Showing papers by "Bernt Krebs published in 1989"

7Li NMR spin-lattice relaxation and ionic diffusion in lithium thioborate glasses

Abstract: 7 Li NMR spin-lattice relaxation rates at 16 MHz and 117 MHz have been measured at various temperatures for glasses in the non-oxide chalcogenide system B 2 S 3 -Li 2 S-LiX with X=Cl, Br, I. As compared with the corresponding oxide glasses these materials are distinguished by a higher ionic conductivity, and the relaxation maxima are better accessible. The relaxation rates display anomalous temperature and frequency dependences. Attempts to interpret the non-BPP-type relaxation in terms of appropriate diffusion models are discussed

Preparation, structure, and properties of manganese toluene-3,4-dithiolate complexes in different oxidation states

Abstract: in acetonitrile, a Hammett plot showed a linear relationship between Hammett u, values and the second reduction potential, indicating that electron density changes on the ligand are transmitted to the metal ions.'O Replacement of the 4-methyl ring substituent by CF3 in I and I1 has been shown to increase Elp for both one-electron-reduction steps in DMF by 0 . 1 4 4 1 9 V, clearly indicating the transmission of a distant electron-withdrawing effect to the copper centers." The wide separation of the two reduction waves of all these compounds indicates significant stability for the one-electron intermediates, as is indicated by the large conproportionation constants (Table VII). The one-electron-reduced species derived from I exhibits a seven-line EPR spectrum at room temperature in both CH2C12 and CH3CN, indicative of interaction of the odd electron with both copper Compound I1 produces a one-electron-reduced species in CH3CN, which also exhibits a seven-line spectrum (Figure 6). The analogous copper tetrafluoroborate complex involving the butylene-bridged macrocyclic ligand derived from 4-tert-butyl-2,6-diformylphenol has also been shown to produce a one-electron-reduced species in CH2C12 or acetone, which exhibits a seven-line spectrum at room temperature." This behavior contrasts with that associated with I11 and IV, which exhibit four-line ~pectra.~*~O Acknowledgment. We thank the Natural Sciences and Engineering Research Council of Canada for financial support for this study, including the purchase of the variable-temperature Faraday susceptometer and EPR spectrometer.

Nickelkomplexe mit sterisch anspruchsvollen Thiolatoliganden: [Ni8S(SC4H9)9]⊖, ein gemischtvalenter Nickel(sulfid)thiolat‐Cluster, und [Ni4(SC3H7)8], ein homoleptisches Nickelthiolat

Abstract: La caracteristique structurale du 1er complexe est un ion sulfure au centre d'un prisme Ni 6 coiffe par 2 atomes de Ni supplementaires et la presence de 9 ponts μ 2 -StBu. L'etat d'oxydation de Ni est +1,25

Bromoselenate(II,IV), ein neuer Typ gemischtvalenter Verbindungen

Abstract: Preparation a partir de SeBr 4 et bromures avec de gros cations dans des solvants faiblement polaires. Structures

Extended X‐ray absorption fine structure (EXAFS) investigations of model compounds for zinc enzymes

Abstract: A test of the ability of extended X-ray absorption fine structure (EXAFS) to determine structural information with specific reference to zinc sites in enzymes has been made. X-ray absorption spectra of 18 compounds of zinc have been measured and the nearest-neighbour scattering has been interpreted using a Fourier transform and an ab initio technique. Empirical Zn-N, Zn-O, Zn-S and Zn-Cl amplitude and phase functions have been extracted from Zn(C3H4N2)4(ClO4)2, ZnO, Zn(S2COC2H5)2 and [N(CH3)4]2[ZnCl4], respectively and tabulated as a function of the wavevector with respect to 9660.0 eV X-ray energy. These amplitude and phase functions were then tested with respect to the other 14 compounds. For a single species of atoms in the first coordination shell the interatomic distances can be established to +/- 0.5 pm (+/- 5 x 10(-3) A) whilst when mixed shells exist errors in distances are +/-4 pm (+/- 40 x 10(-3) A). Coordination numbers are given to +/- 16% for the single species case a and +/- 25% for the mixed coordination case. Using the theoretical amplitude and phase functions of McKale et al. [(1988) J. Am. Chem. Soc. 110, 3763-3768] the deduced distances are systematically too small by an average of 0.6 pm (6 x 10(-3) A). The errors in the coordination numbers are 18%.

Synthese und Struktur von (MeSe)3Sb / Synthesis and Structure of (MeSe)3Sb

Abstract: Tris(methylseleno)stibane (1) has been prepared by reaction of Sb with Me2Se2. The crystal structure of 1 consists of (MeSe)3Sb molecules with trigonal pyramidal SbSe3 units (average distances Sb—Se 2.580 Å and Se—C 1.97 A, angles SeSbSe 83-102°). Intermolecular Sb···Se contacts of 3.55-3.66 Å lead to a distorted octahedral coordination at Sb. In the UV-VIS spectrum of the yellow solid of 1 there is a maximum of absorption at 430 nm with a slope to 540 nm. Raman emissions at 204 and 237 cm-1 are related with vs,as SbSe3.

Cobalt X-ray absorption spectroscopy of glucose isomerase

Abstract: Introduction Glucose isomerases catalyze the isomerization of D-glucose to D-fructose and of D-xylose to D-xylulose. They are of considerable interest in the industrial production of high-fructose corn syrup. Glucose isomerase from Streptomyces albus (GI) is a tetramer (Mr = 172.000) with four identical subunits [1,2]. Each subunit contains two distinct metal bindin of Co2+, Mn f sites, a tight binding site (B-site) and a weaker binding site (A-site). Addition + or Mg2’ * increases the catalytic activity as well as the stability of the enzyme.

Mononuclear and Binuclear Cu(I) Complexes with Metal‐Sulfur Ligation.

Abstract: The 1:4 molar reaction of the tetrameric Cu(I) compounds (I) with pyridine-2-thione, pyridine-4-thione, and pyrimidine-2-thione in toluene or CH2Cl2 results in the formation of the dimeric products (III).