Luminescent lanthanide selenites and tellurites decorated by MoO4 tetrahedra or MoO6 octahedra: Nd2MoSe2O10, Gd2MoSe3O12, La2MoTe3O12, and Nd2MoTe3O12

Solid state reactions of lanthanide oxide, MoO3 and SeO2 (or TeO2) at high temperature in an evacuated quartz tube lead to four new Ln-Mo-Se(Te)-O quaternary phases with four different types of structures, namely, Nd2MoSe2O10, Gd2MoSe3O12, La2MoTe3O12, and Nd2MoTe3O12. The structure of Nd2MoSe2O10 features a 3D architecture built by the intergrowth of the Nd-Se-O layers with the Nd-Mo-O layers. The structure of Gd2MoSe3O12 contains a 3D network of gadolinium selenite with the MoO6 octahedra occupying the cavities of the structure. The structure of La2MoTe3O12 features a 3D network of La2(Te3O8)2+ with the tunnels along the a axis occupied by the MoO4 tetrahedra. Nd2MoTe3O12 features a 2D layer built by the lanthanide ions interconnected by tellurite groups and ditellurite groups, with the MoO4 tetrahedra as the interlayer pendant groups. Room temperature and low temperature luminescent studies indicate that Nd2MoSe2O10 and Nd2MoTe3O12 exhibit strong luminescence in the near-IR region.     

Reactivity of aqua coordinated monoporphyrinate lanthanide complexes: synthetic, structural and photoluminescent studies of lanthanide porphyrinate dimers

Dimerization of monoporphyrinate lanthanide complexes [Yb(Por)(H(2)O)(3)]Cl, (Por = TTP(2-), TMPP(2-) and TPP(2-)) in the presence of sterically hindered tripodal ligand, zinc Schiff-base, dilute HCl, K(2)CO(3) solution, 4,4'-bipyridine (bipy), and basic 8-hydroxyquinaldine (HQ) solution was observed in CH(2)Cl(2) at room temperature. Six neutral dimeric lanthanide porphyrinate complexes, [Yb(TTP)(mu-OH)](2)(mu-THF) (1), [Yb(TMPP)(mu-OH)(H(2)O)](2) (2), [Yb(TPP)(mu-OH)(mu-H(2)O)](2) (4), [Yb(TMPP)(mu-Cl)(H(2)O)](2) (5), [Yb(TMPP)(mu-OH)](2)(THF) (6) and [Yb(TPP)](2)(mu-OH)(mu-Q) (7), were obtained. X-Ray diffraction studies showed that for the dimers, the two lanthanide ions were bridged by OH(-), Cl(-) or H(2)O. Photoluminescent studies showed that the porphyrinate dianion acted as an antenna, transferred its absorbed visible energy to the lanthanide ion and enabled the latter emitting in the near-infrared (NIR) region. In general, the NIR emission is more intense for the dimers than for the monomers, and the NIR emission intensity decreases as the number of O-H oscillators present in the molecule increases.     

Electrocatalytic proton reduction by phosphido-bridged diiron carbonyl compounds: distant relations to the H-cluster?

Intermediates formed during reduction of Fe(2)(mu-PPh(2))(2)(CO)(6) (1) in the presence of protons have been identified by spectroelectrochemical, continuous-flow, and interrupted-flow techniques. The mechanism for electrocatalytic proton reduction suggested by these observations yields digital simulation of the voltammetry in close agreement with measurements conducted in THF over a range of acid concentrations. The mechanism for electrocatalytic proton reduction involves initial formation of the dianion, 1(2-), which is doubly protonated prior to further reduction and dihydrogen elimination. The IR spectra of the singly and doubly protonated forms of 1(2-) indicate structures corresponding to [FeH(CO)(3)(mu-PPh(2))(2)Fe(CO)(3)](-) (1H-) and FeH(CO)(3)(mu-PPh(2))(2)FeH(CO)(3) (1H(2)). The thiolato and dithiolato analogues of 1 exhibit electrocatalytic proton reduction associated with the two-electron reduction step, and this implies that the corresponding two-electron reduced doubly protonated species is unstable with respect to dihydrogen elimination. The stability of 1H(2) is most likely to be due to the weak interactions between the iron centers of the flattened [2Fe2P] core. Whereas 1H(2) is stable in the absence of a reducing potential, 1H- rearranges rapidly to a product previously described as [Fe(2)(mu-PPh(2))(mu-CO)(PHPh(2))(CO)(5)](-) (1H-(W)). Another protonation product of 1(2-), previously formulated as [Fe(2)(mu-PPh(2))(2)(mu-CO)H(CO)(5)](-), has been reformulated as [Fe(2)(mu-PPh(2))(mu-CO)(CO)(6)](-) (2) on the basis of a range of spectroscopic measurements. Solution EXAFS measurements of 1, 1(2-), 1H-(W), and 2 are reported, and these yield model-independent Fe-Fe distances of 2.61 (1), 3.58 (1(2-)), 2.58 (1H-(W)), and 2.59 A (2). The presence of an Fe-Fe bond for both 1H-(W) and 2 is a key aspect of the proposed structures, and this strongly supports the deductions based on spectroscopic evidence. The fits of the solution EXAFS to different structural models give statistics in agreement with the proposed structures.     

