Electrical conductivity of Th3P4-type EnLn2S4

Electrical conductivity measurements of Th₃P₄-type EuLn₂S₄ (Ln = LaGd) compounds have been made as functions of temperature and sulfur vapor pressure. These compounds are all p-type semiconductors, and their conductivities at room temperature have almost the same values for the specimens from EuLa₂S₄ to EuNd₂S₄ but increase on going from EnNd₂S₄ to EuGd₂S₄. In addition, the conductivity of EuGd₂S₄ is sensitive to sulfur vapor pressure and obeys the relationship . The mechanism of electrical transport in these compounds is discussed.     

Halogen cleavage reactions of cis-(threo-PhCHDCHD)Mn(CO)4PEt3

Halogen cleavage reactions of $\text{cis}$-($\text{threo}$-PhCHDCHD)Mn(CO)₄, PEt₃ ($\text{3}$) are studied in detail and are found to proceed either predominantly with retention or inversion, or non-stereospecifically, depending on reaction conditions. Reaction mechanisms involving S_E2 (inversion), S_E2 (retention) and S_E (oxidative) processes are proposed, demonstrating that halogen cleavage reactions of $\text{3}$ straddle the mechanistic borderline between electrophilic substitution and oxidation processes of transition metal alkyl compounds.     

Crystal structures of V3S4 and V5S8

Crystal structures of the ordered phases of V₃S₄ and V₅S₈ were refined with single crystal data. Both are monoclinic. Chemical compositions, space groups and lattice constants are as follows: VS_1.47, $\text{I2}\text{m}$ (No. 12), a = 5.831(1), b = 3.267(1), c = 11.317(2)Å, β = 91.78(1)° and VS_1.64, $\text{F}\text{2}\text{m}$ (No. 12), a = 11.396(11), b = 6.645(7), c = 11.293(4), Å, β = 91.45(6)°. In both structures, short metal-metal bonds were found between the layers as well as within them. In comparison with the structure of Fe₇S₈, the stability of NiAs-type structure was discussed based on the detailed metal-sulfur distances.     

N-lines and chromium-pairs in the luminescence spectra of the spinels ZnAl2O4:Cr3+ and MgAl2O4:Cr3+

It is shown that the N-lines in the luminescence spectra of the two spinels ZnAl₂O₄:Cr³⁺ and MgAl₂O₄:Cr³⁺ exhibit quite similar dependencies on chromium concentration, excitation frequency, and thermal treatment of the samples. While most of these lines are structure dependent, the line N₄ at $\text{ν}{}_{\mathrm{R}}\text{?}\text{ν}\text{≈ 400}\text{cm}{}^{\mathrm{?1}}$ and two very weak lines are in both cases due to chromium-pairs. The exchange Hamiltonian H_ex = JS₁ · S₂ + j(S₁ · S₂)² used for the ground-state splitting is fitted by the parameters J = 40.9 cm^?1, j = 1.5 cm^?1 and J = 45.6 cm^?1, j = 2.0 cm^?1 for ZnAl-spinel and MgAl-spinel, respectively. The differences between the spectra of low-doped and high-doped samples are in both cases caused by the existence of a phonon sideband of the N₄-line, which is in many respects similar to the well-known phonon side band of the R-line.     

Solvolytic behavior of p-dimethylamino-α-bromostyrene in water solutions

Nmr and UV studies show that $\text{p}$-dimethylamino-$\text{α}$-bromostyrene, I, undergoes S_Nl reaction in H₂O and HClO₄ (^kS_Nl = 6 × 10^?1sec.^?1 at 25°). The vinyl cation has an extraordinary selectivity for capture by aromatic amines relative to H₂O, including I itself to give the dimer II.     

