Thermochemistry of intercalation of n-alkylmonoamines into lamellar hydrated barium phenylarsonate

Hydrated layered crystalline barium phenylarsonate, Ba(HO₃AsC₆H₅)₂·2H₂O was used as host for intercalation of n-alkylmonoamine molecules CH₃(CH₂)_n-NH₂ (n = 1-4) in aqueous solution. The amount intercalated (n_f) was followed batchwise at 298 ± 1 K and the variation of the original interlayer distance (d) for hydrated barium phenylarsonate (1245 ppm) was followed by X-ray powder diffraction. Linear correlations were obtained for both d and n_f as a function of the number of carbon atoms in the aliphatic chain (n_c): d = (2225 ± 32) + (111 ± 11)n_c and n_f = (2.28 ± 0.15) − (11.50 ± 0.03)n_c. The exothermic enthalpies of intercalation increased with n_c, which was derived from the monomolecular amine layer arrangements with the longitudinal axis inclined by 60° to the inorganic sheets. The intercalation was followed by titration with amine at the solid/liquid interface and gave the enthalpy/number of carbons correlation: ΔH = −(7.25 ± 0.40) − (1.67 ± 0.10)n_c. The negative Gibbs free energies and positive entropic values reflect the favorable host/guest intercalation processes for this system.     

Thermomorphic fluorous phosphines as organocatalysts for Michael addition reactions

The fluorous phosphines P[(CH₂)_mR_fn]₃ (R_fn = (CF₂)_n−1CF₃; m/n = 2/8, 3/8, 3/10) are efficient nucleophilic catalysts of Michael addition reactions. They can be easily recycled based upon their highly temperature-dependent solubilities (thermomorphism), with recovery by simple liquid/solid phase separation. The phosphonium salt formed by reaction of the nucleophilic phosphine with the α,β-unsaturated system appears to be a significant component of the catalyst rest state.     

UV-VUV-excited photoluminescence of RE-activated CaLaP3O10 (RE=Eu,Tb)

Monazite-type polyphosphate CaLaP₃O₁₀ was synthesized by solid-state reaction at 1000 °C and their photoluminescence of Eu³⁺ and Tb³⁺ in CaLaP₃O₁₀ under ultraviolet (UV) and vacuum-ultraviolet (VUV) excitation were evaluated for the first time. The emission spectra of CaLaP₃O₁₀:Eu³⁺showed that Eu³⁺ are in a site with inversion symmetry because the magnetic dipole transition ⁵D₀-⁷F₁ was the strongest both upon 254 and 147 nm excitation. Monitored at 621 nm the excitation spectra consisted of host absorption bands, charge transfer band of Eu-O and the intraconfiguration 4f⁶ transition of Eu³⁺. Green phosphor CaLaP₃O₁₀:Tb³⁺exhibited better color purity when excited by 147 nm than that excited by 254 nm. With monitored at 542 nm the host absorption bands of CaLaP₃O₁₀:Tb³⁺ were also observed. Besides the host absorption bands there were strong f-d and weak f-f transitions of Tb³⁺.     

Simultaneous spectrophotometric flow-through measurements of pH, carbon dioxide fugacity, and total inorganic carbon in seawater

