Herta Effenberger

Crystal structure refinements of magnesite, calcite, rhodochrosite, siderite, smithonite, and dolomite, with discussion of some aspects of the stereochemistry of calcite type carbonates

The crystal structures of magnesite, calcite, rhodochrosite, siderite, smithonite and dolomite were refined by standard single crystal X-ray methods using diffraction data up to sin,9/A = 1.0A -1. The C-O bond lengths are essentially the same. Attention is drawn to short 0 - 0 contacts (2.85A in both magnesite and smithonite) outside the coordination figures. The Me06 octahedra are always elongated parallel (00.1); the distortion is not a monotone function of the Me-O distance. The approximation of four point charges for the (C03Y- ion for calcite gives good agreement between observation and classical electrostatic calculation when charges of 1+ for carbon and 1 - for oxygen are used.

Crystal structure and chemical formula of schmiederite ,Pb2Cu2(OH)4(SeO3)(SeO4), with a comparison to linarite, PbCu(OH)2(SO4)

SummaryBased on a X-ray structure analysis it was proved that the mineral schmiederite contains both selenite and selenate groups [a = 9.922(3)Å,b = 5.712(2)Å,c = 9.396(3)Å, β = 101.96(3)°, space group P21/m,Z = 2 {Pb2Cu2(OH)4(SeO3)(SeO4)},Rw = 0.055 for 1131 reflections up to sin θ/λ = 0.65 Å−1]. The crystal structure is closely related to that of linarite [a = 9.701(2) Å,b = 5.650(2) Å,c= 4.690(2)Å, β = 102.65(2)°, space group P21/m,Z = 2 {PbCu(OH)2(SO4)},Rw = 0.034 for 1991 reflections up to sin θ/λ = 1.0 Å−1].The Pb atom in linarite and the Pb(1) atom in schmiederite have each three Pb-O bonds < 2.45 Å with trigonal pyramidal arranged ligands; the Pb(2) atom in schmiederite has only one such near O atom. The Cu atoms are approximately square planar coordinated by hydroxil groups. In addition two further O atoms complete the coordination figure to a strongly distorted octahedron. All the anion groups have the usual geometry.ZusammenfassungBasierend auf einer Röntgen-Strukturuntersuchung konnte das Vorliegen von Selenit-und Selenatgruppen im Mineral Schmiederit belegt werden [a=9,922(3) Å,b = 5,712(2) Å,c = 9,396(3) Å, β = 101,96(3)°, Raumgruppe P21/m,Z=2 {Pb2Cu2(OH)4(SeO3)(SeO4)},Rw = 0,055 für 1131 Reflexe bis sin θ/λ, = 0,65 Å−1]. Die Kristallstruktur weist enge Beziehungen zu jener des Linarits auf [a = 9,701(2) Å,b = 5,650(2) Å,c = 4,690(2) Å, β = 102,65(2)°, Raumgruppe P21/m,Z=2 {PbCu(OH)2(SO4)},Rw = 0,034 für 1991 Reflexe bis sin θ/λ = 1,0 Å−1].Das Pb-Atom im Linarit sowie das Pb(1)-Atom im Schmiederit haben jeweils drei Pb-O-Bindungen <,45 Å, wobei die Liganden trigonal pyramidal angeordnet sind; das Pb(2)-Atom im Schmiederit hat hingegen nur ein derart nahes O-Atom. Die Cu-Atome sind etwa quatratisch planar von Hydroxilgruppen koordiniert; zwei weitere O-Atome ergänzen die Koordinationsfigur zur einem stark verzerrten Oktaeder. Die Aniongruppen haben die üblichen Dimensionen.

Die Kristallstrukturen der Kupfer(II)-oxo-selenite Cu2O(SeO3) (kubisch und monoklin) und Cu4O(SeO3)3 (monoklin und triklin)

AbstractSyntheses within the system CuO-SeO2-H2O revealed four copper(II)-oxo-selenites. The crystal structures of these compounds were determined by single crystal X-ray techniques. Chemical formulae, lattice parameters and space groups are: Cu2O(SeO3)-I [a=8.925 (1) Å, P213], Cu2O(SeO3)-II [a=6.987 (5) Å,b=5.953 (4) Å,c=8.429 (6) Å, β=92.17 (3)°, P21/n], Cu4O(SeO3)3-I [a=15.990 (8) Å,b=13.518 (8) Å,c=17.745 (12) Å, β=90.49 (5)°, P21/a], and Cu4O(SeO3)3-II [a=7.992 (6) Å,b=8.141 (6) Å,c=8.391 (6) Å, α=77.34 (3)°, β=65.56 (3)°, γ=81.36 (3)°,

