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Title: Synthesis, structure and electronic structure of a new polymorph of CaGe{sub 2}

Abstract

Reported are the flux synthesis, the crystal structure determination, the properties and the band structure calculations of a new polymorph of CaGe{sub 2}, which crystallizes with the hexagonal space group P6{sub 3}mc (no. 186) with cell parameters of a=3.9966(9) and c=10.211(4)A (Z=2; Pearson's code hP6). The structure can be viewed as puckered layers of three-bonded germanium atoms, {sub {approx}}{sup 2}[Ge{sub 2}]{sup 2-}, which are stacked along the direction of the c-axis in an ABAB-fashion. The germanium polyanionic layers are separated by the Ca cations. As such, this structure is closely related to the structure of the other CaGe{sub 2} polymorph, which crystallizes with the rhombohedral CaSi{sub 2} type in the R3-bar m space group (No. 166), where the {sub {approx}}{sup 2}[Ge{sub 2}]{sup 2-} layers are arranged in an AA'BB'CC'-fashion, and are also interspaced by Ca{sup 2+} cations. LMTO calculations suggest that in spite of the formal closed-shell configuration for all atoms and the apparent adherence to the Zintl rules for electron counting, i.e., Ca{sup 2+}[3b-Ge{sup 1-}]{sub 2}), the phase will be a poor metal due to a small Ca-3d-Ge-4p band overlap. Magnetic susceptibility measurements as a function of the temperature indicate that the new CaGe{sub 2} polymorph exhibits weak, temperaturemore » independent, Pauli-paramagnetism.« less

Authors:
 [1];  [2]
  1. Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716 (United States)
  2. Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716 (United States), E-mail: bobev@udel.edu
Publication Date:
OSTI Identifier:
21015811
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 180; Journal Issue: 5; Other Information: DOI: 10.1016/j.jssc.2007.03.003; PII: S0022-4596(07)00100-4; Copyright (c) 2007 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; CALCIUM COMPOUNDS; CALCIUM IONS; ELECTRONIC STRUCTURE; GERMANIDES; HEXAGONAL LATTICES; LAYERS; MAGNETIC SUSCEPTIBILITY; SHELLS; SPACE GROUPS; SYNTHESIS

