Zur Umwandlung von Greigit (Fe3S4) in Pyrrhotin (FeS) durch Elektronenstrahlen

On the Phase Transition of Greigite (Fe₃S₄) to Pyrrhotite (FeS) by Electron Beam The phase transition of mackinawite to pyrrhotite via greigite, which occurs on heating by means of electron beam in an electron microscope, is examined. An orientation relationship {111}_G//(001)_p and <110>_G//[110]_p can be applied at the transition of greigite to pyrrhotite.     

High-temperature FeS-FeS2 solid-state transitions: Reactions of solid mackinawite with gaseous H2S

Phase transitions and reactions of non-oxidized and surface-oxidized mackinawite (FeS) in helium and H₂S gas were investigated by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT). DFT was used to obtain optimized structures of the iron-sulfur phases mackinawite, hexagonal pyrrhotite, greigite, marcasite and pyrite and to determine the thermochemical properties of reactions of mackinawite with H₂S to these phases. The phase transitions of mackinawite to hexagonal pyrrhotite are endothermic, while reactions to greigite, marcasite and pyrite are exothermic. The experiments show that non-oxidized mackinawite converts into hexagonal pyrrhotite (Fe₉S₁₀ first and then Fe₇S₈) in He and also in H₂S but at a lower temperature. No further reactions can be observed under these conditions. In the case of surface-oxidized mackinawite, the extent of surface oxidation determines the course and the final product of the reaction with H₂S. If the extent of surface oxidation is low, only Fe²⁺ is oxidized to Fe³⁺. Under these conditions mackinawite converts into the mixed-valence thiospinel compound greigite. In case of pronounced surface oxidation all surface Fe centers are oxidized to the Fe³⁺ state and S²⁻ is oxidized to SO₄²⁻. Oxidation of sulfur is a prerequisite for the formation of pyrite.     

Structural study of a manganese(II) `picket‐fence' porphyrin complex

`Picket‐fence' porphyrin compounds are used in the investigation of interactions of hemes with dioxygen, carbon monoxide, nitric monoxide and imidazole ligands. (Cryptand‐222)potassium chlorido[meso‐tetra(α,α,α,α‐o‐pivalamidophenyl)porphyrinato]manganese tetrahydrofuran monosolvate (cryptand‐222 is 4,7,13,16,21,24‐hexaoxa‐1,10‐diazabicyclo[8.8.8]hexacosane), [K(C₁₈H₃₆N₂O₆)][Mn(C₆₄H₆₄N₈O₄)Cl]·C₄H₈O or [K(222)][Mn(TpivPP)Cl]·THF [systematic name for TpivPP: 5,10,15,20‐tetrakis(2‐tert‐butanamidophenyl)porphyrin], is a five‐coordinate high‐spin manganese(II) picket‐fence porphyrin complex. It crystallizes with a potassium cation chelated inside a cryptand‐222 molecule; the average K—O and K—N distances are 2.83 (4) and 2.995 (13) Å, respectively. All four protecting tert‐butyl pickets of the porphyrin are ordered. The porphyrin plane is nearly planar, as indicated by the atomic displacements and the dihedral angles between the mean planes of the pyrrole rings and the 24‐atom mean plane. The axial chloride ligand is located inside the molecular cavity on the hindered porphyrin side and the Mn—Cl bond is tilted slightly off the normal to the porphyrin plane by 3.68 (2)°. The out‐of‐plane displacement of the metal centre relative to the 24‐atom mean plane (Δ₂₄) is 0.7013 (4) Å, indicating a noticeable porphyrin core doming.     

