Electronic structure of ZrCuSiAs and ZrCuSiP by X-ray photoelectron and absorption spectroscopy

The electronic structures of quaternary pnictides ZrCuSiPn (Pn=P, As) were analyzed by X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge spectroscopy (XANES). Shifts in the core-line XPS and the XANES spectra indicate that the Zr and Cu atoms are cationic, whereas the Si and Pn atoms are anionic, consistent with expectations from simple bonding models. The Cu 2p XPS and Cu L-edge XANES spectra support the presence of Cu¹⁺. The small magnitudes of the energy shifts in the XPS spectra suggest significant covalent character in the Zr-Si, Zr-Pn, and Cu-Pn bonds. On progressing from ZrCuSiP to ZrCuSiAs, the Si atoms remain largely unaffected, as indicated by the absence of shifts in the Si 2p_3/2 binding energy and the Si L-edge absorption energy, while the charge transfer from metal to Pn atoms becomes less pronounced, as indicated by shifts in the Cu K-edge and Zr K, L-edge absorption energies. The transition from two-dimensional character in LaNiAsO to three-dimensional character in ZrCuSiAs proceeds through the development of Si-Si bonds within the [ZrSi] layer and Zr-As bonds between the [ZrSi] and [CuAs] layers.     

Composition dependent frequency upconversion of Er/Yb-codoped lead chloride tellurite glasses

The green and red upconversion luminescence of Er³⁺ in lead chloride tellurite glasses excited at 980 nm is investigated. Three intense emission bands centered at 530, 545, and 658 nm corresponding to the transitions ⁴S_3/2→⁴I_15/2, ²H_11/2→⁴I_15/2 and ⁴F_9/2→⁴I_15/2, respectively, were simultaneously observed at room temperature. With increasing PbCl₂ content, the intensity of green (530 nm) emissions increase slightly, while the green (545 nm) and red (658 nm) emissions increase significantly. The results indicate that PbCl₂ has more influence on the green (545 nm) and red (658 nm) emissions than the green (530 nm) emission. The dependence of upconversion intensities on excitation power and possible upconversion mechanisms are discussed and evaluated.     

Two New Iron Coordination Polymers Based on Fe-pyta ChainsIncorporating Pyridine-2,4,6-tricarboxylate

Reaction of FeCIz＇6H20, pyridine-2,4,6-tricarboxylic acid（H3pyta） and NaOH in the hydrothermal system at 185 ℃ resulted in the formation of 1D coordination polymer[Fe（Hpyta）（H2O）2]（1） based on Fe-Hpyta chains. When the abpt[abpt=-4-amino-3,5-bis（4-pyridyl）-l,2,4-triazole] ligand was employed in the reaction system, a 3D supramolecular porous network （H2bpt）[Fe（pyta）（H2O）2]·4H2O（2） was obtained. The framework was constructed with negative （Fe-pyta） chains and the positive H3bpt^＋ in situ, formed from the abpt reagent, to form 1D channels filled with guest water molecules via hydrogen-bonds. X-Ray diffraction crystal structure analysis shows that complex 1 crystallized in the monoclinic system, space group C2/c, a=1.1490（5） nm, b=0.9008（4） nm, c=1.0058（5） nm, B=107.254（9）°, V=0.9942（8） nm3, Z=4; and complex 2 crystallizes in the triclinic system, space group P1 with a=0.90392（11） nm, b=0.96027（11 ） nm, c=1.55540（18） nm, a=73.558（2）°,B= 86.126（2）°,r= 68.745（2）°, V=1.2059（2） nm^3 and Z=2.     

