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PubMed2002

SrInGe and EuInGe: new Zintl phases with an unusual anionic network derived from the ThSi(2) structure.

Two new isostructural Zintl phases, EuInGe and SrInGe, are obtained from high-temperature reactions of the pure elements in welded Ta tubes. Both ternary phases crystallize in a new structure type in space group Pnma (No. 62), with a = 4.921(1) A, b = 3.9865(9) A, and c = 16.004(3) A for EuInGe; and a = 5.021(1) A, b = 4.0455(9) A, and c = 16.188(4) A for SrInGe. The crystal structures established by single-crystal X-ray diffraction feature zigzag chains of 3-bonded Ge atoms and puckered layers of 4-bonded In atoms. The two structural units are linked into an anionic network with channels composed of 5-membered and 7-membered rings. The channels are filled by the respective divalent cations. The chemical bonding of the anionic [InGe](2)(-) network, derived from a one-electron oxidative distortion of the alpha-ThSi(2) structure, is explained using extended-Hückel band structure calculations. Magnetic measurements indicate that EuInGe exhibits Curie-Weiss paramagnetic behavior above 35 K and antiferromagnetic behavior below 35 K. The calculated effective moment, mu(eff) = 8.11 mu(B), of EuInGe and the diamagnetic behavior of SrInGe are consistent with the oxidation states of Eu(II) and Sr(II), respectively.

Journal Article↗
PubMed2002

Polyatomic clusters of the triel elements. Palladium-centered clusters of thallium in A(8)Tl(11)Pd, A = Cs, Rb, K.

Reactions of the elements within welded Ta containers at approximately 600 degrees C followed by slow cooling give new A(8)Tl(11)Pd(x) products from an apparently continuous encapsulation of Pd atoms into the pentacapped trigonal prismatic anions in the isotypic rhombohedral (R3 macro c) A(8)Tl(11) phases. All systems also produce other phases at x < 1 as well, the simplest being the cesium system in which only trigonal Pd(13)Tl(9) is also formed. Cs(8)Tl(11)Pd(0.84(1)) was characterized by single-crystal means as close to the upper x limit in that system (R3 macro c, Z = 6, a = 10.610(1) A, c = 54.683(8) A). The Pd insertion causes an expansion of the D(3) host anion, particularly about the waist, to generate a trigonal bipyramidal PdTl(5) unit (d(Pd-Tl) approximately 2.6-2.8 A) centered within a somewhat larger Tl(6) trigonal prism, the remainder of the Tl(11) cluster. Strong Tl cage bonding is retained. Extended Hückel calculations show significant involvement of all Tl 6s, 6p and Pd 4d, 5s, 5p orbital sets in the central and cage bonding. The last valence electron is considered to be delocalized in a conduction band, as in A(8)Tr(11) examples, rather than occupying an antibonding e'' LUMO across a gap of approximately 2.4 eV.

Journal Article↗
PubMed2002

KNa(3)In(9): a Zintl network phase built of layered indium icosahedra and zigzag chains. Synthesis, structure, bonding, and properties.

This phase was discovered following direct fusion of the elements in welded Nb tubes at 550 degrees C and equilibration at 300 degrees C for 1 week. Single-crystal X-ray diffraction analysis reveals that KNa(3)In(9) crystallizes in an orthorhombic system (Cmca, Z = 8, a = 9.960(1) A, b =16.564(2) A, c = 17.530(2) A, 23 degrees C). The structure contains a three-dimensional indium network built of layers of empty In(12) icosahedra that are each 12-bonded and interconnected by 4-bonded indium atoms that also form zigzag chains. All cations bridge between cluster faces or edges, and their mixed sizes appear critical to the stability of this particular structure, which does not occur in either binary system. Both empirical electron counting and EHTB band structure calculations on the macroanion indicate that the bonding in this structure is closed-shell, whereas resistivity and magnetic susceptibility measures show that the compound is a moderately poor metal.

Journal Article↗
PubMed2003

Large scale synthesis of dysprosium and neodymium diiodides.

DyI(2) and NdI(2), which may become useful reagents in organic synthesis, can be prepared in up to 50 g quantities in a few hours without using welded tantalum tubes or temperatures over 1000 degrees C by direct reaction of the metal and iodine.

Journal Article↗
PubMed2004

Synthesis and structure of Ca(18)Li(5)In(25.07): a novel intergrowth of Li-centered in(12) icosahedral clusters and electron-precise Zintl layers.

