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| 2. |
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| 3. |
- Doverbratt, Isa, et al.
(författare)
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Ca(10)Pt(7)Tt(3) (Tt = Si, Ge): New Platinide Phases Featuring Electron-Rich 4c-6e Bonded [Pt(7)Tt(3)](20-) Intermetalloid Clusters.
- 2012
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 1520-510X .- 0020-1669. ; 51:21, s. 11980-11985
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Tidskriftsartikel (refereegranskat)abstract
- Two new phases Ca(10)Pt(7)Tt(3) (with Tt = Si, Ge) were obtained by reacting stoichiometric mixtures of the elements at high temperature. Their structures were refined from single crystal X-ray diffraction data. They are isostructural and crystallize in the Ba(10)Al(3)Ge(7) type structure, space group P6(3)/mcm (No. 193) with a = b = 8.7735(3) Å, c = 13.8260(5) Å, V = 921.66(6) Å(3), Z = 2 for Tt = Si, and a = b = 8.7995(6) Å, c = 13.9217(14) Å, V = 933.56(16) Å(3) for Tt = Ge phase. The most interesting structural features in these phases are the propeller shape {Pt(7)Tt(3)} (Tt = Si, Ge) intermetalloid clusters in a D(3h) local symmetry. LMTO electronic structure calculations and COHP analyses reveal that both Ca(10)Pt(7)Tt(3) (Tt = Si, Ge) phases are charge optimized, which is not predicted by the classical Zintl concept and the octet or Wade-Mingo's rules, but rather by a more complex bonding model based on the unprecedented electron-rich 4c-6e multicenter bonding. The clusters are best described as three-condensed trigonal planar [TtPt(3)](8-) units, resulting in a central Pt atom also with a trigonal planar coordination of three symmetrical equivalent Si/Ge atoms that are further connected to two terminal Pt atoms each. The "trefoil" electron-rich multicenter bonding is proposed here for the first time, and may be viewed as a unique bonding feature with potential relevance for the catalytic properties of the noble metal platinum.
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| 4. |
- Doverbratt, Isa, et al.
(författare)
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Ca2Pd3Ge, a new fully ordered ternary Laves phase structure
- 2013
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Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596. ; 197, s. 312-316
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Tidskriftsartikel (refereegranskat)abstract
- The title compound, Ca2Pd3Ge, was prepared as a part of a systematic investigation of the Ca-Pd-Ge ternary phase diagram. The structure was determined and refined from single-crystal X-ray diffraction data. It is a new fully ordered ternary Laves phase with the space group R-3m, Z=3, a=5.6191 (5) angstrom, c=12.1674 (7) angstrom. wR(2)=0.054 (all data) and is isostructural to Mg2Ni3Si (Noreus et al., 1985 [17]) but due to the larger size of all elements in Ca2Pd3Ge, the cell axes are approximately 10% longer. The compound may formally be considered as a Zintl compound, with [Pd3Ge](4-) forming a poly-anionic network and divalent Ca cations located in truncated tetrahedral interstices. The electronic structure and chemical bonding of Ca2Pd3Ge is discussed in terms of LMTO band structure calculations and compared with CaPd2 (MgCu2-type). (C) 2012 Elsevier Inc. All rights reserved.
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| 5. |
- Euchner, H., et al.
