Theoretical study on the ClO/ClO- system electron-transfer reactivity by the golden-rule

The structures, properties and electron transfer reactivity of the ClO/ClO- coupling system are studied in this paper at ab initio (UHF and UMP2) levels and the Density Functional Theory (DFT: UB3LYP, UB3P86, UB3PW91) levels employing 6311 + G(3df) basis set and on the basis of the Golden-rule of the time-dependent perturbation theory. Investigations indicate that the results obtained using the UB3LYP method employing 6-311 + G(3df) basis set is in excellent agreement with the experiment. For this coupling system, six stable coupling modes have been found which correspond to six different encounter complexes and denote six different electron transfer mechanism: four O-O directly linked structures (one collinear: D-h, one anti-parallel: C-s, two twist: C-2) and two Cl-O linked structures (cis- and anti- C-s structures). The activation energies, the stabilization energies and the electronic coupling matrix elements have also been calculated for the electron transfer reactions via these six different mechanism at the UB3LYP/6-311 + G(3df) level, and then the electron transfer rates are determined at the same level. The most favorable coupling mode to the electron transfer is the anti-parallel mechanism. The averaged electron transfer rate is about 5.58 X 10(11) M-1 s(-1). It is also implied that the B3LYP method can give more reasonable results for the electron transfer reactivity of this system. (C) 2003 Elsevier B.V. All rights reserved.

Chemical bond characteristics, thermal expansion property and compressibility of AR(2)O(4) (A = Ca, Sr, Ba; R = rare earths)

Theoretical researches were performed on the CaFe2O4-type binary rare earth oxides AR(2)O(4) (A = Ca, Sr, Ba; R = rare earths) by using chemical bond theory of dielectric description. The chemical bond properties of these crystals were explored, and then the thermal expansion property and compressibility were studied. The theoretical values of linear thermal expansion coefficient (LTEC) and bulk modulus were presented. The calculations revealed that the LTECs and the bulk moduli do have linear relationship with the ionic radii of the rare earths. In the cases of Sc and Y, both the LTEC and bulk modulus values are larger than the lanthanide series. We attribute this to the difference in the electronic configuration between Sc (Y) and lanthanide series. For SrY2O4 and BaY2O4 crystals, the theoretical values of LTEC and bulk modulus agree well with experimental ones.

Synthesis, structure and optical properties of new organic-inorganic haloplumbates complexes (C5H10N3)PbX4 (X = Br, Cl), (C2H2N4)PbBr3

Layered organic-inorganic composite materials (C5H10N3)PbX4 (X = Br 1, Cl 2) containing histaminium dications were grown via a solution-cooling process, and their structure and optical properties were determined. The organic ligand-histaminium introduced into the corner-sharing octahedra of the 'PbX4- layer' contains both primary ammonium and imidazolium different from the traditionally primary amine found in this system. As comparison, another analogous amine of 3-amino-1,2,4-triazol was used as ligand to coordinate with PbBr2 in acid solution. A novel complex (C2H2N4)PbBr3 (3) was obtained with zigzag PbBr2 chains different from the PbX4 layer in compound as 1 and 2. The hybrid (C5H10N3)PbX4 show exciton absorption at 339 nm for X = Cl and 419 nm for X = Br with the corresponding emission at 360 and 436 nm, respectively. The different PbBr2 chain structure of compound 3 does not show photo luminescence.

Preparation and luminescent properties of rare earth ions in M2B5O9Cl : Re(M = Ca, Sr, Ba; Re=Eu, Tb)

M2B5O9X: Re(M = Ca, Sr, Ba; X = Cl, Br; Re = Eu, Th) phosphors were synthesized via solid state method. The products were characterized with X-ray powder diffraction and luminescence spectrometer. The luminescent properties as well. as the influences of the matrix composition and other doping ions on the luminescence of the rare earth ions of the co-doped phosphors were investigated. The coexistence of Eu3+, Eu2+ and Th3+ were observed in these matrices. The phenomenon may be explained by the electron transfer theory. The sensitization of Ce3+ ion improves the intensity of emission of Eu2+, and Tb3+. The competition between electron transfer among conjugate rare earth ions and energy migration might be the reasons for the observation. We predict a novel trichromatic phosphor co-doped with Eu3+ Tb3+ in M2B5O9X.

Hydrothermal synthesis, structure, and characterization of two one-dimensional chainlike hybrid complexes [(CuX)(2)(o-phen)](infinity) (X = Br, Cl; o-phen = o-phenanthroline)

Two novel organic-inorganic hybrid complexes [(CuX)(2)(o-phen)](infinity) (X = Br (1), Cl (2); o-phen = o-phenanthroline) have been synthesized hydrothermally and characterized structurally by elemental analyses, IR, ESR, XPS spectrum, TG analyses and single-crystal X-ray diffraction. Both title compounds exhibit novel one-dimensional chainlike copper halide scaffolding constructed by the unusual [Cu3X3] hexagon motifs by sharing opposite edges, where a single Cu site of each [Cu3X3] hexagon is chelated with N donors of o-phen group. To our knowledge, such basic o-phen-copper halide skeleton has not been reported hitherto. Moreover, TG analyses indicate that both title compounds possess high thermal stability.