A new ternary polar intermetallic, Ca(18)Li(5)In(25.07), was obtained from high-temperature reactions of the elements in welded Nb tubes. Its crystal structure, established by single-crystal X-ray diffraction, was found to crystallize in the orthorhombic space group Cmmm (No. 65). Unit cell parameters are a = 9.9151(6) A, b = 26.432(2) A, and c = 10.2116(6) A; Z = 2. The structure of Ca(18)Li(5)In(25.07) features two distinct types of indium anionic layers. An "electron-deficient" layer is made up of Li-centered In(12) icosahedra that are interconnected by bridging planar In(4) units and In atoms. A second In(3)(5-) layer is an electron-precise Zintl layer formed by fused four-, five-, and six-membered rings of three- and four-bonded indium atoms. The two distinct layers are alternately stacked and linked into a complex three-dimensional network. Vacancies are observed to occur only at the In(12) icosahedral and the bridging indium units within the "electron-deficient" layers. Magnetic property measurements indicate that Ca(18)Li(5)In(25.07) exhibits temperature-independent paramagnetism consistent with metallic behavior. Band structure calculations were performed to elucidate the role of defects and vacancies in the electronic structure of the electron-deficient "metallic" Zintl phase.

Journal Article↗
PubMed2005

A5InPb8 (A = K, Rb): an apparent zintl phase with lead tetrahedra interbridged by mu6-In atoms.

Reaction of elemental In, Pb, and K, or Rb within welded Ta containers at 900 degrees C followed by subsequent annealing at 350 degrees C gives the new phases A5InPb8 (A = K, Rb). These crystallize in the trigonal space group R3m (No. 166, Z = 3) with cell dimensions of a = 6.8835(6) and 6.885(1) A and c = 37.591(5) and 37.64(2) A for K5InPb8 and Rb5InPb8, respectively. The structure contains clusters built of pairs of Pb4 tetrahedra that are interbridged by a mu6-In atom. The InPb8 units, which in the isolated case would behave as ideal 40-electron Wade's rule clusters, are weakly interlinked into sheets in the ab plane by long (3.5 A) intercluster Pb-Pb interactions. According to the EHTB calculations, these cause a broadening of the valence band and thus generate a number of new states at the Fermi level. Compound K5InPb8 is metallic (rho298 approximately 42 microohms cm, (delta rho/delta T)/rho approximately 1.4(2) x 10(-1) K(-1)) which is in agreement with the expectations according to calculations on the anion network.

Journal Article↗
PubMed2005

Ca6Cu2Sn7: novel 3D open framework with unusual Sn4 tetramers.

The new ternary polar intermetallic phase, Ca6Cu2Sn7, has been synthesized by the solid-state reaction of the stoichiometric mixture of the pure elements in welded Ta tubes at high temperature. Its structure was established by single-crystal X-ray diffraction studies. Ca6Cu2Sn7 crystallizes in the monoclinic space group C2/m (No. 12) with cell parameters of a=14.257(7), b=4.564(2), and c=12.376(7) A, beta=93.979(6) degrees, V=803.3(7) A3, and Z=2. The structure of Ca6Cu2Sn7 belongs to a new structure type and features a 3D anionic open-framework composed of [Cu2Sn3] layers interconnected by unusual Sn4 tetramers, forming large tunnels along the b axis which are composed of Cu4Sn12 16-membered rings. The calcium atoms are located in these large tunnels. Ca6Cu2Sn7 is metallic and exhibits temperature-independent paramagnetism.

Journal Article↗
PubMed2006

Syntheses, structure, and bonding of Rb14(Mg1-xInx)30. A nonstoichiometric phase with an unusual substitution in the anion framework.

The title compound Rb(14)(Mg(1-x)In(x))(30) (x = 0.79-0.88) has been obtained from high-temperature reactions of the elements in welded Ta tubes. There is no analogous binary compound without Mg. The crystal structure established by single-crystal X-ray diffraction means (space group P2m (No. 189), Z = 1 and a = b = 10.1593(3) Angstroms, c = 17.783(1) Angstroms for x = 0.851) features two distinct types of anionic layers: isolated pentacapped trigonal prismatic In(11)(7-) clusters and condensed [(Mg(x)In(1-x))(5)In(14)](7-) layers. The latter consists of analogous M(11) (M = Mg/In) fragments that share prismatic edges and are interbridged by trigonal M(3) units. The structure shows substantial differences from related A(15)Tl(27) (A = Rb, Cs) in which the cation A that centers a six-membered ring of Tl(11) fragments is replaced by M(3.) Both linear muffin-tin orbital and extended Hückel calculations are used to analyze the observed phase width and site preferences. We further utilize the results to rationalize the distortion of the M(11) fragment in the condensed layer and also to correlate with electrical properties. An isomorphous phase region (Rb(y)K(1-)(y))(14)(Mg(1-x)In(x))(30) (y = 0.52, 0.66 for x = 0.79) is also formed.

