Layer-by-layer multilayer films self-assembled from a rare-earth-containing poly-oxometalate Na-9[Eu(W5O18)(2)] and poly (allylamine hydrochloride) and their photoluminescent properties

Ultrathin multilayer films of a rare-earth-containing polyoxometalate Na-9[Eu(W5O18)(2)] (EW) and Poly (allyamine hydrochloride) (PAH) have been prepared by layer-by-layer self-assembly from dilute aqueous solutions. The fabrication process of the EW/PAH multilayer films was followed by UV-vis spectroscopy and ellipsometry, which show that the deposition process is linear and highly reproducible from layer to layer. An average EW/PAH bilayer thickness of ca. 2.1 nm was determine,by ellipsometry. In addition, the scanning electron microscopy (SEM) image of the EW/PAH film indicates that the film sufface is relatively uniform and smooth. The photoluminescent properties of these films were also investigated by fluoresence spectroscopy.

Photoluminescent organic-inorganic composite films layer-by-layer self-assembled from the rare-earth-containing polyoxometalate Na-9[EuW10O36] and poly(allylamine hydrochloride)

Photoluminescent organic-inorganic composite films incorporating the rare-earth-containing polyoxometalate Na-9[EuW10O36] (EW) and poly(allylamine hydrochloride) (PAH) have been prepared by the layer-by-layer self-assembly method. UV-vis spectroscopy and ellipsometry were used to follow the fabrication process of the EW/PAH composite films. The experimental results show that the deposition process is linear and highly reproducible from layer to layer. An average EW/PAH bilayer thickness of ca. 2.1 nm was determined by ellipsometry. In addition, scanning electron microscopy and atomic force microscopy images of the EW/PAH composite films indicate that the film surface is relatively uniform and smooth. The photoluminescent properties of these films were investigated by fluorescence spectroscopy.

Sol-gel-derived carbon ceramic electrode containing 9,10-phenanthrenequinone, and its electrocatalytic activity toward iodate

9,10-Phenanthrenequinone (PQ) supported on graphite powder by adsorption was dispersed in propyltrimethoxysilane-derived gels to yield a conductive composite which was used as electrode material to fabricate a PQ-modified carbon ceramic electrode. In this configuration, PQ acts as a catalyst, graphite powder guarantees conductivity by percolation, the silicate provides a rigid porous backbone, and the propyl groups endow hydrophobicity and thus limit the wetting region of the modified electrode. Square-wave voltammetry was exploited to investigate the pH-dependent electrochemical behavior of the composite electrode and an almost Nernstian response was obtained from pH 0.42 to 6.84. Because the chemically modified electrode can electrocatalyze the reduction of iodate in acidic aqueous solution (pH 2.45), it was used as an amperometric sensor for the determination of iodate in table salt. The advantages of the electrode are that it can be polished in the event of surface fouling, it is simple to prepare, has excellent chemical and mechanical stability, and the reproducibility of surface-renewal is good.

Infrared spectra and VUV excitation properties of BaLnB(9)O(16): Re (Ln = La, Gd; Re = Eu, Tb)

The infrared spectra of BaLnB(9)O(16):Re, along with the VUV excitation spectra, have been measured. The spectra were tentatively interpreted in terms of the data on absorptions of the borate groups and band structure. It was observed that there are absorption due to BO3 and BO4 groups, indicating that there are BO3 and BO4 groups in BaLnB(9)O(16). It is found that absorption of the borate groups is located in the range from 120 to 170 mn. This result reveals that there is an energy transfer from host to the rare earth ions. It also observed that the energy of charge transfer band, the host absorption, the total crystal field splitting of d-levels of Tb3+ increase with the decrease in the Ln(3+) radius. (C) 2001 Elsevier Science B.V. All rights reserved.

BaCe_(0.8)Ln_(0.2)O_(2.9)(Ln=Gd,Sm,Eu)固体电解质的低温制备及其燃料电池性质

利用溶胶 凝胶法低温合成了BaCe0 .8Ln0 .2 O2 .9(Ln =Gd ,Sm ,Eu)固体电解质 ,X射线粉末衍射表明 90 0℃即形成正交钙钛矿结构 ,较高温固相反应合成温度降低了约 6 0 0℃ .测定了样品的阻抗谱和电导率 ,研究了其导电机理 ,溶胶 凝胶法合成可减小或消除固体电解质的晶界电阻 ,80 0℃时BaCe0 .8Gd0 .2 O2 .9的σ =7.87× 10 -2S·cm-1,以它为电解质的氢氧燃料电池开路电压接近 1V ,最大输出功率密度为 30mW·cm-2 .

