Magnetic and Electrical Properties, Eu Mössbauer Spectroscopy, and Chemical Bonding of REAgMg (RE=La, Ce, Eu, Yb) and EuAuMg

Single-phase samples of REAgMg (RE=La, Ce, Eu, Yb) and EuAuMg were prepared by reacting the elements in sealed tantalum tubes in a high-frequency furnace. LaAgMg and CeAgMg adopt the hexagonal ZrNiAl-type structure, while EuAgMg, YbAgMg, and EuAuMg crystallize with the orthorhombic TiNiSi type. Chemical bonding was exemplarily investigatedfor EuAgMg and EuAuMg on the basis of TB-LMTO-ASAcalculations. Magnetic susceptibility measurements indicatePauli paramagnetism for LaAgMg and YbAgMg with room-temperature susceptibilities of 2.4(1)×10⁻⁹ and 1.5(1)×10⁻⁹ m³/mol, respectively. CeAgMg remains paramagnetic down to 2 K. The experimental magnetic moment of 2.52(2) μ_B/Ce above 50 K is compatible with trivalent cerium. EuAgMg and EuAuMg are paramagnetic above 50 K with experimentalmagnetic moments of 7.99(5) μ_B/Eu for the silver and 7.80(5) μ_B/Eu for the gold compound, indicating divalent europium. Ferromagnetic ordering is detected at T_C=22.0(3) K (EuAgMg) and T_C=36.5(5) K (EuAuMg). At 4.2 K and 5 T the saturation magnetizations are 7.1(1) and 7.3(1) μ_B/Eu for EuAgMg and EuAuMg, respectively. According to the very small hysteresis, EuAgMg and EuAuMg may be classified as soft ferromagnets. All compounds are metallic conductors. For EuAgMg and EuAuMg freezing of spin-disorder scattering is observed below T_C. At 78 K ¹⁵¹Eu Mössbauer spectra show isomer shifts of −9.00(4) and −8.72(8) mm/s for EuAgMg and EuAuMg, respectively. Full magnetic hyperfine field splitting is detected at 4.2 K with hyperfine fields of 17.4(1) and 18.3(2) T at the europium nuclei of EuAgMg and EuAuMg.     

Decomposition of EuPdIn and EuPtIn at high temperature and high pressure—formation of the hexagonal Laves phases EuPd0.72In1.28 and EuPt0.56In1.44

EuPd_0.72In_1.28 and EuPt_0.56In_1.44 were prepared under multianvil high-pressure (10.5 GPa) high-temperature (1500 and 1400 K) conditions from the precursor compounds EuPdIn and EuPtIn. They were investigated by X-ray diffraction on both powders and single crystals: MgZn₂-type, space group P6₃/mmc, a=578.7(1) pm, c=944.9(3) pm, wR2=0.0734, 263 F² values for EuPd_0.72In_1.28 and a=591.1(2) pm, c=933.8(2) pm, wR2=0.0853, 151 F² values for EuPt_0.56In_1.44 with 13 variable parameters per refinement. Both structures are built up from face- and corner-sharing tetrahedra of palladium (platinum) and indium atoms. The europium cations are located in cavities within the three-dimensional [Pd_0.72In_1.28] and [Pt_0.56In_1.44] networks. The 2a and 6 h positions of the tetrahedral networks show mixed Pd/In and Pt/In occupancy in EuPd_0.72In_1.28 and EuPt_0.56In_1.44, respectively. The crystal chemistry of these indides is briefly discussed.     

Direct fission versus sequential evaporation mechanism of sputtered caesium iodide cluster ions

A triple stage hybrid mass spectrometer was scanned for the trapping of the reaction intermediates of the over-all loss of two CsI-moieties from size-selected caesium iodide cluster ions of the general formula Cs (CsI)⁺ _n . In addition to appropriate MS/MS/MS-methods an electrically floated collision cell has been applied to trap intermediates of unimolecular and collision-induced evaporations. In comparison with other experimental findings the features of the evaporation mechanism are discussed.     