Cis-trihetero-tris-σ-homobenzenes as tridentate ligands - X-ray crystal. Structure analyses of the Co(C6H9N3)2(NO3)3 and Ba(C6H6O3)4(ClO4)2-complexes

According to X-ray crystal structure analyses “cis-benzenetrisimine” ($\text{2}$) and “cis-benzenetrioxide” ($\text{1}$) act as tridentate ligands in their 2:1- and 4:1-complexes $\text{7}$ (Co(C₆H₉N₃)₂(NO₃)₃) and $\text{8}$ (Ba(C₆H₆O₃)₄(ClO₄)₂), resp. The latter is the rare example of an organic complex with the (approximate) T-symmetry.     

Structural behavior of the ferromagnetic spinels AlxMo2S4 and GaxMo2S4, containing tetrahedral clusters of molybdenum atoms

The structure of the ferromagnetic spinels Al_xMo₂S₄ and Ga_xMo₂S₄ (x ～ 0.5) was determined from powder diffraction data. The Al and Ga atoms order on the tetrahedral sites. The space group is $\text{F}\text{4}\text{3m; a = 9.726}$ Å for Al_xMo₂S₄ and 9.739 Å for Ga_xMo₂S₄. The Mo atoms were found to shift towards the tetrahedral site vacancies, created by the lower Al and Ga concentrations. This results in tetrahedral clusters of Mo around the vacancies. Their semiconducting and magnetic behavior was explained on the basis of the structural behavior of the molybdenum lattice in these spinel compounds.     

Etude par diffraction de neutrons de la phase Sr0,5La1,5Li0,5Fe0,5O4

A neutron diffraction study has been carried out on Sr_0.5La_1.5Li_0.5Fe_0.5O₄ of K₂NiF₄-type derived structure and it has shown that iron in the tetravalent state has a high spin configuration (t³_2ge¹_g) and that the material has some stacking defects. At room temperature this compound shows an ordering between iron and lithium atoms leading to a nuclear cell a₀√2, a₀√2, c₀ (a₀ and c₀ are the parameters of the K₂NiF₄-type cell). At low temperature ($\text{T <}\text{T}{}_{\mathrm{<mtext>N</mtext>}}\text{2}$) the magnetic structure can be described as antiferromagnetic, corresponding likely to a colinear pattern with a propagation vector of 0.5 ($\text{2π}\text{a}{}_0$) along the [110] axis. At higher temperature ($\text{T}{}_{\mathrm{<mtext>N</mtext>}}\text{2}\text{< T < T}{}_{\mathrm{<mtext>N</mtext>}}$) helimagnetic structure is consistent with a propagation vector of 0.47 ($\text{2π}\text{a}{}_0$) [110].     

The phase relationship among compounds Ba1+xFe2S4

The dependence of composition of the phases Ba_1+xFe₂S₄ on sulfur vapor pressure and starting composition was investigated at 650, 747, and 800°C. The infinitely adaptive series Ba_1+xFe₂S₄ spans the compositions 0.072 ≤ x ≤ 0.142. The value of x decreases as the sulfur vapor pressure increases at a given temperature. Varying the ratio of $\text{Ba}\text{Fe}$ in the starting mixture has no effect on the Ba_1+xFe₂S₄-sulfur fugacity relationship. The phase BaFe₂S₄ is not part of the infinitely adaptive series.     

Mössbauer spectra,magnetic and electrical behavior of Ba1+xFe2S4 phases

The Mössbauer spectra, and magnetic and electrical properties of Ba_1+xFe₂S₄ infinitely adaptive phases with 0.074 ≤ x ≤ 0.142 and of BaFe₂S₄ were studied. The properties are highly anisotropic because of the presence in the structure of one-dimensional infinite chains of edge sharing FeS₄ tetrahedra. BaFe₂S₄ is a semiconductor, E_g = 0.66 eV; magnetic susceptibility can be fit by a one-dimensional Heisenberg model with spin $\text{5}\text{2}$ and $\text{J}\text{k}\text{= ?30°}\text{K}$. The Ba_1+xFe₂S₄ phases have Curie-Weiss behavior with an effective moment of about 2 B.M. The moment increases with x. These phases are metallic. The Mössbauer isomer shift varies linearly with valence, increasing with increasing x. The single quadrupole split absorption line characteristic of these compounds disappears at about 270°K and a complex spectrum consisting of overlapping hyperfine patterns appears at lower temperatures. Magnetic short-range ordering is responsible for this behavior although the susceptibility in this temperature range does not reflect this effect.     