(+/-)-7,7,9,9-Tetramethyl-2,3 : 4,5-dinaphthol,6,8-trioxa-7,9-disilacyclonona-2,4-diene

The title compound, C24H24O3Si2, is a twofold symmetric silicocrown ether with the two dimethylsilyl groups attached to the O atoms of 1,1'-bi-2-naphthol, and bridged by another O atom.

La_(0.9)Ni_2储氢合金的电化学性能

本文研究了稀土AB_2型非整比储氢合金La_(0.9)Ni_2的结构和电化学性能。结果表明,与LaNi_2储氢合金相比,La_(0.9)Ni_2合金显示了更易活化、更高的放电容量和突出的倍率性能,但荷电保持率较低。此外,合成工艺,退火处理和球磨对储氢合金的电极性能有很大影响。

Synthesis, structure and properties of alpha-Keggin-type of K6H3[ZnW11O40Al]center dot 9.5H(2)O

A new heteropolycomplex, K6H3[ZnW11O40Al] . 9.5H(2)O was prepared and characterized by means of elemental analysis, IR, UV spectroscopy, Al-27 NMR, electrochemistry and X-ray crystallography. The crystal of K6H3[ZnW11O40Al] . 9.5H(2)O is cubic, space group Fm-3m, with lattice constants a=b=c=2. 144 8(2) nm, V = 9.866(2) nm(3), Mo radiation, R = 0.057 8 for 497 independent data with [I>2 delta(I)]. The anion is of alpha-type Keggin structure with C-s symmetry.

Synthesis, crystal structure and magnetic properties of a series of polymeric lanthanoid-copper complexes [Ln(2)Cu(3){O(CH2-CO2)(2)}(6)].nH(2)O (Ln=La, Nd, n=9; Ln=Er, n=6)

The reaction of diglycolic acid, O(CH2CO2H)(2), with Cu(NO3)(2) . H2O and lanthanoid nitrate hydrate produces a series of novel Ln-Cu mixed metal complexes, [Ln(2)CU(3){O(CH2CO2)(2)}(6)]. nH(2)O (Ln = La, Nd, n = 9; Ln = Er, n = 6), which have been characterized by elemental analysis, i.r. spectroscopy, magnetic measurements and X-ray crystallography. The Ln(3+) and Cu2+ ions are connected by the carboxylate groups of the ligands, resulting in the formation of a complicated network.

Ab initio study of C-9 and LaC9+ clusters

The energies and geometries of C-9 and LaC9+ clusters were calculated at HF, MP2 and DFT levels. For C-9, all theoretical levels show that the linear chain is the most stable structure. For LaC9+, two isomers were considered. In the first case La has two single bonds (A), while it forms a double bond in the second (B). Our results showed that in HF calculation, B is marginally more stable than A, while for MP2 and DFT, A is favored. Our results also revealed that there is not enough space for C-9 ring to accommodate lanthanum. Our conclusion agrees well with experiment.

The exciplex as an intermediate for photocycloaddition of 9-vinyl anthracene and p-N, N-dimethylamino styrene

The appearence of the new fluorescence peak at about 570 nm demonstrates exciplex formation between the singlet states of 9-vinyl anthracene and p-N, N-dimethylamino stytene. With increasing the polarity of solvents t the red-shift of the emission wavelength occurs and the fluorescence quantum yield of the exciplex decreases. For example t the fluorescence peak is at 550 nm in totuene and at 595 nm in butanone. The fluorescence quatum yields in totuene and in butanone are 0.053 and O respectively. Both the relative yield of the photocycloaddition dimer and the ratio of the relative yields of the trans and cis dimers decrease with increasing the polarity of solvents. For example, the relative yields of the dimer are 1.0 in totuene and 0.04 in butanone respectively. The ratio of the relative yields of traits and cis dimers are 0.54 and 0 in totuene and butanones t respectively. In addition, the exciplex intermediate mechanism was suggested for the photocycloaddition between 9-vinyl anthracene and 9-N, N-dimethylamino styrene.

