Stickstoffverbindungen von Elementen der dritten Hauptgruppe mit intra- und intermolekularen Donor-Akzeptor-Bindungen. - IV : Polycyclische Alumina-, Lithia-, Magnesia- und Sodia-Silazane

Die Lewis-aciden Elemente Li, Na, Mg und Al lassen sich leicht in cyclische Strukturen einbauen, die als gemeinsames Molekülfragment die Einheit Me2Si-(NtBu)2 besitzen: Die Röntgenstrukturanalysen an [Me2Si(NtBu)2Mg·THF]2 (II) und [Me2Si(N(tBu)AlMe2)(N(tBu)MgI)]2 (X) weisen die Verbindungen als Dimere aus. Im Falle von II sind zwei SiN2Mg-Vierringe wechselseitig über N-Mg-Bindungen verbunden, so dass ein dritter N2Mg2-Vierring mit der Punktsymmetrie Ci ( ) entsteht. Das Magnesiumatom ist vierfach koordiniert mit drei unterschiedlichen Mg---N-Bindungslängen (199.3(4), 211.2(4) und 218.8(4) pm) und einer Mg---O-Bindung von 204.9(6) pm zu einem Sauerstoffatom eines koordinierten Tetrahydrofurans. In X bedingen I---Mg-Wechselwirkungen die Ausbildung eines Dimeren mit einem zentrosymmetrischen Mg2I2-Rechteck. Das Magnesiumatom hat als weitere Liganden zwei Stickstoffatome in Abständen Mg---N 225.9(6) und 229.9(6) pm und eine Methylgruppe in einer Entfernung von 261(1) pm. Das herausragende Strukturmerkmal ist eine N(Mg,Al,Si)N-Bipyramide, die auf intramolekulare Zwei-Zentren- und Donor-Akzeptor-Bindungen zurückgeht (Al---N 187.7(6) und 188.6(6) pm, Si---N 180.6(5) und 181.0(6) pm). Die drei Nachbarelemente des Periodensystems Mg, Al und Si sind auf diese Art und Weise an ein gemeinsames Stickstoffatom gebunden, das als weiteren Liganden eine t-Butylgruppe besitzt. Es konnten Derivate zu X erhalten werden, die monomer vorliegen: Me2Si(N(tBu)AlMe2)-(N(2Bu)MgR) R = Me, Bz, 2Bu, Ph. Als Vorstufe zu diesen Verbindungen lässt sich die Lithiumvrbindung Me2Si(N(tBu)AlMe2(N(tBu)Li) und das entsprechende Natriumderivat isolieren. Aus dem 1H-NMR-Spektrum folgt abermals eine bi-pyramidale N(Li,Al,Si)N-Anordnung als Grundgerüst des Moleküls

A Comparative Study of Lead Oxide Modified Graphite Paste Electrodes and Solid Graphite Electrodes with Mechanically Immobilized Lead Oxides

The cyclic voltammetry of red PbO, α-PbO2, β-PbO2 and BaPbO3 was studied with two different types of electrodes in acidic and alkaline media. In one case, microcrystalline particles of lead oxides were mechanically immobilized on the surface of paraffin-impregnated graphite rod electrodes (PIGE), while in the other case, lead oxides were added to a paste of graphite and silicone oil. The overall behaviour of lead oxides in both electrodes is very similar to the well-known behaviour of electrodes made of lead oxide powders. The results show that the binder does not effect the overall electro-chemistry of lead oxides. Moreover, the electrochemical reactions are more reversible for the paste electrode than in the case of the PIGE

The Ursinus Weekly, April 29, 1976

Board announces promotions; Six granted tenure • S.F.A.R.C. discusses calendar reform • Egyptian Ambassador speaks on Middle East • Cub and Key holds reunion • Ec. Club meets • Whitians elect new members • U.C. professors attend national conferences • Editorial: Stewing students ask what\u27s cooking? • Letter to the editor: Correction on discussion of birth control policy • Wyeth show at Museum • Pi Gamma Mu accepts 22 students • Book Store robbery • Forum review: The Israeli stand • Mattress fun • U.S.D.A. open house • Zacharias\u27 inferno • Travelin\u27 9 delayed • Golfers swing • Track races • Baseball: Phillies • Baseball: Ursinus season report • ETS tests itself • Comparing college tuitions • PCO sponsors Vision Centerhttps://digitalcommons.ursinus.edu/weekly/1055/thumbnail.jp