Journal Article↗
PubMed2006

Synthesis and structure of K3Mg20In14, a stuffed variant of the BaHg11 structure type with a magnesium-indium network.

The phase K3Mg20In14 was synthesized via high-temperature reactions of the elements in welded Ta tubes. The cubic crystal structure established by single-crystal X-ray diffraction means [space group Pm3m, Z = 1, a = 9.769(1) angstroms] features a 3D Mg-In network formed by K@Mg12In10 units plus cuboctahedral fillers, In@Mg12. This is the first example of a well-ordered stuffed BaHg11 structure (Pearson symbol cP37). On the basis of tight-binding linear muffin-tin orbital, atomic sphere approximation calculations, the electronic structure of the compound shows dominant Mg-In interactions and substantial participation of Mg in the overall network bonding. Both In-In and Mg-In bondings are effectively optimized at the Fermi level. The Fermi energy cuts through substantial densities of states, consistent with the measured metallic property.

Journal Article↗
PubMed1996

Synthesis, Structure, and Bonding of Two Lanthanum Indium Germanides with Novel Structures and Properties.

The new tetragonal phases La(3)In(4)Ge and La(3)InGe are obtained from high-temperature reactions of the elements in welded Ta followed by annealing. The structures of both were established by single-crystal X-ray diffraction in tetragonal space group I4/mcm (Z = 4 and 16, a = 8.5165(3) and 12.3083(2) Å, c = 11.9024(4) and 16.0776(4) Å, respectively). La(3)In(4)Ge contains layers or slabs of three-connected indium built of puckered 8-rings and 4-rings, or of squashed tetrahedra ("butterflies") interlinked at all vertices, and these are separated by layers of La and isolated Ge. The phase is deficient of being a Zintl phase by three electrons per formula unit and is better described in terms of an alternate optimized and delocalized bonding picture and an open-shell metallic behavior for the In slabs. The more complex La(3)InGe, isostructural with Gd(3)Ga(2), is also layered. This phase contains pairs of mixed-occupancy (0.75 In, 0.25 Ge) sites separated by 3.020 Å, as well as isolated In and Ge atoms. The former appear to be fully reduced closed-shell atoms (relative to the bonded Ga dimers in Gd(3)Ga(2)) that are held in somewhat close proximity by cation matrix effects. The compound appears to be semiconducting and thus is a classical Zintl phase, (La(+3))(3)In(-5)Ge(-4) in the simplest oxidation state notation. High Coulomb energies are presumably important for the nature of the bonding and the stabilities of both compounds.

Journal Article↗
PubMed1997

Intermetallic Hydrides as Zintl Phases: A(3)TtH(2) Compounds (A = Ca, Yb; Tt = Sn, Pb) and Their Structural Relationship to the Corresponding Oxides.

Shiny crystals of the isotypic title compounds are obtained in high yield from suitable proportions of AH(2), metal A, and Sn or Pb in welded Ta containers slowly cooled from 1100 degrees C. These were characterized by single-crystal X-ray diffraction for Ca(3)SnH(2) and Ca(3)PbH(2) (orthorhombic, Cmcm (No. 63), Z = 4, a = 8.866(1), 8.937(1) Å, b = 11.371(2), 11.470(2) Å, c = 5.220(1), 5.2551(7) Å, respectively). The structure contains distorted hcp layers of Ca(3)Tt between which hydrogen occupies all tetrahedral voids formed by Ca atoms. These tetrahedra share three edges to form double chains along the c axis that are separated by Tt atoms. Both calcium compounds are diamagnetic semiconductors, and the family can all be formulated in terms of oxidation states as Zintl phases (A(+2))(3)Tt(-4)(H(-))(2). Their structure may be derived from the hexagonal version of the cubic perovskitic Ca(3)SnO by distortions that split the octahedral site in the oxide into edge-sharing tetrahedral pairs.

Journal Article↗
PubMed2000

La48Br81Os8: isolated clusters in an unusual superstructure with significantly greater intercluster bonding.

