The Structure of [HSi9]3− in the Solid State and Its Unexpected Highly Dynamic Behavior in Solution

We report on the first unambiguous detection of the elusive [HSi₉]^3? anion in solutions of liquid ammonia by various ²⁹Si and ¹H NMR experiments including chemical exchange saturation transfer (CEST). The characteristic multiplicity patterns of both the ²⁹Si and ¹H resonances together with CEST and a partially reduced ¹H,²⁹Si coupling constant indicate the presence of a highly dynamic Si₈ entity and a Si?H moiety with slow proton hopping. Theoretical calculations corroborate both reorganization of Si₈ on the picosecond timescale via low vibrational modes and proton hopping. In addition, in a single‐crystal X‐ray study of (K(DB[18]crown‐6))(K([2.2.2]crypt))₂[ HSi₉ ]?8.5 NH₃, the H atom was unequivocally localized at one vertex of the basal square of the monocapped square‐antiprismatic cluster. Thus experimental studies and theoretical considerations provide unprecedented insight into both the structure and the dynamic behavior of these cluster anions, which hitherto had been considered to be rigid.     

Energy Conversion Efficiency in Low- and Atmospheric-Pressure Plasma Polymerization Processes,Part II: HMDSO

For at least forty years, there has been an interest to correlate the structure of plasma polymer coatings with fabrication parameters during deposition, most particularly with the energy input per monomer molecule, \( E_{\text{m}} \). In our two laboratories, we have developed methods for measuring \( E_{\text{m}} \) (or somewhat equivalent activation energy, \( E_{\text{a}} \)) in low- (LP) and atmospheric-pressure (AP) discharge plasmas. We earlier proposed energy conversion efficiency, ECE, as a new parameter which permits direct comparison of LP and AP experiments. This is done here for the case of a much-studied organosilicon precursor (monomer), hexamethyl-disiloxane. “Critical” \( E_{\text{m}} \) (or \( E_{\text{a}} \)) values that demarcate ECE regimes separating different fragmentation/reaction mechanisms are found to agree remarkably well, and to correlate with specific mechanisms. Furthermore, deposition rates, and structural (for example, “organic/inorganic” content ratio) characteristics are seen to display very similar behaviors, despite additional drastically differing fabrication conditions like pure or highly diluted (in Ar carrier gas) monomer feed in the LP and AP cases, respectively.     

NaPr9S2[SiO4]6: Ein Sulfidsilicat des Praseodyms mit Bromapatitstruktur

NaPr₉S₂[SiO₄]₆: A Sulfide Silicate of Praseodymium with the Structure of Bromapatite NaPr₉S₂[SiO₄]₆ is obtained as pale green single crystals of hexagonal columnar shape from reactions of Pr, Pr₆O₁₁, S, SiO₂ and NaCl (850°C, 7 d) in fused evacuated silica tubes. The crystal structure (hexagonal, P6₃/m, Z = 1, a = 981.05(4), c = 689.68(2) pm) corresponds with a modified bromapatite structure where orthosilicate ([SiO₄]^4?) and sulfide (S^2?) anions provide coordination numbers of eight and nine to the two crystallographically different cations. These occupy the positions 4 f (Na⁺ together with Pr³⁺ in a molar ratio of 1:3) and 6h (Pr³⁺ only) to realize an average Ca₅Br[PO₄]₃-type structure.     

SINGLE PHOTONS ARE SUFFICIENT TO TRIGGER MOVEMENT RESPONSES IN Chlamydomonas reinhardtii

Abstract— The unicellular green alga Chlamy domonas reinhardtii shows two distinct movement responses upon changes in green light irradiance: These are direction changes and stop responses. The dependence of both responses on the intensity of applied flashes was measured and analysed with the help of Poisson statistics. In dark-adapted cells both responses were 'single-photon' events. Preillumination of cells or background irradiation decreased the sensitivity for the stop response, now requiring two or more photons to trigger it. In the blind, carotenoid-negative mutant FN 68 the light-sensitivity for a stop-response was reconstituted by addition of all trans retinal. This result indicated that not only the receptor for phototaxis but also that for the stop response is a retinal protein. In addition, stimulus-response curves from the literature were analysed by Poisson statistics.     

Gold

Ohne Zusammenfassung     

Functionalized cyclopentanes via Sc(III)-catalyzed intramolecular enolate alkylation

We report herein the intramolecular α-tert-alkylation of unsaturated β-ketoesters which gives rise to highly functionalized cyclopentanes. This transformation is characterized by its operational simplicity, mild reaction conditions and the use of scandium (III) triflate as a Lewis acid catalyst. Of interest, cyclopentanes bearing heterocycles, sites for post reaction functionalization and spirocyclic architectures are accessible with this strategy.     

Initial Growth of Functional Plasma Polymer Nanofilms

To gain deeper insights into the initial growth mechanism, with respect to functional group density and cross-linking, plasma polymer films (PPFs) were deposited from C₂H₄/NH₃ discharges. Keeping gas phase processes and electrical discharge conditions constant all over the deposition process, the mass deposition rate of the PPF was found to be initially lower and regularly increasing before reaching steady-state conditions after a film thickness of about 5 nm on metal oxide substrates. The first gradient nano-layer, i.e. the first 5 nm deposited, were observed to possess less amino functional groups and to be more cross-linked and thus more stable compared to the film prepared in steady state conditions, in which the uniform film comprises more amino functional groups, yet is less cross-linked and thus less stable. Due to its sticking probability, the substrate thus influences the initial deposition rate. Over plasma exposure time, the substrate becomes covered by an initial layer of PPF and the film-forming species are no longer deposited onto the pristine substrate but onto the already deposited organic polymer film. The preparation of the highly stable functional nanofilm, i.e. the initial PPF layer, can lead to new possible applications and fast deposition processes.