Metastable Se6 as a ligand for Ag+: from isolated molecular to polymeric 1D and 2D structures

Attempts to prepare the hitherto unknown Se6 2+ cation by the reaction of elemental selenium and Ag[A] ([A]- = [Sb(OTeF5)6]-, [Al(OC(CF3)3)4]-) in SO2 led to the formation of [(OSO)Ag(Se6)Ag(OSO)][Sb(OTeF5)6]2 1 and [(OSO)2Ag(Se6)Ag(OSO)2][Al(OC(CF3)3)4]2 2a. 1 could only be prepared by using bromine as co-oxidant, however, bulk 2b (2a with loss of SO2) was accessible from Ag[Al(OC(CF3)3)4] and grey Se in SO2 (chem. analysis). The reactions of Ag[MF6] (M= As, Sb) and elemental selenium led to crystals of 1/∞{[Ag(Se6)]∞[Ag2(SbF6)3]∞} 3 and {1/∞[Ag(Se6)Ag]∞}[AsF6]2 4. Pure bulk 4 was best prepared by the reaction of Se4[AsF6]2, silver metal and elemental selenium. Attempts to prepare bulk 1 and 3 were unsuccessful. 1–4 were characterized by single-crystal X-ray structure determinations, 2b and 4 additionally by chemical analysis and 4 also by X-ray powder diffraction, FT-Raman and FT-IR pectroscopy. Application of the PRESTO III sequence allowed for the first time 109Ag MAS NMR investigations of 4 as well as AgF, AgF2, AgMF6 and {1/∞[Ag(I2)]∞}[MF6] (M= As, Sb). Compounds 1 and 2a/b, with the very large counter ions, contain isolated [Ag(Se6)Ag]2+ heterocubane units consisting of a Se6 molecule bicapped by two silver cations (local D3d sym). 3 and 4, with the smaller anions, contain close packed stacked arrays of Se6 rings with Ag+ residing in octahedral holes. Each Ag+ ion coordinates to three selenium atoms of each adjacent Se6 ring. 4 contains [Ag(Se6)+]∞ stacks additionally linked by Ag(2)+ into a two dimensional network. 3 features a remarkable 3-dimensional [Ag2(SbF6)3]- anion held together by strong Sb–F … Ag contacts between the component Ag+ and [SbF6]- ions. The hexagonal channels formed by the [Ag2(SbF6)3]- anions are filled by stacks of [Ag(Se6)+]∞ cations. Overall 1–4 are new members of the rare class of metal complexes of neutral main group elemental clusters, in which the main group element is positively polarized due to coordination to a metal ion. Notably, 1 to 4 include the commonly metastable Se6 molecule as a ligand. The structure, bonding and thermodynamics of 1 to 4 were investigated with the help of quantum chemical calculations (PBE0/TZVPP and (RI-)MP2/TZVPP, in part including COSMO solvation) and Born–Fajans–Haber-cycle calculations. From an analysis of all the available data it appears that the formation of the usually metastable Se6 molecule from grey selenium is thermodynamically driven by the coordination to the Ag+ ions

Multi-scale sensible heat fluxes in the urban environment from large aperture scintillometry and eddy covariance

Sensible heat fluxes (QH) are determined using scintillometry and eddy covariance over a suburban area. Two large aperture scintillometers provide spatially integrated fluxes across path lengths of 2.8 km and 5.5 km over Swindon, UK. The shorter scintillometer path spans newly built residential areas and has an approximate source area of 2-4 km2, whilst the long path extends from the rural outskirts to the town centre and has a source area of around 5-10 km2. These large-scale heat fluxes are compared with local-scale eddy covariance measurements. Clear seasonal trends are revealed by the long duration of this dataset and variability in monthly QH is related to the meteorological conditions. At shorter time scales the response of QH to solar radiation often gives rise to close agreement between the measurements, but during times of rapidly changing cloud cover spatial differences in the net radiation (Q*) coincide with greater differences between heat fluxes. For clear days QH lags Q*, thus the ratio of QH to Q* increases throughout the day. In summer the observed energy partitioning is related to the vegetation fraction through use of a footprint model. The results demonstrate the value of scintillometry for integrating surface heterogeneity and offer improved understanding of the influence of anthropogenic materials on surface-atmosphere interactions

Low-temperature stability of body-centered cubic PdCu membranes

Concerns about limited durability at ambient temperatures are a major obstacle for the utilization of Pd-type membranes for H-2 purification in local, on-demand H-2 production. It is clear that pure Pd membranes are not suitable for applications that involve fast regular start-up and shut-down of purification systems but knowledge remains sparse about the performance of Pd alloy membranes in such situations. Here we investigated the stability of thin-layered, supported PdCu membranes with body-centered cubic (bcc) structure between room temperature and 673 K at H-2 pressure differences Delta P-H2 up to 1 MPa. Three PdCu layers with 46-50% Pd have been prepared by alternating electrodeposition of multiple Cu and Pd layers onto metallized ceramic membranes and subsequent alloying at 673-773 K. The H-2 permeation rates of all membranes can be described by single permeation laws in the entire investigated temperature range. The nominal H-2 permeability of a Pd48Cu52 membrane amounted to 2.3 x 10(-9) mol m(-1) s(-1) Pa-0.5 at 673 K and Delta P-H2 = 100 kPa with an ideal H-2/N-2 selectivity of 3382. The H-2 fluxes and N-2 leak rates of the three membranes were not affected by cycling between room temperature and 673 K under up to 1.1 MPa H-2 which included more than a dozen H-2/N-2 exchanges at 298 K. These fluxes remained also stable through 100 h continuous operation in H-2 at that temperature. The excellent low-temperature tolerance of these membranes is attributed to the marginal hydrogen solubility in bcc PdCu alloys rendering them promising membrane materials for H-2 purification involving everyday operation at ambient temperatures