On the system cerium-platinum-silicon

Phase relations in the ternary system Ce-Pt-Si have been established for the isothermal section at 800 °C based on X-ray powder diffraction, metallography, scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) techniques on about 120 alloys, which were prepared by various methods employing arc-melting under argon or powder reaction sintering. Nineteen ternary compounds were observed. Atom order in the crystal structures of τ₁₈-Ce₅(Pt,Si)₄ (Pnma; a=0.77223(3) nm, b=1.53279(8) nm c=0.80054(5) nm), τ₃-Ce₂Pt₇Si₄ (Pnma; a=1.96335(8) nm, b=0.40361(4) nm, c=1.12240(6) nm) and τ₁₀-CePtSi₂ (Cmcm; a=0.42943(2) nm, b=1.67357(5) nm, c=0.42372(2) nm) was determined by direct methods from X-ray single-crystal CCD data and found to be isotypic with the Sm₅Ge₄-type, the Ce₂Pt₇Ge₄-type and the CeNiSi₂-type, respectively. Rietveld refinements established the atom arrangement in the structures of Pt₃Si (Pt₃Ge-type, C2/m, a=0.7724(2) nm, b=0.7767(2) nm, c=0.5390(2) nm, β=133.86(2)°), τ₁₆-Ce₃Pt₅Si (Ce₃Pd₅Si-type, Imma, a=0.74025(8) nm, b=1.2951(2) nm, c=0.7508(1) nm) and τ₁₇-Ce₃PtSi₃ (Ba₃Al₂Ge₂-type, Immm, a=0.41065(5) nm, b=0.43221(5) nm, c=1.8375(3) nm). Phase equilibria in Ce-Pt-Si are characterised by the absence of cerium solubility in platinum silicides. Cerium silicides and cerium platinides, however, dissolve significant amounts of the third component, whereby random substitution of the almost equally sized atom species platinum and silicon is reflected in extended homogeneous regions at constant Ce content such as for τ₁₃-Ce(Pt_xSi_1−x)₂, τ₆-Ce₂Pt_3+xSi_5−x or τ₇-CePt_2−xSi_2+x.     

Phase Equilibria Laws in the SrS-Ln2S3 (Ln = Yb-Lu,Y, or Sc) Systems

Complex sulfides with the SrS: Ln₂S₃ ratio equal to 3: 1, 1: 3, or 1: 4 for Ln = Y or Lu have been predicted on the basis of thermodynamic analysis of previously designed SrS-Ln₂S₃ (Ln = Tb, Dy, or Er) phase diagrams. Phase diagrams for the SrS-Ln₂S₃ (Ln = Tm, Lu, or Sc) systems have been designed for the first time. These systems form congruently melting compounds SrLn₂S₄ (CaFe₂O₄ type structure, orthorhombic crystal system). Unit cell parameters, heats of melting, and microhardnesses have been determined. For SrTm₂S₄, the respective values are as follows: a = 1.181 nm, b = 1.421 nm, c = 0.396 nm, 2040 K, ΔH _m = 188 kJ/mol, 3500 MPa; for SrLu₂S₄: a = 1.187 nm, b = 1.416 nm, c = 0.392 nm, 2070 K, ΔH _m = 190 kJ/mol, 3540 MPa; and for SrSc₂S₄: a = 1.180 nm, b = 1.410 nm, c = 0.390 nm, 2100 K, ΔH _m = 206 kJ/mol, 3650 MPa. The increase in the melting temperatures and the heats of melting calculated for the SrLn₂S₄ compounds correlate with their classification as thio salts.     

Spin trapping of alkoxyl radicals generated from 5-methyl and 5-aryl-3-alkoxy-4-methylthiazole-2(3H)-thiones in photochemically induced and microwave-initiated reactions

Methoxyl and isopropoxyl radicals were generated from N-alkoxy-4,5-dimethylthiazole-2(3H)-thiones (λ_max∼320 nm) and 5-aryl derivatives (aryl=p-XC₆H₄; X=MeO, H, AcNH, Cl) (λ_max∼335 nm) in photochemically and microwave-induced reactions. Alkoxyl radicals were trapped with dimethylpyrrolidine N-oxide and characterized as spin adducts via EPR. Cumyloxyl radicals were liberated in a similar manner from N-cumyloxy-5-(4-methoxyphenyl)-4-methylthiazole-2(3H)-thione. A noteworthy bathochromic shift was found for the lowest energy transition of N-(hydroxy)indeno[2,1-d]thiazole-2(3H)-thione (λ_max=376 nm), if compared to the UV-vis absorption of N-hydroxy-4-methyl-5-phenylthiazole-2(3H)-thione (λ_max=338 nm). Syntheses of alkoxyl radical precursors and procedures for conducting N,O-homolysis are described in a full account.     