Chemiluminescence determination of trace ascorbic acid with chromium (VI)-H2O2-luminol system

A new chemiluminescence(CL) system for the determination of ascorbic acid has been established. By the fast reduction reaction between chromium(VI) and ascorbic acid, chromium(M was generated to react with luminol and hydrogen peroxide in alkaline aqueous solution and hydrogen peroxide to produce CL. The CL emission intensity was correlated with ascorbic acid concentration in the range 8.0 x 10(-9) to 1.6 x 10(-4) mol/L, and the detection limit was 8.0 x 10(-9) mol/L ascorbic acid. The relative standard deviation (n = 11) for 1.0 x 10(-6) mol/L ascorbic acid is 0.9%. The method has been applied to the determination of ascorbic acid in vitamin C tablets with satisfactory results.

The luminescence of Eu2+ in mixed phase system

The dependence of the structure of the hosts on the M ion radius in MMgAl10O17 (M = Be, Mg, Ca, Sr, Ba, Pb, Eu, Mn, Fe, Co, Ni, Zn, Cd, Sn) system was studied and the luminescence of Eu2+ the mixed phase system was discussed. When M ion radius is less than 0.10 nm, the system MMgAl10O17 constructs by the mixed phases consisting of manegtoplumbite and spinel, alpha-alumina or spinel and alpha-alumina. In the mixed phase of manegtoplumbite and spinel and alpha-alumina, Eu2+ ion preferentially occupies lattice site of the cations in manegtoplumbite well matched with the radius and charge of Eu2+. There exists only d-->f transition emission of Eu2+ and no characteristic emission of Eu3+ occurs in those hosts. In the mixed phase of spinel and alpha-alumina, Eu2+ can enter the lattice site of Mg2+ ion or Al3+ ion and the d-->f and f-->f transition of Eu2+ can been observed respectively. Meanwhile, since the radius and charge of matrix lattice ions substituted by Eu2+ do not match with those of Eu2+, the valence state of Eu2+ is unstable. Eu2+ is partly changed into Eu3+ and the emission of Eu3+ is obviously observed even under the condition of reduction atmosphere. If reaction temperature is more than 1 150 degrees C, Al2O3 forms alpha-Al2O3 structure, the f-->f transition of Eu2+ appears. If reaction temperature is less than 1 150 degrees C, a mixed phase of alpha-Al2O3 and gamma-Al2O3 is formed, the f-->f transition of Eu2+ disappears and a new band emission from d-->f transition of Eu2+ occurs.

Evaluation of bond covalency and bond valence in Sr-doped perovskite-type compounds

Formulas for decomposing of complex crystals to a sum of binary crystals are described and applied to the study of bond covalency in La1-xSrxFeO3 (0.0 less than or equal to x less than or equal to 0.9) and Ca1-xSrxMnO3 (0.0 less than or equal to x less than or equal to 0.5). The bond valence is treated by bond-valence sums scheme. The results indicate that, for both compounds, with the increasing doping level, the bond covalency and bond valence show the same trend, namely, larger bond covalency corresponds to higher bond valence. For La1-xSrxFeO3, with the increase of doping level, the bond covalency of La-O, Ca-O decreases in the orthorhombic (0.0 less than or equal to x less than or equal to 0.2) and rhombohedral (0.4 less than or equal to x less than or equal to 0.7) systems, then increases slightly for the cubic (0.8 less than or equal to x less than or equal to 0.9) system, but that of Fe-O increases for all crystal systems. A sharp decrease in bond covalency was observed where the crystal changes from orthorhombic to rhombohedral, while a smooth trend was seen for the rhombohedral-to-cubic transition. On the other hand, for orthorhombic Ca1-xSrxMnO3, the bond covalency of Ca-O, Sr-O, and Mn-O (4-coordinate site) decreases with the increasing doping level, that of Mn-O (2-coordinate site) increases.

Luminescence properties of Ce3+ in KMF3(M=Mg, Ca, Sr, Ba) hosts with perovskite structure

KMF3(M = Mg, Ca, Sr, Ba) compounds were synthesized by solid state reaction under argon atmosphere. Their structures were determined by X-ray diffraction. It belongs to cubic system with perovskite structure. The excitation and emission spectra of KMF3:Ce3+ were measured. According to the characteristics of spectral structures, the occupation site of Ce3+ is discussed.