An autonomous multi-parameter flow-through CO₂ system has been developed to simultaneously measure surface seawater pH, carbon dioxide fugacity (fCO₂), and total dissolved inorganic carbon (DIC). All three measurements are based on spectrophotometric determinations of solution pH at multiple wavelengths using sulfonephthalein indicators. The pH optical cell is machined from a PEEK polymer rod bearing a bore-hole with an optical pathlength of ∼15 cm. The fCO₂ optical cell consists of Teflon AF 2400 (DuPont) capillary tubing sealed within the bore-hole of a PEEK rod. This Teflon AF tubing is filled with a standard indicator solution with a fixed total alkalinity, and forms a liquid core waveguide (LCW). The LCW functions as both a long pathlength (∼15 cm) optical cell and a membrane that equilibrates the internal standard solution with external seawater. fCO₂ is then determined by measuring the pH of the internal solution. DIC is measured by determining the pH of standard internal solutions in equilibrium with seawater that has been acidified to convert all forms of DIC to CO₂. The system runs repetitive measurement cycles with a sampling frequency of ∼7 samples (21 measurements) per hour. The system was used for underway measurements of sea surface pH, fCO₂, and DIC during the CLIVAR/CO₂ A16S cruise in the South Atlantic Ocean in 2005. The field precisions were evaluated to be 0.0008 units for pH, 0.9 μatm for fCO₂, and 2.4 μmol kg⁻¹ for DIC. These field precisions are close to those obtained in the laboratory. Direct comparison of our measurements and measurements obtained using established standard methods revealed that the system achieved field agreements of 0.0012 ± 0.0042 units for pH, 1.0 ± 2.5 μatm for fCO₂, and 2.2 ± 6.0 μmol kg⁻¹ for DIC. This system integrates spectrophotometric measurements of multiple CO₂ parameters into a single package suitable for observations of both seawater and freshwater.     

Conventional and fast gas chromatography analysis of biodiesel blends using an ionic liquid stationary phase

The present research is focused on the GC-FID determination of fatty acid methyl esters (FAMEs) in diesel blends, by means of an ionic liquid stationary phase, characterized by a dicationic 1,9-di(3-vinyl-imidazolium)nonane bis(trifluoromethyl)sulfonylimidate structure (SLB-IL100). The high polarity of the ionic liquid stationary phase allowed the separation of the FAMEs, from the less-retained hydrocarbons, thus avoiding the requirement of a hydrocarbon LC pre-separation. The results derived from the analyses of a soybean FAMEs B20 sample, carried out on an SLB-IL100 conventional column (30 m × 0.25 mm i.d. × 0.20 mm d_f), were compared with those attained on a polyethylene glycol column, of equivalent dimensions. Conventional and fast GC methods, for the analysis of FAMEs in diesel blends, were developed on an SLB-IL100 30 m × 0.25 mm i.d. × 0.20 μm d_f and on an SLB-IL100 12 m × 0.10 mm i.d. × 0.08 μm d_f column, respectively. The optimized IL methods were subjected to validation: retention time and peak area intra-day precision (n = 5) were good, with CV % values lower than 0.08% and 4.9%, respectively. With regards to the quantitation of FAMEs in biodiesel blends, a five points calibration curve was constructed, using C_17:0 as internal standard.     

Synthesis of π-expanded BODIPYs and their fluorescent properties in the visible-near-infrared region

A series of π-expanded boron-dipyrromethenes (BODIPYs) fused with aromatic rings at β,β-positions, such as benzene, acenaphthylene, and benzofluoranthene were prepared by the reaction of BF₃·OEt₂ with bicyclo[2.2.2]octadiene-fused dipyrromethene and the subsequent retro Diels-Alder reaction. These BODIPYs exhibited the absorptions and the fluorescence emissions over wide range of visible-near-infrared region at 500-800 nm. BODIPYs composed of two fluorantho[8,9-f]isoindoles absorbed and emitted at red-region over 750 nm with absolute fluorescence quantum yield (Φ_f) of ca. 0.3, although they are unstable under air in room light. BODIPY composed fluorantho[8,9-f]isoindole and acenaphtho[1,2-c]pyrrole was stable and showed a bright fluorescence emission at 695 nm with high Φ_f of 0.70.     

