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PubMed2000

Electron impact and chemical ionisation mass spectrometry in the characterisation of organometallic silicon, germanium, tin and lead compounds

The electron impact and chemical ionisation mass spectra of a number of organometallic derivatives of silicon, germanium, tin and lead, incorporating inter alia 2-bis(trimethylsilyl)methylpyridyl or cyclopentadienyl ligands have been recorded. Representative spectra are presented and illustrate the utility of these mass spectrometric techniques in the characterisation of such compounds, particularly so in light of the highly informative nature arising from their fragmentation patterns and the numerous isotopes of the nuclei involved. Copyright 2000 John Wiley & Sons, Ltd.

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PubMed2001

Synthesis and characterization of germanium, tin, phosphorus, iron, and rhodium complexes of tris(pentafluorophenyl)corrole, and the utilization of the iron and rhodium corroles as cyclopropanation catalysts.

The germanium(IV), tin(IV). and phosphorus(v) complexes of tris(pentafluorophenyl)corrole were prepared and investigated by electrochemistry for elucidation of the electrochemical HOMO-LUMO gap of the corrole and the spectroscopic characteristics of the corrole pi radical cation. This information was found to be highly valuable for assigning the oxidation states in the various iron corroles that were prepared. Two iron corroles and the rhodium(I) complex of an N-substituted corrole were fully characterized by X-ray crystallography and all the transition metal corroles were examined as cyclopropanation catalysts. All iron (except the NO-ligated) and rhodium corroles are excellent catalysts for cyclopropanation of styrene, with the latter displaying superior selectivities. An investigation of the effect of the oxidation state of the metal and its ligands leads to the conclusion that for iron corroles the catalytically active form is iron(III), while all accesible oxidation states of rhodium are active.

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PubMed2007

Synthetic, structural, and theoretical investigations of alkali metal germanium hydrides--contact molecules and separated ions.

The preparation of a series of crown ether ligated alkali metal (M=K, Rb, Cs) germyl derivatives M(crown ether)nGeH3 through the hydrolysis of the respective tris(trimethylsilyl)germanides is reported. Depending on the alkali metal and the crown ether diameter, the hydrides display either contact molecules or separated ions in the solid state, providing a unique structural insight into the geometry of the obscure GeH3- ion. Germyl derivatives displaying M--Ge bonds in the solid state are of the general formula [M([18]crown-6)(thf)GeH3] with M=K (1) and M=Rb (4). The compounds display an unexpected geometry with two of the GeH3 hydrogen atoms closely approaching the metal center, resulting in a partially inverted structure. Interestingly, the lone pair at germanium is not pointed towards the alkali metal, rather two of the three hydrides are approaching the alkali metal center to display M--H interactions. Separated ions display alkali metal cations bound to two crown ethers in a sandwich-type arrangement and non-coordinated GeH3- ions to afford complexes of the type [M(crown ether)2][GeH3] with M=K, crown ether=[15]crown-5 (2); M=K, crown ether=[12]crown-4 (3); and M=Cs, crown ether=[18]crown-6 (5). The highly reactive germyl derivatives were characterized by using X-ray crystallography, 1H and 13C NMR, and IR spectroscopy. Density functional theory (DFT) and second-order Møller-Plesset perturbation theory (MP2) calculations were performed to analyze the geometry of the GeH3- ion in the contact molecules 1 and 4.

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PubMed2002

Molecules for materials: germanium hydride neutrals and anions. Molecular structures, electron affinities, and thermochemistry of GeHn/GeHn- (n = 0-4) and Ge2Hn/Ge2Hn(-) (n = 0-6).

