The role of the lone pair of electrons of Pb(II) in determining the coordination geometry is analyzed from crystallographic studies and ab initio molecular orbital optimizations. Of particular interest are factors that contribute to the disposition of ligands around the lead with geometries that are (1) holodirected, in which the bonds to ligand atoms are distributed throughout the surface of an encompassing globe, and (2) hemidirected, in which the bonds to ligand atoms are directed throughout only part of an encompassing globe, i.e., there is an identifiable void in the distribution of bonds to the ligands. The preferred coordination numbers for lead were found to be 4 for Pb(IV) and 4 and 6 for Pb(II). All Pb(IV) structures in the CSD have a holodirected coordination geometry. Pb(II) compounds are hemidirected for low coordination numbers (2−5) and holodirected for high coordination numbers (9, 10), but for intermediate coordination numbers (6−8), examples of either type of stereochemistry are found. A...

Lone Pair Functionality in Divalent Lead Compounds

This review article focuses on the sol-gel preparation of high temperature superconducting oxides wherein different classes of gel technologies were utilized. These involve: 1) the sol-gel route based upon hydrolysis-condensation of metal-alkoxides, 2) the gelation route based upon concentration of aqueous solutions involving metal-chelates, often called as “chelate gel” or “amorphous chelate” route, and 3) the organic polymeric gel route. This paper reviews the current status of these sol-gel processes, and illustrates the underlying chemistry involved in each sol-gel technology. It is demonstrated that the chemical homogeneity of the gel is often disturbed by the differences in the chemistries of the cations. Prior to gelation the starting precursor solution containing various forms of metal-complexes must be chemically modified to overcome this problem. Illustration of a variety of strategies for success in obtaining a homogeneous multicomponent gel with no precipitation is focal point of this review article.

Invited review “sol-gel” preparation of high temperature superconducting oxides

/pdf/rational-design-of-sequestering-agents-for-plutonium-and-4tqw2sjhps.pdf

Rational Design of Sequestering Agents for Plutonium and Other Actinides

Nanoscale functional materials such as luminescent materials (ZnS:Ag+, Cl–; LaPO4:Ce3+,Tb3+; Y2O3:Eu3+), color pigments (CoAl2O4; Cr2O3; ZnCo2O4; (Ti0.85Ni0.05Nb0.10)O2; α-Fe2O3; Cu(Fe,Cr)O4; TiO2), transparent conducting oxides (ZnO:In3+), and catalytically active oxides (CeO2; Mn3O4; V2O5) are prepared with the polyol method. All these materials are yielded as crystalline, spherical, and almost monodisperse particles, 30–200 nm in size. Characterization is carried out based on scanning electron microscopy (SEM), X-ray powder diffraction (XRD), optical spectroscopy, and conductance measurements. The preparation via the polyol method is singled out due to its broad and easy applicability. The resulting material properties are similar to or better than nanoscale materials prepared by other measures. Some materials and their properties, e.g., ZnS:Ag+,Cl– as a phosphor, ZnCo2O4 and Cu(Fe,Cr)O4 as pigments, and ZnO:In3+ as transparent conductive oxide, are presented for the first time at the nanoscale.

Polyol-Mediated Synthesis of Nanoscale Functional Materials†

Iridium(III)-based phosphorescent complexes have received considerable attention due to their possible applications in organic light-emitting diodes (OLEDs). [1] Tuning of emission colors over the entire visible spectra has been achieved by ingenious modification of the cyclometalated and/or ancillary ligands. [2] However, reports concerning the design and preparation of saturated blue or even near-UV phosphorescent materials are relatively rare. [3] Increasing the emission energy gap means that there is a gradual decrease in the admixture of the ligand-centered p ! p * and metal-to-ligand charge-transfer (MLCT) transition, [4] the net result of which is a reduction in the T 1 ! S 0 transition probability and hence a low emission quantum efficiency (QE). Moreover, increasing the emission gap to blue raises the likelihood that thermal population of the higher lying dd , [5] MLCT, [6] n p *, [7a] or even ligand-to-ligand charge-transfer states (LLCT) [8] could be invoked to account for the fast quenching at room temperature. It the are the a low turn-on voltage of around 4 a peak external quantum efficiency of up to 6.0% photons per a peak luminance efficiency of 6.3 cdA (cid:3) 1 , and a peak power efficiency of 4.0 lmW (cid:3) 1 . At the practical brightness of 100 cdm (cid:3) 2 , the external quantum efficiency, luminance efficiency, and power efficiency drop to about 2.7%, 3.0 cdA (cid:3) 1 , and 0.9 lmW (cid:3) 1 , respectively. These efficiency roll-offs are to be expected for phosphorescent OLEDs at higher current densities. the other well-known blue phosphorescent dopants (FIrpic, Fir6, [17] which CIE y (cid:6) 0.2 and CIE x + y (cid:6) 0.4. deep-blue

