The room-temperature superstructure of ZrP2O7 is orthorhombic: there are no unusual 180 degrees P-O-P bond angles

The structure of room-temperature ZrP2O7 is shown to be orthorhombic by a combination of high-resolution synchrotron powder diffraction and single-crystal synchrotron diffraction data. Small nontwinned single crystals were obtained by synthesizing the compound using solvothermal methods at temperatures below the cubic to orthorhombic phase transition. The average P-O-P angle is 146 degrees. DFT calculations (B3LYP/AUG-cc-pVDZ) on the isolated P2O7(4-) anion yield a P-O-P angle of 153.42 degrees and indicate that the barrier to inversion is of the order 3.6 kJ mol(-1).     

Simple DFT model of clusters embedded in rare gas matrix: trapping sites and spectroscopic properties of Na embedded in Ar

We present a theoretical model to study the dynamics of metallic clusters embedded in a rare gas matrix. We describe the active electrons of the embedded cluster using time dependent density functional theory, while the surrounding matrix is described in terms of classical molecular dynamics of polarizable atoms. The coupling between the cluster and the rare gas atoms is deduced from the work of Gross and Spiegelmann [J. Chem. Phys. 108, 4148 (1998)] and reformulated explicitly in a simple and efficient density functional form. The electron rare gas interaction takes the form of an averaged dipole fluctuation term, which retains the van der Waals long range interaction, and a short range repulsive pseudopotential, which accounts for the Pauli repulsion of the electron by the rare gas atom. We applied our model to Na clusters embedded in Ar matrix. For the latter we developed an efficient local pseudopotential, which allows studying systems containing more than 10(3) Ar atoms. We show that large systems are indeed necessary to account properly for long range polarization of the matrix, that competes with the matrix confinement effect. We focus our study on Na(2), Na(4), and Na(8). For each system, we have determined the geometry of the most favorable trapping site by means of damped molecular dynamics. We present the effect of matrix embedding on the optical absorption spectrum. For Na(2), the trapping site can be unambiguously identified by comparison of the absorption spectrum with experiment. For Na(4) the spectrum of the embedded cluster is significantly different from the free cluster spectrum, while for Na(8) differences are less pronounced.     

Estrogen fluoroimmunoassay with a fluorimeter designed for low-intensity light detection

A small, highly sensitive, inexpensive fluorimeter for the detection of very low fluorescence intensities for analytical and clinical purposes is described. High sensitivity is achieved by use of an inexpensive continuous wave laser with a power of a few milliwatts. The optical arrangement of the instrument has been thoroughly designed so that the effects of Rayleigh and Raman scattering are minimized. Fluorescence is dected through optical filters with a side-on photomultiplier. Concentrations of rhodamine B in ethanol as low as 10^?11 M can be measured. To use this instrument for a fluoroimmunoassay of urinary estrogens (10^?9?10^?7 M), a purified monoclonal IgG, raised against estradiol, was labelled with RITC (rhodamine isothiocyanate) in a 1:1 molar ratio. It was possible to measure IgG-RITC concentrations between 10^?9 and 10^?10 M with good accuracy and reproducibility.     

Corrigendum

Reactions of NaMn(CO)₃ with RuCl₂(PMe₃)₄, RuCl₂(dppm)₂ and RuCl₂(PPh₃)₃ lead either to an ionic species [Ru₂Cl₃(PMe₃)₆]+[Mn(CO)₅]^? or to metal—metal bonded RuMn compounds such as RuMn(μ-CO)₂(CO)₃(μ-dppm)₂ Cl, and, quite unexpectedly, to the μ-phosphido complex RuMn(μ-PPh₂)(CO)₆(PPh₃)₂ via a hydride intermediate.     

Structural and Spectroscopic Investigations of the 1:1 Complex between Europium Nitrate and a Tetraoxadiaza Macrocycle