Crystal structure and luminescence of Sr0.99Eu0.01AlSiN3

Strontium europium aluminum silicon nitride, Sr_0.99Eu_0.01AlSiN₃, was synthesized by heating a mixture of binary nitrides at 2173 K and a N₂ gas pressure of 190 MPa. Single crystals of Sr_0.99Eu_0.01AlSiN₃ approximately 30 μm were obtained. The structure was confirmed to be an isotypic structure of CaAlSiN₃ in the orthorhombic space group Cmc2₁, analyzed by single-crystal X-ray diffraction. The lattice parameters are a=9.843(3), b=5.7603(16), c=5.177(2) Å, cell volume=293.53(17) Å³. It shows an orange-red photoluminescence by 5d→4f transition of Eu²⁺ at around 610 nm under excitation ranging from ultraviolet to 525 nm. The photoluminescence intensity, temperature characteristics, and oxidative stability were comparable or superior to those of CaAlSiN₃:Eu²⁺ phosphor.     

Kinetic study on external mass transfer in high performance liquid chromatography system

External mass transfer coefficients (k_f) were measured for a column packed with fully porous C₁₈-silica spherical particles (50.6 μm in diameter), eluted with a methanol/water mixture (70/30, v/v). The pulse response and the peak-parking methods were used. Profiles of elution peaks of alkylbenzene homologues were recorded at flow rates between 0.2 and 2.0 mL min⁻¹. Peak-parking experiments were conducted under the same conditions, to measure intraparticle and pore diffusivity, and surface diffusion coefficients. Finally, the values of k_f for these compounds at 298 K were derived from the first and second moments of the elution peaks by subtracting the contribution of intraparticle diffusion to band broadening. As a result, the Sherwood number (Sh) was measured under such conditions that the Reynolds (Re) and the Schmidt numbers (Sc) varied from 0.004 to 0.05 and from 1.8 × 10³ to 2.7 × 10³, respectively. We found that Sh is proportional to Re^α and Sc^β and that the correlation between these three nondimensional parameters is almost the same as those given by conventional literature equations. The values of α and β were close to those in the literature correlations, between 0.26 and 0.41 and between 0.31 and 0.36, respectively. The use of the Wilson–Geankoplis equation to estimate k_f values entails a relative error of ca. 15%. So, conventional literature correlations provide correct estimates of k_f in HPLC systems, even for particle sizes of the order of a micrometer.     

Pyrolytic synthesis and Eu→Eu reduction process of blue-emitting perovskite-type BaLiF3:Eu thin films

Perovskite-type barium lithium fluoride (BaLiF₃) was synthesized by pyrolysis of metal trifluoroacetates. The reaction temperature necessary for producing a single-phase material was found to be 600°C, which was lower than that for a conventional solid-state reaction or a melting method. Eu-doped BaLiF₃ was also prepared and characterized to examine the suitability of trifluoroacetates for precursors in synthesizing homogeneous complex metal fluoride materials. It was demonstrated that trivalent Eu³⁺, which was used as acetate for a starting material, was reduced to divalent Eu²⁺ in the pyrolysis process of BaLiF₃, as indicated by a broad blue emission due to an allowed 4f⁶5d→4f⁷ transition at 408 nm with a ultraviolet excitation at 254 nm. The concentration quenching of the blue emission occurred at 5 at% of Eu in BaLiF₃, indicating that Eu was homogeneously dispersed in the BaLiF₃ host lattice. Mechanisms of the formation and reduction process of BaLiF₃ were discussed based on pertinent chemical reactions.     

Thermal analysis techniques for characterization of polymer materials

Routine DSC and TGA techniques, used to characterise polymer thermal stability, have been further used for assessment of comparative thermal stability of various polymer materials and for prediction of material lifetimes. The following materials were investigated: (1) commercial and experimental polymer materials - results for poly(vinyl chloride) (PVC) and bisphenol A polycarbonate (PC) are presented; (2) a polydimethylsiloxane-polytetrafluoroethylene (SIL-PTFE) coating system; and (3) commercially available linear low density polyethylene (PE-LLD), unmodified and modified chemically and physically. The plot of reciprocal temperature of initial decomposition 1/T_di vs log heating rate β has been recommended for assessment of comparative thermal stability. The lifetime of polymer materials was calculated from the plots of log time-to-failure, log t_f, vs reciprocal temperature 1/T, where t_f values were obtained using T_di from TGA measurements or directly from the oxidation induction time (OIT) data as criteria for initial deterioration of polymer thermal stability. The following sequences of increasing thermal stability were found for investigated materials:

(1)

PVC ? PC;

(2)

SIL < SIL-PTFE 20% < SIL-PTFE 50% ? PTFE;

(3)

(B) PE-LLD, grafted < (A) PE-LLD, unmodified < (C) PE-LLD, filled.