Lateglacial and Holocene climate and environmental change in the northeastern Mediterranean region: Diatom evidence from Lake Dojran (Republic of Macedonia/Greece)

The juncture between the west-east and north-south contrasting Holocene climatic domains across the Mediterranean is complex and poorly understood. Diatom analysis of Lake Dojran (Republic of Macedonia/Greece) provides a new insight into lake levels and trophic status during the Lateglacial and Holocene periods in the northeastern Mediterranean. Following a very shallow or even desiccated state at the core base at ca. 12,500 cal yr BP, indicated by sedimentological and hydro-acoustic data, diatoms indicate lake infilling, from a shallow state with abundant benthos to a plankton-dominated relatively high lake level and eutrophic state thereafter. Diatom-inferred shallowing between ca. 12,400 - 12,000 cal yr BP and a very low lake level and eutrophic, oligosaline state between ca. 12,000 - 11,500 cal yr BP provide strong evidence for Younger Dryas aridity. The earliest Holocene (ca. 11,500 - 10,700 cal yr BP) was characterised by a high lake level, followed by a lake-level reduction and increased trophic level between ca. 10,700-8,500 cal yr BP. The lake was relatively deep and exhibited peak Holocene trophic level between ca. 8,500-3,000 cal yr BP, becoming shallow thereafter. The diatom data provide more robust evidence and strengthen previous lake-level interpretation based on sedimentological and geochemical data during the earliest, mid and late Holocene, and also clarify previous uncertainty in interpretation of Lateglacial and early-Holocene lake-level change. Our results are also important in disentangling regional climate effects from local catchment dynamics during the Holocene, and to this end we exploit extant regional palynological evidence for vegetation change in the highlands and lowlands. The importance of seasonality in driving Holocene climate change is assessed by reference to the summer and winter latitudinal temperature gradient (LTG) model of Davis and Brewer (2009). We suggest that increased precipitation drove the high lake level during the earliest Holocene. The early- Holocene low lake level and relatively high trophic state may result climatically from high seasonality of precipitation and locally from limited, nutrient-rich catchment runoff. We argue that the mid- Holocene relatively deep and eutrophic state was driven mainly by local vegetation succession and associated changes in catchment processes, rather than showing a close relationship to climate change. The late-Holocene shallow state may have been influenced by a temperature-induced increase in evaporative concentration, but was coupled with clear evidence for intensified human impact. This study improves understanding of Lateglacial and Holocene climate change in the northeastern Mediterranean, suggests the important role of the LTG on moisture availability during the Holocene, and clarifies the influence of catchment processes on palaeohydrology

The Ursinus Weekly, December 2, 1976

Ursinus news in brief: Field hockey places second; Take \u27em to court?; McCarthy addresses Pre-Legal group; Forum Committee finalizes program • Alumni Directory published • Board plans tuition increase; Welcomes two new members • Career night planned • RPR addresses faculty • CR\u27s make a difference • Letters to the editor: More on Fritz ; A backside view of Wismer cafeteria • Comment: A tale of two students • Musical notes • Forum reviews: Tapestry, Mostovoys • Two gentlemen at Ursinus • Movie review: Network • Union board meets • Philly Co. • Bears 0-9 ... but the future looks brighter • Ursinus Equestrian Club news • Swim season opens • Phils not shoppinghttps://digitalcommons.ursinus.edu/weekly/1063/thumbnail.jp

The Ursinus Weekly, October 9, 1975

\u2779 elects Delli-Bovi; Jill Leauber fills vacancy • Ursinus hosts family fete • Danforth Foundation offers fellowships • Dept. addition • From the cluttered desk of the U.S.G.A. President • Correction • Editorial: The Fact, after or before • Focus: Dr. Parsons • Overview: Intro. Philosophy • Lions in another Bowl? • The Throwaway children • U.S.G.A. Carnival • Phila. singers open season • Aerosmith: Bedlam • Opportunity for women • Reflections: A letter home • AFC forecast • George McGinnis: $3 million man • Field hockey report • Lebanon Valley crushes Ursinushttps://digitalcommons.ursinus.edu/weekly/1042/thumbnail.jp