Exploration of reactions in the La-Br-Z system for Z = Fe, Ru, and Os in welded Nb containers at 900-950 degrees C resulted in only the title phase. The La48Br81Os8 stoichiometry is very close to that of known triclinic Pr6Br10Os but with an approximately 32-times larger cell, 138 independent atoms, and completely different intercluster connectivities in a complex monoclinic superstructure (a = 33.076(5) A, b = 23.466(3) A, c = 23.537(2) A, beta = 110.701(4) degrees, P2(1)/c (No. 14), Z = 4, 23 degrees C). Tetragonally compressed, approximately 16 e- lanthanum octahedra centered by Os are heavily interbridged by Br, including Br(f-a) (f = face) and Br(i-a-a) functions, to increase coordination numbers about some Br (to 4) and La (to 6) and to give an average of 19.63 bonded Br/La6Os vs the usual 18. These result in a cell volume 10% less than for an equivalent (hypothetical) La6Br10Os and Br-Br contacts as short as 3.30 A. Increased polar La-Br interactions presumably drive these changes. Optimal atom sizes for this structure have been found so far only in this novel compound.

Journal Article↗
PubMed2003

Lead contamination in Portuguese red wines from the Douro region: from the vineyard to the final product.

To quantify lead contamination in wines and to try to identify major lead sources, two winemaking processes were followed during one annual cycle of wine production. Two vineyards from the Douro Portuguese region and two types of wine, one red table wine, which has been produced in a very modern winery, and one red fortified wine (similar to Port), which has been produced by a traditional vinification process, were selected for this study. Aerosols from the vineyards atmosphere, vineyard soil, vine leaves, grapes, and samples from the intermediary and final wine product were collected. Suitable pretreatments, namely, high-pressure microwave assisted digestion (soil, leaves, and grapes) and UV-irradiation (grape juices and samples from the different steps of the vinification processes), were used. The samples were analyzed in terms of lead total concentration and respective isotope ratios by using inductively coupled plasma mass spectrometry and atomic absorption spectrophotometry with electrothermal atomization. It was observed that the major sources of lead were in the vinification system, the more traditional one introducing more lead than the modern one. For the fortified wine, the lead concentration increased from 4.7 microg L(-1), in the grape juice, to 17.2 microg L(-1), in the final product, while for the table wine the increase was from 4.1 to 13.1 microg L(-)(1). Therefore, only about 1/4 (fortified wine) and 1/3 (table wine) of the lead total content of the final products came from soil and atmospheric deposition. Therefore, it is expected that marked reductions of the lead content in the wines would occur if the sources of lead were removed from the tubes and containers used in the vinification system, particularly by using welding alloys and small fittings free of lead. The lead levels in the vine leaves (global mean of 0.43 microg g(dry leave)(-1)) and grapes (global mean of 35 ng g(dry grape)(-1)) were similar in both vineyards.

Air↗
PubMed2005

Reversible transformations of gold nanoparticle morphology.

Herein is reported a metamorphosis taking place in a gold nanosized system. The observed phenomenon of shape and size transformations was found to be completely reversible. Unlike most procedures in the literature where shape and size control occur in the synthetic step by adding growth- and shape-controlling agents such as surfactants or polymers, in this system postsynthetic changes in shape and size can be carried out simply by changing the ratio of reactive, competing reagents, more specifically, alkylthiols versus tetralkylammonium salts. Interestingly, the transfer of gold metal occurs (large prismatic particles to small particles and vice versa) under the influence of reagents that do not cause such interactions with bulk gold. All intermediate steps of the morphology change were observed using HRTEM and electron diffraction. The processes of breaking down and "welding back" solid metal nanoparticles occur under mild conditions and are remarkable examples of the unique chemical properties of nanomaterials. The described process is expected to be relevant to other nanoscale systems where similar structural circumstances could occur.

Letter↗
PubMed2007

The SERS and TERS effects obtained by gold droplets on top of Si nanowires.

We show that hemispherical gold droplets on top of silicon nanowires when grown by the vapor-liquid-solid (VLS) mechanism, can produce a significant enhancement of Raman scattered signals. Signal enhancement for a few or even just single gold droplets is demonstrated by analyzing the enhanced Raman signature of malachite green molecules. For this experiment, trenches (approximately 800 nm wide) were etched in a silicon-on-insulator (SOI) wafer along <110> crystallographic directions that constitute sidewalls ({110} surfaces) suitable for the growth of silicon nanowires in <111> directions with the intention that the gold droplets on the silicon nanowires can meet somewhere in the trench when growth time is carefully selected. Another way to realize gold nanostructures in close vicinity is to attach a silicon nanowire with a gold droplet onto an atomic force microscopy (AFM) tip and to bring this tip toward another gold-coated AFM tip where malachite green molecules were deposited prior to the measurements. In both experiments, signal enhancement of characteristic Raman bands of malachite green molecules was observed. This indicates that silicon nanowires with gold droplets atop can act as efficient probes for tip-enhanced Raman spectroscopy (TERS). In our article, we show that a nanowire TERS probe can be fabricated by welding nanowires with gold droplets to AFM tips in a scanning electron microscope (SEM). TERS tips made from nanowires could improve the spatial resolution of Raman spectroscopy so that measurements on the nanometer scale are possible.

