a–c,e–g, j,k) were obtained in 26–46% overall
yield, from the ketone (2). The herbicidal activity of the alkenes was
evaluated at a concentration of 6.6 µg g−1.
All compounds showed an inhibitory effect (21–66%) on the
Sorghum bicolor radicle growth. The inhibition of the
accumulation of fresh and dried weight of the aerial parts of
Cucumis sativus, after 14 days, varied from 7.1 to
60.7% and from 0.0 to 41.6%, respectively. Compounds
(5a,e–g) caused 100% mortality of
C. sativus, after 20 days. Compound (5g)
(exo-6,exo-7-isopropylidenedioxy-3-(3-methylphenyl)-8-
oxabicyclo[3.2.1]oct-2-ene) was evaluated against several weeds, and
it caused 100% mortality of Desmodium tortuosum
and Pennisetum setosum.