European Public Sector Accounting Standards (EPSAS) : neue Herausforderungen für das Rechnungswesen im öffentlichen Sektor Deutschlands

Für das Haushaltswesen deutscher Verwaltungen könnte das gerade begonnene Jahrzehnt erhebliche Änderungen bringen. Es „droht“ – vor dem Hintergrund der Finanz- und Staatsschuldenkrise in Europa – die Einführung von „European Public Sector Accounting Standards“ – kurz EPSAS – auf der Grundlage der bereits vorhandenen „International Public Sector Accounting Standards“ – kurz IPSAS. Die EU drängt verstärkt auf deren Entwicklung. Diese verständlich nachzuzeichnen, inhaltlich vergleichend zu beschreiben und zu analysieren sowie auch kritisch vor dem Hintergrund der Ziele von (vermeintlichen) EPSAS zu würdigen, ist Gegenstand dieser Schrift

Scripts and Datasets for Manuscript: The highly rugged yet navigable regulatory landscape of the bacterial transcription factor TetR

Scripts and Datasets for Manuscript: The highly rugged yet navigable regulatory landscape of the bacterial transcription factor Tet

Permeation hysteresis in PdCu membranes

H-2 permeation hysteresis has been observed during cycling of a 3 mu m thick supported PdCu membrane with similar to 50 atom % Pd through the fcc/bcc (face-centered cubic/body-centered cubic) miscibility gap between 723 and 873 K. Structural investigations after annealing of membrane fragments under H-2 at 823 K reveal retardation of the fcc(H) -> bcc(H) transition, which is attributed to the occurrence of metastable hydrogenated fee PdCu(H) phases. The H-2 flux at 0.1 MPa H-2 pressure difference in the well-annealed bcc single phase regime below 723 K can be described by J(H2) = (1.3 +/- 0.2) mol.m(-2).s(-1) exp[(-11.1 +/- 0.6) kJ.mol(-1)/(RT)] and that in the fcc single phase regime above 873 K by J(H2) = (7 +/- 2) mol.m(-2).s(-1) exp[(-30.3 +/- 2.5) kJ.mol(-1)/(RT)]

Platinum/Apatite Water-Gas Shift Catalysts

Water-gas shift (WGS) micro and membrane reactors are interesting components for compact H₂ production and purification devices, but they require catalysts with very high activity for optimum efficiency to minimize catalyst bed thickness and mass transfer limitations. On the other hand, activation of H₂O is known to be more challenging than CO in this reaction. Catalysts comprising ca. 2 nm large Pt particles on hydrophilic apatites are found to have very high WGS activity, with specific reaction rates exceeding those of a highly active Pt/CeO₂ catalyst by up to 50% at 573 K. These apatite-supported catalysts exhibit stable CO conversions at 673 K without showing any CH₄ formation tendencies up to 723 K. WGS activity increases with Ca/P ratio in the apatite, leveling off around Ca/P ≈ 1.75, and formate has been identified as the main reaction intermediate. The outstanding WGS performance is attributed to the superior activation of H₂O on these ionic oxides due to coordination of H₂O to Lewis acidic Ca²⁺ ions and H bonding to basic O atoms of PO₄^3– units. This renders H₂O molecules highly polarized and thus reactive on apatite surfaces with the ensuing formate-like intermediates being well stabilized through bonding to multiple Ca²⁺ ions, as well. Thus, apatites provide an intriguing alternative to increasingly expensive rare-earth oxides in high-performance noble-metal WGS catalysts not only for micro and membrane reactors

Neues Kommunales Haushalts- und Rechnungswesen in Niedersachsen : Kommentar

In Kapitel A werden die gesetzlichen Normen des neuen Niedersächsischen Kommunalverfassungsgesetzes zum „doppischen“ Gemeindehaushaltsrecht behandelt. Hier sind vor allem die Prüfungsvorschriften neu berücksichtigt worden. * In Kapitel B folgen die Vorschriften der niedersächsischen Gemeindehaushalts- und -kassenverordnung. * Kapitel C behandelt das „Einführungsgesetz“, soweit es sich auf das Haushaltswesen der niedersächsischen Kommunen bezieht. Seit Erscheinen der zweiten Auflage sind drei Jahre vergangen. Mit Ablauf des Jahres 2011 geht nun die Übergangszeit zur Umstellung auf die Doppik zu Ende. Am 1. November 2011 wird zudem das „Niedersächsische Kommunalverfassungsgesetz – NKomVG“ in Kraft treten. Alle diese Veränderungen – vor allem die neue Rechtsgrundlage des NKomVG – sind Anlass, eine neue Auflage des Kommentars auf den Markt zu bringen. Neben Aktualisierungen und Anpassungen werden bisher kommentierte Vorschriften weiter vertieft und Kommentierungen zu zusätzlichen Vorschriften neu aufgenommen. Das gilt nicht zuletzt für die Vorschriften zum Prüfungswesen. Dazu konnte mit Frau BERTA DIEKHAUS erfreulicherweise eine weitere kompetente und engagierte Praktikerin gewonnen werden, die das Autorenteam (siehe unten) nun ergänzt. - Einige Vorschriften sind allerdings immer noch unkommentiert und bleiben zukünftigen Auflagen vorbehalten