The GeH(n) (n = 0-4) and Ge(2)H(n) (n = 0-6) systems have been studied systematically by five different density functional methods. The basis sets employed are of double-zeta plus polarization quality with additional s- and p-type diffuse functions, labeled DZP++. For each compound plausible energetically low-lying structures were optimized. The methods used have been calibrated against a comprehensive tabulation of experimental electron affinities (Chemical Reviews 102, 231, 2002). The geometries predicted in this work include yet unknown anionic species, such as Ge(2)H(-), Ge(2)H(2)(-), Ge(2)H(3)(-), Ge(2)H(4)(-), and Ge(2)H(5)(-). In general, the BHLYP method predicts the geometries closest to the few available experimental structures. A number of structures rather different from the analogous well-characterized hydrocarbon radicals and anions are predicted. For example, a vinylidene-like GeGeH(2) (-) structure is the global minimum of Ge(2)H(2) (-). For neutral Ge(2)H(4), a methylcarbene-like HGë-GeH(3) is neally degenerate with the trans-bent H(2)Ge=GeH(2) structure. For the Ge(2)H(4) (-) anion, the methylcarbene-like system is the global minimum. The three different neutral-anion energy differences reported in this research are: the adiabatic electron affinity (EA(ad)), the vertical electron affinity (EA(vert)), and the vertical detachment energy (VDE). For this family of molecules the B3LYP method appears to predict the most reliable electron affinities. The adiabatic electron affinities after the ZPVE correction are predicted to be 2.02 (Ge(2)), 2.05 (Ge(2)H), 1.25 (Ge(2)H(2)), 2.09 (Ge(2)H(3)), 1.71 (Ge(2)H(4)), 2.17 (Ge(2)H(5)), and -0.02 (Ge(2)H(6)) eV. We also reported the dissociation energies for the GeH(n) (n = 1-4) and Ge(2)H(n) (n = 1-6) systems, as well as those for their anionic counterparts. Our theoretical predictions provide strong motivation for the further experimental study of these important germanium hydrides.

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PubMed1994

A new 99mTc-complex with a germanium-hydrazide (GeTH) ligand.

A new tetrahydrazido-germanium (GeTH) ligand was synthesized, characterized and complexed with 99mTc. The negatively charged 99mTc-chelate was shown to form in high yields at neutral pH in the absence of other reducing agents and exhibits high in vitro and in vivo stability.

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PubMedDate not supplied

Extension of the efficiency calibration of germanium detectors using the GESPECOR software.

To avoid losses due to coincidence summing, the efficiency calibration of gamma-spectrometers is often carried out by means of radionuclides emitting only one photon during a single decay. Calibration with this kind of radionuclides has, however the disadvantage that the energy range of the gamma rays (46 keV<E<1115 keV) is limited. Coincidence-summing corrections can be calculated with the Monte Carlo program Germanium Spectrometry Correction for multi gamma radionuclides which emit photons with energies above this range. The efficiency curve as a function of energy can therefore be extended up to 2.7 MeV with uncertainties below 4%.

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PubMedDate not supplied

Monte Carlo simulation of the response of a germanium detector for low-level spectrometry measurements using GEANT4.

In this paper, we will expose the work performed for the adaptation and refinement of the GEANT4 simulation toolkit (originally designed for Monte Carlo simulations in High-Energy Physics) in order to simulate Ge detectors in low-level gamma spectrometry. Special emphasis will be given to show and validate our own algorithms implemented in GEANT4 code for variance reduction and data analysis, that have been used for a quicker and precise efficiency calibration at different source-detector configurations of one of the low-level germanium gamma systems available in our laboratory.

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PubMed2005

n-Heptyl xanthate adsorption on a ZnS layer synthesized on germanium: an in situ attenuated total reflection IR study.

Adsorption of n-heptyl xanthate on synthesized zinc sulfide was followed in situ by monitoring the methylene absorption band at 2925 cm(-1). The zinc sulfide surface used in the adsorption experiments was synthesized on a germanium internal reflection element using the chemical bath deposition method. Characterization of the adsorbent surface was performed by X-ray photoelectron spectroscopy. The time needed to reach adsorption equilibrium varied with the initial concentration of the aqueous potassium heptyl xanthate solution. The amount of adsorbed xanthate ions increased with the concentration of the solution within the range studied (10 microM-50 mM). The experimental data are reasonably well described by the Langmuir adsorption isotherm. Polarized infrared attenuated total reflection (ATR) was used to determine the average orientation of the heptyl chains by measuring the absorbance of the infrared beam polarized perpendicularly and parallely to the plane of incidence. Measured absorbances were corrected for contribution from heptyl xanthate in bulk solution.