Highly Efficient Blue‐Emitting Iridium(III) Carbene Complexes and Phosphorescent OLEDs

The synthesis of Cp/sub 2/*Th(PPh/sub 2/)/sub 2/ (1), and the preparation (eq 1) of Cp/sub 2/*Th(..mu..-PPh/sub 2/)/sub 2/Ni(CO)/sub 2/ (2), Cp/sub 2/*Th(PPh/sub 2/)/sub 2/ + Ni(COD)/sub 2/ + 2CO ..-->.. Cp/sub 2/*Th(..mu..-PPh/sub 2/)/sub 2/Ni(CO)/sub 2/ + 2COD (1) the first phosphido-bridged heterobimetallic complex incorporating an actinide element have been reported. The X-ray structure of 2 revealed distorted tetrahedral environments about both metal centers, as well as two unexpected features: (1) acute Th-P-Ni angles which average 76.2 (4)/sup 0/ and (2) a short thorium-nickel separation of 3.206 (2) A. These data led to postulation of the existence of a direct, albeit weak, thorium-nickel interaction, one that could be formulated as a donor-acceptor bond from Ni(0) to the electron-deficient Th(IV) center. Because bonding interactions between actinides (An) and transition metals (M) were unprecedented in discrete complexes, additional experimental evidence was sought for donor-acceptor bonding in Cp/sub 2/*An(..mu..-PR/sub 2/)/sub 2/ML/sub n/ systems. Replacement of the Ni(CO)/sub 2/ fragment of 2 with an electron-rich transition-metal donor was a logical first step toward providing that evidence. Here the synthesis, properties and structure of a new thorium-platinum complex are described and some theoretical insight is provided on the nature of the Th-Pt bond contained therein. 30more » references, 2 figures.« less

Synthesis and x-ray structure of (C5Me5)2Th(.mu.-PPh2)2Pt(PMe3): a complex with a thorium-platinum bond

Isolation and structural characterization of the copper-barium-alkoxide cluster Ba2Cu2(OR)4(acac)4.2HOR (R = CH2CH2OCH3) from precursor solutions to yttrium barium copper oxide (YBa2Cu3O7) thin films

The purpose of this study was to identify and correlate the microstructural and luminescence properties of europium-doped Y 2 O 3 (Y 1-x Eu x ) 2 O 3 thin films deposited by metallorganic chemical vapor deposition (MOCVD), as a function of deposition time and temperature. The influence of deposition parameters on the crystallite size and microstructural morphology were examined, as well as the influence of these parameters on the photoluminescence emission spectra. (Y 1-x -Eu x ) 2 O 3 thin films were deposited onto (111) silicon and (001) sapphire substrates by MOCVD. The films were grown by reacting yttrium and europium tris(2,2,6,6-tetramethyl-3,5-heptanedionate) precursors with an oxygen atmosphere at low pressures (5 torr (1.7 x 10 3 Pa)) and low substrate temperatures (500°-700°C). The films deposited at 500°C were smooth and composed of nanocrystalline regions of cubic Y 2 O 3 , grown in a textured [100] or [110] orientation to the substrate surface. Films deposited at 600°C developed, with increasing deposition time, from a flat, nanocrystalline morphology into a platelike growth morphology with [111] orientation. Monoclinic (Y 1-x -Eu x ) 2 O 3 was observed in the photoluminescence emission spectra for all deposition temperatures. The increase in photoluminescence emission intensity with increasing postdeposition annealing temperature was attributed to the surface/grain boundary area-reduction effect.

Characterization of Photoluminescent (Y1–xEux)2O3 Thin Films Prepared by Metallorganic Chemical Vapor Deposition

Crystal and molecular structure of tricyclopentadienyltetrahydrofuranuranium (III), (η5-C5H5)3U•OC4H8

The synthesis of UCl/sub 3/(18-crown-6) is reported. /sup 1/HNMR studies are underway for the purpose of establishing the coordination of the uranium in the complex. Although the substance is insoluble in tetrahydrofuran, a dispersed solution will react with sodium borohydride to yield a soluble product, U(BH/sub 4/)/sub 3/(18-crown-6). Analytical data suggest that the stoichiometry of the complex is probably correct. The /sup 1/HNMR spectrum supports the formulation as a 1 : 1 adduct with an integration of BH/sub 4//sup -/ to crown ether protons of 1 : 2. The 12 BH/sub 4//sup -/ protons are equivalent on the NMR time scale, and are shifted downfield due to the paramagnetic U(III) center. The complex has been recrystallized from THF/ethyl ether solutions. Preliminary x-ray diffraction results establish a stoichiometry of U(BH/sub 4/)/sub 3/(18-crown-6), and show that the uranium is actually located inside the crown ether cavity for 2 of the 3 different U atoms in the unit cell.

Chemistry of trivalent uranium. 2. Synthesis of UCl/sub 3/(18-crown-6) and U(BH/sub 4/)/sub 3/(18-crown-6)

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