Tschortnerite, a copper-bearing zeolite from the Bellberg volcano, Eifel, Germany

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Synthesis and crystal structure of Sr(AsO3OH) and Ba(AsO3OH): crystal chemistry of related MHXO4 (X = As, P, S) compounds

].All the Cu atoms are-with one exception-[4], [4+1], and [4+2] coordinated by O atoms. The four nearest O atoms are more or less distorted “square planar” arranged. Within the CuO4 squares the Cu-O bond lengths are significantly shorter for the [4] coordinated O atoms as compared with those of the [4+1] and [4+2] coordinated Cu atoms. The exception in the coordination of the Cu atoms is the Cu(1) atom in Cu2O(SeO3)-I with the site symmetry 3, which is trigonal dipyramidal [5] coordinated. A common feature of these four crystal structures is, that O atoms outside the SeO3 groups are tetrahedrally coordinated by four Cu(II) atoms. The Se atoms are as usual [3] coordinated, building up SeO3 pyramids. In all these four compounds the copper-oxygen polyhedra are combined to a three-dimensional network.

Re-examination of berlinite (AlPO4) from the Cioclovina Cave, Romania

The refinement of the crystal structure of Cu2O(SO4), dolerophanite, [a=9.370 (1) A,b=6.319 (1) A,c=7.639 (1) A, β=122.34 (1)°; space group C 2/m;Z=4;R=0.035] confirmed the trigonal dipyramidal coordination of one Cu(II) atom (mean distance Cu-O=2.025 A). One O atom is tetrahedrally surrounded by four Cu(II) atoms; the mean Cu(II)-O distance of 1.918 A compares well to [O Cu(II)4] tetrahedra found in inorganic crystal structures.

Hydroxylellestadite from Cioclovina Cave (Romania) : Microanalytical, structural, and vibrational spectroscopy data

Abstract Crystals of sodium heptasilicate (Na8Si7O18) have been grown at 9 GPa, 1000 0C using the MA6/8 superpress at Edmonton. The X-ray structure was determined at room pressure (R = 5.8%). Sodium heptasilicate is trigonal with a = 7.180(1) Å. α = 87.26(1)°, space group Rbu671, Z= I, and Dx = 3.009 g/cm3. The structure contains isolated six-membered UDUDUD rings of SiO4 tetrahedra interconnected by SiO6 octahedra with [6]Si:[4]Si =1:6, giving a structural formula of Na8Si[Si6018]. The mixed [4]Si,[6]Si framework is undersaturated because only one of the non-bridging O atoms in the SiO4 tetrahedron is shared with the SiO6 octahedron. Six Na cations per formula unit (pfu) are in eightfold coordination with O, and two are in a distorted and compressed octahedral coordination. Sodium heptasilicate belongs to the homologous series Na2kNa2(m-k)Sim-k[Sin-m+kO2n+m]. with k < m < ti and (n - m + k) ≥ (3/2)(m - k). The X-ray structure is consistent with microprobe analysis data and revises the earlier characterization of this phase as (ξ-Na2Si2O5. The sodium heptasilicate structure doesjiot fiilly_relax with decompression and undergoes incipient displacive transformation (R3̅m -> R3̅) with minor positional disorder of Na cations.

On the crystal chemistry of three copper(II)-arsenates: Cu3(AsO4)2-III, Na4Cu(AsO4)2, and KCu4(AsO4)3

Abstract In inorganic compounds the usual environment of oxygen-coordinated Cu(II) atoms are four nearest atoms at CuO ∼ 2.0 A in a more or less square planar arrangement. In some cases distinct deviations from the ideal “CuO4 square” are found. Obviously the largest distortions occur, if one additional O atom completes the coordination geometry in a “tetragonal pyramidal” Cu(II)[4+I]O5 polyhedron. Now the continuous transition from this “tetragonal pyramidal” polyhedron to a trigonal bipyramidal Cu(II)[5]O5 polyhedron can be verified. In the compound PbCu2(SeO3)3 each of the four crystallographically different Cu atoms has four nearest O atoms, which are “square planar” arranged. The “CuO4 squares” show different kinds of distortion. The crystal structure of PbCu2(SeO3)3 was determined by single-crystal X-ray techniques (a = 7.813(1) A, b = 9.116(1)A, c = 12.570(1) A, α = 82.27(1)°, β = 72.90(1)°, γ = 89.69(1)°, space group P 1 , Z = 4, R w = 0.048 for 5899 reflections up to sin θ λ = 0.81 A−1).