Probing the Metal Composition of Ternary 12–12′‐16 Nanoclusters via Electrospray Ionization Mass Spectrometry

The reaction of [(3,5‐Me₂–C₅H₃N)₂Zn(SeSiMe₃)₂] with a solution of Cd(OAc)₂, Se(Ph)SiMe₃ and PPr₃ at low temperature was used to prepare single crystals of ternary group 12–12′‐16 nanoclusters with the composition [Zn_1.8Cd_8.2Se₄(SePh)₁₂(PPr₃)₄]. A ligand exchange reaction using Na[SePh] was performed to displace the neutral PPr₃ ligands. The resulting clusters were probed using electrospray ionization mass spectrometry to determine the number of zinc and cadmium atoms in the cluster and compared to the all cadmium cluster [Cd₁₀Se₄(SePh)₁₂(PPr₃)₄]. The dianionic clusters [Zn_xCd_10–xSe₄(SePh)₁₄]^2– where x = 0, 1, 2 were assigned in the mass spectra, revealing that the clusters exhibit elemental distributions that are quite narrow in these experiments.     

The magnetic and thermoelectric properties of NiAs-type Fe0.89Se

The magnetic structure of NiAs-type Fe_1–x Se is made up by two sets of oppositely aligned ferromagnetic layers parallel to the hexagonal (001) plane. The imbalance of the sublattice magnetizations resulting in ferrimagnetism is usually attributed to the ordered arrangement of the metal vacancies. The results of the present paper provide a direct experimental proof of the correlation between the crystallographic order and the magnetic properties. It could not be distinguished whether the observed effects on the magnetization are due to a combined ordering of vacancies and Fe³⁺ ions or to the ordering of the Fe³⁺ ions only. Partial disorder was obtained by quenching samples of Fe_0.89Se from temperatures high enough to destroy the ordered arrangement. As inferred from the magnetization data the order parameter varied from 0.83 to 0.47 according to quenching temperatures ranging from 670 K to 1 270 K. In contrast to the magnetization the ferri-antiferromagnetic transformation occurred invariantly at about 170 K irrespective of the different degree of order. The thermoelectric power was positive and increased with decreasing temperature reaching +49µVK^–1 at 85 K. The discontinuity observable at about 170 K coincides roughly with the magnetic transformation indicating magnetic contributions to the thermoelectric power.

---

Die magnetischen und thermoelektrischen Eigen-schaften von Fe_0.89Se mit NiAs-Struktur

Zusammenfassung Die magnetische Struktur von Fe_0,89Se (NiAs-Typ) besteht aus zwei Sätzen entgegengesetzt gerichteter ferromagnetischer Schichten parallel zur hexagonalen (001)-Ebene. Die Ungleichheit der Magnetisierungen der Untergitter, welche den Ferrimagnetismus verursacht, wird üblicherweise der geordneten Verteilung von Leerstellen zugeschrieben. Die Resultate der vorliegenden Arbeit liefern einen direkten experimentellen Beweis für den Zusammenhang zwischen kristallographischer Ordnung und magnetischen Eigenschaften. Es konnte nicht unterschieden werden, ob die beobachtete Auswirkung auf die Magnetisierung durch die gemeinsame Ordnung der Leerstellen und Fe³⁺-Ionen oder durch die Ordnung der Fe³⁺-Ionen allein bedingt ist. Durch Abschrecken der Proben von Temperaturen, welche hoch genug waren, um die geordnete Verteilung zu zerstören, wurde eine teilweise Entordnung erhalten. Die Ordnungsparameter, welche aus den Magnetisierungsdaten abgeleitet wurden, variierten von 0,83 bis 0,47, entsprechend den Abschrecktemperaturen von 670 K bis 1 270 K. Im Gegensatz zur Magnetisierung vollzog sich die ferri-antiferromagnetische Transformation konstant bei ca. 170 K unabhängig vom unterschiedlichen Ordnungsgrad. Die thermoelektrische Kraft war positiv, nahm mit abnehmender Temperatur zu und erreichte bei 85 K einen Wert von 49µVK^–1. Die Diskontinuität, welche bei 170 K beobachtbar war, fällt mit der magnetischen Transformation zusammen und läßt magnetische Beiträge zur thermoelektrischen Kraft erkennen.

     

Stereoselective synthesis of (E)-1-iodo-1-selenoalkenes via hydroalumination-iodination of 1-alkynyl selenides

syn-Hydroalumination of 2,4,6-triisopropylphenylselanyl-1-alkynes 22 with DIBAL-H, followed by Al/I exchange with I₂, afforded selectively the corresponding (E)-1-iodo-1-selenoalkenes in good yields. The sterically hindered 2,4,6-triisopropylphenyl group proved to be mandatory and prevented the formation of undesired by-products.     