(författare)
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Anomalous vibrational dynamics in the Mg(2)Zn(11) phase
- 2011
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 83:14, s. 144202-
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Tidskriftsartikel (refereegranskat)abstract
- We present a combined experimental and theoretical study of the structure and the lattice dynamics in the complex metallic alloy Mg(2)Zn(11), by means of neutron and x-ray scattering, as well as ab initio and empirical potential calculations. Mg(2)Zn(11) can be seen as an intermediate step in structural complexity between the simple Laves-phase MgZn(2) on one side, and the complex 1/1 approximants and quasicrystals ZnMgAl and Zn(Mg)Sc on the other. The structure can be described as a cubic packing of a triacontahedron whose center is partially occupied by a Zn atom. This partially occupied site turned out to play a major role in understanding the lattice dynamics. Data from inelastic neutron scattering evidence a Van Hove singularity in the vibrational spectrum of Mg(2)Zn(11) for an energy as low as 4.5 meV, which is a unique feature for a nearly-close-packed metallic alloy. This corresponds to a gap opening at the Brillouin zone boundary and an interaction between a low-lying optical branch and an acoustic one, as could be deduced from the dispersion relation measured by inelastic x-ray scattering. Second, the measured phonon density of states exhibits many maxima, indicating strong mode interactions across the whole energy range. The origin of the low-energy modes in Mg(2)Zn(11) and other features of the vibrational spectra are studied, using both ab initio and empirical potential calculations. A detailed analysis of vibrational eigenmodes is presented, linking features in the vibrational spectrum to atomic motions within structural building blocks.
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| 6. |
- Fredrickson, Daniel C., et al.
(författare)
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Bonding schemes for polar intermetallics through molecular orbital models : Ca-supported Pt-Pt Bonds in Ca10Pt7Si3
- 2013
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Ingår i: Crystals. - : MDPI AG. - 2073-4352. ; 3:3, s. 504-516
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Tidskriftsartikel (refereegranskat)abstract
- Exploratory synthesis in the area of polar intermetallics has yielded a rich variety of structures that offer clues into the transition in bonding between Zintl and Hume-Rothery phases. In this article, we present a bonding analysis of one such compound, Ca10Pt7Si3, whose large Ca content offers the potential for negative formal oxidation states on the Pt. The structure can be divided into a sublattice of Ca cations and a Pt-Si polyanionic network built from Pt7Si3 trefoil units linked through Pt-Pt contacts of 3.14 Å. DFT-calibrated Hückel models reveal that the compound adheres well to a Zintl-like electron counting scheme, in which the Pt-Si and Pt-Pt contacts are equated with two-center two-electron bonds. The experimental electron count is in excess of that predicted by 2%, a discrepancy which is attributed to the electron transfer from the Ca to the Pt-Si network being incomplete. For the Pt-Pt contacts, the occupancy of the bonding orbitals is dependent on the participation of the surrounding Ca atoms in bridging interactions. This use of multi-center interactions isolobal to classical two-center two-electron bonds may illustrate one path by which the bonds delocalize as one moves from the Zintl phases toward the Hume-Rothery domain.
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| 7. |
- Ghasemi, Masoomeh, et al.
(författare)
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Bonding in intermetallics may be deceptive – the case of the new type structure Au2InGa2
- 2014
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Ingår i: Intermetallics. - : Elsevier BV. - 0966-9795. ; 46, s. 40-44
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the crystal and the electronic structure of a new ternary phase, Au2InGa2 using powder and single crystal X-Ray Diffraction (XRD) and Stuttgart Tight Binding LMTO-ASA methods, respectively. Complementary methods including Thermo-Gravimetric Differential Thermal Analysis (TG-DTA), Energy Dispersive X-ray Spectroscopy (EDS) and Scanning Electron Microscopy (SEM) were also employed. As a result, the complete structure was determined and the role of homoatomic and heteroatomic bonding is discussed.
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| 8. |
- Ghasemi, Masoomeh, et al.
(författare)
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The phase equilibria in the Au-In-Ga ternary system
- 2014
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388. ; 588, s. 474-480
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Tidskriftsartikel (refereegranskat)abstract
- The phase equilibria of the Au–In–Ga system were investigated for the first time using Differential Thermal Analysis (DTA), X-Ray Diffractometry (XRD), Energy Dispersive X-ray Spectroscopy (EDS) and Scanning Electron Microscopy (SEM). A new ternary phase (Au2InGa2) with the hexagonal structure (P63/mmc) was discovered which melts incongruently at 394 °C. From the experimental results, several invariant reactions have been identified and discussed.
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| 9. |
- Hermes, Wilfred, et al.
