Strong intramolecular Si-N interactions in the chlorosilanes Cl3-nHnSiOCH2CH2NMe2 (n = 1-3)

The compounds Cl 3SiOCH 2CH 2NMe 2 ( 1) and Cl 2HSiOCH 2CH 2NMe 2 ( 2) were prepared by reactions of lithium 2-(dimethylamino)ethanolate with SiCl 4 and HSiCl 3. The analogous reaction with H 2SiCl 2 gave ClH 2SiOCH 2CH 2NMe 2 ( 3), but only in a mixture with Cl 2HSiOCH 2CH 2NMe 2 ( 2), from which it could not be separated. All compounds were characterized by IR and NMR ( (1)H, (13)C, (29)Si) spectroscopy, 1 and 2 by elemental analyses and by determination of their crystal structures. Cl 3SiOCH 2CH 2NMe 2 ( 1) and Cl 2HSiOCH 2CH 2NMe 2 ( 2) crystallize as monomeric ring compounds with pentacoordinate silicon atoms participating in intramolecular Si-N bonds [2.060(2) A ( 1), 2.037(2) A ( 2)]. The dative bonds in 1 and 2 between the silicon and nitrogen atoms could also be proven to exist at low temperatures in solution in (1)H, (29)Si-HMBC-NMR experiments by detection of the scalar coupling between the (29)Si and the protons of the NCH 2 and NCH 3 groups. A function describing the chemical shift delta exp (29)Si dependent on the chemical shifts of the individual equilibrium components, the temperature, and the free enthalpy of reaction was worked out and fitted to the experimental VT-NMR data of 1 and 2. This provided values of the free reaction enthalpies of Delta G = -28.8 +/- 3.9 kJ x mol (-1) for 1 and Delta G = -22.3 +/- 0.4 kJ x mol (-1) for 2 and estimates for the chemical shifts of open-chain (index o) and ring conformers (index r) for 1 of delta r = -94 +/- 2 ppm and delta o = -36 +/- 5 ppm and for 2 of delta r = -82 +/- 1 ppm and delta o = -33 +/- 4 ppm. The value of delta r for 1 is very close to that obtained from a solid-state (29)Si MAS NMR spectrum. Quantumchemical calculations (up to MP2/TZVPP) gave largely differing geometries for 1 (with a Si...N distance of 3.072 A), but well reproduced the geometry of 2. These differences are due to Cl...H and Cl...C repulsions and solid state effects, which can be modeled by conductor-like screening model calculations and also rationalized in terms of the topology of the electron density, which was analyzed in terms of the quantum theory of atoms in molecules.     

Synthesis and Structure of the Ordered Modification of Ba6EuF12Cl2

Crystals of ordered Ba₆EuF₁₂Cl₂ were found to form during high temperature flux growth. The structure was refined in the hexagonal space group P 6 to R^F(R ) = 0.024(0.024) for 326 reflections and 46 parameters. Lattice parameters are a = b = 1059.27(8) pm and c = 416.36(2) pm; Z = 1. The structure is isotypic to Ba₇F₁₂Cl₂. No solid solution of Ba/Eu was observed, the Eu²⁺ ions are located in the channels formed by 3 + 6 fluorine ions, occupying only one of the three metal sites of the Ba₇F₁₂Cl₂ structure.     

A search for monojet events produced by virtual Z0 bosons in e+e− annihalation at petra

A search was performed for the associated production of two different Higgs bosons via a virtual Z⁰ in e⁺e^? annihilation (e⁺e^? → h₁⁰h₂⁰) using the JADE detector at PETRA. This was motivated by the interpretation of the monojet events observed at the CERN p$\text{p}$ collider as anomalous Z⁰ decays into two neutral Higgs bosons (h₁⁰ and h₂⁰), where h₁⁰ is stable and escapes detection while h₂⁰ decays into hadrons. Single- or di-jet events with large momentum imbalance are then expected at PETRA energies. No evidence for such events was found in our data; this excludes h₂⁰ masses in the range of 1 to 21 GeV with 95% CL, if the branching fraction for Z⁰ → h₁⁰h₂⁰ is a larger than one half that for $\text{Z}{}^0\text{→ v}{}_{\mathrm{\mu }}\text{v}{}_{\mathrm{\mu }}$. The possibility that the monojets could originate from supersymmetric higgsino production from Z⁰ decay is also examined.     