Assymetric reduction of ketones using LiAlH4 modified with chiral 1,2-aminodiols.txt

Four chiral aminodiols from ring opening of ($\text{S}$)-propylene oxide and ethylene oxide wiht n-butylamine and ($\text{R}$) or ($\text{S}$)-α-methylbenzylamine were used to modify LiAlH₄. Assymetric reduction of acetophenone and propiophenone gave the highest percent enantiomeric excess when the modifier was made from ($\text{S}$)-oxide and ($\text{S}$)-amine.     

New SbS2 strings in the BaSb2S4 structure

The new compound BaSb₂S₄ crystallizes in the monoclinic system (space group: $\text{P2}{}_1\text{c}$, No. 14) with a = 8.985(2) Å, b = 8.203(3) Å, c = 20.602(5) Å, β = 101.36(3)°. SbS₃ ψ tetrahedra and ψ-trigonal SbS₄ bipyramids are connected by common corners and edgers to infinite strings. These are arraged cross-wise in sheets perpendicular to the c axis.     

Evidence for N2N3N45 super coster kronig processes in metallic Nb,Mo, Ru and Rh

The 4p photoelectron spectra of metallic Nb, Mo, Ru and Rh have been recorded. By use of a deconvolution procedure it is shown that the 4p_{$\text{1}\text{2}$} spin-orbit component has a linewidth which significantly exceeds that of the 4p_{$\text{3}\text{2}$} component. This suggests that N₂N₃N₄₅ super Coster Kronig processes give a considerable contribution to the decay rata of the 4p_{$\text{1}\text{2}$} hole state.     

Chiral discrimination in the reactions of the enolate E-[(η5-C5H5)Fe(CO)(PPh3)COCHMe]−Li+ with cis and trans but-2-ene oxides in the presence of BF3·OEt3

$\text{cis}$ and $\text{trans}$-but-2-ene oxides undergo S_N2 opening with the lithium enolate derived from [(η⁵-C₅H₅)Fe(CO)(PPh₃)COCH₂CH₃] in the presence of BF₃·OEt₂; preferential opening occurs where the enolate configuration at iron matches that of the epoxide carbon being attacked.     

The preparation of hot-pressed chalcogenide spinels. II. Stoichiometry and optical transparency in CdCr2S4 and CoCr2S4

The compounds CdCr₂S₄ and CoCr₂S₄ have been hot pressed into disks that are highly transparent in the infrared. Stoichiometry has been altered by varying the $\text{Cr}{}^{\mathrm{3+}}\text{M}{}^{\mathrm{2+}}$ ratio, where M²⁺ is Cd²⁺ or Co²⁺. The effects of nonstoichiometry on optical transmission were determined. Excess M²⁺ attenuates the transmission much more than excess Cr³⁺.     

The spin 32 state (?) in six-coordinate iron (III). A Mössbauer and EPR investigation

Tris-(4-morpholinecarbodithioato-S,S′) iron (III) (FeM) and its dichloromethane solvate, (FeM·CH₂Cl₂), have been prepared and their temperature-dependent Mössbauer and EPR spectra have been determined at temperatures between liquid nitrogen and ambient. The Mössbauer spectra of FeM·CH₂Cl₂ differ considerably from that of FeM and is interpreted in terms of a four-line spectrum at 77 K. The EPR spectra of the two complexes indicate that the lower spin state of FeM·CH₂Cl₂ populates much more rapidly in the temperature range studied (100–300 K) than does FeM. These results support the postulation of an S = $\text{5}\text{2}$ ? S = $\text{1}\text{2}$ spin-equilibrium for FeM and a corresponding S = $\text{5}\text{2}$ ? S = $\text{3}\text{2}$ equilibrium for FeM·CH₂Cl₂.     