The crystal and molecular structure of dioxo bis (2,2,6,6 - tetramethylheptane -3,5 dionato)methanol uranium (VI)

UO₂(thd)₂ CH₃OH (thd = tetramethylheptane-3,5-dione) is monoclinic, with a = 10.602(11), b = 22.883(20), c = 12.054(11) Å and β = 105.90(3)°, Z = 4 and space group P2₁/c. The structure, which is molecular, was solved by conventional Patterson and Fourier techniques with 3173 independent (hkl) reflexions collected with MoKα radiation (λ = 0.7107 Å), and refined to R = σ(|Fo|-|Fc|)/σ|Fo| = 0.093. The uranium coordination polyhedron is a pentagonal bipyramid, with UO (carbonyl) distances between 2.25 and 2.37 Å and a longer UO (methanol) distance of 2.50 Å. The uranyl group is linear (uranyl angle 179.3(8)°). The pentagon oxygen atoms and uranium do not form a planar system, as there are deviations of up to 0.17 Å from the mean plane. If the methanol oxygen atom O(7) is excluded from the plane calculation, the remaining atoms are more nearly planar. The four carbonyl oxygens are coplanar, with uranium 0.08 Å from their plane. The methanol oxygen is 0.28(4) Å from this second plane.The two (thd) molecules, excluding methyl carbons, are planar and are inclined at 43.6° to each other in a boat form and at 29.1 and 14.5° to the pentagonal plane. The methanol CO bond is inclined at 133° to the UO bond, confirming the ligand is the neutral CH₃OH molecule, and not CHO^?₃.     

Contribution to the crystal chemistry of tetrametaphosphates(II)

Chemical preparations and crystal structures of two hydrated forms of CsNa₃P₄O₁₂ are described. CsNa₃P₄O₁₂ · 4H₂O with a = 14.50(2), b = 7.804(3), c = 7.006(3)Å crystallizes in space group Imm2, Z = 2. The crystal structure has been determined using 745 independent reflexions with a final R value of 0.028 (R = 0.040 with the 934 collected reflexions), CsNa₃P₄O₁₂ · 3H₂O with a = 11.39(1), b = 10.92(1), c = 11.81(1)Å, β = 95.24(5)° in $\text{P2}{}_1\text{c}\text{, Z = 4}$. The crystal structure has been solved with 2975 independent reflexions with a final R-value of 0.018 (R = 0.057 with all the 6531 collected reflexions). In both structures there are four-membered rings built up with corner-sharing phosphate tetrahedron. For the tetrahydrate, the ring symmetry is mm whereas in the trihydrate, one observes two independent ring anions of symmetry $\text{1}$. In both cases hydrogen atoms have been located and refined.     

A moderate distortion of the `picket‐fence' porphyrin (cryptand‐222)potassium chlorido[meso‐α,α,α,α‐tetrakis(o‐pivalamidophenyl)porphyrinato]ferrate(II) n‐hexane monosolvate

As representative porphyrin model compounds, the structures of `picket‐fence' porphyrins have been studied intensively. The title solvated complex salt {systematic name: (4,7,13,16,21,24‐hexaoxa‐1,10‐diazabicyclo[8.8.8]hexacosane)potassium(I) [5,10,15,20‐tetrakis(2‐tert‐butanamidophenyl)porphyrinato]iron(II) n‐hexane monosolvate}, [K(C₁₈H₃₆N₂O₆)][Fe(C₆₄H₆₄N₈O₄)Cl]·C₆H₁₄ or [K(222)][Fe(TpivPP)Cl]·C₆H₁₄ [222 is cryptand‐222 or 4,7,13,16,21,24‐hexaoxa‐1,10‐diazabicyclo[8.8.8]hexacosane, and TpivPP is meso‐α,α,α,α‐tetrakis(o‐pivalamidophenyl)porphyrinate(2−)], [K(222)][Fe(TpivPP)Cl]·C₆H₁₄, is a five‐coordinate high‐spin iron(II) picket‐fence porphyrin complex. It crystallizes with a potassium cation chelated inside a cryptand‐222 molecule; the average K—O and K—N distances are 2.81 (2) and 3.05 (2) Å, respectively. One of the protecting tert‐butyl pickets is disordered. The porphyrin plane presents a moderately ruffled distortion, as suggested by the atomic displacements. The axial chloride ligand is located inside the molecular cavity on the hindered porphyrin side and the Fe—Cl bond is tilted slightly off the normal to the porphyrin plane by 4.1°. The out‐of‐plane displacement of the metal centre relative to the 24‐atom mean plane (Δ₂₄) is 0.62 Å, indicating a noticeable doming of the porphyrin core.     