Citation Formats

Tobash, Paul H., and Bobev, Svilen. Synthesis, structure and electronic structure of a new polymorph of CaGe{sub 2}. United States: N. p., 2007. Web. doi:10.1016/j.jssc.2007.03.003.
Tobash, Paul H., & Bobev, Svilen. Synthesis, structure and electronic structure of a new polymorph of CaGe{sub 2}. United States. doi:10.1016/j.jssc.2007.03.003.
Tobash, Paul H., and Bobev, Svilen. Tue . "Synthesis, structure and electronic structure of a new polymorph of CaGe{sub 2}". United States. doi:10.1016/j.jssc.2007.03.003.
@article{osti_21015811,
title = {Synthesis, structure and electronic structure of a new polymorph of CaGe{sub 2}},
author = {Tobash, Paul H. and Bobev, Svilen},
abstractNote = {Reported are the flux synthesis, the crystal structure determination, the properties and the band structure calculations of a new polymorph of CaGe{sub 2}, which crystallizes with the hexagonal space group P6{sub 3}mc (no. 186) with cell parameters of a=3.9966(9) and c=10.211(4)A (Z=2; Pearson's code hP6). The structure can be viewed as puckered layers of three-bonded germanium atoms, {sub {approx}}{sup 2}[Ge{sub 2}]{sup 2-}, which are stacked along the direction of the c-axis in an ABAB-fashion. The germanium polyanionic layers are separated by the Ca cations. As such, this structure is closely related to the structure of the other CaGe{sub 2} polymorph, which crystallizes with the rhombohedral CaSi{sub 2} type in the R3-bar m space group (No. 166), where the {sub {approx}}{sup 2}[Ge{sub 2}]{sup 2-} layers are arranged in an AA'BB'CC'-fashion, and are also interspaced by Ca{sup 2+} cations. LMTO calculations suggest that in spite of the formal closed-shell configuration for all atoms and the apparent adherence to the Zintl rules for electron counting, i.e., Ca{sup 2+}[3b-Ge{sup 1-}]{sub 2}), the phase will be a poor metal due to a small Ca-3d-Ge-4p band overlap. Magnetic susceptibility measurements as a function of the temperature indicate that the new CaGe{sub 2} polymorph exhibits weak, temperature independent, Pauli-paramagnetism.},
doi = {10.1016/j.jssc.2007.03.003},
journal = {Journal of Solid State Chemistry},
number = 5,
volume = 180,
place = {United States},
year = {Tue May 15 00:00:00 EDT 2007},
month = {Tue May 15 00:00:00 EDT 2007}
}
  • A new monoclinic polymorph of Ba(AsO{sub 3}OH) was synthesized under hydrothermal conditions. It represents a previously unknown structure type. Its crystal structure was determined from a racemic twin using single-crystal X-ray diffraction data collected at 120 and 293 K [space group P2{sub 1}, a=7.2149(14)/7.2370(2), b=7.7028(15)/7.7133(2), c=21.7385(43)/21.8079(5) A, {beta}=95.95(3)/96.073(1){sup o}, V=1201.6(4)/1210.51(5) A{sup 3}, Z=12]. The crystal structure of P2{sub 1}-Ba(AsO{sub 3}OH) has a layered character and is built up of four types of regularly alternating layers parallel to (0 0 1). Every AsO{sub 3}OH tetrahedron is chelating to two Ba atoms and bridged by another two Ba atoms. Each OH groupmore » acts as hydrogen bond donor toward the oxygen atoms positioned in the same or adjacent layers. Although the H atoms could not be located, no ambiguities are present in the hydrogen-bonding scheme. Single-crystal vibrational spectroscopy (FTIR and Raman) was used to describe the vibrational behavior of the hydrogen bond system; particularly the spectroscopic manifestation of the very short and short hydrogen bonds (2.462(7)-2.575(7) A). In order to complement spectroscopic data on protonated orthoarsenates, infrared spectra of triclinic F1-bar -Sr(AsO{sub 3}OH) and the orthorhombic variety of Pbca-Ba(AsO{sub 3}OH) were recorded and discussed. Furthermore, structural features of other alkaline earth hydrogen arsenates are discussed. -- Graphical Abstract: Mesh type and topological structure of the cation layers seen along [0 0 1]; a-axis vertical, b-axis horizontal. A trace of the unit cell is drawn for reference. Display Omitted« less
  • The high pressure behavior of β-In{sub 2}S{sub 3} (I4{sub 1}/amd and Z=16) has been studied by in situ synchrotron radiation X-ray diffraction combined with diamond anvil cell up to 71.7 GPa. Three pressure-induced phase transitions are evidenced at ∼6.6 GPa, ∼11.1 GPa at room temperature and 35.6 GPa after the high-temperature annealing using a portable laser heating system. The new polymorph of In{sub 2}S{sub 3} at 35.6 GPa is assigned to the denser cubic defect Th{sub 3}P{sub 4} structure (I4¯3d and Z=5.333), whose unit-cell parameters are a=7.557(1) Å and V=431.6(2) Å{sup 3}. The Th{sub 3}P{sub 4}-type phase can be stablemore » at least up to 71.7 GPa and cannot be preserved at ambient pressure. The pressure–volume relationship is well described by the second-order Birch–Murnaghan Equation of State, which yields B{sub 0}=63(3) GPa and B{sub 0}′=4 (fixed) for the β-In{sub 2}S{sub 3} phase and B{sub 0}=87(3) GPa and B{sub 0}′=4 (fixed) for the defect Th{sub 3}P{sub 4}-type phase respectively. - Graphical abstract: The structure and Rietveld refinement of new polymorph the defect Th{sub 3}P{sub 4}-type In{sub 2}S{sub 3}. This structure was observed at 35.6 GPa after laser heating by X-ray diffraction. Display Omitted - Highlights: Three pressure-induced phase transitions of β-In{sub 2}S{sub 3} were observed. β-In{sub 2}S{sub 3} was stable up to 6.6 GPa. The defect Th{sub 3}P{sub 4}-type In{sub 2}S{sub 3} was identified at 35.6 GPa after laser heating and was stable up to 71.7 GPa. Elastic properties of β-In{sub 2}S{sub 3} and Th{sub 3}P{sub 4}-type In{sub 2}S{sub 3} are well presented by Birch–Murnaghan EoS.« less