Syntheses and crystal structures of organoindium(III) 1-D coordination polymers with bis(diphenylphosphino)alkane dioxides

Abstract

Bromomethyl-dibromo-indium(III), Br₂InCH₂Br, obtained from indium monobromide and methylene dibromide, reacts with hard and soft donor ligands to afford the corresponding indium(III) organometallic complexes. In this work, we investigated the conditions to prepare adducts of Br₂InCH₂Br using bis(diphenylphosphino)alkane dioxides acting as hard ligands. We report here the synthesis and crystal structures of two 1-D coordination polymers with the hard donor ligands Ph₂P(O)(CH₂)_mP(O)Ph₂ (m = 2, dppeO₂ and m = 6, dpphO₂). Compounds 1 and 2 with formulas [Br₂In(CH₂Br)(dppeO₂)]_n (1) and [Br₂In(CH₂Br)(dpphO₂)]_n (2) were characterized by IR and Raman spectroscopy and elemental analysis. We also obtained an ionic indium(III) compound with dppeO₂ acting as a chelating ligand with formula [InBr₂(dppeO₂)₂][InBr₃(CH₂Br)] (3). The crystal structures were determined for 1–3 using single crystal X-ray diffractometry. The geometry around the In(III) can be described as a trigonal bipyramid in 1 and 2, and the chains were packed onto the plane giving layers that are stabilized mainly by intermolecular interactions. Compound 3 has a square bipyramidal In(III) cation with formula [Br₂L₂In]⁺ and tetrahedral organoindium(III) anion with formula [Br₃InCH₂Br]^–. Hirshfeld surface analysis employing 2-D fingerprint plots have been used to analyze intramolecular and intermolecular interactions present in the solid state of the structures.     

Proficiency tests to evaluate commercially available IVD kits for glucose and cholesterol measurements

The first proficiency testing round 630-IL-1002, was carried out with a Reference Material DMR-180a with reference values obtained by using gas chromatography isotope dilution mass spectrometry methods, in which glucose, cholesterol and creatinine were measured. The serum pool was obtained from blood donors and all the analytes were at the normal concentration in Mexican population. The laboratories participants used different field methods to measure the analytes. The Mexican compulsory standard NOM-064-SSA1-1993 “specifications for equipments in vitro diagnostic (IVD)” requests 5% precision and 5% maximum bias of the IVD equipments in the measurements of analytes like glucose and cholesterol. The results obtained by field laboratories in the proficiency testing round are compared to the reference value and uncertainty provided by the National Metrology Institute (CENAM). The quality of measurements is dependent not only on the laboratory competence but also on the methods used by those commercially available IVD kits. It is concluded that quality assessment of measurements in clinical laboratories should be critically evaluated by using stable and certified reference materials. Presented at MEFNM 2008, September 2008, Budapest, Hungary.     

LC Determination of Gallic Acid in Preparations Derived from Schinus terebinthifolius Raddi

The aim of the present paper was to develop and validate a method to determine gallic acid and tannins by LC. Validation was carried out in accordance with Brazilian Resolution 899/2003. The method showed satisfactory results for precision, accuracy, specificity and linearity. Variations on the composition and flow rate of the mobile phase influenced the peak area and retention time. The method was applied to determine the amount of hydrolysable tannins in preparations containing Schinus terebinthifolius Raddi.