The crystal structure of tetrachloro(diethylphthalate)titanium(IV)

The crystal structure of [C₆H₄(OCOC₂H₅)₂TiCl₄], which in the presence of activators is a good catalyst for olefin polymerization, has been determined by X-ray diffraction methods and refined by full-matrix least-squares techniques to R = 0.045 for 2000 independent non-zero reflexions. Crystals are orthorhombic, space group Pnma, with four molecules in a cell of dimensions: a 11.45(1), b 14.07(1), c 10.56(1) Å. The structure consists of discrete molecules possessing crystallographic m (C_s) point symmetry. The Ti atoms are octahedrally coordinated by four chlorine atoms and two carbonyl oxygen atoms of diethylphthalate. The chelating ligand atoms together with the titanium atom form a seven-membered ring with the Cl and Ti atoms located above the benzene ring.     

Crystal and molecular structure of bis(N,N-dipropyl-N′-diphenoxythiophosphoryl-thioureato) nickel(II) [(C6H5O)2P(S)NC(S)N(C3H7)2]2Ni

The Ni complex [C₆H₅O₂P(S)N(C₃H₇₂]₂Ni is monoclinic, space group P2₁/n with a = 8.890(3), b = 21.692(5), c = 11.670(4) Å, β = 108.35(5)°, V = 2136(1) ų, F(000) = 916, M_r = 534.01, Z = 2, D_m = 1.318, D_x = 1.358 Mg m^?3, graphite monochromatized MoKα ^? radiation, π = 0.7107 Å, μ = 0.76 mm^?1, T = 293 K. The structure was solved by a heavy atom method and refined to R = 0.044 for 3095 independent reflexions. The Ni atom lies in the centre of symmetry and is coordinated by four S atoms of the two molecules of the ligand in a planar arrangement. Ni? S bond lengths are 2.205 and 2.226 Å resp., the angles S? Ni? S are 97.65 and 82.35° resp.     

Untersuchungen an katalytisch aktiven Oberflächenverbindungen. II. Zur Existenz unterschiedlicher Vanadium(V)-oxid-Oberflächenphasen auf SiO2 und ihre katalytischen Eigenschaften

Studies on Catalytically Active Surface Compounds. II. On the Existence of Different Vanadium(V) Oxide Surface Phases on SiO₂ and their Catalytic Properties In dependence on the SiOH concentration of the Aerosil surface two different disperse vanadium(V) oxide phases are obtained, which differ characteristically in their reflexion spectra, their chemisorption behaviour towards butene and their catalytic properties in the oxidation of butene and ethanol. At high values of the original concentration of SiOH groups a δ″ phase is formed which gives after desorption of adsorbed water at 250°C, a reflexion spectrum that points at a tetrahedral coordination of the V^v; this phase shows a relative low activity for both reactions. At a lower original concentration of SiOH a δ″ phase of the vanadium(V) oxide is formed, the reflexion spectrum of which, points at an octahedrally coordinated vanadium(V) oxide. This phase is considerably more active than the former.     

Synthesis and crystal structure of 4,7,13,16,21,24-hexaoxa-1,10-diazoniabicyclo[8.8.8]hexacosane bis(hydrogen oxalate)

A crystalline salt of 2.2.2-cryptand and oxalic acid, 4,7,13,16,21,24-hexaoxa-1,10-diazoniabicyclo[8.8.8]hexacosane bis(hydrogen oxalate), [H₂(Crypt-222)]²⁺·2(C₂HO₄)^?, was synthesized and studied by single crystal X-ray diffraction. In the crystal structure of this salt, the 2.2.2-cryptand cation has a rare conformation of the exo-exo type in which the H atoms at the two protonated N atoms are oriented outside the cryptand cavity. The geometric parameters (bond lengths, bond angles, torsion angles) of the [H₂(Crypt-222)]²⁺ cation and two independent C₂HO ₄ ^? anions were found with a fairly high accuracy, and the crystal packing was determined. These ions are linked by interionic hydrogen bonds to form thick infinite layers parallel to the (xz) plane.     