On the 1 μm system of iron hydride

The 987.7 nm system of FeD has been shown by rotational analysis of the (1,0) and (0,0) bands to be due to a ⁴Δ-⁴Δ electronic transition. The bond lengths in the ν = 0 levels of the upper and lower states are r_o⁴ = 0.1705 nm and r_o¹¹=0.1589 nm. respectively and the (ν′= 1) - (ν′ = 0) vibrational interval of the upper state is 1035 cm^?1.     

Spectrophotometric study of complexes of mercury(II) with mono- and dithiosemicarbazones

The formation of complexes at pH 4.7 of the Hg(II) with five monothiosemicarbazone and two dithiosemicarbazone has been studied. The mercury(II) reacts with monothiosemicarbazones of salicylaldehyde (λ_max = 363 nm, E = 1.69 × 10⁴liters · mol^?1cm^?1), pi-colinadehyde (λ_max = 363 nm, E = 2.38 × 10⁴liters · mol^?1cm^?1), 6-methyl-picolinaldehyde (λ_max = 363 nm, E = 2.28 × 10⁴liters · mol^?1cm^?1), di-2-pyridylketone (λ_max = 380 nm, E = 2.08 × 10⁴liters · mol^?1cm^?1), and o-naphthoquinone (λ_max = 540 nm, E = 1.03 × 10⁴liters · mol^?1cm^?1) and with dithiosemicarbazones of 1,4-dihydroxyphthalimide (λ_max = 430 nm, E = 2.56 × 10⁴liters · mol^?1cm^?1) and dipyridylglyoxal (λ_max = 363 nm, E = 2.37 × 10⁴liters · mol^?1cm^?1). A critical comparison of the stoichiometry and apparent stability constant of complexes with mono- and dithiosemicarbazones is given.     

Synthesis and nonlinear optical properties of new symmetrically substituted stilbenes

Three new chromophores and trans-4-(N-(ethyl 4″-nitrobenzoate)-N-ethyl amino)-4′-(dimethyl amino) stilbene (DMANHAS) have been synthesized and whose chemical structures have been characterized by ¹H NMR, IR, and elemental analyses. Linear absorption, single-photon-induced fluorescence and two-photon-induced fluorescence are experimentally studied. Trans-4-(N-2-hydroxyethyl-N-ethyl amino)-4′-(dimethyl amino)stilbene (DMAHAS) and trans-4-(N-2-hydroxyethyl-N-ethyl amino)-4′-(diethyl amino)stilbene (DEAHAS) have effective two-photon absorption cross-sections of σ₂=0.91×10⁻⁴⁶ cm⁴ s/photon and σ₂=1.19×10⁻⁴⁶ cm⁴ s/photon at 532 nm by using an open aperture Z-scan technique, respectively. When pumped with 800 nm laser irradiation, DMAHAS and DEAHAS indicate strong two-photon-induced blue fluorescence of 436 and 440 nm, respectively, while trans-4-(N-(ethyl 4″-nitrobenzoate)-N-ethyl amino)-4′-(diethyl amino) stilbene (DEANHAS) and DMANHAS exhibit no fluorescence.     

Effect of capping and particle size on Raman laser-induced degradation of γ-Fe2O3 nanoparticles

Diol capped γ-Fe₂O₃ nanoparticles are prepared from ferric nitrate by refluxing in 1,4-butanediol (9.5 nm) and 1,5-pentanediol (15 nm) and uncapped particles are prepared by refluxing in 1,2-propanediol followed by sintering the alkoxide formed. X-ray diffraction (XRD) shows that all the samples have the spinel phase. Raman spectroscopy shows that the samples prepared in 1,4-butanediol and 1,5-pentanediol and 1,2-propanediol (sintered at 573 and 673 K) are γ-Fe₂O₃ and the 773 K-sintered sample is Fe₃O₄. Raman laser studies carried out at various laser powers show that all the samples undergo laser-induced degradation to α-Fe₂O₃ at higher laser power. The capped samples are however, found more stable to degradation than the uncapped samples. The stability of γ-Fe₂O₃ sample with large particle size (15.4 nm) is more than the sample with small particle size (10.2 nm). Fe₃O₄ having a particle size of 48 nm is however less stable than the smaller γ-Fe₂O₃ nanoparticles.     