The lifetime of polymer materials predicted from the plots of log t_f vs 1/T are in reasonable agreement with experimental data and users' observations, e.g. approximately 1 year for PC and unmodified PE-LLD both at 373 K (100 °C) and for PVC at temperature of outdoor conditions about 298 K (25 °C).     

Syntheses of fluorous quaternary ammonium salts and their application as phase transfer catalysts for halide substitution reactions in extremely nonpolar fluorous solvents

Perfluoromethyldecalin solutions of the fluorous alkyl halides R_f8(CH₂)_mX (m=2, 3; X=Cl, I) are inert toward aqueous NaCl, KI, KCN, and NaOAc. However, substitution occurs at 100 °C in the presence of 10 mol % of the fluorous ammonium salts (R_f8(CH₂)₂)(R_f8(CH₂)₅)₃N⁺ I⁻ (1) or (R_f8(CH₂)₃)₄N⁺ Br⁻ (2) (10 mol %), which are fully or partially soluble in perfluoromethyldecalin under these conditions. Stoichiometric reactions of (a) 1 and R_f8(CH₂)₃Br, and (b) 2 and R_f8(CH₂)₂I are conducted in perfluoromethyldecalin at 100 °C, and yield the same R_f8(CH₂)_mI/R_f8(CH₂)_mBr equilibrium ratio (60-65:40-35). This shows that ionic displacements can take place in extremely nonpolar fluorous phases, and suggests a classical phase transfer mechanism for the catalyzed reactions. Interestingly, the non-fluorous ammonium salt mixture CH₃(CH₃(CH₂)_m)₃N⁺ Cl⁻ (3, Aliquat^® 336; m=2:1 7/9) also catalyzes halide substitutions, but under triphasic conditions with 3 suspended between the lower fluorous and upper aqueous layers. NMR experiments establish very low solubilities in both phases, suggesting interfacial catalysis.     

Reactions of fluorinated silanes with 2-nitrocinnamates

The interaction of 2-nitrocinnamates with silicon reagents Me₃SiR_f (R_f = CF₃, C₂F₅, and C₆F₅) promoted either by sodium acetate in DMF or by tetrabutylammonium acetate in dichloromethane has been described. The reactions proceed as conjugate addition of fluorinated carbanion at the CC bond and afford 3-aryl-2-nitrobutanoates bearing a fluorinated substituent in good yields as diastereomeric mixtures in ratio from 1:1 to 1.6:1.     

Synthesis and characterization of organophosphine/phosphite stabilized silver(I) methanesulfonates: Crystal structures of [Ph3PAgO3SCH3] and [(Ph3P)2AgO3SCH3]

Six organophosphine/phosphite stabilized silver(I) methanesulfonates of type [L_nAgO₃SCH₃] (L = Ph₃P, n = 1, 2a; n = 2, 2b; n = 3, 2c; L = (EtO)₃P; n = 1, 2d; n = 2, 2e; n = 3, 2f) were synthesized by the reaction of silver methanesulfonates with triphenylphosphine or triethylphosphite in dichloromethane under nitrogen atmosphere. These complexes were obtained in high yields and characterized by elemental analysis, ¹H-, ¹³C{H} NMR, IR spectroscopy and thermogravimetric analysis (TGA), respectively. X-ray single crystal analysis reveals that complex 2a is a tetramer [Ph₃PAgO₃SCH₃]₄ and complex 2b is a monomer. The thermal stability of 2a has been studied by applying thermogravimetric analysis. It starts to decompose between 50 and 440 °C in a three-step process. The final residue (Ag) is about 20.50%.     