Contributions to the Chemistry of the Binary Compounds of the Transition Elements

Phase and structural relationships of the sulfur, selenium, and tellurium compounds of the 4d and 5d transition elements of groups IV to VII of the periodic system are discussed. Homologous elements behave very similarly with respect to the chalcogens, and this is particularly the case for niobium and tantalum, and for molybdenum and tungsten. However, zirconium, niobium, and molybdenum have a greater tendency towards formation of chalcogen-poor phases than their homologues hafnium, tantalum, and tungsten. Subchalcogenides are known only for zirconium and niobium. The number of phases and the tendency towards formation of solid solutions are considerably smaller among the tellurides than among the sulfides and selenides. The crystal structures of the telluride phases also differ from those of the sulfide and selenide phases of analogous composition. In addition, a review of the phase and structural relationships of the arsenic and antimony compounds of the 4d and 5d transition elements of groups V to VII is given.     

A novel regioselective reaction of styrene with magnesium organoselenolates to afford unsymmetrical selenides catalyzed by CuI and l-proline

A novel regioselective reaction of styrene with the prepared magnesium organoselenolates from magnesium, alkyl or aryl bromides, and selenium has been developed in one pot. The reaction catalyzed by CuI and l-proline proceeded in THF, water, and toluene. The scope and limitations of this reaction have been examined. The reaction afforded unsymmetrical selenides containing 12 new compounds in good to high yields.     

Synthesis of arylselenide ethers by photoinduced reactions of selenobenzamide, selenourea and selenocyanate anions with aryl halides

Selenobenzamide (⁻SeCNH(Ph), 1), selenourea (⁻SeCNH(NH₂), 2) and selenocyanate (⁻SeCN, 3) anions afford areneselenolate ions (ArSe⁻) under photostimulation in the presence of tert-butoxide or 2-naphthoxide ions as electron donors (entrainment conditions) in DMSO. In a ‘one-pot’ procedure, ArSe⁻ anions can be trapped by a subsequent aliphatic nucleophilic substitution giving aryl methyl selenides in good to excellent yields (67-100%). This simple approach is compatible with electron-donating and electron-withdrawing substituents, such as nitro and carbonyl groups.     

Crystal and electronic structure study of AgPd3Se

The AgPd₃Se compound was synthesised from individual elements by solid-state chemical reactions and structurally characterized by powder X-ray diffraction data. AgPd₃Se displays cubic symmetry, space group Pa3?, unit cell parameter a=8.6289(1) Å and Z=8. Double-Friauf polyhedra (DFP), defined by Pd and Se atoms, form the basic structural building block of the AgPd₃Se crystal structure. The Ag atoms occupy the centres of DFPs forming an Ag–Ag dimer (2.792(2) Å). The packing of DFPs forms two kinds of interpenetrating networks that show similar features as three-dimensional Penrose tiles. AgPd₃Se is isostructural with CaAu₃Ga. The electric resistivity as well as the electronic structure calculation suggests metallic behaviour.     

Structural Characterization of Pb6Sb6Se17

The ternary selenide Pb₆Sb₆Se₁₇ was synthesized hydrothermally from the binaries (PbSe and Sb₂Se₃) and crystallizes in the orthorhombic space group Pbam (a = 15.835(3), b = 24.043(5), c = 4.134(2)Å, Z = 2). The main building blocks of the crystal structure are ribbons made of square pyramidal [(Pb,Sb)Se₅] groups running along [010].     

Nd4N2Se3 und Tb4N2Se3: Zwei nicht‐isotype Lanthanoid(III)‐Nitridselenide

Nd₄N₂Se₃ and Tb₄N₂Se₃: Two non‐isotypical Lanthanide(III) Nitride Selenides The non‐isotypical nitride selenides M₄N₂Se₃ of neodymium (Nd₄N₂Se₃) and terbium (Tb₄N₂Se₃) are formed by the reaction of the respective rare‐earth metal with sodium azide (NaN₃), selenium and the corresponding rare‐earth tribromide (MBr₃) at 900 °C in evacuated silica ampoules after seven days. Each of them crystallizes monoclinically in the space group C2/c with Z = 4 for Nd₄N₂Se₃ (a = 1300.47(4), b = 1009.90(3), c = 643.33(2) pm, β = 90.039(2)°) and in the space group C2/m with Z = 2 for Tb₄N₂Se₃ (a = 1333.56(5), b = 394.30(2), c = 1034.37(4) pm, β = 130.377(2)°), respectively. The crystal structures differ fundamentally in the linkage of the structure dominating N^3‐ centred (M³⁺)₄ tetrahedra. In Nd₄N₂Se₃, the [NNd₄] units are edge‐linked to bitetrahedra which are cross‐connected to [N(Nd1)(Nd2)]³⁺ layers via their remaining four corners, whereas the [NTb₄] tetrahedra in Tb₄N₂Se₃ share cis‐oriented edges to form strands [N(Tb1)(Tb2)]³⁺. Both structures contain two crystallographically different M³⁺ cations, that show coordination numbers of six and seven (Nd₄N₂Se₃) or twice six (Tb₄N₂Se₃), respectively, relative to the anions (N^3‐ und Se^2‐). Each of the two independent kinds of Se^2‐ anions provide the three‐dimensional linkage as well as the charge balance. The particular axial ratio a/c and the monoclinic reflex angle offer two choices for fixing the unit cell of Tb₄N₂Se₃.