Synthetic Cu0.507(5)Pb8.73(9)Sb8.15(8)I1.6S20.0(2) nanowires

Nanowires of an iodine containing Pb-Sb-sulfosalt have been synthesized by chemical vapor transport. Their structure was studied using high-resolution transmission electron microscopy and X-ray powder diffraction. The lattice parameters show values equal to a=4.9801(4) nm, b=0.41132(8) nm (with two-fold superstructure), c=2.1989(1) nm and β=99.918(6)°. These parameters and the results of a multislice simulation are in good agreement with the mineral pillaite, Cu_0.10Pb_9.16Sb_9.84S_22.94Cl_1.06O_0.5 (space group C2/m, a=4.949(1) nm, b=0.41259(8) nm, c=2.1828(4) nm, and β=99.62(3)°). Microprobe and EDX analyses yielded a chemical composition of Cu_0.507(5)Pb_8.73(9)Sb_8.15(8)I_1.6S_20.0(2) which is close to natural pillaite but contains no oxygen and iodine instead of chlorine. The structure of the investigated material is based on chains of M-S polyhedra (M=Pb or Sb) typical for the architecture of sulfosalts implying iodine atoms in trigonal prismatic coordination with Pb atoms from the M-S polyhedra of neighboring chains. The [010] superstructure of the specimen was found to be unstable under electron beam irradiation with a rapid decrease of the b lattice parameter from 0.8 to 0.4 nm within 5 min.     

Photochemistry of dienones—X: Photochemistry of (e)-β-ionone oxime ethyl ether

(E)-β-ionone oximc ethyl ether [(E, E)-4] upon direct irradiation with λ either254or 313 nm yields the geometrical isomer (E, Z)-4 and (Z)-retro-γ-ionone oxime ethyl ether (Z,E)-5 as the sole primary products, illustrating (E)-(Z) isomerization (φ₃₁₃ =0.49) and a 1, 5-hydrogen shift (φ313 =0.15) respectively. From studies with triplet photosensitizers and with ethyl iodide (to enhance the singlet-triplet intersystem crossing) it is concluded that these two products in the direct irradiation result only from the singlet excited state, and that the inter-system crossing quantum yield is relatively low. Upon prolonged irradiation of (E,E)-4 with λ 313 nm the eventual products are (Z,E)-5 and (Z,Z)-5, whereas with λ 254 nm they are (E,E)-5 and [(Z,E)-5 and/or (E,Z)-5]. Upon triplet photosensitization (E,E)-4 undergoes only (E)-(Z) isomerization, leading to a mixture of all the four geometrical isomers of4. From the dependence of the geometrical isomer distribution in the photostationary state on the triplet energy of the sensitizer the triplet energies of (E,E)-4, (E, Z)-4, (Z, E)-4, and (Z, Z)-4 have been determined to be ca 55, < 55,57, and 57 $\text{kcal}\text{mol}$ respectively.     

Synthesis and crystal structure of the A6B5O18 perovskite-like compounds

New members of the A_nB_n−1O_3n perovskite-like family (Ba₅KNb₅O₁₈ and Sr₆Nb₄SnO₁₈ compounds) with n = 6 have been synthesized and studied by the X-ray powder diffraction. Their crystal structures were found to belong to the Ba₆Nb₄TiO₁₈-type with a = 0.57840(7) nm, c = 4.2532(5) nm and a = 0.5661(1) nm, c = 4.186(1) nm for Ba₅KNb₅O₁₈ and Sr₆Nb₄SnO₁₈, respectively. It was shown that Ba and K (A-atoms) are completely disordered in the crystal structure of Ba₅KNb₅O₁₈ compound. But Nb and Sn atoms (B-atoms) in the crystal structure of the Sr₆Nb₄SnO₁₈ compound are quite ordered with the preferred Sn⁺⁴ and Nb⁵⁺ cations localization in the center of perovskite-like block and on the boundaries of these blocks, respectively. Temperature and frequency dependencies of the real components of electric conductivity σ^I and dielectric permeability ɛ^I; specific electric conductivity at the direct current σ_dc have been obtained by the impedance spectroscopy method for Sr₆Nb₄SnO₁₈.     

