Jan Curda

Li8MgSi6, a novel Zintl compound containing quasi-aromatic Si5 rings

Abstract Li 8 MgSi 6 is the compound with the highest silicon content in the ternary system Li/Mg/Si. The gray compound forms columnlike crystals with metallic lustre and is very sensitive to moisture. It reacts spontaneously with water to silanes and amorphous silicon. Li 8 MgSi 6 is a diamagnetic semiconductor with E g = 0.72 eV, ϱ(292 K) = 1.3 × 10 3 Ω cm − . The compound is monoclinic and crystallizes in space group P2 1 m , a = 12.701, b = 4.347, c = 10.507 A, β = 107.58°, Z = 2. The structure of Li 8 MgSi 6 contains isolated silicon atoms and planar five-membered Si 5 rings which form 1 ∞ [LiSi 5 ] sandwich stacks. Semiempirical SCF calculations are in accordance with the physical properties and support a description of the five-membered silicon rings as quasi-aromatic 26 electron systems. A generalization of the electron counting rules of Zintl and Klemm is proposed. A remark on the ambiguous Li 11 Ge 6 is given.

Structure redetermination and high pressure behaviour of AgCuO2

Abstract AgCuO2 has been obtained via a low temperature route. The structure has been redetermined with Rietveld refinements using neutron powder diffraction data [C2/m, a=6.0756(3), b=2.8088(1), c=5.8728(3) A, β=107.987(4)°, Z=2, Rp=6.36%, Rwp=7.22%]. The crystal structure consists of chains of ladder-like CuO4-rectangles running along [010], interconnected by AgO2-dumbbells. For physical and crystal chemical reasons the oxidation states +I for silver, and +III for copper, respectively, have been assigned. High-pressure X-ray powder diffraction experiments have been made. AgCuO2 is stable with respect to decomposition and structural distortion up to 36.3 GPa. The zero pressure bulk modulus of AgCuO2 is estimated as 118.2 GPa.

Al7Te10 — das erste Chalcogenid mit zweiwertigem Aluminium / Al7Te10 — the First Chalcogenide of Divalent Aluminum

Al7Te10 is prepared from a melt of the elements in stoichiometric amounts in a corundum crucible contained in a sealed quartz ampoule. The ruby red cube shaped crystals are stable below 840 K. The structure of Al7Te10 (R32-D37 a = 1439.5 pm, c = 1793.2 pm, Z = 6, R = 0.03) is a distorted defect variant of a tetrahedral arrangement of the 4H-polytype. The central unit, a double barrelane [Te4Al4-Al4Te4], contains an Al -Al bond of 260 pm, which is somewhat longer (n = 0.83) than an expected single bond (250 pm, n = 1). This homopolar bond disturbs the electrostatically favorable (Al-Te-)n sequence in the structure which is compensated by the occurrence of four-membered Al2Te2 rings. Al7Te10 is a Zintl phase according to 1/2{[Al2+-Al2+][Al3+]12[Te2-]20} and exhibits semiconducting and diamagnetic behaviour.

Ag2HgO2: the first silver mercurate

The silver mercurate Ag2HgO2 is accessible by oxygen high pressure synthesis; the compound crystallizes in a novel structure type with three interpenetrating Ag–O–Hg (10, 3) nets.

Dilead mercury chromate(VI), Pb2HgCrO6

The structure of Pb(2)HgCrO(6) (space group P-1) can be described as consisting of isolated [CrO(4)](2-) tetrahedra and nearly linear [HgO(2)](2-) dumb-bells, which form layers of composition [HgCrO(6)](4-). These are intercalated with corrugated pseudo-hexagonal Pb(2+) layers. The Pb(2+) cation is stereochemically active and has coordination 3+5.

Ag13I4(AsO4)3: Synthesis, Crystal Structure and Ionic Conductivity

Ruby-red single crystals of Ag13I4(AsO4)3 were prepared for the first time by reacting a stoichiometric mixture of Ag2O, AgI and As2O3 at elevated oxygen pressure of 120 MPa and at a temperature of 350 ◦C. The polyhedral crystals belong to the monoclinic space group P21/m with a = 9.247(1), b = 7.152(1), c = 17.674(2) Å , β = 91.492(2)◦, and Z = 2. The structure is fully ordered and was solved by Direct Methods, and refined on single crystal diffraction data (10376 observed reflections, R1 = 3.28 %). The crystal structure is built up of two two-dimensional interlocked partial structures, one consisting of silver and iodine ions, the other of silver and arsenate(V) ions. The slabs extend in the ac plane, and the Ag-I framework is linked to the AsO43− units by Ag-O contacts. The silver-oxygen interactions perturb the tetrahedron of the arsenate group, resulting in As-O distances ranging from 1.670 to 1.697 Å, and angles varying from 107.3 to 112.1◦. Pure Ag13I4(AsO4)3 is a solid ion conductor with a r. t. conductivity of 6.4×10−6 Ω−1 cm−1 at 30 ◦C. The activation energy for silver ion conduction is 0.41 eV in the temperature range from 30 to 130 ◦C Graphical Abstract Ag13I4(AsO4)3: Synthesis, Crystal Structure and Ionic Conductivity

Dilead(II) trimercury(II) tetraoxide chromate(VI), Pb2(Hg3O4)(CrO4).

Pb2(Hg3O4)(CrO4) consists of [CrO4]2- tetrahedra, linear O-Hg-O dumbbells and divalent Pb atoms in [3+5]-coordination. The HgO2 dumbbells are condensed into [Hg3O4]2- units and can be regarded as a section of the HgO structure. The [Hg3O4]2- complex anions are connected by interstitial Pb2+ ions, while the [CrO4]2- tetrahedra are isolated.

Novel Polyanionic Topologies in Ag2VAsO6 and Ag6V2As2O13

Two new silver vanadate arsenates, Ag2VAsO6 and Ag6V2As2O13, have been prepared applying high oxygen pressure syntheses in stainless-steel autoclaves. Ag2VAsO6 crystallizes in space group P1 with unit cell parameters a=639.1(1), b=646.1(1), c=706.6(1) pm, α =116.105(3), ß =91.759(4), γ = 90:067(4)°, and Z =2 (R1 =0.058, 3935 independent reflections). The structure consists of AsO4 tetrahedra and VO6 octahedra which are linked to form two-dimensional 2¥[VAsO6]2- polyanions, separated by silver cations. Ag6V2As2O13 (C2=c, a=1895.9(2), b=536.40(6), c=1308:5(2) pm, ß =113:578(2)°, Z =4; R1 =0.030, 2571 independent reflections) displays as primary building units AsO4 tetrahedra and VO5 trigonal bipyramids which are condensed by sharing edges to one-dimensional 1¥[V2As2O13]6- ladder-like strands, set apart by the silver cations. These heteropolyanions are without precedent Graphical Abstract Novel Polyanionic Topologies in Ag2VAsO6 and Ag6V2As2O13