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961.
962.
X-ray diffraction measurements on 1M yttrium(III) and erbium(III) nitrate and chloride solutions in dimethyl sulfoxide (DMSO) have shown that Er(III) and Y(III) solutions of equal compositions are isostructural. The intensity difference functions can then be used to derive the detailed structure of the coordination sphere around the metal ions. The DMSO molecules are coordinated over oxygen with average M-O-S bond angles of about 130°. Two different conformations, corresponding to different relative orientations of the M-O and O-S bonds, seem to be prevalent. In the nitrate solutions an average of about 1.5 nitrate ions are coordinated as bidentate ligands to each metal ion. In the chloride solutions about 1.3 chloride ions belong to the inner-coordination sphere.On leave from the Department of Inorganic Chemistry, Royal Institute of Technology, S-10044 Stockholm, Sweden 相似文献
963.
Georg Schreckenbach 《Theoretical chemistry accounts》2002,108(4):246-253
In this article the formal equivalence between the “gauge including atomic orbitals” (GIAO) and the simpler common gauge
(cg) formulations of the nuclear magnetic resonance (NMR) shielding tensor is proven. To be able to give this proof, one has
to assume exactly solved zeroth order quantum mechanical equations and complete basis sets. The proof of the equivalence has
been known in the literature for some time (e.g. S.T. Epstein `The variation method in quantum chemistry', Academic Press,
1974). However, our approach has the advantage that, by comparing the GIAO and cg methods, it provides insight into the para-
and diamagnetic contributions of the shielding. Thus, it yields justification for qualitative analysis schemes that have been
used to explain trends in chemical shifts. Our formal proof is based on density functional theory. However, it is argued that
very similar arguments should apply to other levels of theory as well.
Received: 25 June 2002 / Accepted: 18 July 2002 / Published online: 15 October 2002
Acknowledgments. The author would like to acknowledge Tom Ziegler, Calgary, for numerous discussions on the subject. The reviewer is acknowledged
for the insightful and detailed comments.
Correspondence to: G. Schreckenbach e-mail: schrecke@alcor.concordia.ca 相似文献
964.
[reaction: see text] Dynamic gas-phase thermoisomerization (DGPTI) of (-)-2-phenylisoborneols effects stereo- and regioselective ring opening under formation of (+)-trans-alpha-campholanic acid derivatives. Similarly, (-)-alpha-2-phenylfenchol underwent under DGPTI conditions ring opening to (-)-fencholic acid derivatives. In both cases, DGPTI led to cleavage of the weakest bond in the isomeric bicyclic structures. A reaction mechanism involving a diradical intermediate is supported by a deuterium labeling study. 相似文献
965.
A method was developed for the direct determination of 14 naturally occuring rare earth elements (REE, La–Lu) by means of inductively coupled plasma mass spectrometry in seepage waters caused by acid mine drainage. The analytical procedure includes the additional determination of oxide and hydroxide formation by Ba and REE. The determined polyatomic ion formation can be used to correct spectral interferences of oxides and hydroxides of Ba and the light REE on middle and heavy REE. The total REE content in the acidic seepage waters investigated is up to 220µgL–1. The concentration of the REE normalized to Post Archean Australian Shale (PAAS) is shown, and fractionation of the REE is discussed. The PAAS-normalized REE-patterns feature an enrichment of middle and heavy REE as opposed to the light ones. For one seepage water sampled over a period of about half a year, the REE patterns show very high reproducibility. The accuracy of the method was demonstrated by the analysis of two water samples containing certified concentrations of REE. 相似文献
966.
Jurriaan M Zwier Albert M Brouwer Tamás Keszthelyi Gurusamy Balakrishnan Jesper F Offersgaard Robert Wilbrandt Frédérique Barbosa Urs Buser Jér?me Amaudrut Georg Gescheidt Stephen F Nelsen Charles D Little 《Journal of the American Chemical Society》2002,124(1):159-167
The radical cation of 1,3,6,8-tetraazatricyclo [4.4.1.1(3,8)]dodecane (TTD) has been studied using magnetic resonance and optical spectroscopic methods and computational techniques. With the help of deuterated isotopomers, assignments of EPR and resonance Raman spectra could be unequivocally established. The results demonstrate that the radical cation has D(2d) symmetry, and instantaneous electron delocalization over the four equivalent nitrogen atoms occurs. This extensive delocalization in a completely saturated system is a unique feature of the TTD radical cation. The spectroscopy of TTD, in contrast to that of simpler diamines such as 1,4-diaza[2.2.2]bicyclooctane, simultaneously reveals the consequences of orbital interactions through space and through bonds. The relationship between nitrogen pyramidalization and hyperfine coupling constants in nitrogen-centered radical cations with a number of different bonding arrangements is reviewed. 相似文献
967.
968.
Albrecht Brandenburg Rainer Edelhäuser Tobias Werner Huarui He Otto S. Wolfbeis 《Mikrochimica acta》1995,121(1-4):95-105
Detection of ammonia in the gas phase by means of integrated optical components, coated with sensitive films which reversibly change their spectral absorption with ammonia concentration, is demonstrated. The evanescent wave of the guided light continuously probes the absorbance of the sensor membrane at 633 nm. The output intensity is compared with that of a reference channel not influenced by the sensitive film. With Bromocresol Green and Bromophenol Blue in silicone as indicators, ammonia levels of less than 1 ppm are detectable, the dynamic range being from 1 to 200 ppm. The response depends on the relative humidity, and acidic gases including sulphur dioxide, carbon dioxide, and nitric oxides are found to reduce the relative signal change caused by ammonia, whilst in the absence of ammonia they remain inert. Aging of the film is observed within a few months after film preparation. 相似文献
969.
π,π-Excitation of bis(2-methyl-1-propenyl)ether leads to products derived from a vinyl-vinyloxy radical pair; photochemical decarbonylation (n,π) of the title ketone provides an entry into the diradical manifold of the oxydi-π-methane rearrangement. 相似文献
970.
Mesogens containing rod-shaped moieties as well as one disk-shaped group exhibit nematic phase behavior and are entirely miscible with rod- and disk-shaped mesogens in the nematic phase. In the phase diagram, an extra nematic phase appears at nearly equimolar disk-rod ratios, where the nematic biaxial phase has been predicted. 相似文献