Reactions of (Me2C)(Me2Si)[(η-C5H3)Mo(CO)3]2 with nitrile and subsequent cleavage of the CN bond by cooperation of molybdenum and ruthenium

Reaction of the doubly bridged dinuclear molybdenum complex (Me₂C)(Me₂Si)[(η⁵-C₅H₃)Mo(CO)₃]₂ (1) with benzonitrile in refluxing xylene afforded complexes (Me₂C)(Me₂Si)[(η⁵-C₅H₃)₂Mo₂(CO)₄(μ-η²-η²(⊥)-NCPh)] (2) (50%) and (Me₂C)(Me₂Si)[(η⁵-C₅H₃)₂Mo₂(CO)₄(μ-η¹-η²-NCPh)] (3) (6%) with different coordination of nitrile. The corresponding μ-η²-η² acetonitrile and propionitrile complexes 4 and 5 could be obtained from the reactions of (Me₂C)(Me₂Si)(C₅H₄)₂ with (RCN)₃Mo(CO)₃ (R = Me, Et) in refluxing xylene. Reactions of 1 with isonitriles generated μ-η¹-η²-CNR (R = ^tBu, Ph, C₆H₁₁) bridged complexes 6-8 in 53-63% yields. Subsequent reaction of 4 with Ru₃(CO)₁₂ yielded two CN bond cleavaged MoRu clusters (Me₂C)(Me₂Si)(η⁵-C₅H₃)₂Mo₂Ru₃(CO)₁₀(μ-CO)(μ₃-CMe)(μ₄-N) (9) (7%) and [(Me₂C)(Me₂Si)(η⁵-C₅H₃)₂]₂Mo₄Ru₆(CO)₁₆(μ-CO)(μ₄-CO)₂(μ₃-η¹-η²-η²-NCMe)(μ₃-CMe)(μ₅-N) (10) (8%). All the new complexes have been fully characterized. The molecular structures of 2, 4, 6, 9, and 10 have been determined by X-ray diffraction analysis.     

NaZr2N2SCl: Ein flußmittelstabilisiertes Derivat von Zirconium(IV)–Nitridsulfid (Zr2N2S)

NaZr₂N₂SCl: A Flux‐Stabilized Derivative of Zirconium(IV) Nitride Sulfide (Zr₂N₂S) The oxidation of zirconium metal with elemental sulfur and sodium azide (NaN₃) should give access to zirconium(IV) nitride sulfide, Zr₂N₂S, which could crystallize isotypically with the trigonal rare‐earth(III) oxide sulfides M₂O₂S (M = Y, La–Lu). Appropriate molar admixtures of these reactants together with NaCl added as flux were heated for seven days at 850 °C in torch‐sealed evacuated silica tubes. As main product, however, pale yellow platelets with the composition NaZr₂N₂SCl (trigonal, R 3 m; a = 363.56(3), c = 2951.2(4) pm; Z = 3) emerged as single crystals. This pseudo‐quaternary compound crystallizes isotypically with e. g. Li_xEr₂H_yCl₂ (x ≤ 1, y ≤ 2) in a (doubly) stuffed ZrBr‐type structure and contains at least structural domains of the hypothetical Ce₂O₂S‐analogous Zr₂N₂S. Zr⁴⁺ resides in monocapped trigonal anti‐prismatic sevenfold coordination of the anions (d(Zr–N) = 218 (3 ×) and 220 pm (1 ×), d(Zr–S/Cl) = 266 pm, 3 ×). Closest packed double‐layers of Zr⁴⁺ with all tetrahedral interstices occupied with N^3– are sandwiched by layers of isoelectronic S^2– and Cl^– anions. These anionic six‐layer slabs (S/Cl–Zr–N–N–Zr–S/Cl) pile up parallel (001) in a cubic closest packed fashion. Charge balance and structural consistence occurs between these layers by intercalation of Na⁺ within octahedral voids (d(Na–S/Cl) = 282 pm, 6 ×) of double‐layers of the indistinguishable heavy anions (S^2– and Cl^–).     

Novel Asymmetric and Stereospecific Aziridination of Alkenes with a Chiral Nitridomanganese Complex

The addition of pyridine N -oxide is necessary to obtain high enantioselectivities in the asymmetric aziridination of styrene derivatives through transfer of a nitrogen atom from chiral, toluenesulfonic anhydride activated nitridomanganese complex 1 [Eq. (a)]. Remarkably, high stereospecificity was observed in all the aziridinations of trans- and cis-1,2-disubstituted alkenes. R¹=H, Me, nPr, iPr; R²=H, Me; Ts=p-toluenesulfonyl.     

[ScCl2{N(SiMe3)2}(THF)2] als Vorläufer für die Synthese von Scandiumnitrid

[ScCl₂{N(SiMe₃)₂}(THF)₂] – a Precursor for the Synthesis of Scandium Nitride [ScCl₂{N(SiMe₃)₂}(THF)₂] ( 1 ) has been prepared by the reaction of [ScCl₃(THF)₃] with the trisamide Sc[N(SiMe₃)₂]₃ in tetrahydrofurane solution forming colourless moisture sensitive crystals, which were characterized by a crystal structure determination. Space group P 1, Z = 2, lattice dimensions at –50 °C: a = 841.4(1), b = 924.2(1), c = 1550.0(1) pm, α = 90.046(7)°, β = 95.671(9)°, γ = 106.066(6)°, R₁ = 0.0329. In the molecular structure of 1 the scandium atom has a distorted trigonal‐bipyramidal coordination with the THF molecules in apical positions. At 400 °C 1 is converted into scandium nitride, ScN, by stepwise leaving of THF and ClSiMe₃.     

