A.A. Shmyreva, M. Safdari, I. Furó, S.V. Dvinskikh
“NMR longitudinal relaxation enhancement in metal halides by heteronuclear polarization exchange during magic-angle spinning”
J. Chem. Phys., 2016, 144, 224201
Orders of magnitude decrease of 207Pb and 199Hg NMR longitudinal relaxation times T 1 upon magic-angle-spinning (MAS) are observed and systematically investigated in solid lead and mercury halides MeX2 (Me = Pb, Hg and X = Cl, Br, I). In lead( ii) halides, the most dramatic decrease of T 1 relative to that in a static sample is in PbI2, while it is smaller but still significant in PbBr2, and not detectable in PbCl2. The effect is magnetic-field dependent but independent of the spinning speed in the range 200–15 000 Hz. The observed relaxation enhancement is explained by laboratory-frame heteronuclear polarization exchange due to crossing between energy levels of spin-1/2 metal nuclei and adjacent quadrupolar-spin halogen nuclei. The enhancement effect is also present in lead-containing organometal halide perovskites. Our results demonstrate that in affected samples, it is the relaxation data recorded under non-spinning conditions that characterize the local properties at the metal sites. A practical advantage of fast relaxation at slow MAS is that spectral shapes with orientational chemical shift anisotropy information well retained can be acquired within a shorter experimental time.
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| Tags: Shmyreva
Excursion was carried out for masters students from Alma-Ata in CMR.
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M.A. Sandzhieva, A.N. Kazakova, I.A. Boyarskaya, A.Yu. Ivanov, V.G. Nenajdenko, A.V. Vasilyev
“Friedel–Crafts Alkylation of Arenes with 2-Halogeno-2-CF3-styrenes under Superacidic Conditions. Access to Trifluoromethylated Ethanes and Ethenes”
J. Org. Chem., 2016, 81, 5032-5045
The formation of the corresponding benzyl cations [ArHC+–CH(X)CF3] takes place under protonation of E-/Z-2-halogeno-2-CF3 styrenes [ArCH═C(X)CF3, X = F, Cl, Br] in superacids. The structures of these new electrophiles were studied by means of NMR and theoretical DFT calculations. According to these data, in the case of bromo derivatives, the formed cations, most probably, exist as cyclic bromonium ions; however, in the cases of chloro and fluoro derivatives, open forms are more preferable. Subsequent reaction of these benzyl cations with arenes proceeds as Friedel–Crafts alkylation to afford 1,1-diaryl-2-halo-3,3,3-trifluoropropanes [Ar(Ar′)CH–CH(X)CF3] in high yields (up to 96%) as a mixture of two diastereomers. The prepared halogenopropanes were easily converted into the corresponding mixtures of E-/Z-trifluoromethylated diarylethenes [Ar(Ar′)C═CCF3] (in yields up to 96%) by dehydrohalogenation with base (KOH or t-BuOK). The mechanism of elimination (E2 and Ecb) depends on the nature of the leaving group and reaction conditions.
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| Tags: Ivanov
A.A. Osipov, V.E. Eremyashev, A.S. Mazur, P.M. Tolstoi, L.M. Osipova
“Coordination State of Aluminum and Boron in Barium Aluminoborate Glass”
Glass Physics and Chemistry, 2016, 42(3), 230–237
This paper considers the coordination state of boron and aluminum ions in barium aluminoborate glass with a constant ratio of BaO : B2O3 = 0.5 and a variable ratio of Al2O3 : BaO = 0–3. The dependence of the concentrations of boron and aluminum atoms with a variable coordination number on the Al2O3 content was estimated by IR, 11B and 27Al NMR spectroscopy. The nonlinear nature of the obtained dependences was attributed to variations in the aluminum oxide properties. At a content of less than 30 mol % Al2O3 serves primarily as a network former, while an increase in the Al2O3 concentration results in its higher modifying role in the studied glass.
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| Tags: Mazur
Stanislav Selivanov has presented report about specific use of NMR spectroscopy in the conformational analysis of small molecules.
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On June 2nd-3rd CMR has participated in Startup Village 2016 in Skolkovo (Moscow). The capabilities of SPbU Research Park of performing investigations by requests of external organisations have been presented. Video clip about Startup Village 2016 can be found here.
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| Tags: Tolstoy
Michael Vovk has presented a lecture for students of Academic gymnasium. Our guests acquainted with the magnetic resonance research methods and modern equipment represented in CMR.
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Total in May 1400 service applications were carried out.
All together measured:
- 1352 1H spectra
- 283 13C spectra
- 97 DEPT spectra
- 26 COSY spectra
- 6 NOESY spectra
- 58 31P spectra
- 48 19F spectra
168 applications were carried out.
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