Die Koordinationszahl von Lanthaniden: Thermodynamik der LnIIIEDTA-Mischkomplexe mit den Anionen der 8-Hydroxychinolin-5-sulfonsäure,Iminodiessigsäure und Nitrilotriessigsäure

The values of ΔG, ΔH and ΔS for the formation of the mixed 1:1:1 lanthanide EDTA complexes with the anions of 8-hydroxyquinoline-5-sulfonic acid, iminodiacetic acid and nitrilotriacetic acid were determined by pH-titrations and a direct calorimetric method. These thermodynamic data are discussed and compared with those for the formation of the Ln(III)EDTA complexes. Contrary to current opinion it is concluded that all trivalent lanthanide aquoions have the same coordination number in dilute solution. However, in the series of the lanthanide EDTA complexes the coordination number changes between Sm and Tb. In this region, equilibria occur between two types of EDTA complexes with different numbers of coordinated water molecules: The corresponding equilibrium constants could be evaluated. The coordination number changes also in many other Ln complexes along the lanthanide series, and similar equilibria occur.     

Formation of the corannulene core by nickel-mediated intramolecular coupling of benzyl and benzylidene bromides: a versatile synthesis of dimethyl 1,2-corannulene dicarboxylate

[reaction: see text] A practical synthesis of dimethyl 1,2-corannulene dicarboxylate (5) is reported, with the final ring-forming step achieved by the double intramolecular nickel powder mediated coupling of benzyl and benzylidene bromide groups with 60% isolated yield.     

Koordinationszahl und nephelauxetischer Effekt von Komplexen der Lanthaniden

The Eu^IIIEDTA complex exhibits a strong temperature dependence of its absorption band at 395 nm in dilute aqueous solution. Similar but much weaker effects can be observed in solutions of SmEDTA and GdEDTA, whereas EDTA complexes of the other lanthanide ions as well as the aquo ions of the whole series show no significant change of their absorption spectra in nation number along the series of the lanthanide EDTA complexes that takes place from Sm to Tb at room temperature. It can be concluded from the nephelauxetic effect that the coordination number decreases with increasing atomic number. The coordination numbers of the aquo ions are the same for all trivalent lanthanide ions in dilute solutions.     

Investigation of vacuum polarization in t-channel radiative Bhabha scattering

We discuss the possibility of a precision measurement of vacuum polarization in t-channel radiative Bhabha scattering at a high luminosity collider. For illustration, the achievable precision is estimated for the BaBar experiment at PEP-II and for the OPAL experiment at LEP. Received: 6 June 2001 / Published online: 21 September 2001     

Highlighting gyroscopic motion in crystals in 13C CPMAS spectra by specific isotopic substitution and restricted cross polarization

The temperature-dependent exchange rate and signal coalescence in the 13C CPMAS NMR spectrum of a crystalline molecular gyroscope are exposed by specifically deuterating the overlapping static carbons.