(författare)
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The composite structure of mixed tau-(Ag, Cu)(x)V2O5 bronzes Evidence for T dependant guest-species ordering and mobility
- 2013
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Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596. ; 199, s. 84-89
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Tidskriftsartikel (refereegranskat)abstract
- The complex structural behavior of tau-[AgCu](similar to 0.92)V4O10 has been elucidated by single crystal X-ray diffraction and thermal analysis. The tau-phase region is apparently composed of several distinct phases and this study identifies at least three: tau(1rt) tau(2rt) and tau(1t), tau(1rt) and tau(2rt) have slightly different compositions and crystal habits. Both phases transform to Tit at low temperature. The room temperature modification tau(1rt) crystallizes in an incommensurately modulated structure with monoclinic symmetry C2(0 beta 1/2) [equivalent to no 5.4, B2(01/2 gamma) in the Intnl. Tables for Crystallography, Volume C] and the cell parameters a=11.757(4) angstrom, b=3.6942(5) angstrom c = 9.463(2) beta=114.62(2)degrees and the q-vector (0 0.92 1/2), but it is more convenient to transform this to a setting with a non-standard centering X=(1/2 1/20 0; 0 0 1/2 1/2; 1/2 1/2 1/2 1/2;) and an axial q vector (00.92 0). The structure features a vanadate host lattice with Cu and Ag guests forming an incommensurate composite. The structural data indicates perfect Ag/Cu ordering. At low temperature this modification is replaced by a triclinic phase characterized by two independent q-vectors. The tau(2rt) phase is similar to the low temperature modification tau(lt) but the satellite reflections are generally more diffuse. (C) 2012 Elsevier Inc. All rights reserved.
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| 10. |
- Hlukhyy, Viktor, et al.
(författare)
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Extreme differences in oxidation states : Synthesis and structural analysis of the germanide oxometallates A 10[Ge 9] 2[WO 4] as well as A 10+x[Ge 9] 2[W 1-xNb xO 4] with A = K and Rb containing [Ge 9] 4- polyanions
- 2012
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 51:7, s. 4058-4065
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Tidskriftsartikel (refereegranskat)abstract
- Semitransparent dark-red or ruby-red moisture- and air-sensitive single crystals of A 10+x[Ge 9] 2[W 1-xNb xO 4] (A = K, Rb; x = 0, 0.35) were obtained by high-temperature solid-state reactions. The crystal structure of the compounds was determined by single-crystal X-ray diffraction experiments. They crystallize in a new structure type (P2 1/c, Z = 4) with a = 13.908(1) Å, b = 15.909(1) Å, c = 17.383(1) Å, and α = 90.050(6)° for K 10.35(1)[Ge 9] 2[W 0.65(1)Nb 0.35(1)O 4]; a = 14.361(3) Å, b = 16.356(3) Å, c = 17.839(4) Å, and α = 90.01(3)° for Rb 10.35(1)[Ge 9] 2[W 0.65(1)Nb 0.35(1)O 4]; a = 13.8979(2) Å, b = 15.5390(3) Å, c = 17.4007(3) Å, and α = 90.188(1)° for K 10[Ge 9] 2WO 4; and a = 14.3230(7) Å, b = 15.9060(9) Å, c = 17.8634(9) Å, and α = 90.078(4)° for Rb 10[Ge 9] 2WO 4. The compounds contain discrete Ge 9 4- Wades nido clusters and WO 4 2- (or NbO 4 3-) anions, which are packed according to a hierarchical atom-to-cluster replacement of the Al 2Cu prototype and are separated by K and Rb cations, respectively. The alkali metal atoms occupy the corresponding tetrahedral sites of the Al 2Cu prototype. The amount of the alkali metal atoms on these diamagnetic compounds corresponds directly to the amount of W substituted by Nb. Thus, the transition metals W and Nb appear with oxidation numbers +6 and +5, respectively, in the vicinity of a [Ge 9] 4- polyanion. The crystals of the mixed salts were further characterized by Raman spectroscopy. The Raman data are in good agreement with the results from the X-ray structural analyses.
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