Absence of magnetic order in dichloro [1,2-bis(diphenylphosphino)ethane] nickel~(2+) single crystal

Dichloro [1,2-bis(diphenylphosphino) ethane] nickel~(2+)(Ni Cl_2(dppe)) is an organic compound containing C_(26)H_(24)P_2(dppe) molecules and Cl-, Ni~(2+)ions. The large-size Ni Cl_2(dppe) single crystals with longest dimension of4 mm were grown by the method of slow evaporation of organic solution. Single crystal x-ray diffraction spectrum indicates that the single crystal is of high quality. Magnetization results of the Ni Cl_2(dppe) single crystals show an anisotropic paramagnetism behavior and diamagnetic background, which come from Ni~(2+) ions and benzene ring, respectively. However, according to the specific heat results with temperature down to 0.1 K and magnetic field up to 14 T, no expected field-induced quantum phase transition was observed in Ni Cl_2(dppe) single crystals.     

Spin dynamics and ferromagnetic resonance in an [Mn{(R/S)-pn}]2[Mn{(R/S)-pn}2(H2O)][Cr(CN)6]2 molecular magnetic

Ferrimagnetic resonance spectra of the [Mn{(R/S)-pn}]₂[Mn{(R/S)-pn}]₂(H₂O)][Cr(CN)₆]₂ molecular magnetics were examined. It was established that, within the high-temperature (paramagnetic) region (T > 53 K), the EPR spectrum features a single Lorentz-shaped peak, while, at temperatures below 53 K, in a three-dimensional ferrimagnetic state, this peak splits into several components, some of which correspond to different states of spins in the helical chains of atoms comprising the chiral crystalline structure.     

Quantitative elucidation of macrocyclic effect on extraction-ability and -selectivity. Benzo-18-crown-6 and its open-ring analog 1,2-bis[2-(2-methoxyethoxy)ethoxy]benzene–alkali metal picrate systems

The constants of overall extraction equilibrium (K_ex) and partition (K_D,MLA) for various diluents and aqueous ion-pair formation (K_MLA) of alkali metal (Li–Cs) picrate (MA) 1:1:1 complexes (MLA) with benzo-18-crown-6 (B18C6) and its open-ring analogue 1,2-bis[2-(2-methoxyethoxy)ethoxy]benzene (AC·B18C6) were determined at 25 °C, L being B18C6 or AC·B18C6; the distribution constants of AC·B18C6 were measured at 25 °C. The partition behavior of AC·B18C6 and the MLA complexes closely obeys regular solution theory, omitting chloroform; the molar volumes and the solubility parameters of AC·B18C6 and the MLA complexes were determined. The extraction selectivities of AC·B18C6 and B18C6 for the alkali metal picrates increase in the order Li < Na < Cs < K or Rb < or ≈ Rb or K and Li  Na < Cs < Rb < K, respectively. The extraction selectivity of B18C6 for neighboring alkali metal ions in the periodic table is superior to that of AC·B18C6. The macrocyclic effect on the extraction-ability and -selectivity was quantitatively elucidated by the four fundamental equilibrium constants.     

De Haas-van Alphen oscillations in the quasi-two-dimensional organic metal (BEDO-TTF)5[CsHg(SCN)4]2

The magnetization oscillations in the quasi-two-dimensional organic metal (BEDO-TTF)₅[CsHg(SCN)₄]₂ are thoroughly investigated over a wide range of magnetic field directions at different temperatures down to 0.4 K. The results obtained are in good agreement with the shape and sizes of the Fermi surface calculated from the x-ray diffraction data. Apart from the fundamental frequencies, the combination frequencies are found in the magnetization oscillation spectrum. It is demonstrated that these combination frequencies are governed by the motion of charge carriers along the real closed orbits inside the network of magnetic breakdown orbits formed under the action of the magnetic field. It is uniquely established that the combination frequencies previously revealed in the magnetoresistance oscillation spectrum of the same metal are associated with the quantum interference effect. The angular dependences of the oscillation amplitude exhibit minima, which are explained by the spin splitting of the Landau levels.     

