Showing papers by "University of Duisburg-Essen published in 1984"

Accurate Wide-Range Design Equations for the Frequency-Dependent Characteristic of Parallel Coupled Microstrip Lines

Abstract: In this paper, closed-form expressions are presented which model the frequency-dependent even- and odd-mode characteristics of parallel coupled microstrip lines with hitherto unattained accuracy and range of validity. They include the effective dielectric constants, the characteristic impedances using the power-current formulation, as well as the open-end equivalent lengths for the two fundamental modes on coupled microstrip. The formulas are accurate into the millimeter-wave region. They are based on an extensive set of accurate numerical data which were generated by a rigorous spectral-domain hybrid-mode approach and are believed to represent a substantial improvement compared to the state-of-the-art and with respect to the computer-aided design of coupled microstrip filters, directional couplers, and related components.

Deep-level analysis in (AlGa)As—GaAs 2-D electron gas devices by means of low-frequency noise measurements

Abstract: Low-frequency noise of (AlGa)As-GaAs heterostructures grown by molecular-beam epitaxy was investigated. The temperature of the samples was varied between 100 and 400 K. In the frequency range from 1 Hz to 25 kHz noise spectra can be described as superposition of several generation-recombination (GR) noise components. Four deep levels (E = 0.40, 0.42, 0.54, 0.60 eV) were detected, three of which are in agreement with those measured independently by deep-level transient spectroscopy (DLTS).

Microscopic theory of optical line narrowing of a coherently driven solid

Abstract: The optical Bloch equations which incorporate the phenomenological population $({T}_{1})$ and dipole dephasing $({T}_{2})$ times have been tested recently by optical free-induction-decay (FID) measurements on an impurity-ion crystal ${\mathrm{Pr}}^{3+}$:${\mathrm{La}}_{3}$ at 1.6 K. At low optical fields, the observed ${\mathrm{Pr}}^{3+}$ optical linewidth is dominated by magnetic fluctuations arising from pairs of fluorine nuclear flip-flops where the condition ${T}_{1}\ensuremath{\gg}{T}_{2}$ prevails. At elevated fields, this nuclear broadening mechanism is quenched and the Bloch equations are violated with ${T}_{2}\ensuremath{\rightarrow}{T}_{1}$. In this paper, a microscopic theory appropriate for a low-temperature impurity solid is presented which reveals the above features both for optical and radio frequencies, and a simple physical interpretation of this line narrowing phenomenon is given. Modified Bloch equations of a novel form are derived to second order and yield analytic FID solutions over the entire range of optical-field strength. A discussion of the earlier NMR theories is given, pointing out similarities and differences.

Azaborolinyl‐Komplexe, XIII. Synthese und Eigenschaften von Bis(1‐tert‐butyl‐2‐methyl‐η‐1,2‐azaborolinyl)nickel

Abstract: Die Reaktion von 1-tert-Butyl-2-methyl-1,2-azaborolinyllithium (1) mit NiBr2 fuhrt zum Sandwichkomplex Bis(1-tert-butyl-2-methyl-η3-1,2-azaborolinyl)nickel (2) Erstmals wird beobachtet, daβ der Azaborolinyl-Ring nicht als η5-, sondern als η3-Ligand dient Das 1H-NMR-Spektrum zeigt das Vorliegen von zwei Isomeren (2a,b), von denen eines rontgenstrukturanalytisch untersucht werden konnte Danach haben nur die drei Ringkohlenstoffe bindende Abstande zum Nickelatom, wahrend Bor und Stickstoff keine kovalenten Wechselwirkungen mit dem Metall zeigen Die Lage der Ringprotonen-Signale im 1H-NMR-Spektrum weicht charakteristisch von der Lage in anderen Azaborolinyl-Sandwichkomplexen und in π-Allylverbindungen ab Azaborolinyl Complexes, XIII Synthesis and Properties of Bis(1-tert-butyl-2-methyl-η3-1,2-azaborolinyl)nickel The reaction of 1-tert-butyl-2-methyl-1,2-azaborolinyllithium (1) with NiBr2 leads to the sandwich complex bis(1-tert-butyl-2-methyl-η3-1,2-azaborolinyl)nickel (2) For the first time it is noticed that the azaborolinyl ring does not serve as η5 but as η3 ligand The 1H NMR spectrum shows the existence of two isomers (2a,b), one of them could be investigated by X-ray analysis As a result only the three ring carbon atoms possess binding distances to the nickel atom, whereas boron and nitrogen do not show any covalent interactions with the metal The position of the signals of the ring protons in the 1H NMR spectrum differs characteristically from the position in other azaborolinyl sandwich complexes and in π-allyl compounds

