Combination of Cobalt and Iron Polypyridine Complexes for Improving the Charge Separation and Collection in Ru(terpyridine)2‐Sensitised Solar Cells

Mixtures of polypyridine Fe^II and Co^II complexes are used as electron mediators in Ru–thienyltpy‐sensitised solar cells (tpy=terpyridine). The use of the metalorganic redox couples allows for improved charge‐collection efficiency with respect to the classical iodide/iodine couple which, when associated to Ru–tpy₂ dyes, usually produces poor performance. The improved charge collection is explained by a combination of effective dye regeneration and decreased recombination with the oxidised electrolyte on the basis of data obtained by transient spectroscopy and photoelectrochemical measurements. The efficiency of the regeneration cascade is also critically dependent upon the ability of the Co^II complex to intercept Fe^III centres, as clearly indicated by chronocoulometry experiments.     

Study of amorphous ytterbium iron alloys by57Fe and174Yb mössbauer spectroscopy

Mössbauer spectroscopy and magnetic measurements are used to get information about the valence state of the ytterbium, the magnetic properties and the local structural order.     

Pulsed NMRON measurements on insulators

Selective single and double quantum excitation pulsed NMRON has been utilized to obtain rotation patterns, free induction decays, and spin echoes in antiferromagnetic⁵⁴Mn−MnCl₂·4H₂O and the quasi-2 dimensional ferromagnet⁵⁴Mn−Mn(COOCH₃)₂·4H₂O. The pulsed technique is well suited to observing fast spin-lattice relaxation and T₁ values down to 100 ms have been measured in these systems. These short times may make magnetic insulators viable hosts for on-line experiments. The dependence on field and temperature of the⁵⁴Mn spin-lattice relaxation time T₁ has been investigated and a T₁ minimum at high fields observed in both systems. A spin-spin relaxation time T₂≈50 μs is measured in⁵⁴Mn−MnCl₂·4H₂O. The observation of NMRON in the paramagnetic phase of MnCl₂·4H₂O allows the resonant frequencies in the antiferromagnetic and paramagnetic phases to be compared, yielding a value for the zero point spin deviation in the former phase.     

Isothermal crystallization kinetics and spherulitic morphology of poly(4‐hydroxybutyric acid‐alt‐glycolic acid)

Isothermal crystallization behavior of a new regular polyester constituted by glycolic acid and 4‐hydroxybutyric acid units is studied by means of differential scanning calorimetry and hot‐stage optical microscopy. A wide range of crystallization conditions were experimentally accessible, allowing various morphological features to be observed and accurate estimates made of characteristic growth parameters, including radial growth and nucleation rates. Three‐dimensional spherulitic growth from heterogeneous nuclei is deduced from the Avrami analysis, whereas optical micrographs reveal two different spherulitic textures that agree with the existence of two crystallization regimes. These can be well distinguished from the breaks observed in the Lauritzen and Hoffman plots when the linear crystal growth rate or the overall crystallization rate is considered. Ringed and nonringed spherulites with negative and positive birefringence, respectively, can be obtained depending on crystallization conditions and regimes. The studied polyester shows rather complex melting behavior which is interpreted in terms of a recrystallization process involving the two different kinds of spherulites. This study allows polymorphism to be discounted. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2640–2653, 2007     

Convenient multi-gram scale synthesis of polybrominated imidazoles building blocks

The multi-gram scale polybromination of variously substituted imidazoles has been realized using a stoichiometric amount of the Br₂-DMF complex. Good yields have been obtained compared to other methods using large amounts of acetic acid-sodium acetate buffer.     

Régulateurs syntomiques et valeurs de fonctionsL p-adiques II

Sans résuméOblatum 15-III-1991 & 2-X-1992 & 14-I-1992 & 3-III-1993 & 17-V-1993     

Performance of ion chromatography in the determination of anions and cations in various natural waters with elevated mineralization

The performance of ion chromatography in the determination of anions and cations in natural mineral waters of different composition and different total mineralization was evaluated. Up to 12 ions of the 20 usually included in extended chemical analysis of natural waters were successfully determined by ion chromatography alone. At least 98.60% and up to 99.96% of total cation composition of mineral waters was determined by ion chromatography. Hydrogen carbonate predominated in anion composition of mineral waters and was determined titrimetrically. The percentage of anions determined by ion chromatography in the remaining anion composition of mineral waters was between 98.90% and 99.96%. The agreement between total concentrations of anions and cations in individual mineral waters determined predominantly by ion chromatography is very good and the performance of ion chromatography for the basic and for the extended chemical analysis of highly mineralized water samples is very high. Method development was assisted by previously developed algorithms and appropriate experimental conditions are also discussed.     

Deprotonative metalation of chloro- and bromopyridines using amido-based bimetallic species and regioselectivity-computed CH acidity relationships

A series of chloro- and bromopyridines have been deprotometalated by using a range of 2,2,6,6-tetramethylpiperidino-based mixed lithium-metal combinations. Whereas lithium-zinc and lithium-cadmium bases afforded different mono- and diiodides after subsequent interception with iodine, complete regioselectivities were observed with the corresponding lithium-copper combination, as demonstrated by subsequent trapping with benzoyl chlorides. The obtained selectivities have been discussed in light of the CH acidities of the substrates, determined both in the gas phase and as a solution in THF by using the DFT B3LYP method.     

TBAF-catalysed silver oxide-mediated cross-coupling of functional trimethysilylpyridines: access to arylpyridines and bihetaryl compounds

The concomitant use of silver oxide and catalytic amount of TBAF allowed the efficient and chemoselective coupling of readily available 4-chloro- and 4-methyl-2-trimethyl-silyl-pyridines with heteroaromatic and aromatic halides. Based on control experiments, a mechanism involving the formation of a pyridylsilver intermediate and TBAF recycling is postulated.