Effect of solvent upon competitive liquid-liquid extraction of alkali metal cations by isomeric dibenzo-16-crown-5-oxyacetic acids

The selectivity and efficiency of competitive liquid-liquid extraction of alkali metal cations into organic solvents containingsym-(octyl)dibenzo-16-crown-5-oxyacetic acid (2) andsym-bis[4(5)-tert-butylbenzo]-16-crown-5-oxyacetic acid (3) have been determined. Solvents examined include: dichloromethane, chloroform, carbon tetrachloride, 1,2-dichloroethane, 1,1,1-trichloroethane, benzene, toluene,p-xylene, chlorobenzene, 1,2-dichlorobenzene, and 1,2,3,4-tetrahydronaphthalene. The Na⁺/K⁺ and Na⁺/Li⁺ extraction ratios are highest in chloroform. The extraction selectivity is found to correlate with the diluent parameter (DP) of the organic solvent.This paper is dedicated to the memory of the late Dr C. J. Pedersen.     

Darstellung,Ramanspektren und Kristallstrukturen von V2O3(SO4)2, K[VO(SO4)2] und NH4[VO(SO4)2]

Preparation, Raman Spectra, and Crystal Structures of V₂O₃(SO₄)₂, K[VO(SO₄)₂], and NH₄[VO(SO₄)₂] The oxo-sulfato-vanadates(V) V₂O₃(SO₄)₂, K[VO(SO₄)₂], and NH₄[VO(SO₄)₂] have been prepared as crystals suitable for X-ray structure determination. In all structures sulfate acts as an unidentate ligand only toward a single vanadium atom. The structure of V₂O₃(SO₄)₂ consists of a threedimensional network of pairs of cornershared VO₆ octahedra with one terminal oxygen atom each, and SO₄ tetrahedra. All oxygen atoms of the sulfate ions are coordinated. NH₄[VO(SO₄)₂] and K[VO(SO₄)₂] are isostructural. VO₆ octahedra with one terminal oxygen atom and pairs of sulfate tetrahedra form infinite chains by corner sharing. The chains are weakly interlinked to layers. The sulfate ions are distorted towards planar SO₃ molecules and single oxygen atoms attached to vanadium. This structural detail gives an explanation for the mechanism of the reversible reaction K[VO(SO₄)₂] ? K[VO₂(SO₄)] + SO₃ at 400°C. Raman spectra of the compounds have been recorded and interpreted with respect to their structures. Crystal data: V₂O₃(SO₄)₂, monoclinic, space group P2₁/a, a = 947.2(4), b = 891.3(3), c? 989.1(4) pm, β = 104.56(3)°, Z = 4, 878 unique data, R(R_w) = 0.039(0,033); K[VO(SO₄)₂], orthorhombic, space group P2₁2₁2₁, a = 495.3(2), b = 869.6(9), c = 1 627(1)pm, Z = 4, 642 unique data, R(R_w) = 0,11(0,10); NH₄[VO(SO₄)₂], orthorhombic, space group P2₁2₁2₁, a = 495.3(1), b = 870.0(2), c = 1 676.7(4)pm, Z = 4, 768 unique data, R(R_w) = 0.088(0.083).     

α-Methylidene- and α-Alkylidene-β-lactams from Nonproteinogenic Amino Acids

Treatment of methyl 2-(1-hydroxyalkyl)prop-2-enoates 1 with conc. HBr solution afforded methyl (Z)-2-(bromomethyl)alk-2-enoates 2 , which were transformed regioselectively into N-substituted methyl (E)-2- (aminomethyl)alk-2-enoates 3 (S_N2 reaction) and into N-substituted methyl 2-(1-aminoalkyl)prop-2-enoates 4 (S_N2′ reaction). Regiocontrol of nucleophilic attack by amine was accomplished simply by choice of solvent, the S_N2 reaction occurring in MeCN and the S_N2′ reaction in petroleum ether. Hydrolysis and lactamization afforded β-lactams 7 and 8 , containing an exocyciic alkylidene and methylidene group at C(3), respectively.     

Pseudochelin A,a siderophore of Pseudoalteromonas piscicida S2040

A new siderophore containing a 4,5-dihydroimidazole moiety was isolated from Pseudoalteromonas piscicida S2040 together with myxochelins A and B, alteramide A and its cycloaddition product, and bromo- and dibromoalterochromides. The structure of pseudochelin A was established by spectroscopic techniques including 2D NMR and MS/MS fragmentation data. In bioassays selected fractions of the crude extract of S2040 inhibited the opportunistic pathogen Pseudomonas aeruginosa. Pseudochelin A displayed siderophore activity in the chrome azurol S assay at concentrations higher than 50 μM, and showed weak activity against the fungus Aspergillus fumigatus, but did not display antibacterial, anti-inflammatory or anticonvulsant activity.