Search results for "Alkali metal"

ChemInform Abstract: Synthesis, Structures and DFT Calculations on Alkaline-Earth Metal Azide-Crown Ether Complexes.

2008

The first examples of azide complexes of calcium, strontium or barium with crown ethers have been prepared and fully characterised, notably [Ba([18]crown-6)(N3)2(MeOH)], [Sr([15]crown-5)(N3)2(H2O)], [Ca([15]crown-5)(N3)2(H2O)] and [Sr([15]crown-5)(N3)(NO3)]. Crystal structures reveal the presence of a variety of coordination modes for the azide groups including 1-, -1,3- and linkages via H-bonded water molecules, in addition to azide ions. The [Ba([18]crown-6)(N3)2(MeOH)]1/3 MeOH contains dinuclear cations with three -1,3-NNN bridges, the first example of this type in main group chemistry. The structures obtained have been compared with molecular structures computed by density functional th…

Über die möglichkeit der bildung makrocyclischer polyoxyniethylene. 29. mitt über polyoxymethylene1

1966

Bei der kationischen Polymerisation von 1,3,5-Trioxan in Cyclohexan entstehen Polyoxymethylene, welche partiell thermisch stabil und alkalibestandig sind, ohne das irgendwelche bekamiten stabilen Endgruppen nachgewiesen werden konnten. Moglicberweise handelt es sich hierbei um Makrocyclen. Cationic polymerization of 1,3,5-trioxan in cyclohexane yields polyoxymethylene which is partially stable to heat and to alkali but does not contain any of the known stable endgroups. These polymers possibly have a macrocyclic structure.

Kronenethersubstituierte 1,4-Distyrylbenzole und ihre Komplexierung mit Alkalipikraten

2000

Crown Ether Substituted 1,4-Distyrylbenzenes and their Complexation with Alkali Picrates The 1,4-distyrylbenzenes 8 and 9, which contain two crown ether units, each, were prepared by Wittig—Horner reactions. Their complexation tendencies with alkali picrates (Li—Cs) in water/dichloromethane were investigated. Potas sium ions give the strongest complexes. Generally monomo-lecular 1:1-complexes are formed; however, [K-8] + [Pik]—, [K-9]+ [Pik]— and [Rb-8] + [Pik]— generate aggregates, for which a stairway structure is proposed.

Lithium Ion Recognition with Nanofluidic Diodes through Host-Guest Complexation in Confined Geometries

2018

[EN] The lithium ion recognition is receiving significant attention because of its application in pharmaceuticals, lubricants and, especially, in energy technology. We present a nanofluidic device for specific lithium ion recognition via host guest complexation in a confined environment. A lithium-selective receptor molecule, the aminoethyl-benzo-12-crown-4 (BC12C4-NH2), is designed and functionalized on single conical nanopores in polyethylene terephthalate (PET) membranes. The native carboxylic acid groups on the pore walls are covalently linked with the crown ether moieties and the process is monitored from the changes in the current voltage (I-V) curves. The B12-crown-4 moieties are kno…

Untersuchungen zum oxidativen Abbau nativer Cellulose, 2. Einfluß der Alkalibehandlung auf die Viskositäts-Molekulargewichts-Beziehungen

1974

Um die Kinetik des oxidativen Abbaus nativer Cellulose viskosimetrisch verfolgen zu konnen, mussen neue [η]-M-Eichbeziehungen aufgestellt werden, da die Behandlung der Cellulose mit konzentriertem Alkali den Staudingerindex [η] erniedrigt, ohne das Molekulargewicht M zu verandern. Es wurden zwei Reihen oxidativ abgebauter, verschieden lange mit Alkali vorbehandelter Cellulosen hergestellt und an diesen die Konstanten der Kuhn-Mark-Houwink-Gleichung fur die Cellulosenitrate in Aceton und die Cellulosen in Cuoxam (Cu(NH3)4(OH)2) durch Vergleich mit Lichtstreuungsmessungen bestimmt. For kinetic studies of cellulose degradation by molecular oxygen it is necessary to establish new [η]-M-relation…

Calix Crowns Derived from para-Bridged Calix[4]arenes

2000

Two calix[4]arenes, bridged by aliphatic chains of five and eight carbon atoms spanning two opposite para positions, have been converted into their 1,3-crown ether derivatives by reaction with tetraethylene and pentaethylene glycol ditosylates. Of the two possible 1,3-crown derivatives, only the formation of those isomers is observed in which the phenolic units connected at the para positions are etherified. This has been established in one case by a single-crystal X-ray analysis. Preliminary results for the extraction of selected alkali and alkaline-earth metals are reported.

Über katalytische einflüsse bei der polykondensation des p-kresoldialkohols

1952

Wird natriumfreier p-Kresoldialkohol in Silber- oder Platingeraten bei 130°C kondensiert, so ist durch den Geruch kein Formaldehyd wahrnehmbar. p-Kresoldialkohol enthalt oft von seiner Darstellung uber das Natriumsalz her geringe Mengen an Natrium, dessen Anteil im Bereich von 0,0 bis 5,00/00 liegt (0,000 bis 0,037 Mol Natrium je Mol Phenolalkohol). Die bei der Hartung des p-Kresoldialkohols in Platin- oder Silbergeraten beobachteten Gewichtsverluste und die Formaldehydabspaltung sind umso hoher, je groser der Natriumgehalt ist. Natriumfreier p-Kresoldialkohol in Gefasen aus Jenaer Gerateglas 20 und aus gewohnlichem Glas gehartet zeigt in Ubereinstimmung mit der Abgabefahigkeit an Alkali de…

ChemInform Abstract: Cobalt Clusters with Cubane-Type Topologies Based on Trivacant Polyoxometalate Ligands.

2016

Four novel cobalt-substituted polyoxometalates having cobalt cores exhibiting cubane or dicubane topologies have been synthesized and characterized by IR, elemental analysis, electrochemistry, UV–vis spectroscopy, X-ray single-crystal analysis, and magnetic studies. The tetracobalt(II)-substituted polyoxometalate [Co4(OH)3(H2O)6(PW9O34)]4– (1) consists of a trilacunary [B-α-PW9O34]9– unit which accommodates a cubane-like {CoII4O4} core. In the heptacobalt(II,III)-containing polyoxometalates [Co7(OH)6(H2O)6(PW9O34)2]9– (2), [Co7(OH)6(H2O)4(PW9O34)2]n9n– (3), and [Co7(OH)6(H2O)6(P2W15O56)2]15– (4), dicubane-like {CoII6CoIIIO8} cores are encapsulated between two heptadentate [B-α-PW9O34]9– (in…

Mechanism of stereospecific polymerization of styrene with alkali metal alkyls

2007

The initial stages of the heterogeneous degradation of alkali cellulose by oxygen in relation to the morphology of native cotton cellulose

2007

Treatment of cotton cellulose with sodium hydroxide solutions of varying concentration over extended periods in the absence of oxygen markedly decreases the intrinsic viscosity of both the cellulose in cuoxam and its cellulose trinitrate derivative (CTN) in acetone. Light-scattering measurements show that the molecular weight does not change while the radius of gyration decreases and the second virial coefficient increases. The narrow molecular weight distribution of the native cotton is still maintained. Mild oxidation first causes the intrinsic viscosity to increase. At more prolonged oxidation times the viscosity decreases. These results are interpreted by an intramolecular cross-linking…