Kinetics of the polymerization of isoprene with isopropoxyneodymium dichloride/triethylaluminium binary lanthanide catalyst system

The kinetics of the polymerization of isoprene with the heterogeneous rare earth catalyst system isopropoxyneodymium dichloride/triethylaluminium (Nd(OPri)Cl-2-AlEt(3)) was examined in a specially designed dilatometer. The rate of polymerization is expressed as R(p) approximate to -d[M]/dt = k'(p)[Nd](1.40)[M]. The main kinetical parameters such as the concentration of active propagating chain, the efficiency of lanthanide catalyst used (ELCU), the absolute rate constant of propagation as well as the average life time of growing chains, were determined at 30 degrees C, 40 degrees C, 45 degrees C and 50 degrees C.

Studies on the synthetic, structural, electrical and magnetic properties of Ln(n)MCo(n)O(3n+1) (Ln=Sm, Gd; M=Sr, Ba; n=1,2)

Three new oxides Sm2SrCo2O7, Sm2BaCo2O7 and Gd2SrCo2O7 have been synthesized successfully by solid state reaction mathod. The X-Ray diffraction spectra show that they are all isostructural with Sr3Ti2O7, and Ln(2)SrCo(2)O(7)(Ln=Sm,Gd) crystallized in tetragonal system, Sm2BaCo2O7 in orthrhombic system. The Co-O bonds in CoO2 planes of Ln(2)SrCo(2)O(7) are shorter than those of LnSrCoO(4)(Ln=Sm, Gd), and so their delectrons are more delocalized and their electrical resistivities are smaller. The electrical resistivities versus temperature in the range 300 similar to 1100K showed that the five brides show the characters of weakly localized systems. In the lower temperature range, the magnetic behaviors of Gd2SrCo2O7 and GdSrCoO4 fit Curie-Weiss law well, and the magnetic exchange reaction in CoO2 sublattices of Gd2SrCo2O7 is ferromagnetic, but that of GdSrCoO4 is antiferromagnetic. The other three oxides with Sm3+ showed complex magnetic behaviors which is perhaps related with the complexity of Sm3+.

THE EFFECT ON PHYSICAL-PROPERTIES OF THE SUBSTITUTION OF CA OR BA FOR SR IN NDSRNIO4

A new solid solution series, NdSr(1-x)M(x)NiO(4) (M = Ca: 0.0 less than or equal to x less than or equal to 1.0; M = Ba: 0.0 less than or equal to x less than or equal to 0.6), was synthesized by solid state reaction, and the structures, magnetic and electrical properties and optical spectra of this series have been studied. All the samples crystalized in tetragonal systems, with the exception of NdCaNiO4, which crystallized in the orthohombic system. IR spectra of NdSr1-xCaxNiO4 indicated that the lengths of two Ni-O bonds decrease with increasing Ca content. The electrical conduction changed from metallic-type to semiconductive-type when x greater than or equal to 0.4 (M = Ca, Ba), and the room temperature resistivities of NdSr1-xCaxNiO4 increased with the increase of Ca content. Magnetic susceptibility measurements revealed that Ni+3 ions in all the samplies were in low-spin state over the temperature range 77-300 K.

THE ISOLATION, CHARACTERIZATION AND OXIDATION REACTION OF ACTIVE INTERMEDIATES OF CYTOCHROME-P-450 MODEL SYSTEM OXOCHROMIUM(V) TETRAPHENYLPORPHYRIN COMPLEXES

Oxochromium (V) tetraphenylporphyrin complexes, O = Cr (V) TPP (Cl) PhI. O = Cr-(V) TPP (N3) PhI and O = Cr (V)TPP (p-CH3OC6H4O)1/2PhI were isolated from the reaction of Cr (III) TPP (Cl). Cr (III) TPP (N3) Py or Cr (III) TPP (p-CH3OC6H4O) THF with iodosy

A STUDY OF SITE OCCUPATION OF EU-3+ IN ME2Y8(SIO4)6O2 (ME=MG, CA, SR)

Alkaline earth (Mg, Ca. Sr) yttrium silicate oxyapatites doped with Eu3+ show red luminescence with comparable intensity. In this system of phosphors, the Eu3+ ions enter 4f sites and 6h sites simultaneously according to the fluorescence spectra, in which

STRUCTURE-ANALYSIS OF MOLTEN CACL2-KCL SYSTEM BY X-RAY-DIFFRACTION

Radial distribution function of CaCl2-KCl (1:2 mol) melt was measured by X-ray scattering of high temperature liquid. The nearest neighbour distances of Ca2+-Cl-, K+-Cl- and Cl--Cl- ionic pairs are 0.278, 0.306 and 0.380 nm, respectively, Discussion on the relation between structure and physicochemical properties in the melt was simply done in this paper.