Adsorption of sodium bis(2-ethylhexyl) sulfosuccinate and wettability in polytetrafluoroethylene-solution-air system

The role of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) adsorption at water-air and polytetrafluoroethylene-water (PTFE) interfaces in wetting of low energy PTFE was established from measurements of the contact angle of aqueous AOT solutions in PTFE-solution drop-air systems and the aqueous AOT solution surface tension measurements. For calculations of the adsorption at these interfaces the relationship between adhesion tension (γ_LV cos θ) and surface tension (γ_LV), and the Gibbs and Young equations were taken into account. On the basis of the measurements and calculations the slope of the γ_LV cos θ-γ_LV curve was found to be constant and equal −1 over the whole range of surfactant concentration in solution. It means that the amount of surfactant adsorbed at the PTFE-water interface, Γ_SL, is essentially equal to its amount adsorbed at water-air interface, Γ_LV. By extrapolating the linear dependence between γ_LV cos θ and γ_LV to cos θ = 1 the determined value of critical surface tension of PTFE surface wetting, γ_C, was obtained (23.6 mN/m), and it was higher than the surface tension of PTFE (20.24 mN/m). Using the value of PTFE surface tension and the measured surface tension of aqueous AOT solution in Young equation, the PTFE-solution interface tension, γ_SL, was also determined. The shape of the γ_SL-log C curve occurred to be similar to the isotherm of AOT adsorption at water-air interface, and a linear dependence existed between the PTFE-solution interfacial tension and polar component of aqueous AOT solution. The dependence was found to be established by the fact that the work of adhesion of AOT solution to the PTFE surface was practically constant amounting 46.31 mJ/m² which was close to the work of water adhesion to PTFE surface.     

2,6-双(三甲基锡)-4,8-双(2-乙基己氧基)苯并[1,2-b∶4,5-b']二噻吩的合成与多核NMR研究

以苯并[1,2-b∶4,5-b´]二噻吩-4,8-二酮为原料合成了一种聚合物太阳能电池材料的单体2,6-双(三甲基锡)-4,8-双(2-乙基己氧基)苯并[1,2-b∶4,5-b´]二噻吩. 通过多核1D和2D NMR技术（包括1D ¹H、¹³C、¹¹⁹Sn、¹¹⁷Sn NMR、DEPT、选择性1D TOCSY及2D¹H-¹H COSY、gHSQC、gHMBC）表征了目标分子结构,完成了 ¹H、¹³C、¹¹⁹Sn 与¹¹⁷Sn NMR化学位移归属,并探讨了该化合物的NMR谱线特征.     

Fluorescence,Photophysical Behaviour and DFT Investigation of E,E-2,5-bis[2-(3-pyridyl)ethenyl]pyrazine (BPEP)

E,E-2,5-bis[2-(3-pyridyl)ethenyl]pyrazine (BPEP) has been prepared by aldol condensation between 2,5-dimethylpyrazine and pyridine-3-carboxaldehyde. It is characterized by IR, ¹H NMR, and ¹³C NMR. The electronic absorption and emission properties of BPEP were studied in different solvents. BPEP displays a slight solvatochromic effect of the absorption and emission spectrum, indicating a small change in dipole moment of BPEP upon excitation. The dye solutions (1 × 10^?4 M) in CHCl₃, EtOH and dioxane give laser emission in blue region upon excitation by a 337.1 nm nitrogen pulse (λ = 337 nm). The tuning range, gain coefficient (α) and emission cross – section (σ_e) have been determined. Ground and excited states electronic geometric optimizations were performed using density functional theory (DFT) and time-dependent density functional theory (TD-DFT), respectively. A DFT natural bond analysis complemented the ICT. The simulated maximum absorption and emission wavelengths are in line the observed ones in trend, and are proportionally red-shifted with the increase of the solvent polarity. The stability, hardness and electrophilicity of BPEP in different solvents were correlated with the polarity of the elected solvents. BPEP dye displays fluorescence quenching by colloidal silver nanoparticles (AgNPs). The fluorescence data reveal that radiative and non-radiative energy transfer play a major role in the fluorescence quenching mechanism.     

High Spin States in 70 Ge [Erratum: APH N.S., Heavy Ion Physics 11 (2000) 189]

High spin states in70Ge nucleus have been studied in two different experiments using heavy ion fusion evaporation reaction. The Gamma Detector Array comprising of eight Compton-suppressed High Purity Ge detectors, was used in conjunction with a Recoil Mass Spectrometer — the HIRA — in order to identify and measure the transitions of this weakly populated nucleus. The level scheme is extended up to an excitation energy of13MeV for spin-parity 21- with several newly observed transitions placed in it. A rotational like band is also observed in this nucleus for the first time.     