Chelatkomplexe von Rheniumtetrachlorid. Die Kristallstrukturen von ReCl4(DME) und ReCl4(DPPE) · Tolan

Chelate Complexes of Rhenium Tetrachloride. The Crystal Structures of ReCl₄(DME) and ReCl₄(DPPE) · Tolan Bright green crystals of ReCl₄(DME) have been prepared by the reaction of rhenium pentachloride with dimethoxyethane (DME) in dichloromethane. ReCl₄(DPPE) · tolan was obtained in form of red crystals by the reaction of the alkyne complex [ReCl₄(Ph? C?C? Ph)(POCl₃)] with bis(diphenylphosphino)ethane (DPPE) in dichloromethane. The complexes were characterized by X-ray structure determinations. ReCl₄(DME): Space group I4 2d, Z = 8, 829 observed unique reflexions, R = 0.022. Lattice dimensions at 19.5°C: a = b = 960.60(6), c = 2337.2(6) pm. The complex forms monomeric molecules with DME as chelating ligand; the Re? O bond lengths are 213.1 pm. The chlorine atoms, arranged in trans position to the chelating ligand, have slightly shorter Re? Cl bonds than the chlorine atoms in cis position (232,1 pm). ReCl₄(DPPE) · tolan: Space group P2₁/n, Z = 4,4313 observed unique reflexions, R = 0.040. Lattice dimensions at ?80°C: a = 1095.7(1), b = 1764.2(2), c = 1898.0(2) pm, β = 99.229(8)°. The compound consists in form of monomeric molecules [ReCl₄(DPPE)] and diphenylacetylene molecules, which are incorporated in the lattice. The two phenyl rings of the tolan molecules are twisted towards each other along the C? C axis with a dihedral angle of 21°. The DPPE molecules are bonded to the rhenium atom in a chelating fashion with medium Re? P lengths of 250.4 pm. The chlorine atoms, arranged in trans position to this ligand, with Re? Cl bond lengths of 234.5 pm are slightly longer than the Re? Cl bonds in cis position with 232.3 pm.     

An independent investigation of the crystal structure of 1,8-dinitronaphthalene (orthorhombic form) at 22 and 97°C

The crystal and molecular structure of the orthorhombic form of 1,8-dinitronaphthalene, C₁₀H₆N₂O₄, has been reinvestigated at 22°C and examined at 97°C using single-crystal diffractometer data in order to throw some light on the structural aspects of the polymorphism of the title compound. The space group of the crystal is P2₁2₁2₁ with a = 11.375 (1), b = 14.974 (5), c = 5.388 (1) Å at 22°C and a = 11.475 (1), b = 15.002 (1), c = 5.425 (6) Å at 97°C. Z = 4 at both temperatures. The data, collected with CuK_α radiation, were refined by full-matrix least squares to R = 0.049 for 1087 reflexions (22°C) and R = 0.061 for 1078 reflexions (97°C). The structure was found to be in agreement with that determined by Z. A. Akopian, A. I. Kitaigorodskii, T. J. Struchkov (Zh. Strukt. Khim.6, 729 (1965)). Changes occurring on heating to a temperature of 97°C, which is close to the transition temperature (of c → pc type) 100–105°C, suggest that the possible mechanism of the phase transition is that of the displacive transformation of secondary coordination. Anistotropic temperature factors of the majority of atoms increased by ca. 50% with no particular direction of atom vibrations being distinguished.     

Synthesis and crystal structure of (S)-(+)-2-[(1,1-dimethylethoxy)carbonyl] amino-2-phenylethanol

The preparation and the crystal structure of the title compound are described. C₆H₅CH[NHCOOC(CH₃)₃]CH₂OH is monoclinic with the following unit-cell dimensions: a = 10.354(2), b = 6.533(3), c = 10.505(1) Å, β = 98.58(1)∘. The space group is P2₁ and Z = 2. The crystal-structure determination was run by using 1481 independent reflexions with a final R value of 0.033 (R_w = 0.043).     