Structural analysis of modulated crystals. A new structure of Ce<Subscript>4</Subscript>Pd<Subscript>13.6</Subscript>Sn<Subscript>5.9</Subscript>

Incommensurate modulated structure of Ce₄Pd_13,6Sn_5,9 intermetallic is studied by (3+1)D analysis in a rhombic basic cell a = 2.08458(4) nm, b = 0.47129(1) nm, and c = 0.92874(1) nm; q = 0,2407(1)b*. Xmmm(0β0)000 group determines the symmetry of the crystal. The superspace analysis is compared to the analysis of the superstructure with a, 4b, and c periods in three dimensions.     

[Cu(en)2]0.5[Al3P3O12(OH)]-aluminophosphate with zeotype AWO: Synthesis, crystal structure and phase transformation

A new aluminophosphate [Cu(en)₂]_0.5[Al₃P₃O₁₂(OH)] (denoted as AlPO-CJ53; en = ethylenediamine) with zeotype AWO topology has been synthesized under hydrothermal conditions in which the self-assembled Cu(en) ₂ ²⁺ cations in the reaction system act as the template. AlPO-CJ53 crystallizes in the monoclinic space group P2₁/n (No. 14) with a = 0.85547(11) nm, b = 1.7671(2) nm, c = 0.90500(12) nm, β = 107.725(2)°, V = 1.3031(3) nm³. Its framework consists of AlO₄(OH)/AlO₄ and PO₄ units forming 8-ring channels along the c direction, where the copper complex cations Cu(en) ₂ ²⁺ are located to neutralize the negative charges of the framework. AlPO-CJ53 transforms to AlPO₄-25 with zeotype ATV upon calcination at 400 °C.     

New water-soluble hydrogen donors for the enzymatic spectrophotometric determination of hydrogen peroxide

Eight N -alkyl-N-V-sulphopropylaniline derivatives have been synthesized and assessed as water-soluble hydrogen donors for the spectrophotometric determination of hydrogen peroxide in the presence of peroxidase. The sodium salts of N-ethyl-N-sulphopropylaniline (ALPS), N-ethyl-N-sulphopropyl-m-toluidine (TOPS) and N -ethyl-N-sulphopropyl-m-anisidine (ADPS) are recommended. They have excellent water solubilities, and the optimum pH range for oxidative condensation with 4-aminoantipyrine in the presence of hydrogen peroxide and peroxidase is 5.5–9.5. The absorbances of the resulting chromogens are 2–3 times higher than that achieved with phenol. The molar absorptivities of the chromogens with 4-aminoantipyrine are 41300 (ALPS, λ_max 561 nm), 37400 (TOPS, λ_max 550 nm) and 27900 (ADPS, λ_max 540 nm). Calibration graphs for the determination of hydrogen peroxide in the presence of a control serum are linear for 7–40 × 10^-6 mol H₂O₂ l^-1.     

Nonlinear optical properties of systems based on (tetra-15-crown-5-phthalocyaninato)indium(III)