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PubMed2000

Low level gamma-ray germanium-spectrometer to measure very low primordial radionuclide concentrations

A new germanium spectrometer especially suited for large sample measurements is described in detail. It is operated in the Gran Sasso underground laboratory under shielding rock of 3300 m water equivalent, which reduces the muon flux by six orders of magnitude. The integral background counting rate in the energy range from 50 to 2750 keV is about 0.15 min(-1). The low peak count rates of mostly less than 1 count per day together with a relative efficiency of 102% and the high sample capacity makes this spectrometer one of the most sensitive worldwide. Some sample measurements for the solar neutrino experiment BOREXINO and the detector efficiency calibration by the Monte Carlo method are discussed as well.

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PubMed1998

Ostwald Ripening of Self-Assembled Germanium Islands on Silicon(100).

: We describe here real-time, in situ observations of the formation of nanosize germanium (Ge) islands on silicon (Si). The deposition of Ge onto electron-transparent Si(100) takes place in a UHV transmission electron microscope that has been modified to allow chemical vapor deposition to be carried out in the polepiece. We recorded the growth process at video rate and were therefore able to follow the evolution of individual islands. As the islands grew, we observed a coarsening process similar to classical Ostwald ripening, but which leads at certain times to a bimodal distribution of island sizes. We show that this phenomenon can be understood using a model in which a conventional coarsening process is modified by a transition between two different island shapes.

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PubMed2000

Adduct formation or metathesis reactions of silver complexes containing the fluorinated ligands [HB(3,5-(CF3)2Pz)3]- and [CF3SO3]-: formation of silver adducts containing unsupported silver-germanium bonds.

A mixture of [HB(3,5-(CF3)2Pz)3]Ag(eta 2-toluene) and [(Me)2ATI]GeCl in CH2Cl2, rather than undergoing metathesis, formed a 1:1 adduct [HB(3,5-(CF3)2Pz)3]Ag<--GeCl[(Me)2ATI] (1, where [HB(3,5-(CF3)2Pz)3] = hydrotris(3,5-bis(trifluoromethyl)pyrazolyl)borate and [(Me)2ATI] = N-methyl-2-(methylamino)troponiminate) featuring a silver-germanium bond. Solutions of 1 (in CH2Cl2 or toluene) did not precipitate AgCl even after several days. However, it easily underwent metathesis with CF3SO3Ag, leading to the chloride-free product [HB(3,5-(CF3)2Pz)3]Ag<--Ge(OSO2CF3)[(Me)2ATI] (2). Compounds 1 and 2 were characterized by X-ray crystallography. The Ag-Ge bond distances of 1 and 2 are 2.4215(9) and 2.4116(10) A, respectively.

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PubMed2003

Germanium-rich pentaruthenium carbonyl clusters including Ru(5)(CO)(11)(mu-GePh(2))(4)(mu(5)-C) and its reactions with hydrogen.

The reaction of Ru(5)(CO)(15)(mu(5)-C), 1, with Ph(3)GeH at 150 degrees C has yielded two new germanium-rich pentaruthenium cluster complexes: Ru(5)(CO)(11)(mu-CO)(mu-GePh(2))(3)(mu(5)-C), 2; Ru(5)(CO)(11)(mu;-GePh(2))(4)(mu(5)-C), 3. Both compounds contain square pyramidal Ru(5) clusters with GePh(2) groups bridging three and four of the edges of the Ru(5) square base, respectively. When treated with 1 equiv of Ph(3)GeH at 150 degrees C compound 2 is converted to 3. Reaction of 3 with H(2) at 150 degrees C yielded Ru(5)(CO)(10)(mu-GePh(2))(4)(mu(5)-C)(mu-H)(2), 4, containing two hydride ligands and one less CO ligand. Reaction of 4 with hydrogen at 150 degrees C yielded the compound Ru(5)(CO)(10)(mu-GePh(2))(2)(mu(3)-GePh)(2)(mu(3)-H)(mu(4)-CH), 5, by loss of benzene and conversion of two of the bridging GePh(2) groups into triply bridging GePh groups. Compound 5 contains one triply bridging hydride ligand and a quadruply bridging methylidyne ligand formed by addition of one hydrogen atom to the carbido carbon atom.

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PubMed2002

Dianionic complexes with hexacoordinate silicon(IV) or germanium(IV) and three bidentate ligands of the hydroximato(2-) type: syntheses and structural characterization in the solid state.