     

Synthesis, structures and phase transitions in the double perovskites Sr2−xCaxCrNbO6

The synthesis and crystal structures of nine members of the rock-salt ordered double perovskites Sr_2−xCa_xCrNbO₆ is presented. The crystal structures of the end members of the series Sr₂CrNbO₆ and Ca₂CrNbO₆ were refined using powder neutron diffraction data and are cubic in and monoclinic in P2₁/n, respectively, in both cases there being considerable anti-site Cr-Nb mixing. Variable temperature and/or composition studies suggest a direct first-order P2₁/n to transition, a suggestion supported by selected area electron diffraction studies.     

Highly hydrophilic and nonionic poly(2-vinyloxazoline)-grafted silica: a novel organic phase for high-selectivity hydrophilic interaction chromatography

A new hydrophilic and nonionic poly(2-vinyloxazoline)-grafted silica (Sil-VOX _n ) phase was synthesized and applied for the separation of nucleosides and nucleobases in hydrophilic interaction chromatography (HILIC). Polymerization and immobilization onto silica were confirmed by using characterization techniques including ¹H NMR spectroscopy, elemental analysis, and diffuse reflectance infrared Fourier transform spectroscopy. The hydrophilicity or wettability of Sil-VOX _n was observed by measuring the contact angle (59.9°). The chromatographic results were compared with those obtained with a conventional HILIC silica column. The Sil-VOX _n phase showed much better separation of polar test analytes than the silica column, and the elution order was different. Differences in selectivity between these two columns indicate that the stationary phase cannot function merely as an inert support for a water layer into which the solutes are partitioned from the bulk mobile phase. To elucidate the interaction mechanism, the separation of dihydroxybenzene isomers was performed on both columns in normal-phase liquid chromatography. Sil-VOX _n was very sensitive to the dipole moments of the positional isomers of polycyclic aromatic compounds in normal-phase liquid chromatography. The interaction mechanism for Sil-VOX _n in HILIC separation is also described.

Improving prediction market forecasts by detecting and correcting possible over-reaction to price movements

We examine the impact of price trends on the accuracy of forecasts from prediction markets. In particular, we study an electronic betting exchange market and construct independent variables from market price (odds) time series from 6058 individual markets (a dataset consisting of over 8.4 million price points). Using a conditional logit model, we find that a systematic relationship exists between trends in odds and the accuracy of odds-implied event probabilities; the relationship is consistent with participants over-reacting to price movements. In particular, in different time segments of the market, increasing and decreasing odds lead, respectively, to under- and over-estimation of odds-implied probabilities. We develop a methodology to detect and correct the erroneous forecasts associated with these trends in odds in order to considerably improve the quality of forecasts generated in prediction markets.     

Structural investigation of mM Ni(II) complex isomers using transmission XAFS: the significance of model development

High‐accuracy transmission XAFS determined using the hybrid technique has been used to refine the geometries of bis(N‐n‐propyl‐salicylaldiminato) nickel(II) (n‐pr Ni) and bis(N‐i‐propyl‐salicylaldiminato) nickel(II) (i‐pr Ni) complexes which have approximately square planar and tetrahedral metal coordination. Multiple‐scattering formalisms embedded in FEFF were used for XAFS modelling of the complexes. Here it is shown that an IFEFFIT‐like package using weighting from experimental uncertainty converges to a well defined XAFS model. Structural refinement of (i‐pr Ni) was found to yield a distorted tetrahedral geometry providing an excellent fit, χ_r² = 2.94. The structure of (n‐pr Ni) is best modelled with a distorted square planar geometry, χ_r² = 3.27. This study demonstrates the insight that can be obtained from the propagation of uncertainty in XAFS analysis and the consequent confidence which can be obtained in hypothesis testing and in analysis of alternate structures ab initio. It also demonstrates the limitations of this (or any other) data set by defining the point at which signal becomes embedded in noise or amplified uncertainty, and hence can justify the use of a particular k‐range for one data set or a different range for another. It is demonstrated that, with careful attention to data collection, including the correction of systematic errors with statistical analysis of uncertainty (the hybrid method), it is possible to obtain reliable structural information from dilute solutions using transmission XAFS data.