Übergangsmetallkomplexe instabiler Ylide, II1). Koordinationschemische Stabilisierung von phosphino- und arsinomethylsubstituierten Phosphonium- bzw. Arsoniummethyliden an Tetracarbonylchrom

Abstract: Die Schwefelylidkomplexe (CO)5Cr[CH2S(O)Me2] (1) und (CO)4Cr[CH2S(O)Me2]2 (7) reagieren mit den symmetrischen ditertiaren Phosphanen und Arsanen 5 zu den funfgliedrigen Metallacylen 6, welche die im freien Zustand nicht bestandigen Ylide H2C = ER21 – CR22 – ER21 (E = P, As) als Chelatliganden tragen. Die Strukturen von 6 werden durch IR-, 1H- und 31P-NMR-Spektren sowie durch die Rontgenstrukturanalyse des Arsenylidkomplexes 6f ermittelt. Transition Metal Complexes of Instable Ylides, II1). Stabilization of Phosphino- and Arsinomethyl-substituted Phosphonium- and Arsonium Ylides by Coordination to Tetracarbonylchromium The sulfur ylide complexes (CO)5Cr[CH2S(O)Me2] (1) and (CO)4Cr[CH2S(O)Me2]2 (7) react with symmetrically substituted ditertiary phosphanes or arsanes such as 5 to yield five-membered metallacycles (6), in which the ylides CH2 = ER21 – ER21 – CR22 – ER21 (E = P, As) are incorporated as chelate ligands. The free ylidic ligands are not stable. The structures of 6 are elucidated by means of IR, 1H and 31P. NMR spectroscopy as well as by an X-ray structure analysis of 6f.

Azaborolinyl-Komplexe, X1). Darstellung und Eigenschaften von (1-tert-Butyl-2-methyl-η-1,2-azaborolinyl)carbonylmangan- und -molybdän-Komplexen

Abstract: 1-tert-Butyl-2-methyl-1,2-azaborolinyllithium (1) reagiert mit [(CH3CN)3Mn(CO)3]PF6 zum (1-tert-Butyl-2-methyl-η-1,2-azaborolinyl)tricarbonylmangan (2). Neutrales 1-tert-Butyl-2-methyl-1,2-azaborolin (3) und Mo(CO)6 bilden π-Allyl(1-tert-butyl-2-methyl-η-1,2-azaborolinyl)-dicarbonylmolybdan (4). Die Bildung der Allygruppe ist auf den Zerfall eines Azaborolin-Ringes unter den Reaktionsbedingungen zuruckzufuhren. 2 und 4 werden durch Massen-, IR- und NMR-Spektren charakterisiert. Von 4 konnte eine Rontgenstrukturanalyse durchgefuhrt werden: orthorhombisch, Raumgruppe Pbca, Z = 8, a = 1697.4(9), b = 1441.8(5), c = 1219.4(7) pm. Die Chiralitat des Azaborolinyl-Ringes bedingt die Bildung von Enantiomeren, die im Kristall als Racemat vorliegen. Azaborolinyl Complexes, X1). Synthesis and Properties of (1-tert-Butyl-2-methyl-η-1,2-azaborolinyl)carbonylmanganese and-molybdenum Complexes 1-tert-Butyl-2-methyl-1,2-azaborolinyllithium (1) reacts with [CH3CN)3Mn(CO)3]PF6 to give (1-tert-butyl-2-methyl-η-1,2-azaborolinyl)tricarbonylmanganese (2). Neutral 1-tert-butyl-2-methyl-1,2-azaboroline (3) and Mo(CO)6 form π-ally(1-tert-butyl-2-methyl-η-1,2-azaborolinyl)-dicarbonylmolybdenum (4). The formation of the allyl group is due to the decomposition of an azaborolinyl ring under the reaction conditions. 2 and 4 are characterized by mass, IR, and NMR spectra. 4 could be investigated by X-ray analysis. Orthorhombic, space group Pbca, Z = 8, a = 1697.4(9), b = 1441.8(5), c = 1219.4(7) pm. The chirality of the azaborolinyl ring causes the formation of enantiomers which exist as a racemate in the crystal.