Synthesis,Structure, and Decomposition of (NH4)2[Mo6Cl14] · H2O

(NH₄)₂[Mo₆Cl₁₄] · H₂O ( 1 ) was prepared from reactions of MoCl₂ in ethanol with aqueous NH₄Cl solution. It crystallizes in the monoclinic space group I2/a (no. 15), Z = 4 with a = 912.3(1), b = 1491.2(2), c = 1724.8(2) pm, β = 92.25(1)°; R1 = 0.023 (based on F values) and wR2 = 0.059 (based on F² values), for all measured X‐ray reflections. The structure of the cluster anion can be given as [(Mo₆Cl)Cl]^2– (i = inner, a = outer ligands). Thermal stability studies show that 1 loses crystal water followed by the loss of NH₄Cl above 350 °C to yield MoCl₂. The water‐free compound (NH₄)₂[Mo₆Cl₁₄] ( 2 ) was synthesized by solid state reaction of MoCl₂ and NH₄Cl in a sealed quartz ampoule at 270 °C. No single‐crystals could be obtained. Decompositions of 1 and 2 under nitrogen and argon exhibited the loss of NH₄Cl at about 350 °C. Decomposition under NH₃ resulted in the formation of MoN and Mo₂N at 540 °C and 720 °C, respectively.     

Synthesis and structure of the ternary and quaternary strontium nitride halides, Sr2N(X, X′) (X, X′=Cl, Br, I)

A number of new, layered nitride mixed halides have been synthesised in the quaternary phase systems Sr-N-Cl-Br and Sr-N-Br-I. The variation in structure with composition has been investigated by powder X-ray and powder neutron diffraction techniques and the structure of strontium nitride iodide, Sr₂NI, has been determined for the first time (rhombohedral space group R-3m, , , Z=3). A continuous solid solution exists between Sr₂NCl and Sr₂NBr with intermediate compounds adopting the same anti-α-NaFeO₂ structure (rhombohedral space group R-3m) as the ternary end members. A similar smooth and linear relationship between structure and composition is seen from Sr₂NBr to Sr₂NI and hence cubic close packing of metal-nitrogen layers is adopted regardless of halide, X (X′). While nitride and halide anions occupy distinct crystallographic sites, there is no ordering of the halides in the quaternary materials irrespective of stoichiometry or temperature (between 3 and 673 K).     

Electron-carrier generation by edge dislocations in InN films: First-principles study

Electronic structures of edge dislocations in InN films are studied using the first-principles calculation. We found that dangling-bond states of In atoms localized in the dislocation core are located above the conduction-band bottom and thus supplies the electron carriers to the conduction band of bulk InN, in agreement with the experimental suggestion by Wang et al. [Appl. Phys. Lett. 90 (2007) 151901]. Moreover, it is shown that the Fermi energy in the conduction band has the tendency to be pinned at the energy positions of N-related dangling-bond states.     

Emission studies of InGaN layers and LEDs grown by plasma-assisted MBE

We prepared InGaN layers on GaN/sapphire substrates using rf-MBE. Photoluminescence (PL) from these layers, grown at different temperatures T_S, shows that there is a strong tendency of GaN to form a separate phase as T_S is increased from 600°C to 650°C. Concomitant with the phase separation, the PL from the InGaN phase broadens, which indicates that indium composition in this phase becomes increasingly non-uniform. Indium compositions measured by Rutherford backscattering (RBS) are consistent with these results. We also observed an increase in PL intensity for InGaN layers grown at higher temperatures. In this paper, we also report on preparing a top-contact InGaN/GaN light emitting diode. The device was operated at 447 nm and had the emission line width of 37 nm with no observable impurity related features. The turn-on voltage was 3.0 V. The output power was 20 μW at 60 mA drive current.     

Spatially and spectrally resolved measurement of optical loss in InGaN laser structures

The optical loss co-efficient in InGaN laser diodes, emitting at 410 nm, has been measured. The measurement technique is based on the transmission of internally generated spontaneous emission through varying lengths of the laser waveguide. It is unique in that it provides spectral and spatial information on the optical loss. The lasers studied are typical of InGaN structures showing a high degree of waveguide loss, _i=40cm⁻¹. The measurements also show clear evidence of higher order transverse modes in the direction perpendicular to the growth plane with resonant leakage of the optical field into the outer layers of the structure. This produces a modulation in the loss of these modes.     

AlGaN-based UV photodetectors

Al_xGa_1−xN alloys are very attractive materials for application to ultraviolet photodetection. AlGaN photoconductors, Schottky photodiodes, metal–semiconductor–metal photodiodes, p–n junction photodetectors and phototransistors have been recently developed. In this work we analyse the performance of AlGaN-based photodetectors, discussing present achievements, and comparing the characteristics of the various photodetector structures developed to date.