Competition of two mechanisms of retardation of domain walls in the molecular ferrimagnet [Mn{(R/S)-pn}]2[Mn{(R/S-pn}2(H2O)][Cr(CN)6]2

The temperature dependence of the magnetization reversal dynamics of the chiral molecular ferrimagnet [Mn{(R/S)-pn}]₂[Mn{(R/S)-pn}₂(H₂O)][Cr(CN)₆]₂ has been studied at low frequencies of 1–1400 Hz, which are characteristic of the domain wall motion. It has been found from the Cole-Cole plots that domain walls undergo relaxation (at temperatures T > 10 K) and creep (at T < 10 K), and the main parameters determining these modes and the transition between them have been determined. It has been shown that the quantitative regularities of the transition between the modes of the domain wall motion correspond to the concepts of the competition between the contributions of two mechanisms to the domain wall retardation (the periodic Peierls relief and random structural defects).     

Conformational Analysis of (S)-4,5,6,7-Tetrahydro-5-Methylimidazo [4,5,1-jk][1,4]-Benzodiazepin-2(1H)-one (R78362)

The solution and solid state conformation of (S)-4,5,6,7-tetrahydro-5-methylimidazo [4,5,1-jk][1,4]-benzodiazepin-2(1H)-one (R78362) have been investigated by low temperature NMR and x-ray diffraction studies. The ¹H NMR spectrum of R78362 shows no evidence of the presence of multiple conformers in the temperature range 340K - 177K. Molecular mechanisms and semiempirical molecular orbital calculations suggest that the nitrogen and ring inversion barriers of R78362 are small and thus a time-averaged ¹H NMR spectrum is probably occurring at 298K. The x-ray diffraction data indicated that there were two independent molecules in the asymmetric unit of the crystal. The two molecules had similar conformations with the benzoimidazole ring being planar and the diazepine ring in a “half-chair” conformation.     

On the magnetic order in R(57Fe)Mn2

In the present study,⁵⁷Fe is used as a local probe in order to monitor both the development of the Mn moment and its temperature dependence. The different crystal structures present (C15 and C14) were found to only insignificantly influence the hyperfine pattern. Both the simultaneous presence of magnetic and non-magnetic Mn atoms and the specific easy axis of magnetization in a given compound is found to lead to the occurrence of additional subspectra. Within the Mössbauer effect time window, no substantial magnetic correlations could be detected aboveT _C.     

Spin interaction and magnetic field strength effects on the system of two interacting electrons in a 2D quartic confinement potential

In this study we review concepts of double quantum dot, quantum chaos with shifted 1/N expansion method associated with semiquantum nonlinear system. We present a numerical study of two interacting particle motions in a time dependent magnetic field in quartic geometry. It is evident that, the area where the interaction particle motions are stochastic decreases as the spin interaction strength decreases, as well as, the magnetic field strength decreases. Moreover, we describe their possible connections with other aspects of quantum information. Furthermore, we pay attention to a system of two interacting electrons in a two-dimensional quartic confinement potential and hypothesis leading to analytical energy expression. The dynamics of double quantum dot gallium arsenide are of great importance and are also emphasized.     

Exchange interaction at the supramolecular level. EPR investigation of two copper (II) compounds: [Cu2(acac)2(phen)2(bpe)](CIO4)2·(bpe)·CH3CN·H2O and [Cu2(acac)2(phen)2(bpp)](CIO4)2·6H2O (bpe=trans-1,2-bis(4-pyridyl)ethylene, bpp=bis(4-pyridyl)propane)