Übergangsmetallkomplexe instabiler Ylide, III. Präparative, stereochemische und mechanistische Aspekte bei der koordinationschemischen Stabilisierung instabiler Ylid‐Chelatliganden

Abstract: Der Schwefelylid-Komplex (CO)5Cr[CH2S(O)Me2] (1) bildet mit den unsymmetrisch substituierten Diphosphanen bzw. Arsanen R12E1CH2E2R22 (4a – d) regioselektiv die Chelatkomplexe 5a – d, bei denen das starker nucleophile Ende von 4 als Oniumfunktion auftritt. Demgegenuber reagiert (CO)4Cr[CH2S(O)Me2]2 (2) mit 4a – d regioselektiv zu den isomeren Chelatkomplexen 6a – d, in denen die starker nucleophile Donorfunktion von 4 am Chromatom gebunden ist. Transition Metal Complexes of Instable Ylides, III1). Preparative, Stereochemical, and Mechanistic Aspects of the Stabilization of Instable Ylidic Chelate Ligands by Coordination to Chromium The sulfur ylide complex (CO)5Cr[CH2S(O)Me2] (1) reacts with unsymmetrically substituted diphosphanes and arsanes of the type R12E1CH2E2R22 (4a – d) to give regioselectively the chelate complexes 5a – d. In 5 the more nucleophilic end of 4 is transformed to the onium centre. On the other hand, (CO)4Cr[CH2S(O)Me2]2 (2) and 4a – d produce regioselectively the isomeric chelate complexes 6a – d, in which the more nucleophilic donor function of 4 is ligated to the chromium atom.

Kinetische und mechanistische Untersuchungen von Übergangsmetall‐Komplex‐Reaktionen, XV. Übergangsmetall‐Schwefelylid‐Komplexe, XX. Reaktionskinetischer Nachweis von [(CO)5Cr=CH2] bei der Umsetzung von Pentacarbonyl[(dimethyloxosulfonio)methanid]‐chrom(0) mit tertiären Phosphanen

