Search results for "Bond length"
showing 10 items of 209 documents
When Does Gold Behave as a Halogen? Predicted Uranium Tetraauride and Other MAu4 Tetrahedral Species, (M = Ti, Zr, Hf, Th)
2003
Quantum chemical calculations suggest that a series of molecules with the general formula MAu4 are stable, where M = U, Th, and a group-4 atom. They correspond to Au in the formal valence state -1 and indicate that gold can act as a ligand similar to the halogen series. Of the MAu4 species studied, UAu4, the first predicted mixed gold uranium compound, has a short M-Au bond distance, 2.71 A, which would locate Au between Br and I from the bond length point of view in the U-tetrahalide series. Energetically, the U-Au bond is weaker than the corresponding U-Br and U-I bonds.
Beyond ideal two-dimensional metals: Edges, vacancies, and polarizabilities
2018
Recent experimental discoveries of graphene-stabilized patches of two-dimensional (2D) metals have motivated also their computational studies. However, so far the studies have been restricted to ideal and infinite 2D metallic monolayers, which is insufficient because in reality the properties of such metallic patches are governed by microstructures pervaded by edges, defects, and several types of perturbations. Here we use density-functional theory to calculate edge and vacancy formation energies of hexagonal and square lattices of 45 elemental 2D metals. We find that the edge and vacancy formation energies are strongly correlated and decrease with increasing Wigner-Seitz radii, analogously…
Investigation of the local structure of As-related acceptor centres in InSe by means of fluorescence-detected XAS
2002
In this paper we report on fluorescence-detected XAS measurements in arsenic-doped p-type indium selenide. Absorption spectra taken at the arsenic K-edge allow for an unambiguous determination of the bond length of the As atoms with their first neighbours that turns out to be 2.56 ± 0.02 A. The XANES spectrum and the bond length (as determined from EXAFS oscillations) exhibit weak anisotropy as the angle between the crystal c-axis and the x-ray polarization vector is changed. These results are fully compatible with the model of a single substitutional acceptor (As in Se site), with no bonds along the c-axis (that would give rise to strong linear dicroism in the XANES spectrum). The In–As bo…
XRD and XAS structural study of CuAlO2under high pressure
2013
International audience; We present the results of x-ray diffraction and x-ray absorption spectroscopy experiments in CuAlO2 under high pressure. We discuss the polarization dependence of the x-ray absorption near-edge structure at the Cu K-edge. XRD under high pressure evidences anisotropic compression, the a-axis being more compressible than the c-axis. EXAFS yields the copper-oxygen bond length, from which the only internal parameter of the delafossite structure is deduced. The combination of anisotropic compression and the internal parameter decrease results in a regularization of the AlO6 octahedra. The anisotropic compression is related to the chemical trends observed in the lattice pa…
Preparation and XAFS studies of organotin(IV) complexes with adenosine and related compounds and calf thymus DNA
2007
Complexes of adenosine and related compounds (adenosine-5’-monophosphate, adenosine-5’-triphosphate and pyridoxal-5-phosphate) with Bu2SnO and/or BuSnCl2 were prepared in the solid state. The compositions of the complexes were determined by standard analytical methods. It was found that the complexes contain the organotin(IV) moiety and the ligand in a ratio of 1:1. The FT-IR spectra demonstrated that Bu2SnO reacts with the D-ribose moiety of the ligands, while Bu2SnCl2 is coordinated to the deprotonated phosphate group. The basic part of the ligands does not participate directly in complex formation. Comparison of the experimental Mossbauer Δ (quadrupole splitting) values with those calcul…
Lattice dynamics of superconducting zirconium and hafnium nitride halides
2003
We have performed a study of the Raman active modes of β-HfNCl, β-ZrNCl, and β-ZrNBr and Na-doped β-HfNCl in various scattering configurations. The experimental values are compared with a lattice dynamical calculation andassigned to definite atomic motions. The variation of the atomic force constants are analyzed as a function of the bond length, relating their relative strength with the atomic characteristics of the compound.
Über gemischte bindungen in der IV. hauptgruppe
1987
Abstract Reaction of Ph3SnLi with Ph2SiCl2 or Ph2GeCl2 at −78°C in THF yields (Ph3Sn)2SiPh2 (1) and (Ph3Sn)2GePh2 (2). The crystal structure of 1 (R = 0.075) exhibits SnSi distances of 257.2(4) and 257.9(5) pm, an SnSiSn angle of 118.5(2)°, and a central C3SnSiC2SnC3 molecular skeleton with symmetry close to C2. The geminal NMR coupling 2J(119Sn ⋯ 119Sn) in 1, and in a tri-, tetra- and pentastannane series shows a linear correlation to their respective non-bonded d(Sn ⋯ Sn) distances (I(t-Bu2Sn)4I: 20 Hz/496 pm; 1: 724 Hz/443 pm).
CFRP sheets bonded to natural stone: interfacial phenomena
2004
The effectiveness of the reinforcing technique consisting of fiber reinforced polymer sheets bonded to the structural elements depends on a good connection at the joint. This has to be able to ensure the transfer length of the shear stress in order to avoid a premature failure due to debonding. In this paper, the bond phenomenon at the interface is examined with reference to the calcarenite stone and carbon fiber reinforced polymer (CFRP) sheets in order to evaluate the possibility of utilizing this technique on masonry structural members, consisting of calcarenite ashlars and mortar. An experimental investigation is carried out on nine specimens obtained by applying unidirectional CFRP she…
Synthesis, characterisation, and molecular and electronic structure of CpMoCl2(R1C≡CR2) (R1, R2 = Ph, Et, Me): a new class of half-sandwich 17-electr…
2000
International audience; Addition of alkyne to [CpMoCl2]2 affords compounds CpMoCl2(η2-alkyne) (alkyne = EtC[triple bond, length as m-dash]CMe, 1; EtC[triple bond, length as m-dash]CEt, 2; PhC[triple bond, length as m-dash]CMe, 3; PhC[triple bond, length as m-dash]CPh, 4) in good yields. The compounds have been characterised by C,H analyses, IR, EPR and mass spectroscopies, magnetic susceptibility, and cyclic voltammetry. In addition, a single crystal X-ray diffraction analysis has been carried out for compound 4. The alkyne ligand adopts an almost parallel conformation relative to the Cp ring, essentially identical with that of previously reported Nb, Ta, and W analogues. Geometry optimisat…
Ejection of molecules from WO3 under ion bombardment: the role of the crystal structure
1992
Abstract Emission of molecular ions from WO 3 and Na x WO 3 was studied by SIMS. It was found that the phenomenon of ejection of molecules had not arisen from specific WO bond lengths and strengths in tungsten trioxide.