Spectrophotometric pK a determination for p-tert-butylcalix [5]arene (H 5 L) in acetonitrile (pK a1 = 11.5 ± 0.7, pK a2 = 15.4 ± 1.0 at 298 K) evidenced both intra-and inter-molecular stabilisation of the deprotonated forms. Dimeric complexes [Ln 2 (H 2 L) 2 (dmso) 4 ] (Ln = Eu III , GdIII , or Tb III; dmso = dimethyl sulfoxide) were isolated from tetrahydrofuran (thf) in the presence of NaH as base. A single-crystal analysis of [Eu 2 (H 2 L) 2 (dmso) 4 ]ؒ 10thf showed the deformation of the cone conformation of the calixarene upon complexation and co-ordination of dmso molecules by inclusion through the hydrophobic cavity of the ligand. A photophysical investigation revealed a total quenching of the metal luminescence by a ligand-to-metal charge-transfer state in the case of Eu III while luminescence of Tb III is sensitised (quantum yield in thf: 5.1%). The temperature-dependent lifetime of Tb III is analysed in terms of a potential metal-to-ligand back-transfer process.The cyclic framework of calixarenes, 1 associated with the presence of phenol oxygen donor atoms, affords an interesting platform for the complexation of metal atoms, 2 while the hydrophobic cavity allows the inclusion of charged 3 and neutral 4 organic guests. The relative facility with which calixarenes can be partially or totally functionalised at the upper or lower rims, coupled with their easy large-scale synthesis, at least for the even members of the series (n = 4, 6 or 8), has opened further perspectives for their use in supramolecular chemistry. 5In particular, the hard acid character of the lower rim makes calixarenes interesting potential ligands for the complexation of trivalent lanthanide ions, either for extraction purposes 6 or for the design of efficient lanthanide-based luminescent devices.7-9 Antenna effects 10 can be generated directly by the phenol units or by lower or upper rim substitution.Previous work on the complexation of lanthanides with calix[n]arenes has mainly focused on the four-, six-and eightmembered systems. While p-tert-butylcalix [8] 19 who isolated water-soluble inclusion complexes between p-sulfonatocalix [5]arene with La, Gd, Eu, Tb and Yb and showed by X-ray crystallography that the interaction is either outer sphere or occurs exclusively via one sulfonato functionality, the metal centre acting often as a bridging brick. In this paper we present the isolation and the structural and photophysical properties of lanthanoid() (Ln = Eu, Gd or Tb) phenolate-bonded inner-sphere complexes with p-tert-butylcalix [5]arene (H 5 L). The reported data add valuable information on the interaction between lanthanoid() ions and p-tert-butylcalix [n]arenes and demonstrate that multiple bonds between the ligand and the metal ions can be generated only in the presence of a strong base. In addition, the spectrophotometric determination of the first two pK a values of the ligand is reported. Results and Discussion Acid-base behaviour of H 5 L in acetonitrileThe compound H 5 L was titrated at 298 K by Et 3 N in acetonitril...

Chlorofluorocarbons (CFCs) are synthetic halogenated volatile organic compounds that have been manufactured since 1930 and can be detected analytically in water in pg L -1 concentrations. The use as tracers for age dating of pristine groundwater has been summarized by previous review articles, where occasional failure of the CFC age-dating technique caused by local CFC contamination in excess of the equilibrium with modern air was reported. This article summarizes the worldwide occurrence of CFCs in groundwater with a focus on contaminated aquifers. CFC data from 24 aquifers and two regions on four continents are compiled. In 10 aquifers, contamination in more than 20% of samples with either CFC-11, CFC-12, or CFC-113 is reported. Pathways of CFC input to groundwater such as local atmospheric pollution, river water infiltration, landfills, and industrial solvent spills are discussed. The aerobic and anaerobic biotransformation reactions and natural attenuation processes of CFCs in aquifers are also reviewed. Microbially catalyzed reductive dechlorination of CFCs occurs in anaerobic aquifers. Little is known about the presence of other CFCs and degradation products of CFCs, among which some are known to be toxic (HCFC-21) or carcinogenic (HCFC-31). Risk assessment for groundwater resources should include HCFC measurements to better identify transformation reactions.

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