Refine
Year of publication
- 1991 (3) (remove)
Document Type
- Article (3)
Language
- German (3) (remove)
Has Fulltext
- yes (3)
Is part of the Bibliography
- no (3)
Keywords
Institute
- Biochemie und Chemie (3) (remove)
Ion pairs of 1,10-phenanthrolin-5,6-dione radical anion [M · ⊖Me⊕n] ·⊕(n−1) with Me⊕n = Mg⊕⊕, Ca⊕⊕, Sr⊕⊕, Zn⊕⊕, Cd⊕⊕, Pb⊕⊕ and La⊕⊕⊕ are advantageously prepared in aprotic DMF solution containing appropriate metal salts Me⊕nX⊖ by using the ‘mild’ single-electron reducing agent tetra(n-butyl)ammonium-boranate R4N⊕BH4⊖ . For comparison, the ‘naked’ radical anion with the largely interaction-free [K⊕(2.2.2)-cryptand]⊕ counter cation is chosen, which is formed on reduction with potassium in THF solution of (2.2.2)-cryptand. Addition of excess Na⊕[B(C6H5)4]⊖ to the reduction solution only yields a solvent-separated ion pair (M · ⊖)DMF ··· (Na⊕)DMF, whereas in the presence of multiply charged counter cations Me⊕n the respective contact ion pair radical cations [M · ⊖Me⊕n] · ⊕(n−1) are formed. Their g values decrease with increasing nuclear charge of Me⊕n and their metal-s-spin densities increase with the effective counter cation charge n⊕/rMe⊕n. The ESR /ENDOR data recorded suggest Me⊕n complexation by the δ⊖OC -COδ⊖ chelate tongs and the ion pair stability, which is modified by the dielectric properties of the solvent used, may be rationalized by the Coulombic attraction between the radical anion M · ⊖ and the counter cations Me⊕n.
Cyclovoltammetric measurements of solutions containing the rather basic tetra-(2′-pyridyl)pyrazine allow to detect even traces of water and thus can be used as a touchstone for aprotic (cH⊕ < 1 ppm) conditions. On exchange of the “innocent” tetrabutylammonium R4N⊕ as supporting electrolyte cation by “interactive” ones such as Li⊕) or Na⊕, considerable changes in the reduction potentials are observed due to ion pair formation.
Das OH-Radikal, bestehend aus einem Sauerstoff- und einem Wasserstoffatom, ist verantwortlich für den Selbstreinigungsmechanismus der Atmosphäre. Als Oxidationsmittel reagiert es mit praktisch allen Spurengasen, wie z. B. dem giftigen Kohlenmonoxid, dem Treibhausgas Methan und dem Schwefeldioxid, und macht sie wasserlöslich, so daß sie im Regen gelöst ausgewaschen werden können (Waschmitteleffekt). Welche Schlüsselstellung das OH-Radikal in der Atmosphärenchemie hat, beschreibt der Chemiker Franz Josef Comes. Gleichzeitig stellt er das weltweit empfindlichste Absolutverfahren zur Bestimmung von troposphärischen OH-Konzentrationen vor, das in Frankfurt entwikkelt und zur Zeit getestet wird.