Reaction of Si(OMe)(4) with acetohydroxamic acid or benzohydroxamic acid and HNMe(2) (molar ratio 1:3:2) in MeCN yielded dimethylammonium fac-tris[acetohydroximato(2-)]silicate (fac-5) and N,N-dimethylacetamidinium fac-tris[benzohydroximato(2-)]silicate (fac-8), respectively. Reaction of Si(OMe)(4) with benzohydroxamic acid and HNMe(2) (molar ratio 1:3:2) or ethane-1,2-diamine (molar ratio 1:3:1) in MeOH gave dimethylammonium fac-tris[benzohydroximato(2-)]silicate-methanol (fac-6.MeOH) and ethane-1,2-diammonium mer-tris[benzohydroximato(2-)]silicate-dimethanol (mer-9.2MeOH), respectively. Reaction of Ge(OMe)(4) with benzohydroxamic acid and HNMe(2) (molar ratio 1:3:2) in MeOH resulted in the formation of dimethylammonium fac-tris[benzohydroximato(2-)]germanate-methanol (fac-7.MeOH). Single-crystal X-ray diffraction studies showed that the Si(Ge)-coordination polyhedra of the racemic hexacoordinate silicon (germanium) compounds fac-5, fac-6.MeOH, fac-7.MeOH, fac-8, and mer-9.2MeOH are distorted octahedra. All compounds were additionally characterized by solid-state VACP/MAS NMR studies ((13)C, (15)N, (29)Si). The structural investigations were complemented by computational studies of the dianions of fac-5 and mer-5.

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PubMed2003

Density functional theory study of nine-atom germanium clusters: effect of electron count on cluster geometry.

Density functional theory (DFT) at the hybrid B3LYP level has been applied to the germanium clusters Ge(9)(z) clusters (z = -6, -4, -3, -2, 0, +2, and +4) starting from three different initial configurations. Double-zeta quality LANL2DZ basis functions extended by adding one set of polarization (d) and one set of diffuse (p) functions were used. The global minimum for Ge(9)(2)(-) is the tricapped trigonal prism expected by Wade's rules for a 2n + 2 skeletal electron structure. An elongated tricapped trigonal prism is the global minimum for Ge(9)(4)(-) similar to the experimentally found structure for the isoelectronic Bi(9)(5+). However, the capped square antiprism predicted by Wade's rules for a 2n + 4 skeletal electron structure is only 0.21 kcal/mol above this global minimum indicating that these two nine-vertex polyhedra have very similar energies in this system. Tricapped trigonal prismatic structures are found for both singlet and triplet Ge(9)(6)(-), with the latter being lower in energy by 3.66 kcal/mol and far less distorted. The global minimum for the hypoelectronic Ge(9) is a bicapped pentagonal bipyramid. However, a second structure for Ge(9) only 4.54 kcal/mol above this global minimum is the C(2)(v)() flattened tricapped trigonal prism structure found experimentally for the isoelectronic Tl(9)(9)(-). For the even more hypoelectronic Ge(9)(2+), the lowest energy structure consists of an octahedron fused to two trigonal bipyramids. For Ge(9)(4+), the global minimum is an oblate (squashed) pentagonal bipyramid with two pendant Ge vertices.

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PubMed2003

[Ge9=Ge9=Ge9=Ge9]8-: a linear tetramer of nine-atom germanium clusters, a nanorod.

A tetramer of nine-atom deltahedral germanium clusters and charge 8-, [Ge9=Ge9=Ge9=Ge9]8- , has been characterized as a (Rb-18C6)(+) salt (18C6 = 18-crown-6 polyether). The clusters are connected by pairs of parallel bonds, and the electrons are delocalized over the whole anion. The size of the tetramer is of nanorod dimensions, ca. 2 nm.

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PubMed2005

Density functional theory study of 11-atom germanium clusters: effect of electron count on cluster geometry.