SEMICONDUCTOR TO METAL TRANSITION IN LN(2)MO(3)O(9) COMPOUNDS

Ln(2)Mo(3)O(12) and Ce2Mo3O12.25 are reduced by hydrogen yielding Mo4+ oxides of the formula Ln(2)Mo(3)O(9) (Ln = La, Ce, Pr, Nd, Sm, Gd and Dy). The new compound Ce2Mo3O9 has the same structure as other Ln(2)Mo(3)O(9) compounds. All of the products are single phase materials and crystallize in a tetragonal scheelite type structure with Mo2O6 clusters. The IR spectra of the Ln(2)Mo(3)O(9) oxides show two absorption bands. These compounds are black n-type semiconductors, and exhibit Curie-Weiss Law behavior from 100K to 250K. Temperature dependence of the electrical properties of these compounds were measured for the first time, and a semiconductor-metal transition was found at about 250 degrees C.

CRYSTAL-STRUCTURES AND MOSSBAUER-SPECTRA OF LAFE1-XMNXO3 AND LAFE1-XCOXO3 (X=0 TO 0.9)

The crystal structures and Mossbauer spectra of various mixed oxides LaFe1-xMnxO3 and LaFe1-xCoxO3 (x = 0 to 0.9) are determined and measured at room temperature. The results indicate that the crystal structure of both the La-Fe-Mn-O and the La-Fe-Co-O sy

THE CLEAVAGE REACTION OF THE MO-MO TRIPLE BOND - THE CRYSTAL-STRUCTURES OF MOLYBDENUM COMPLEXES [CPMO(CO)(2)(C(5)H(4)NS)], [CPMO(CO)(2)(C(9)H(6)NS)]O=PPH(3) AND [CPMO(CO)(2)(S(2)CNME(2)]

The reactions of [Cp2Mo2(CO)4] (1) with 2,2'-dipyridyl disulphide (C5H4NS-)2, 8,8'-diquinolyl disulphide (C9H6NS-)2 and tetramethyl thiuram disulphide (Me2NC(S)S-)2 in toluene solution resulted in the cleavage of the Mo-Mo triple bond to yield molybdenum complexes [CpMo(CO)2(C5H4NS)] (2), [CpMo(CO)2(C9H6NS)] (3) and [CpMo(CO)2(S2CNMe2)] (4), respectively. The molecular structures of 2, 3 . O=PPh3 and 4 were determined by X-ray diffraction studies. Crystals of 2 are monoclinic, space group P2(1)/n, with Z = 4, in a unit cell of dimensions a = 6.448(1), b = 12.616(2), c = 14.772(2) angstrom, beta = 92.85(1)-degrees. The structure was refined to R = 0.028 and R(w) = 0.039 for 1357 observed reflections. Crystals of 3 . O=PPh3 are triclinic, space group P1BAR, with Z = 2, in a unit cell of dimensions a = 11.351(3), b = 13.409(3), c = 9.895(2) angstrom, alpha = 94.59(2), beta = 90.35(2), gamma = 78.07(2)-degrees. The structure was refined to R = 0.033 and R(w) = 0.037 for 3260 observed reflections. Crystals of 4 are monoclinic, space group P2(1)/a and Z = 4 with a = 12.468(5), b = 7.637(2), c = 13.135(4) angstrom, beta = 96.62(3). The structure was refined to R = 0.032 and R(w) = 0.042 for 1698 observed reflections. Each of complexes 2-4 contains a cyclopentadienyl ligand, a cis pair of carbonyls and a chelate ligand (S,N donor or S,S donor). All the compounds have distorted square-pyramid structures.

SYNTHESIS OF A NEW TYPE OF CH3CN-COORDINATED LANTHANIDE COMPOUNDS LN(CH3CN)9(ALCL4)3CH3CN

Acetonitrile is a weakly donating ligand. The cationic compounds of CH_3CN-coordinated transition metal are versatile homogeneous catalysts for the polymerization and isomerization of olefins and cycloolefins. The cationic compound of lanthanide[Eu(CH_3·CN)_3(BF_4)_3]_n was prepared from the oxidation of Eu with NOBF_4 in CH_3CN by Thomas in 1986. It was found that [Eu(CH_3CN)_3(BF_4)_3]_n can catalyze the polymerization of styrene cyclohexadiene and other olefins. However, there is no information about...