Synthese und Struktur von [(Ph3PAu)6Co(CO)2](PF6) und [(Ph3PAu)7Co(CO)2](PF6)2

Synthesis and Structure of [(Ph₃PAu)₆Co(CO)₂](PF₆) and [(Ph₃PAu)₇Co(CO)₂](PF₆)₂ By the reaction of (Ph₃PAu)₄Co[(CO)₃]⁺ with OH^? in the presence of excess Ph₃PAuCl the larger cluster cations [(Ph₃PAu)₆Co(CO)₂]⁺ ( 1 ) and [(Ph₃PAu)₇Co(CO)₂]²⁺ ( 2 ) can be built up with 1 being the main product. 1 crystallizes with PF^?₆ as counterion in the monoclinic space group C2/c with a = 3008.3(6); b = 1339.1(2); c = 2909.4(6) pm; β = 103.08(1)°; Z = 4. The inner core of the cluster cation 1 with the symmetry C₂ has the form of a bicapped trigonal bipyramid with the heteroatom in equatorial position, and distances Au? Au between 280.4(1) and 288.4(1) pm and Co? Au between 254.9(1) and 257.1(2) pm. 2 · (PF₆)₂ crystallizes in the triclinic space group P1 with a = 2155.7(1); b = 1720.6(1); c = 3543.6(1) pm; α = 91.89(1)°; β = 97.51(1); γ = 89.92(1)°; Z = 4. The unit cell contains two symmetry independent cluster cations 2 of about the same geometry. The cluster skeleton Au₇Co can be described as fragment of an icosahedron formed by seven gold atoms with the Co atom in its center. The Au? Au distances range from 274.8(3) to 332.6(3) pm, and the Co? Au distances are 256.8(6) to 264.7(5) pm. The bonding in 1 and 2 is discussed.     

An Unprecedented Domino Double Allylsilane [3+2] Cycloaddition/Wagner–Meerwein Rearrangement/Friedel–Crafts Alkylation/Elimination Reaction Sequence Leading to a Novel Pentacyclic Ring System

A stereoselective synthesis of the disilyl derivatives 3 is achieved by the title reaction, an unprecedented Lewis acid promoted domino reaction, between the cross-conjugated dienone 1 and the allylsilanes 2 . The configurations of the five stereogenic centers of this novel ring system are established in the first step of the reaction sequence, the double [3+2] cycloaddition.     

Synthesen und Strukturen donorstabilisierter Aluminiumdihalogenide

Syntheses and Structures of Donor-stabilized Aluminiumdihalides During the disproportionation of metastable AlX-solutions (X = Cl, Br, I) donor-stabilized aluminiumdihalides are formed. X-ray diffraction analysis shows that all of them exhibit a dimeric structure DoX₂Al–AlX₂Do (Do = donor-molecule). The Al–Al-bond length which is significantly shorter than in the organometallic R₂Al–AlR₂-species is strongly influenced by the donor-molecule as well as by the halogen ligands. With the help of quantum chemical calculations a deeper understanding of this bonding situation is obtained.     

Unstructured adaptive remeshing finite element method for dusty shock flow

The passage of planar shocks in a dusty gas was investigated to note effects due to particle loading and initial shock Mach number. Two-phase flow equations have been added to a conservative, monotonic flow solver to allow study of compressible particle and droplet flows, which are of importance for shock propagation in two-phase flows and spray propulsion systems. The formulation developed herein employed a conservative Eulerian treatment for the gas and particle phases. The computations were performed using the finite element method-flux corrected transport (FEM-FCT) scheme, which has shown excellent predictive capability of various compressible flows which include both strong and weak shocks. The flux limiting technique was modified to provide monotonic particle velocity fields to increase the scheme's computational stability. Adaptive unstructured methodology based on adapting to high gradients of both the fluid and particle densities was used in conjunction with the conservative shock-capturing scheme to adequately resolve strong flowfield gradients. The shock attenuation of this scheme was then compared with previous experimental and numerical results and was found to yield robust predictions. Various interphase coupling terms were also considered to note their effect on the shock attenuation.This article was processed using Springer-Verlag t_ex Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society.     

The role of Fe during hydride formation in the Mg–Fe system: a Mössbauer investigation

The mechanically assisted hydriding of Mg_1???x Fe _x powder mixtures with x?=?0.02, 0.03, 0.10, 0.20 and 0.33 was studied. The hydriding kinetics up to saturation was followed from the hydrogen absorption during milling. All the steady state samples and some partially hydrided ones, with x?=?0.03 , were characterized by X-ray diffraction and Mössbauer spectroscopy. The catalytic action of Fe in the H₂ sorption by Mg based systems and the influence of complex ternary hydride formation in such processes are discussed.     

Mössbauer characterization of Fe-doped ZnO prepared by mechanical milling

The preparation of massive oxides Zn₁??? _x Fe _x O by means of mechanical milling in diverse gaseous atmospheres and starting with different powder mixtures was investigated. ZnO powder with 10 at.% admixture of Fe, FeO or Fe₂O₃, were milled during 1, 4 or 16 h and characterized by X-ray diffraction and Mössbauer spectroscopy. Different phases were obtained according to the initial conditions (precursor used, atmosphere, etc.) and phase’s formation enthalpies.     

Self-assembly and structure of interconverting multinuclear inorganic arrays: a

Coordination of the pentatopic ligand 3 with AgI leads to the simultaneous self-assembly of two polynuclear architectures: a [4 x 5] grid-type species 10 and a quadruple-helicate 11, which contain twenty and ten silver ions. respectively. Their structures have been established by X-ray diffraction analysis of the crystals obtained as a mixture on crystallisation. Complex 10 contains two [2 x 5]-AgI10 rectangular subgrids located on opposite sides of an array of parallel ligands of 3 that are twisted into a transoid N=C-C=N arrangement around the central C-C bond; it may thus be formulated as a grid of grids: [2 x (2 x 5)]. Complex 11 is an inorganic quadruple helicate that consists of two sets of two parallel ligands of 3 connected by an array of ten silver ions. Both compounds 10 and 11 are novel types of polynuclear complexes that are composed of two subunits. Their formation points to the possibility of generating specific arrays of metal ions by self-assembly, involving, in particular, a combination of subunits within the overall entity. They represent organised patterns of ion dots of special significance in view of their formal relationship to quantum dots.     

Pnictides as symmetrically bridging ligands in novel neutral complexes

The reaction of [LWCl] (3) [L = N(CH2CH2NiPr)3] with LiE(SiMe3)2 (E = P, As, Sb) yields the novel, neutral pnictido-bridged complexes [LW = E = WL] (5-7). By following the reaction, which starts from the LiP-(SiMe3)2 derivative, by 31P NMR spectroscopy, the formation of an intermediate with a terminal pnictido ligand can be ruled out. The paramagnetic complexes 5-7 are comprehensively spectroscopically characterised. The X-ray structure analysis of the heterocumulenes 5-7 reveals a linear structure in which the two W-"tren" units bind to the central pnictido atom in a staggered conformation ["tren" = tren-based ligand; tren = tris(2-aminoethyl)-amine. When N2 is used as the inert gas in the synthesis of the starting material [N(CH2CH2NNp)3WCl] [Np = CH2C-(CH3)3], the complex [[N(CH2CH2NNp)3]W2(mu, eta 1: eta 1-N2)] (4) is formed as a side product. Complex 4 possesses a hydrazido(4-) (N2(4-)) ligand connected by two tungsten-"tren" moieties.