Signature-dependent ml and e2 transition probabilities in 155ho and 157ho

¹⁵⁵Ho and ¹⁵⁷Ho have been populated in the reactions ¹⁴¹Pr(¹⁸O,4n) and ¹⁴⁶Nd(¹⁵N, 4n) at 85 and 74 MeV, respectively. In both nuclei bands built on the $\text{7}\text{2}$?[523] configuration were established to spin values considerably above the first backbend. A signature dependence in the excitation energies as well as in the ratio of M1 to E2 transition rates is observed below, but not above, the backbend in both nuclei. In ¹⁵⁷Ho lifetimes were measured with the recoil-distance method. The ΔI = 2; E2 transition probabilities obtained show very little variation with either signature or spin and no irregularity at the backbend. The signature dependence and strong rise in the ratio B(M1)/B(E2) observed at the backbend in ¹⁵⁷Ho therefore must be caused by the B(M1) values. A signature dependence in the B(E2, I → I ?1)/B(E2, I → I ?2) ratios also found in ¹⁵⁷Ho below the backbend is mainly the result of signature dependence in the ΔI = 1 ; E2 transition rates. Qualitatively, most of the features observed can be explained by nonaxial deformations, which change from large negative to slightly positive values of γ at the backbend.     

Comparison of three-jet events with QCD shower models

Distributions of particles in three-jet events from e⁺e^? → hadrons are compared with different fragmentation schemes, i.e. the Lund string model, independent parton fragmentation and QCD shower models. Effects specific to the string scheme, which have been seen in the data, are also reproduced by QCD shower models if soft gluon interference effects are included.     

Loss of alignment gain in the πh 9/2[541 1/2−] ⊗ (νi 13/2)2 band in 167Tm and neighbouring odd-Z N = 98 nuclei

Theπh_9/2[541 1/2^?] band in ¹⁶⁷Tm has been studied through the ¹²⁴Sn(⁴⁸Ca, p4n)¹⁶⁷Tm reaction at E _beam = 210 MeV. The favoured signature of the πh_9/2[541 1/2^?] band is observed to spin 61/2h?. A remarkable small gain in aligned angular momentum at the AB-band crossing has been found. The crossing frequency and the gain in aligned angular momentum for ¹⁶⁷Tm are compared with data for the N = 98 isotones of Lu, Ta and Re, and contrasted with Cranked Shell Model predictions, based on frequency diabatic configurations. Large deviations are found for the gain in aligned angular momentum.     

The rotational band on the 9− isomer in180Ta

The new radon isotope¹⁹⁷Rn was produced in the reaction¹⁶⁹Tm(³⁵Cl, 7n)¹⁹⁷Rn using bombarding energies from 5.6 to 6.1 MeV/nucleon. Fusion products were separated in-flight from the primary beam using a gas-filled recoil separator. The alpha particle energy and half-life of¹⁹⁷Rn were measured to be (7260±7) keV and (65 _?14 ⁺²⁵ ) ms, respectively. Another new alpha line was assigned to an isomeric state in¹⁹⁷Rn for which an alpha particle energy of (7356±7) keV and a half-life of (19 _?4 ⁺⁸ ) ms were obtained.     

Synthesis and Structure of the new Fluoride Bromide Ba6.668(2)Ca0.332(2)F12Br2 and Solid Solutions with Composition Ba7−xCaxF12(ClyBr1−y)2 with x = ∼0.5, 0 < y < 1

Crystals of the chemical composition Ba₇F₁₂Cl₂ were modified by adding a small amount of Ca²⁺ to allow the synthesis of the corresponding bromine compound Ba^[Ca]₇F₁₂Br₂. These samples were prepared in a NaBr flux and characterized by single crystal x‐ray diffraction. The new structure crystallizes in a disordered arrangement in the hexagonal space group P6₃/m (176). The calcium ion has a coordination number of 6. Solid solutions on the heavy halide position can be synthesised in a NaCl/NaBr flux to obtain the compounds Ba_7?xCa_xF₁₂(Cl_yBr_1?y)₂ with x = ～0.5 and 0 < y < 1. Regardless the amount of calcium used in the preparation process, the Ca stoichiometry in the compound is always between 0.3 and 0.5. The lattice parameters differ depending on the Ca‐ and Br‐content between 1053.81(5) ? a = b ? 1058.93(3) pm and 421.21 ? c ? 426.78(3) pm.     

Design and Control of Perylene Supramolecular Polymers through Imide Substitutions

The number and type of new supramolecular polymer (SMP) systems have increased rapidly in recent years. Some of the key challenges faced for these novel systems include gaining full control over the mode of self-assembly, the creation of novel architectures and exploring functionality. Here, we provide a critical overview of approaches related to perylene-based SMPs and discuss progress to exert control over these potentially important SMPs through chemical modification of the imide substituents. Imide substitutions affect self-assembly behaviour orthogonally to the intrinsic optoelectronic properties of the perylene core, making for a valuable approach to tune SMP properties. Several recent approaches are therefore highlighted, with a focus on controlling 1) morphology, 2) H- or J- aggregation, and 3) mechanism of growth and degree of aggregation using thermodynamic and kinetic control. Areas of potential future exploration and application of these functional SMPs are also explored.