Synthesis and characterization of organophosphine/phosphite stabilized silver(I) complexes bearing 2-acetyl-1,3-indandione ligand,crystal structure of [Ph3P·AgC11H7O3]

Six organophosphine/phosphite stabilized silver(I) complexes of 2-acetyl-1,3-indandione (2-AID) of type L_n·AgC₁₁H₇O₃ (L = PPh₃; n = 1, 2a; n = 2, 2b; L = P(OMe)₃; n = 1, 2c; n = 2, 2d; L = P(OEt)₃; n = 1, 2e; n = 2, 2f) have been prepared by reacting of [AgC₁₁H₇O₃], which could be obtained by reacting of 2-AID with AgNO₃, with triphenylphosphine, trimethylphosphite, or triethylphosphite in 1:1–2 M ratio. These complexes were obtained in high yields and characterized by elemental analysis, ¹H, ¹³C{H} NMR, IR spectroscopy, and thermal analysis (TG and DSC), respectively. The molecular structure of 2a has been determined by X-ray single crystal analysis in which the silver atom is in a distorted trigonal geometry.     

Preparation and properties of antiperovskite-type nitrides: InNNi3 and InNCo3

Two antiperovskite-type ternary nitrides of InNM₃ (M=Ni, Co) have been synthesized from In₂O₃ and Ni or Co powders under NH₃ atmosphere at 600 °C. InNCo₃ is a new ternary nitride whereas InNNi₃ was previously reported as InN_0.5Ni₃ with different nitrogen content. The lattice parameters refined by Rietveld method are 3.8445(1) Å for InNNi₃ and 3.8541(7) Å for InNCo₃, respectively. Both nitrides show metallic behaviors and below 70 K the T² temperature dependence of resistivity was observed indicative of a Fermi liquid behavior. The temperature dependence of the field-cooling (FC) and zero-field-cooling (ZFC) magnetization and time decay of thermoremanent magnetization indicate the spin-glass-like behavior in InNM₃ (M=Ni, Co). The freezing temperatures for this behavior, T_f, are about 300 K for InNNi₃ and 10 K for InNCo₃, respectively.     

Hydrothermal synthesis and luminescent properties of LuBO3:Tb microflowers

Hexagonal vaterite-type LuBO₃:Tb³⁺ microflower-like phosphors have been successfully prepared by an efficient surfactant- and template-free hydrothermal process directly without further sintering treatment. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectrometry, transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), photoluminescence (PL) and cathodoluminescence (CL) spectra as well as kinetic decays were used to characterize the samples. The as-obtained phosphor samples present flowerlike agglomerates composed of nanoflakes with thickness of 40 nm and high crystallinity in spite of the moderate reaction temperature of 200 °C. The reaction mechanism has been considered as a dissolution/precipitation mechanism; the self-assembly evolution process has been proposed on homocentric layer-by-layer growth style. Under ultraviolet excitation into the 4f⁸→4f⁷5d transition of Tb³⁺ at 248 nm (or 288 nm) and low-voltage electron beam excitation, LuBO₃:Tb³⁺ samples show the characteristic green emission of Tb³⁺ corresponding to ⁵D₄→⁷F_{6, 5, 4, 3} transitions with the ⁵D₄→⁷F₅ transition (542 nm) being the most prominent group, which have potential applications in fluorescent lamps and field emission displays.     

Growth and spectroscopic properties of Nd-doped Sr3Y2 (BO3)4 crystal

A new crystal of Nd³⁺:Sr₃Y₂ (BO₃)₄ with a dimension of Φ 15×30 mm³ was grown by the Czochralski method. The grown crystal was characterized using X-ray diffraction. The absorption and emission spectra of Nd³⁺:Sr₃Y₂ (BO₃)₄ were investigated. The absorption transition at 807 nm has an FWHM of 16 nm. The absorption and emission cross sections are 6.32×10⁻²⁰ cm² at 807 nm and 1.07×10⁻¹⁹ cm² at 1065 nm, respectively. The luminescence lifetime τ_f is 51.7 μs at room temperature.     