Density functional theory (DFT) at the hybrid B3LYP level has been applied to the germanium clusters Ge(11)(z) (z = -6, -4, -2, 0, +2, +4, +6) starting from eight different initial configurations. The global minimum within the Ge(11)(2-) set is an elongated pentacapped trigonal prism distorted from D(3)(h) to C(2v) symmetry. However, the much more spherical edge-coalesced icosahedron, also of C(2v) symmetry, expected by the Wade-Mingos rules for a 2n + 2 skeletal electron system and found experimentally in B(11)H(11)(2-) and isoelectronic carboranes, is of only slightly higher energy (+5.2 kcal/mol). Even more elongated D(3)(h) pentacapped trigonal prisms are the global minima for the electron-rich structures Ge(11)(4-) and Ge(11)(6-). For Ge(11)(4-) the C(5v) 5-capped pentagonal antiprism analogous to the dicarbollide ligand C(2)B(9)H(11)(2-) is of significantly higher energy (approximately 28 kcal/mol) than the D(3h) global minimum. The C(2v) edge-coalesced icosahedron is also the global minimum for the electron-poor Ge(11) similar to its occurrence in experimentally known 11-vertex "isocloso" metallaboranes of the type (eta(6)-arene)RuB(10)H(10). The lowest energy polyhedral structures computed for the more hypoelectronic Ge(11)(4+) and Ge(11)(6+) clusters are very similar to those found experimentally for the isoelectronic ions E(11)(7-) (E = Ga, In, Tl) and Tl(9)Au(2)(9-) in intermetallics in the case of Ge(11)(4+) and Ge(11)(6+), respectively. These DFT studies predict an interesting D(5h) centered pentagonal prismatic structure for Ge(11)(2+) and isoelectronic metal clusters.

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PubMed2005

Synthesis, structure, and thermal properties of soluble hydrazinium germanium(IV) and tin(IV) selenide salts.

The crystal structures of two hydrazinium-based germanium(IV) and tin(IV) selenide salts are determined. (N(2)H(5))(4)Ge(2)Se(6) (1) [I4(1)cd, a = 12.708(1) Angstroms, c = 21.955(2) Angstroms, Z = 8] and (N(2)H(4))(3)(N(2)H(5))(4)Sn(2)Se(6) (2) [P, a = 6.6475(6) Angstroms, b = 9.5474(9) Angstroms, c = 9.8830(10) Angstroms, alpha = 94.110(2) degrees, beta = 99.429(2) degrees, gamma = 104.141(2) degrees, Z = 1] each consist of anionic dimers of edge-sharing metal selenide tetrahedra, M(2)Se(6)(4-) (M = Ge or Sn), separated by hydrazinium cations and, for 2, additional neutral hydrazine molecules. Substantial hydrogen bonding exists among the hydrazine/hydrazinium molecules as well as between the hydrazinium cations and the selenide anions. Whereas the previously reported tin(IV) sulfide system, (N(2)H(5))(4)Sn(2)S(6), decomposes cleanly to microcrystalline SnS(2) when heated to 200 degrees C in an inert atmosphere, higher temperatures (>300 degrees C) are required to dissociate selenium from 1 and 2 for the analogous preparations of single-phase metal selenides. The metal chalcogenide salts are highly soluble in hydrazine, as well as in a variety of amines and DMSO, highlighting the potential usefulness of these compounds as precursors for the solution deposition of the corresponding metal chalcogenide films.

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PubMed2005

OH functionality of germanium(II) compounds for the formation of heterobimetallic oxides.

Two novel germanium(II) mu-oxo heterobimetallic oxides with different oxidation states at the metal centers have been reported. The reaction of LGeOH [L = N(Ar)C(Me)CHC(Me)N(Ar) (Ar = 2,6-i-Pr(2)C(6)H(3))] with Cp(2)MMe(2) (M = Zr, Hf) in Et(2)O afforded LGeOM(Me)Cp(2) [M = Zr (2), Hf (3)] in moderate yield. Compounds 2 and 3 were characterized by elemental analysis, IR, NMR, EI-MS, and single X-ray structural analysis. Compounds 2 and 3 crystallized in the space group P, and the geometry at the metal centers is tetrahedral. The Ge-O bond lengths of 2 and 3 are very similar (1.797(2) and 1.799(3) Angstroms, respectively), and a bent M-O-M' angle in 2 (143.8(1) degrees) and 3 (141.9(2) degrees) features both oxide systems. Different orientations of the Cp and Me groups of the metal centers were observed, and deviations of the Cp groups were exhibited.

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