Abstract: Pentacarbonyl[(dimethyloxosulfonio)methanid]chrom(0), (CO)5Cr[CH2S(O)Me2] (1), reagiert mit tertiaren Phosphanen PR3 (2) (R = Ph, C6H4OMe-(p), C6H4Me-(p), C6H4Cl-(p)) nach dem Geschwindigkeitsgesetz erster Ordnung zu Pentacarbonyl(phosphorylid)chrom(0)-Komplexen, (CO)5Cr[CH2PR3] (3), und Dimethylsulfoxid. Die Reaktionsgeschwindigkeit ist von der Art des Phosphans unabhangig. Die Aktivierungsparameter fur die Reaktion in 1,1,2-Trichlorethan im Temperaturbereich von 39.6–68.0°C sind ΔH≠ = 28.1 kcal · mol−1 und ΔS≠ = 12.7 cal · mol−1. K−1. Die Reaktion wird durch irreversible Dissoziation von OSMe2 vom Komplex 1 eingeleitet. An das Carbenkohlenstoffatom des resultierenden Pentacarbonylmethylenchroms, [(CO)5Cr=CH2], addiert sich dann 2 in einem raschen Folgeschritt unter Bildung von 3. Ein Mechanismus uber einen geschwindigkeitsbestimmenden Cr-CH2-Bindungsbruch kann ausgeschlossen werden. Diese Ergebnisse sind der erste Nachweis eines neutralen elektrophilen Carbonylmethylen-Komplexes. Kinetic and Mechanistic Investigations of Transition Metal Complex Reactions, XV1). Transition Metal Sulfur Ylide Complexes, XX2). Kinetic Evidence of [(CO)5Cr=CH2] in the Reaction of Pentacarbonyl[(dimethyloxosulfonio)-methanide]chromium(0) with Tertiary Phosphanes Pentacarbonyl[(dimethyloxosulfonio)methanide]chromium(0), (CO)5Cr[CH2S(O)Me2] (1), reacts with tertiary phosphanes PR3 (2) (R = Ph, C6H4OMe-(p), C6H4Me-(p), C6H4Cl-(p)) to give pentacarbonyl(phosphonium ylide)chromium(0) complexes, (CO)5Cr[CH2PR3] (3), and dimethyl sulfoxide according to the first-order rate law. The reaction rate is independent on the type of the phosphane. The activation parameters for the reaction in 1,1,2-trichloroethane in the temperature range 39.6 to 68.0°C are ΔH≠ = 28.1 kcal · mol−1 and ΔS≠ = 12.7 cal · mol−1 · K−1. The reaction is initiated by irreversible dissociation of OSMe2 from 1. Addition of 2 to the carbene carbon of the resulting pentacarbonylmethylenechromium, [(CO)5Cr=CH2], yields 3 in a fast succeeding step. A mechanism involving rate determining dissociation of the Cr=CH2 bond can be excluded. These results represent the first evidence of a neutral, electrophilic carbonylmethylene complex.

Übergangsmetallkomplexe instabiler Ylide, IV. Neuartige ylidische Chelatliganden mit der Atomsequenz CPNP in Tetracarbonylchrom‐Komplexen

Abstract: Der Schwefelylid-Komplex (CO)5Cr[CH2S(O)Me2] (1) reagiert mit den Iminobis(phosphanen) 3a, b zu den funfgliedrigen Metallacyclen 4a, b, welche die neuartigen Ylide H2C=PPh2–NR-PPh2 als Chelatliganden tragen. Die Umsetzung von (CO)4Cr[CH2S(O)Me2]2 (5) mit (Ph2P)2NH (3d) fuhrt zum salzartigen Komplex 7, der sich am Stickstoffatom protonieren wie auch methylieren last. Transition Metal Complexes of Instable Ylides, IV1). Novel Ylidic Chelate Ligands with the Sequence CPNP as Structural Moiety in Tetracarbonylchromium Complexes The sulfur ylide complex (CO)5Cr[CH2S(O)Me2] (1) reacts with iminobis(phosphanes) 3a, b to yield five-membered metallacycles 4a, b, in which the novel ylides H2C=PPh2–NR-PPh2 are incorporated as chelate ligands. The reaction of (CO)4Cr[CH2S(O)Me2]2 (5) with (Ph2P)2NH (3d) leads to salt-like 7, which can be protonated and methylated at the nitrogen atom.

Ferro‐ and antiferromagnetism of Pd77.5−xCu6Si16.5(Fe,Mn)x glasses

Abstract: ac susceptibility and static magnetization measurements are reported on amorphous alloys Pd67.5Cu6Si16.5TM10, TM=Fe or Mn. The lower concentrated alloys (x≲5 at.% Fe or Mn) show only PM‐SG type transitions. A 10 at.% Fe alloy shows long range ferromagnetic order prior to a transition into a spin glass like state at low temperatures. A 10 at.% Mn alloy, however, undergoes a transition from PM to a mixed magnetic state with predominantly antiferromagnetic order. With further decreasing temperature the AFM becomes unstable causing a rapid upturn of the susceptibility. Finally, a sharp peak of the zero field ac susceptibility marks a transition into a spin frozen state.