Growth and spectroscopic characterization of Nd:Sr6GdSc(BO3)6 crystal

A crystal of Nd³⁺:Sr₆GdSc(BO₃)₆ with the dimension of φ20×30 mm³ was grown by Czochralski method. The grown crystal was characterized by X-ray diffraction and DSC analysis. The DSC analysis showed that the crystal congruently melt at 1306.7°C. The absorption and emission spectra of Nd³⁺:Sr₆GdSc(BO₃)₆ were investigated. The absorption band at 806 nm has a FWHM of 13 nm. The absorption and emission cross-sections are 2.33×10⁻²⁰ cm² at 806 nm and 1.58×10⁻¹⁹ cm² at 1062 nm, respectively. The luminescence lifetime τ_f is 75 μs at room temperature.     

Application of sequential injection-square wave voltammetry (SI-SWV) to study the adsorption of atrazine onto a tropical soil sample

Square wave voltammetry automated by sequential injection analysis was applied to determine the Freundlich adsorption coefficients for the adsorption of atrazine onto a clay rich soil. The detection limit in soil extracts was between 0.18 and 0.48 μmol L⁻¹, depending on the medium used to prepare the extracts (0.010 mol L⁻¹ KCl, CaCl₂ or HNO₃ and 0.0050 mol L⁻¹ H₂SO₄), all of them conditioned in 40 mmol L⁻¹ Britton-Robinson buffer at pH 2.0 in presence of 0.25 mol L⁻¹ NaNO₃. Also in soil extracts the linear dynamic range was between 1.16 and 18.5 μmol L⁻¹ (0.25-4.0 μg mL⁻¹), with a sampling frequency of 190 h⁻¹. The K_f Freundlich adsorption coefficient was 3.8 ± 0.2 μmol^1−1/n Lⁿ kg⁻¹ in medium of 0.010 mol L⁻¹ KCl or CaCl₂, but increased to 7.7 ± 0.1 and 9.0 ± 0.3 μmol^1−1/n Lⁿ kg⁻¹ in 0.010 mol L⁻¹ HNO₃ and 0.0050 mol L⁻¹ H₂SO₄, respectively. The increase of K_f was related to the decrease of pH from 6.4-6.7 in KCl and CaCl₂ to 3.7-4.0 in presence of HNO₃ or H₂SO₄, which favors protonation of atrazine, facilitating electrostatic attractions with negative charges of the clay components of the soil. The 1/n parameters were between 0.76 and 0.86, indicating that the isotherms are not linear, suggesting the occurrence of chemisorption at specific adsorption sites. No statistically significant differences were observed in comparison to the adsorption coefficients obtained by HPLC. The advantage of the proposed SI-SWV method is the great saving of reagent because it does not use organic solvent as in the case of HPLC (50% (v/v) acetonitrile in the mobile phase). Additionally the start up of SI-SWV is immediate (no column conditioning necessary) and the analysis time is only 19 s.     

Synthesis and characterization of rhenium carbonyltrifluoroacetate complexes with phosphites,phosphonites and phosphinites

The rhenium(I) complexes [Re(O₂CCF₃)(CO)₃(L)] (1) and [Re(O₂CCF₃)(CO)₂LL′] (L = Ph₂POCH₂CH₂OPPh₂; L′ = PPh_n(OR)_3−n; R = Me, Et; n = 0–2) (2a–f) have been synthesised by the reaction of the parent bromo derivatives with AgO₂CCF₃. These compounds have been characterized by microanalysis, IR, NMR, mass spectrometry and, in the cases of 1 and 2a, by X-ray diffraction. The metal is in a distorted octahedral environment with the trifluoroacetate ligand acting in a monodentate manner.