Silber(I)-catena-Polysilicat Kristallzüchtung und Strukturanalyse

On Silver(I)-catena-Polysilicate, Crystal Growth, and Structure Determination Ag₂SiO₃ has been synthesized as powder and single crystals from the binary components applying hydrothermal conditions. According to the results of an X-ray crystal structure analysis (P2₁2₁2₁; a = 452.7(1), b = 710.8(1), c = 995.9(1) pm; Z = 4; 1387 reflexions, 57 refined parameters; R = 0.060) the title compound contains a ‘zweier single chain’ catena-polysilicate anion. The UV/VIS absorption spectrum shows an absorption edge at 19700 cm^?1.     

Ein- und zweikernige Dinitrosylkomplexe von Molybdän und Wolfram. Die Kristallstrukturen von (PPh3Me)2[WCl4(NO)2], (PPh3Me)2[MoCl3(NO)2]2 und von (PPh3Me)2[WCl3(NO)2]2

Mono- and Binuclear Dinitrosyl Complexes of Molybdenum and Tungsten. Crystal Structures of (PPh₃Me)₂[WCl₄(NO)₂], (PPh₃Me)₂[MoCl₃(NO)₂]₂, and (PPh₃Me)₂[WCl₃(NO)₂]₂ The complexes (PPh₃Me)₂[MCl₄(NO)₂] (M = Mo, W), and (PPh₃Me)₂[MCl₃(NO)₂]₂, respectively, are prepared by reactions of the polymeric compounds MCl₂(NO)₂ with triphenylmethylphosphonium chloride in CH₂Cl₂, forming green crystals. According to the IR spectra the nitrosyl groups are in cis-position in all cases. The tungsten compounds as well as (PPh₃Me)₂[MoCl₃(NO)₂]₂ were characterized by structure determinations with X-ray methods. (PPh₃Me)₂[WCl₄(NO)₂]: space group C2/c, Z = 4. a = 1874, b = 1046, c = 2263 pm, β = 119.99°. Structure determination with 3492 independent reflexions, R = 0.057. The compound consists of PPh₃Me^⊕ ions, and anions [WCl₄(NO)₂]^2? with the nitrosyl groups in cis-position (symmetry C_2v). (PPh₃Me)₂[WCl₃(NO)₂]₂: Space group C2/c, Z = 4. Structure determination with 2947 independent reflexions, R = 0.059. (PPH₃Me)₂[MoCl₃(NO)₂]₂: Space group P1 , Z = 1. a = 989, b = 1134, c = 1186 pm; α = 63.25°, β = 80.69°, γ = 69.94°. Structure determination with 3326 independent reflexions, R = 0.046. The compounds consist of PPh₃Me^⊕ ions, and centrosymmetric anions [MCl₃(NO)₂]₂^2?, in which the metal atoms are associated via MCl₂M bridges of slightly different lengths. One of the NO groups is in an axial position, the other one in equatorial position (symmetry C_2h).     

Abiotic reduction of uranium by mackinawite (FeS) biogenerated under sulfate-reducing condition

Sulfate-reducing bacteria and their by-products, such as iron sulfides, are widely distributed in groundwater and sediments, and can affect subsurface aqueous chemistry. Here we show the catalytic reduction of hexavalent uranium by FeS particles, which were largely generated by the activities of Desulfovibrio desulfuricans and D. vulgaris in anaerobic condition. Characterization of FeS particles by X-ray diffraction and high-resolution transmission electron microscopy revealed the presence of mackinawite having thin and flexible platy sheets with 0.5-nm lamellar spacing. This biogenic phase mediated abiotic reduction of U(VI) to U(IV) which was confirmed by UV–Vis absorption spectroscopy. The U conversion occurred through surface catalysis that involved adsorption of aqueous U(VI)–carbonate complexes (predominantly UO₂(CO₃) ₃ ^4? ) onto the mackinawite, but the transformed uranium was then released and remained in suspended form in the solution phase. This surface catalysis and subsequent U(IV) remobilization has not been reported as a pathway to occur under sulfate-reducing conditions. Our results suggest that the iron sulfide solid, which is characteristic of conductive property, is very sensitive and variable depending on the electron supplying and transferring environment, negatively affecting the surface uranium to be strongly stabilized and fixed on the FeS surface.     