Laser-induced fluorescence of high-temperature vapor complexes of ErCl3 with AlCl3, GaCl3 and InCl3

Laser excitation of equilibrium vapor mixtures ErCl₃(s)-ACl₃(g) (A = Al, Ga, In) at 475–1100 K gives rise both to resonance fluorescence from the f → f Er³⁺ transitions of the Er-Cl-A vapor complexes, and to Raman scattering due to the vibrational modes of the ACl₃ vapor. The laser-induced fluorescence from the ⁴F_{$\text{9}\text{2}$}, ⁴S_{$\text{3}\text{2}$} and ²H_{$\text{11}\text{2}$} states has been investigated at different temperatures and excitation.     

Comparative reactions between aziridines and F2, COF2, CF3OF

In CFCl₃, aziridines $\text{I}$ react with F₂(6 %/N₂,  20°C), COF₂ (20 %/N₂,  40°C) and CF₃OF [1] (20 %/N₂,  40°C).Substitution products are obtained : l-(aziridine)carbonyl fluorides $\text{II}$ and l-Fluoroaziridines $\text{III}$

In (Et)₂O, aziridines $\text{I}$ react with COF₂ (20 %/N₂, 10°C) and we have the carbonyl fluorides $\text{IV}$.

Products IV can be thermally decomposed into β fluoro isocyanates.In CFCl₃, N substituted aziridines $\text{V}$ react with F₂(6%/N₂, 20°C) and with CF₃OF [2] (20%/N₂, 40°C). No reaction is observed with COF₂in our conditions (5% to 25%/N₂, 80°C to + 40°C).Addition products are obtained : N Fluoro amines β fluorinated $\text{VI}$, N Fluoro and NN difluoro amines β trifluoro methoxylated $\text{VII}$ and $\text{VIII}$.

with R = SO₂Ø, COØNO₂, Cl.     

Structure models for β-MnGa2S4 as derived from electron diffraction and high-resolution electron microscopy

A study by high-resolution electron microscopy and electron diffraction on the tetrahedrally coordinated compound β-MnGa₂S₄ is reported. The structure-imaging technique enabled a new structure model to be proposed for the accommodation of deviations from stoichiometry in compounds of the type $\text{x}\text{MnS}\text{y}\text{Ga}{}_2\text{S}{}_3$. The model is based on the Ga₂S₃ structure wherein by the substitution of MnS layers chemical twin planes are formed. Depending on the spacing of the periodic twin planes a homologous series of compounds is expected and a number of members of this series was identified mainly by electron diffraction. In the β-MnGa₂S₄ compound, two structure modifications are observed mainly differing in the orientation of the twin planes (coherent or incoherent). This conclusion is substantiated by structure image calculations for the interpretation of the high-resolution results.     

The crystal structure of Ca6Eu2Na2(PO4)6F2

The crystal structure of Ca₆Eu₂Na₂(PO₄)₆F₂ has been determined by single crystal X-ray diffraction. The unit cell constants are $\text{a = 9.385(2), c = 6.893(3)}\text{A}\text{?}$ and the space group is $\text{P6}{}_3\text{m}$. The structure was refined by normal full matrix least squares techniques. The final value of the refinement indicator is R = 0.065, based on 419 reflections.The structure of Ca₆Eu₂Na₂(PO₄)₆F₂ contains disordered cations in both the triangle and column positions. The occupation of the six triangle sites is $\text{1}\text{4}\text{Eu}$ and $\text{3}\text{4}\text{Ca}$ and of the four column sites $\text{1}\text{2}\text{Na}\text{,}\text{4}\text{10}\text{Ca}$, and $\text{1}\text{10}\text{Eu}$.