Intra- and intermolecular exchange and dipole-dipole interactions in two supramolecular compounds [Cu₂(acac)₂(phen)₂(bpe)](CIO₄)₂·(bpe)·CH₃CN·H₂O (I) and [Cu₂(acac)₂(phen)₂(bpp)]× (CIO₄)₂·6H₂O (II), which are built up of binuclear fragments through π-π stacking interactions, are investigated. The electron paramagnetic resonance (EPR) spectra of the polycrystalline samples of I and II were measured in the X-band in the temperature range of 300–4.2 K, and in the Q-band atT=300 and 4.2 K. The EPR spectra were interpreted as being due to weakly interacting dimer fragments. Triplet and singlet states of dimer fragments arise from a larger interactionJS ₁ S ₂ between two nearest copper complexes of two neighboring binuclear fragments. The theoretical analysis of the EPR spectrum of the polycrystalline sample for weakly interacting triplet states is carried out. The influence of the weak interaction between triplet states with value ofJ′ is considered in the model of the frequency exchange. A special attention is focused on the presence of the additional signal due to the exchange merging in some orientations where theJ′ value exceeds the fine structure parameters of the spectrum. The analysis of the conditions for the detection of the additional signal and of the influence of this signal on the form of the EPR spectrum allows us to estimate the value of the exchange interactionJ′=o.025±0.005 cm^?1 for compounds I and II and anisotropic part of exchange interaction between two nearest copper complexes asJ _zz =?0.02 cm^?1,J _xx.yy =0.01 cm^?1 for compound I.     

E.S.R. Evidence for dimeric species of Cu(II) and VO(II) ions adsorbed on silica surface

Czechoslovak Journal of Physics -     

Anomalies in oxygen-induced quenching of electronically excited states of 4,4′-bis[2-(1,3)-benzoxazol-2-yl)ethenyl]biphenyl in the vapor phase

From oxygen-induced quenching of polarized fluorescence of 4,4′-bis[2-(1,3-benzoxazol-2-yl)ethenyl]biphenyl, we have observed structural transformation in electronically excited molecules with retention of fluorescent capability, initiated by collisions with oxygen. Replacing two hydrogen atoms with fluorine in the ortho positions of the diphenyl moiety of the molecule leads to absence of quenching upon collisions with oxygen molecules, owing to the electronegative properties of fluorine atoms. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 6, pp. 902–905, November–December, 2008.     

E.S.R. Spectra of the Cyclobutanesemidiones Derived from Three Tricyclo[4. 4. 2. 01,6,]Dodecane-11-OL-12-Ones

The semidione radical anions derived from a variety of alicyclic ketones and α-hydroxyketones have been extensively investigated via esr by Russell and co-workers.¹Studies of the chemistry and spectra of the 1, 2-cyclobutanediones derived from the tricyclo[4. 4. 2. 0^1,6] dodecane-11-o1-12-one system²suggested that an examination of the esr spectra of the related semidiones would be of considerable interest. The recent reports on the esr spectra of cyclobutanes emidione^1cand several substituted cyclo-butanes emidiones^1bfurther prompt this communication.     

Spectroscopic and E. P. R Studies of the Crystal and Molecular Structure of Cu(2-Benzoylpyridine)2(NO3)2.H2O

Abstract

Solid Cu(2-Benzoylpyridine)₂(NO₃)₂ has been studied by UV-Vis, IR, and EPR (X-band, Q-band) techniques. Monoclinic crystal symmetry was determined with two molecules per unit cell. Copper (II) is coordinated by two benzoylpyridine ligands and a single NO₃ group in the chromophore CuN₂O₃ of distorted trigonal bypiramidal stereochemistry. Exchange coupling values were determined from EPR spectra as |J| = 0.0026(2) cm^?1 between magnetically nonequivalent copper (II) sites, and |J| < O.3 cm^?1 between equivalent sites.

Results are discussed by a comparison with Cu(II)-benzoyl-pyridine complexes coordinated with azide N₃ ^? anions.     

Influence of magnetic layer thickness on[Fe_(80)Ni_(20) O/SiO_2]_n multilayer thin films

In the present work, a series of [Fe80Ni20–O/SiO2]n multilayer thin films is fabricated using a reactive magnetron sputtering equipment. The thickness of SiO2 interlayer is fixed at 3 nm, while the thickness values of Fe80Ni20–O magnetic films range from 10 nm to 30 nm. All films present obvious in-plane uniaxial magnetic anisotropy. With increasing the Fe80Ni20–O layer thickness, the saturation magnetization increases slightly and the coercivity becomes larger due to the enlarged grain size, which could weaken the soft magnetic property. The results of high frequency magnetic permeability characterization show that films with thin magnetic layer are more suitable for practical applications. When the thickness of Fe80Ni20–O layer is 10 nm, the multilayer film exhibits the most comprehensive high-frequency magnetic property with a real permeability of 300 in gigahertz range.