The crystal and molecular structure of dinitrato(1,7,10,16-tetraoxa-4,13-diazacyclooctadecane)europium(III) nitrate, ([Eu(NO₃)₂(C₁₂H₂₆N₂O₄)]NO₃) has been determined from single-crystal X- ray diffraction: a = 12.567(3), b = 11.585(3), c = 16.354(5) Å, β = 112.45(2)°, space group P2₁/n, Z = 4. The structure consists of discrete dinitrato complex cations and of nitrate anions. The Eu(III) ion is 10-coordinate, bonding to the six donor atoms of the macrocycle and to four O-atoms of the two bidentate nitrates. The mean distances are Eu? O(ether) = 2.60(2), Eu? O(NO₃) = 2.47(3) and Eu? N = 2.62(2) Å. The metal site has an approximate C₂ symmetry. The IR and Raman spectra show the presence of an ionic and of two bonded bidentate nitrates. These latter have a different v₁-v₄ splitting, which reflects their dissymmetrical bonding. Luminescence spectra have been recorded at 296, 77, and 4 K by laser-excitation techniques. One sharp ⁵D₀←⁷F₀ transition was observed and almost all the sublevels of the ⁷F_J manifold could be identified. The interaction between a sharp distribution of the phonon states (especially between 950 and 1200 cm^?1) and the electronic ⁷F₂ sublevels results in the presence of several satellite lines accompanying the ⁵D₀→⁷F₂ transition. In MeCN solutions, both luminescence and conductivity data point to the presence of the [Eu(NO₃)₂(2,2)]⁺ cation.     

Solid state (47,49)Ti, (87)Sr and (137)Ba NMR characterisation of mixed barium/strontium titanate perovskites

Solid state ^47,49Ti, ¹³⁷Ba, ⁸⁷Sr NMR spectra have been recorded on Ba_xSr_1−xTiO₃ (0 x 1) perovskite samples prepared by the powder sintering method. Multinuclear solid state NMR shows great potential for characterising such systems since the quadrupolar parameters are very sensitive to any geometric deformation around the studied nucleus. ^47,49Ti NMR powder lineshapes appear strongly influenced by the presence of even a small amount of barium (or strontium) in the coordination second sphere of the probed titanium site: substitution of strontium by barium induces the broadening of the peaks, due to quadrupolar effects, while the isotropic chemical shift increases. ¹³⁷Ba NMR spectra exhibit a distribution of the quadrupolar interaction, that could be tentatively quantified, C_Q increasing with the amount of strontium. Preliminary results were also obtained on ⁸⁷Sr NMR showing behaviour comparable to ¹³⁷Ba NMR, i.e. a broadening of the peaks due to an increasing quadrupolar interaction with the amount of barium distorting the environment of the strontium sites.     

Temperature dependence of phase separation and magnetic anisotropy by electron spin resonance in Pr<Subscript>0.6</Subscript> Ca<Subscript>0.4</Subscript> Mn<Subscript>0.9</Subscript> Ru<Subscript>0.1</Subscript>O<Subscript>3</Subscript>

Electron spin resonance (ESR) measurements have been performed on polycrystalline samples of Pr_0.6Ca_0.4Mn_1-xRu_xO₃ (x = 0, 0.1). The substitution of Ru in the Mn-site strengthens ferromagnetic interactions due to the double exchange between the Mn³⁺ and Mn⁴⁺ species and super-exchange between the Ru⁵⁺ and Mn³⁺ species. The temperature dependence of the ESR spectra indicates development of magnetic phase separation in Pr_0.6Ca_0.4Mn_0.9Ru_0.1O₃ in contrast with the un-doped sample.     

Solid state NMR interaction parameters of oxygens linking titanium and silicon in crystalline cyclic titanodiphenylsiloxanes

17O static and magic angle spinning NMR spectra are reported from three crystalline cyclic titanodiphenylsiloxanes at magnetic fields of 5.6, 14.1, and 17.6 T. These compounds allow the NMR parameters characteristic of Ti-O-Si environments to be determined. It appears from these data that the quadrupole interaction (C(Q)) of such environments is in the range of 3-3.5 MHz and that Si-O-TiO3 sites are less shifted than Si-O-TiO5. The relatively large isotropic chemical range observed suggests that for structurally and atomically disordered titanosilicate-based materials the very highest applied magnetic field may not produce the best 17O solid state NMR spectra. There appears to be a correlation between the 17O shift and Ti-O bondlength.     

Phasendiagramm und Strukturuntersuchung von Polystyrol-Polyäthylenoxid-Blockcopolymeren. 1. Mitt. Systeme Polystyrol/Polyāthylenoxid/Diäthylphthalat

Ohne Zusammenfassung     

Lo phonon-plasmon coupling in non-stoichiometric rutile TiO2

The analysis of the infrared reflectivity spectrum of partially reduced rutile TiO_1.96 reveals a plasmon-LO phonon coupling. Pure-phonon and plasmon frequencies and life times are determined by fit with an appropriate model using the factorized form of the dielectric function for the phonon modes added to a plasmon contribution also derived from the factorized form. Results are compared with data obtained in the insulating stoichiometric rutile.