Die Kristallstruktur von [Cl4P{i-Prop-NC(Cl)N-i-Prop}]

Crystal Structure of [Cl₄P{i-Prop-NC(Cl)N-i-Prop}] The monomeric di-isopropylcarbodiimide complex [Cl₄P{i-Prop-NC(Cl)N-i-Prop}] crystallizes in the monoclinic space group C2 with 4 formula units in the unit cell and with the lattice constants a = 1391.2(2), b = 708.6(1), c = 1463.5(2) pm and β = 95.76(1)°. The structure was refined to an R-value of 0.026 (2084 independent, observed reflexions). Main parts of the IR and Raman spectrum of the compound are discussed.     

Synthesis and crystal structure of bis(2,2,2-cryptand potassium) tetrakis(isocyanato)cuprate(II)

A new complex compound, bis(2,2,2-cryptand potassium) tetrakis(isocyanato)cuprate(II), 2[K(Crypt-222)]⁺ [Cu(NCS)4]^2? was prepared and its crystal structure was studied by X-ray structural analysis. The structure includes one symmetrically independent complex cation [K(Crypt-222)]⁺ of a guest-host type and independent one half of [Cu(NCS)₄]^2? anion. Through the center of the anion passes crystallographic symmetry axis 2, the approximate point symmetry of the anion is D ₂, while the approximate point symmetry of the complex cation is D ₃. The coordination polyhedron of the [Cu(NCS)₄]^2? anion (four N atoms) conjugated with Cu²⁺ cation is a nonplanar square considerably screwed into a flattened tetrahedron. The K⁺ cation (coordination number 8) of the complex cation [K(Crypt-222)]⁺ is coordinated by all eight heteroatoms (6O + 2N) of the 2,2,2-cryptand ligand, and its coordination polyhedron can be described as bis-basecentered trigonal prism slightly screwed into an anti-prism.     

Präparation und Kristallstrukturanalyse von Ca(N3)2(C5H5N)2

Diazido-dipyridine-calcium was prepared by the reaction of Ca(N₃)₂ with pyridine. The crystals are tetragonal, space group I 2 m (121),N=2,a=699.7 (1),c=1 450.6 (5) pm. The crystal structure was determined by single crystal X-ray diffraction, 415 independent observed Mo-K-counter reflexions,R=0.049. The calcium atoms are sixcoordinated to four nitrogen atoms of azide groups and to two nitrogen atoms of pyridine. The coordination polyhedra are tetragonal bipyramids which are linked together by four azide groups to form sheets of composition Ca(N₃)₂. The pyridine rings are directed perpendicular to the sheets.

     

Crystal structure of the bis(isothiocyanato)tetrakis(pyridine)nickel(II) clathrate with a pyridine guest [NiPy4(NCS)2]·2Py

The structure of the [NiPy₄(NCS)₂]·2Py clathrate was determined by single crystal X-ray diffraction analysis (Enraf-Nonius CAD4 diffractometer, λCuK_α radiation, Ni filter, ω/2θ scan mode, θ_max, 511 reflections, R=0.046). The crystals are tetragonal, space group 14₁/acd, a=16.079(2), c=27.150(7) Å, Z=8 C₃₂H₃₀N₈NiS₂, d_calc=1.229 g/cm³. The structure is of the island type and consists of distorted octahedral trans-[NiPy₄(NCS)₂] (host) and pyridine (guest) molecules. The Ni(II) cation is coordinated by six nitrogen atoms and occupies the 222 special position. One of the twofold axes passes axially through the nickel(II) cation and the atoms of the isothiocyanate groups, and the two other axes lie in the equatorial plane of the Ni(N_Py)₄ complex as diagonals between the Ni−N_Py bonds. The Ni−N_CS and Ni−N_Py distances are 2.033(7) and 2.121(4) Å, respectively. The rings of the pyridine ligands form angles of 53.2(2)° with the equatorial plane of the complex. The guest pyridine molecules lie inside the winding channels running along the c axis. Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Institute of Physical Chemistry, Polish Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 6, pp. 1074–1082, November–December, 1995. Translated by L. Smolina