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61.
Spectra of single tetra-tert-butylterrylene chromophore molecules embedded in an amorphous polyisobutylene matrix as microprobes were recorded. The individual temperature dependences of the spectral linewidths for the same single molecules (SMs) in a broad temperature interval (1.6 < T < 40 K) have been measured. This enabled us to separate the contributions of tunneling two-level systems and quasilocalized low-frequency vibrational modes (LFMs) to the observed linewidths. The analysis of the T dependences yields the values of LFM frequencies and SM-LFM coupling constants for the LFMs in the local environment of a given chromophore. Pronounced distributions of the observed parameters of LFMs were found. This result can be regarded as the first direct experimental proof of the localized nature of LFMs in glasses. 相似文献
62.
Lothar Helm Karen Deutsch Edward A. Deutsch Andr E. Merbach 《Helvetica chimica acta》1992,75(1):210-217
The kinetics of pyridine exchange on trans-[MO2(py)4]+ have been followed by 1H-NMR in CD3NO2 for M = Re, Tc: k298S?1 = (5.5 ± 0.1) × 10?6, 0.04 ± 0.02; ΔH≠/kJmol?1 = 111 ± 3, 101 ± 9; ΔS≠/JK?1mol?1 = +28 ± 10, +68 ± 35. For the Rev complex, pyridine and oxygen exchanges have been measured simultaneously by 1H- and 17O-NMR in deuterated water: k298/s?1 = (8.6 ± 0.2) × 10?6 (py), (14.5 ± 0.3) × 10?6 (oxygen); ΔH≠/kJmol?1 = 111 ± 1, 91 ± 1; ΔS /JK?1mol?1 = +32 ± 3, ?32 ± 4. For both complexes, the rate law for pyridine exchange is first-order in complex and zero-order in pyridine; together with the activation parameter values, and the fact that the rate does not depend significantly on the nature of the solvent, this strongly implies the operation of a dissociative mechanism. The ratio of pyridine exchange rates for the Tc and Re complexes at room temperature is ca. 8000. The consequences of these observations for radiopharmaceutical synthesis are discussed. 相似文献
63.
Mária Hvastijová Jiri Kohout Marián Okruhlica Jerzy Mroziński Lothar Jäger 《Transition Metal Chemistry》1993,18(6):579-582
Summary Dicyanamide complexes of CuII, NiII and CoII of the type M[N(CN)2]2L2, where L = benzimidazole, 2-methyl- or 2-ethylbenzimidazole, have been prepared and studied by spectroscopy and magnetochemistry. The complexes, except for Co[N(CN)2]2 (benzimidazole)2, are six-coordinate, involving bidentate bridging dicyanamide groups. While the NiII complexes have practically octahedral structures, the CuII complexes are pseudooctahedral with similar tetragonal distortion. The ligand field strength in these complexes depends mainly on the steric effect of the benzimidazole ligands. The CoII complex of benzimidazole is monomeric tetrahedral, but that of 2-ethylbenzimidazole is tetragonal octahedral. The oridging function of dicyanamide in the six-coordinate complexes is realized either through both cyanide or through amide and cyanide nitrogens. The complex Cu[N(CN)2]2 (2-methylbenzimidazole)2 is a weak antiferromagnet (J = -0.1 cm–1), exhibiting under ca. 15 K a long-range antiferromagnetic ordering. 相似文献
64.
Jorge Angulo Cornejo Ketty Ayala Rainer Richter Heinz Bhlig Lothar Hennig Lothar Beyer 《无机化学与普通化学杂志》2005,631(15):3040-3045
Hydrogen Bonds in 1,1‐Bis(2‐hydroxyethyl)‐3‐benzoylthiourea and its Nickel(II)‐ and Copper(II)‐Chelate Complexes The ligand 1,1‐bis(2‐hydroxyethyl)‐3‐benzoylthiourea HL, ( 1 ), yields with nickel(II) and copper(II) ions neutral complexes [NiL2], ( 2 ), and [CuL2], ( 3 ). By X‐ray structure analysis and IR spectroscopy different intramolecular hydrogen bonds (OH…O) and (OH…N) could be identified in both equally coordinated ligands of the [NiL2] molecule. For comparison X‐ray and IR data were also estimated for 1 and 3 . 相似文献
65.
Klaus Burger Gabor Radics Lothar Hennig Christoph B?ttcher Jan Spengler Fernando Albericio 《Monatshefte für Chemie / Chemical Monthly》2005,5(3):763-776
Starting from L-malic, L-citramalic, and rac. thiomalic acids routes to L-homoisoserine, 2-methyl-L-homoisoserine and rac. homoisocysteine have been developed. The new orthogonally protected and carboxy-activated building blocks are GABA as well as -hydroxy and -mercapto acid derivatives, suitable for the construction of peptide and depsipeptide surrogates. 相似文献
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