High speed integrated electronics for communications systems

The functions necessary in broadband communications systems at speeds above 50 Mb/s are discussed. The types of components and functionality that are needed for access to networks and for the transmission and routing of traffic within networks are identified. Integrated circuit components used for customer-network access, network multiplexing, and switching are reviewed. It is shown that currently available digital VLSI technology is capable of achieving both the speeds and the levels of integration necessary to allow broadband network access even to residential subscribers     

Nuclear β-decay. I

In order to clarify the validity of the theory of nuclearβ-transition a new formulation is given. The nuclear properties are contained in form factors, arising from a decomposition of the matrix element of the V-A operator for nuclear states. The connection of these form factors with nuclear physics matrix elements is tabulated. The total transition amplitude can be written as an integral over these form factors folded with off-shell amplitudes for elastic and inelastic electron scattering on nuclei.     

Eine Apparatur zum Verdampfen hochschmelzender Erdalkalichalkogenide

An apparatus is described, which permits the evaporation of nonconducting substances with high melting points by electron bombardment.     

Existenziell abgeschlossene lokal endlichep-Gruppen

Ohne ZusammenfassungDiese Arbeit enthält Ergebnisse aus der an der Albert-Ludwigs-Universität, Freiburg angefertigten Dissertation [11].     

A non‐twinned polymorph of CaTe2O5 from a hydrothermally grown crystal

In contrast with the multiple twinning and/or domain formation found in the mica‐like polymorphs of CaTe₂O₅, calcium pentaoxidoditellurate(IV), that have been prepared by solid‐state reactions and for which complete structure determinations have not been successful up to now, the crystal structure of a hydrothermally grown phase was fully determined from a non‐twinned crystal. The structure is made up of alternating layers of Ca²⁺ cations and of ²_∞[Te₂O₅]²⁻ anions stacked along [100]. The lone‐pair electrons E of the Te^IV atoms are stereochemically active and protrude into channels within the anionic layer. In comparison with analogous M^IITe₂O₅ structures (M = Mg, Mn, Ni or Cu) with ditellurate(IV) anions that are exclusively made up of corner‐sharing TeO_x (x = 3–5) polyhedra resulting in flat ²_∞[Te₂O₅]²⁻ layers, the anionic layers in CaTe₂O₅ are undulating and are built of corner‐ and edge‐sharing [TeO₄] polyhedra.     

Macrocyclic nickel(II) complexes coligated by hydrosulfide and hexasulfide ions: syntheses, structures, and magnetic properties of [NiII2L(mu-SH)]+ and [(LNiII2)2(mu-S6)]2+

The borohydride complex [Ni(II)2L(mu-BH4)]+ (3) where L(2-) represents a sterically demanding hexaaza-dithiophenolate ligand reacts rapidly with elemental sulfur in acetonitrile at ambient temperature to produce the cationic complexes [Ni(II)2L(mu-SH)]+ (4) and [(Ni(II)2L) 2(mu-S6)]2+ (6). Both complexes were isolated as ClO4(-) or BPh4(-) salts and characterized by IR and UV/vis spectroscopy and X-ray crystallography. Complex 4 (also accessible from [Ni(II)2L(ClO4)]+ (5) and Na2S.9H2O) features an unprecedented N3Ni(II)(mu-SR)2(mu-SH)Ni(II)N3 core structure, the hydrosulfide ligand being deeply buried in the binding-cavity of the bowl-shaped [Ni(II)2L]2+ complex. In 6, a helical S6(2-) chain, with a structure reminiscent to that of plastic sulfur, is almost completely encapsulated by two [Ni(II)2L]2+ subunits. In contrast to other triply sulfur-bridged N3Ni(II)(SR)3Ni(II)N3 structures whose ground states are typically of S = 0, 4 reveals an S = 2 ground-state which is attained by a ferromagnetic exchange interaction between the two Ni(II) (S = 1) ions ( J = 18 cm (-1), H = -2JS1S2). Intradimer ferromagnetic exchange interactions are also present in 6 ( J = 23 cm (-1)). A qualitative explanation for this difference is offered.     

A Cobalt(I) Pincer Complex with an η2‐Caryl−H Agostic Bond: Facile C−H Bond Cleavage through Deprotonation,Radical Abstraction,and Oxidative Addition

The synthesis and reactivity of a Co^I pincer complex [Co(ϰ³P,CH,P‐P(CH)P^NMe‐iPr)(CO)₂]⁺ featuring an η²‐ C_aryl−H agostic bond is described. This complex was obtained by protonation of the Co^I complex [Co(PCP^NMe‐iPr)(CO)₂]. The Co^III hydride complex [Co(PCP^NMe‐iPr)(CNtBu)₂(H)]⁺ was obtained upon protonation of [Co(PCP^NMe‐iPr)(CNtBu)₂]. Three ways to cleave the agostic C−H bond are presented. First, owing to the acidity of the agostic proton, treatment with pyridine results in facile deprotonation (C−H bond cleavage) and reformation of [Co(PCP^NMe‐iPr)(CO)₂]. Second, C−H bond cleavage is achieved upon exposure of [Co(ϰ³P,CH,P‐P(CH)P^NMe‐iPr)(CO)₂]⁺ to oxygen or TEMPO to yield the paramagnetic Co^II PCP complex [Co(PCP^NMe‐iPr)(CO)₂]⁺. Finally, replacement of one CO ligand in [Co(ϰ³P,CH,P‐P(CH)P^NMe‐iPr)(CO)₂]⁺ by CNtBu promotes the rapid oxidative addition of the agostic η²‐C_aryl−H bond to give two isomeric hydride complexes of the type [Co(PCP^NMe‐iPr)(CNtBu)(CO)(H)]⁺.     

The Bis(pentafluoroethyl)germylene Trimethylphosphane Adduct (C2F5)2Ge⋅PMe3: Characterization,Ligand Properties,and Reactivity

The synthesis of the germylene phosphane adduct (C₂F₅)₂Ge?PMe₃ is described. Starting from (C₂F₅)₃GeH in an excess of PMe₃, heating was applied, whereupon reductive elimination of C₂F₅H occurred. The molecular structure was ascertained by X‐ray diffraction and compared with information obtained by quantum chemical methods. The ligand properties were derived by studying the IR spectrum of the nickel(0) complex [Ni(CO)₃{Ge(C₂F₅)₂(PMe₃)}] in the CO region. (C₂F₅)₂Ge?PMe₃ turned out to be a π‐accepting ligand comparable to PMe₃, in terms of Tolman's electronic parameter. Furthermore a [2+4] cycloaddition reaction with 2,3‐dimethyl‐1,3‐butadiene, and σ‐bond insertion reactions were recorded. Activation of the C?Cl bond in dichloromethane gives rise to the formation of the phosphonium ylide complex [(C₂F₅)₂Cl₂Ge‐CH₂PMe₃], which was fully characterized by X‐ray diffraction.     

The Influence of Weakly Coordinating Cations on the O−H⋅⋅⋅O− Hydrogen Bond of Silanol-Silanolate Anions

The reaction of a saline phosphazenium hydroxide hydrate with siloxanes led to a novel kind of silanol-silanolate anions. The weakly coordinating behavior of the cation renders the formation of silanol-silanolate hydrogen bonds possible, which otherwise suffer from detrimental silanolate–oxygen cation interactions. We investigated the influence of various weakly coordinating cations on silanol-silanolate motifs, particularly with regard to different cation sizes. While large cations favor the formation of intramolecular hydrogen bonds resulting in cyclic structures, the less bulky tetramethyl ammonium cation encourages the formation of polyanionic silanol-silanolate chains in the solid state.