  • Single crystals of (NH{sub 3}(CH{sub 2}){sub 3}NH{sub 3})(H{sub 3}O){sub 2}(UO{sub 2}){sub 3}(MoO{sub 4}){sub 5} (1), C(NH{sub 2}){sub 3}(UO{sub 2})(OH)(MoO{sub 4}) (2), (C{sub 4}H{sub 12}N{sub 2})(UO{sub 2})(MoO{sub 4}){sub 2} (3) and (C{sub 5}H{sub 14}N{sub 2})(UO{sub 2})(MoO{sub 4}){sub 2}{center_dot}H{sub 2}O (4) have been synthesized hydrothermally by using UO{sub 2}(CH{sub 3}COO){sub 2}{center_dot}2H{sub 2}O, (NH{sub 4}){sub 2}Mo{sub 2}O{sub 7}, HF{sub (aq)}, H{sub 2}O, and the respective organic template. The materials have layered structures with anionic uranium molybdate sheets separated by cationic organic templates. Compound 1 has an unprecedented uranium molybdate topology, whereas 2 is structurally related to johannite, Cu[(UO{sub 2}){sub 2}(SO{sub 4}){sub 2}(OH){sub 2}](H{submore » 2}O){sub 8}, and 3 and f4 have layer topologies similar to zippiete, K{sub 2}[UO{sub 2}(MoO{sub 4}){sub 2}]. Thermogravimetric measurements indicate all that four materials, after template loss, form a crystalline mixture of UO{sub 2}MoO{sub 4} and MoO{sub 3}. Crystal data: (NH{sub 3}(CH{sub 2}){sub 3}(H{sub 3}O){sub 2}(UO{sub 2}){sub 3}(MoO{sub 4}){sub 5}, orthorhombic, space group Pbnm (No. 62), with a = 10.465(1) {angstrom}, b = 16.395(1) {angstrom}, c = 20.241(1) {angstrom}, and Z = 4; C(NH{sub 2}){sub 3}(UO{sub 2})(OH)MoO{sub 4}), monoclinic, space group P2{sub 1}/c (No. 14), with a = 15.411(1) {angstrom}, b = 7.086(1) {angstrom}, c = 18.108(1) {angstrom}, {beta} = 113.125(2){degree}, and Z = 4; (C{sub 4}H{sub 12}N{sub 2})(UO{sub 2})(MoO{sub 4}){sub 2}, triclinic, space group P{bar 1} (No. 2), with a = 7.096(1) {angstrom}, b = 8.388(1) {angstrom}, c = 11.634(1) {angstrom}, {alpha} = 97.008(3){degree}, {beta} = 96.454(2){degree}, {gamma} = 110.456(3){degree}, and Z = 2; (C{sub 5}H{sub 14}N{sub 2})(UO{sub 2})(MoO{sub 4}){sub 2}{center_dot}H{sub 2}O, orthorhombic, space group Pbca (No. 61), with a = 12.697(1) {angstrom}, b = 13.247(1) {angstrom}, c = 17.793(1) {angstrom}, and Z = 8.« less
  • A new polymorph of lithium boron nitride, Li/sub 3/BN/sub 2/, was synthesized by slow-cooling of a mixture of Li/sub 3/N and BN from 1200 K. It has monoclinic symmetry, P2/sup 1//c, a = 5.1502(2), b = 7.0824(2), c = 6.7908(2) A, ..beta.. = 112.956(2)/sup 0/, Z = 4, D/sub m/ = 1.74, D/sub calcd/ = 1.737 g cm/sup -3/, ..mu.. = 0.082 mm/sup -1/. The structure was determined from 1352 unique X-ray reflections from a single crystal and refined to R = 0.023 by full-matrix least-squares method. Two kinds of layers alternate parallel to (100) in the structure. One layermore » includes Li and B atoms, and the other is composed of only N atoms. N(1) and N(2) are coordinated by six Li atoms and one B atom. Each Li atom is in a distorted tetrahedron of N atoms. Boron is linearly coordinated by two N atoms. The N(1)single bond B single bond N(2) bond angle is 179.12(4)/sup 0/. The bond lengths of N(1)single bond B and N(2)single bond B are 1.3393(5) S, respectively. Bonding electrons between boron and nitrogen atoms are clearly observed. Lithium ion conductivity of 6 x 10/sup -5/ Sm/sup -1/ was measured at 400 K on a polycrystalline sample and an activation energy was 64 kJ/mole.« less
  • The synthesis, structure, and characterization of a new centrosymmetric borate Pb{sub 2}O[BO{sub 2}(OH)] based on anion-centered OPb{sub 4} tetrahedra are reported. Pb{sub 2}O[BO{sub 2}(OH)] crystallizes in monoclinic space group C2/m with a=12.725(7) Å, b=5.698(3) Å, c=7.344(4) Å, β=116.277(6)°. The electronic band structure and density of states of Pb{sub 2}O[BO{sub 2}(OH)] have been calculated via the density functional theory (DFT). Electron density difference calculation indicates that lone-pair electrons of Pb{sup 2+} cation should be stereoactive. - Graphical abstract: An indirect gap compound of Pb{sub 2}O[BO{sub 2}(OH)] with 2D inorganic layers motif based on OPb{sub 4} tetrahedra has been synthesized and fullmore » characterized by crystallographic, IR, TG, UV–vis-NIR Diffuse Reflectance, and theoretical calculations. Display Omitted - Highlights: • A centrosymmetric borate Pb{sub 2}O[BO{sub 2}(OH)] was synthesized and characterized. • The crystalstructure, electronic band and density states was analyzed. • The lone-pair electrons of Pb{sup 2+} were proved to be stereoactive.« less