Gold↗
PubMed2005

Indium triflate-catalyzed vinylation of beta-ketoesters with acetylene gas.

[reaction: see text]. An In(OTf)(3)-catalyzed addition of a beta-ketoester to acetylene in the presence of molecular sieves produces a alpha-vinylated ketoester in good to excellent yield. The vinylation reaction proceeds without any loss of elements in starting molecules under solvent-free conditions and allows the use of welding-grade acetylene, providing a practical method for synthetic utilization of acetylene gas.

Journal Article↗
PubMed2001

Occupational risk factors, ultraviolet radiation, and ocular melanoma: a case-control study in France.

BACKGROUND: Ultraviolet radiation has been suspected as a possible cause of ocular melanoma. Because this association is controversial, we examine the role of occupational exposure to ultraviolet radiation on the occurrence of this rare cancer. MATERIAL AND METHODS: A population-based case-control study was conducted in 10 French administrative areas (départements). Cases were 50 patients with uveal melanoma diagnosed in 1995-1996. Controls were selected at random from electoral rolls, after stratification for age, gender, and area. Among 630 selected persons, 479 (76%) were interviewed. Data on personal characteristics, occupational history, and detailed information on each job held were obtained from face-to-face interviews using a standardized questionnaire. Estimates of occupational exposure to solar and artificial ultraviolet light were made using a job exposure matrix. RESULTS: Results show elevated risks of ocular melanoma for people with light eye color, light skin color, and for subjects with several eye burns. The analysis based on the job exposure matrix showed a significantly increased risk of ocular melanoma in occupational groups exposed to artificial ultraviolet radiation, but not in outdoor occupational groups exposed to sunlight. An elevated risk of ocular melanoma was seen among welders (odds ratio = 7.3; 95% confidence interval = 2.6-20.1 for men), and a dose-response relationship with job duration was observed. The study also showed increased risk of ocular melanoma among male cooks, and among female metal workers and material handling operators. CONCLUSION: Following the present study, the existence of an excess risk of ocular melanoma in welders may now be considered as established. Exposure to ultraviolet light is a likely causal agent, but a possible role of other exposures in the welding processes should not be overlooked.

Case-Control Studies↗
PubMed2001

Environmental risk factors for non-Hodgkin's lymphoma: a population-based case-control study in Languedoc-Roussillon, France.

OBJECTIVE: To investigate the occupational and environmental risk factors related to non-Hodgkin's lymphoma (NHL). METHODS: A case-control study was performed during the 1992-1996 period in Languedoc-Roussillon, southern France. Four hundred and forty-five cases of histologically diagnosed NHL were declared. One thousand and twenty-five randomly selected population controls were interviewed about their medical histories; occupational exposures, such as chemicals, pesticides, and electromagnetic radiation; and toxic habits. RESULTS: The following factors were independently and significantly related to NHL as a result of the multivariate analysis: a previous hematopoietic malignancy (ORa = 11.5, 95% CI 2.4-55.4), a history of hives (ORa = 1.7, 95% CI 1.2-2.2), benzene exposure > 810 days (ORa = 4.6, 95% CI 1.1-19.2), daily welding (ORa = 2.5, 95% CI 1.2-5.0), and activity of radio operator (ORa = 3.1, 95% CI 1.4-6.6). To be an agricultural professional seemed slightly related to NHL in reference to non-professionals (ORa = 1.5, 95% CI 1.0-2.1). All of these results have also been adjusted for age, gender, education level, and urban setting. CONCLUSIONS: As some of the reported associations were based on a very small proportion of exposed subjects, further investigations are necessary to confirm our results. However, the findings suggest that factors related to altered immune functions such as a history of hematopoietic malignancy, history of hives, occupational exposure to benzene, or being an agricultural professional might increase the risk of NHL. Currently, underlying mechanisms for these associations are still unclear, and further investigations focused on interactions between immunity alterations and different chemicals would be of great interest.

Adult↗

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