The nonlinear optical properties of solutions of (2,3,9,10,16,17,23,24-tetra-15-crown-5-phthalocyaninato)indium(III) [(15C5)₄Pc]In(OH) in tetrachloroethane (TCE) have been studied by the z-scan method. It has been found that a nonlinear optical response is due to supramolecular associates formed in a tetrachloroethane solution by heating to 90°C/slow cooling to room temperature cycling. The formation of the supramolecular associates has been studied by atomic force microscopy (AFM) and electronic absorption spectroscopy (EAS). It has been shown that a single thermal treatment of [(15C5)₄Pc]In(OH) solutions in TCE results in the predominant formation of dimers, as evidenced by both a short-wavelength shift of the Q-absorption band of the monomeric complex (λ_max = 692 nm) to the band of λ_max = 653 nm and height doubling of molecular entities as measured by AFM. The dimers are responsible for the two-photon absorption measured in the femtosecond range, which has a relatively high cross section of σ₂ = 1.38 × 10^?46 cm⁴ s/(molecule, photon) or 1.38 × 10⁴ GM. According to the AFM data, three cycles of heat treatment of the solution leads to the formation of supramolecular assemblies of about 200 nm length. The optical spectrum exhibits long-wavelength absorption at λ_max = 841 nm and the long-wavelength edge near 1300 nm. In the case of nanosecond 1064-nm laser irradiation, the linear absorption S ₀ → S ₁ is primary, having the cross section of σ₀ = α₀/N = 2.3 × 10^?20 cm². The known high quantum yield (close to unity) of triplet states of indium phthalocyanines suggests that the main nonlinear optical effect is determined by intersystem crossing S ₁ → T ₁ and triplet-triplet absorption T ₁ → T ₂. The absorption cross section is σ _T-T = 1.14 × 10^?19 cm².     

The Fluorescence of native DNA at room temperature

The fluorescence spectra (300–500nm) quantum yields (φ_f) and excitation spectra (240–285 nm) are reported for neutral aqueous sloutions of purified native DNA from calf thymus, E. coli bacterium, and hen erythrocyte near 20°C. The same properties were also measured for a reference solution of mononucleotides, and direct comparisons were made. Whether purified or not, the DNA spectra all closely resemble that from the monomer mixture between 300 and 360 nm but shows a broad, low level shoulder at λ_max ≈ 450nm which is absent in the monomer spectrum. The φ_f for the purified DNA is (4 = 1) x 10^-5, about half that of the monomer reference solution and unpurified DNA. The excitation spectrum is slightly red-shifted from the absorption for both the DNA and the monomer mixture, but not for the individual monomers. The fluorescence exhibits abrupt changes associated with the denaturation of DNA at ≈ 80°C and pII) <4 or > 11.     

Preparation of Mn3O4 nanocrystallites by low-temperature solvothermal treatment of γ-MnOOH nanowires

The preparation of trimanganese tetroxide (Mn₃O₄) nanocrystallites from γ-MnOOH nanowires under mild conditions has been achieved by two steps: first, γ-MnOOH nanowires with a mean diameter of about 12 nm and lengths of up to several micrometers were directly prepared via hydrothermal reaction between KMnO₄ and toluene in water at 180°C for 24 h; then, pure Mn₃O₄ nanocrystallites could be obtained by solvothermal treatment of the γ-MnOOH nanowires in ethylenediamine (EDA) and ethylene glycol (EG) at 150°C for 24 h. It was found that the Mn₃O₄ product obtained in EDA comprised well-defined nanocrystallites with the size in the range of 15-35 nm, while the one obtained in EG consisted of aggregated nanoparticles with the size of less than 18 nm.The possible formation mechanism of nanocrystalline Mn₃O₄ in EDA and EG and reasons for the different effects of various solvents on the products were also proposed.     

123 Phases of composition CaBa2Cu2WO8 with substitutions of sodium and potassium for calcium and barium

Tetragonal (123) phases of compositions Ca_0.7Na_0.3Ba₂Cu₂WO₈, CaBa_1.7Na_0.3Cu₂WO₈, and CaBa_1.7K_0.3Cu₂WO₈, where tungsten occurs in Cu(1) positions and Cu³⁺ is in Cu(2) positions, were prepared from CaWO₄, BaCuO₂, and sodium and potassium nitrates at 1073 K in an oxygen flow. These phases constitute at least 90% of the samples; their unit call parameters are as follows: a = b = 0.4177(3) nm, c = 1.2561(8) nm; a = b = 0.4182(3) nm, c = 1.2564(8) nm; and a = b = 0.4194(3) nm, c = 1.2603(8) nm, respectively. Their X-ray diffraction patterns feature peaks that indicate a superstructure with all three unit cell parameters being doubled. The samples have weak conductive properties (room-temperature electrical conductivity ranges between 10^?6 and 10^?7 Ohm^?1 cm^?1). Conductivity versus temperature curves are indicative of the semiconductor character of the samples. Superconducting transitions do not occur up to 65 K.