The practicality of obtaining liquid‐ and solid‐state 207Pb nuclear magnetic resonance (NMR) spectra with a low permanent‐field magnet is investigated. Obtaining 207Pb NMR spectra of salts in ...solution is shown to be viable for samples as dilute as 0.05 M. The concentration dependence of the 207Pb chemical shifts for lead nitrate was investigated; the results are comparable with those obtained with high‐field instruments. Likewise, the isotope effect of substituting D2O for H2O as the solvent was investigated and found to be comparable with those reported previously. Obtaining solid‐state 207Pb NMR spectra is challenging, but we demonstrate the ability to obtain such spectra for three unique solid samples. An axially symmetric 207Pb powder pattern for lead nitrate and the powder pattern expected for lead chloride reveal linewidths dominated by shielding anisotropy, while 207Pb‐35/37Cl J‐coupling dominates in the methylammonium lead chloride perovskite material. Finally, recent innovations and the future potential of the instruments are considered.
Lead‐207 NMR spectroscopy on the bench!
Well polarized: Two new polarizing agents PyPol and AMUPol soluble in glycerol/water mixtures are used for dynamic nuclear polarization (DNP) NMR spectroscopy. The enhancement factors (ε) are about ...3.5 to 4 times larger than for the established agent TOTAPOL at 263 and 395 GHz. For AMUPol, the temperature dependence of ε allows DNP experiments to be performed at temperatures significantly higher than for typical high‐field DNP NMR experiments.
The reasons for capacity fading of LiCoPO
4 cathodes in 1
M LiPF
6 EC/DMC 1:1 electrolyte solutions were investigated using
19F,
31P NMR and XPS spectroscopy. The origin of the poor performance of ...LiCoPO
4 cathodes in LiPF
6 containing electrolyte solutions is a nucleophilic attack of F
− anions in solution on the P atoms, resulting in the breaking of the P―O bonds of the phosphate anions and the formation of soluble LiPO
2F
2 moieties.
► Reasons for capacity fading of LiCoPO
4 cathodes in LiPF
6 containing electrolytes. ► Nucleophilic attack of F
− anions on the P atoms of LiCoPO
4. ► Breaking of the P―O bonds of the phosphate anions with the formation of LiPO
2F
2.
The synthesis and reactivity of the heavier group 13 phosphaketene complexes (2,6-Mes
2
C
6
H
3
)
2
EPCO (
1
, E = Ga;
2
, E = In) were reported. The reaction of
1
and
2
with ...1,2,3,4-tetramethylimidazolin-2-ylidene, IMe
4
, gave rise to the formation of (2,6-Mes
2
C
6
H
3
)
2
EP(O)C(IMe
4
) (
3
, E = Ga;
4
E = In; Mes = mesityl). Subsequent addition of elemental tellurium proceeded
via
insertion into the E-P bond and provided (2,6-Mes
2
C
6
H
3
)
2
ETeP(O)C(IMe
4
) (
5
, E = Ga;
6
, E = In) comprising five-membered ETePCO-heterocycles. Compounds
1-6
were fully characterized by X-ray crystallography and heteronuclear NMR spectroscopy. The electronic structures of
1-6
were studied by DFT calculations and analyses of a complementary set of real-space bonding indicators (AIM, ELI-D, NCI) derived from the electron and pair densities, with focus on the bond characteristics of the PCO fragment.
Kinetically stabilized group 13 phosphaketene complexes (2,6-Mes
2
C
6
H
3
)
2
EPCO were used to prepare (2,6-Mes
2
C
6
H
3
)
2
ETeP(O)C(IMe
4
) comprising five-membered ETePCO-heterocycles (E = Ga, In; IMe
4
= 1,2,3,4-tetramethylimidazol-2-ylidene).
The yttrium gallabenzene complex (1‐Me‐3,5‐tBu2−C5H3Ga)(μ‐Me)Y(2,4‐dtbp) is accessible from Y(GaMe4)3 and K(2,4‐dtbp) via a tandem salt metathesis/methane elimination ...(2,4‐dtbp=2,4‐di‐tert‐butyl‐pentadienyl). The pentadienyl ligand in (1‐Me‐3,5‐tBu2−C5H3E)(μ‐Me)Y(2,4‐dtbp) (E=Al, Ga) is easily displaced by salt metathesis with KC5Me5 and KTpMe,Me (TpMe,Me=tris(pyrazolyl‐Me2‐3,5)borato) affording (1‐Me‐3,5‐tBu2−C5H3E)(μ‐Me)Y(TpMe,Me) and (1‐Me‐3,5‐tBu2−C5H3E)(μ‐Me)Y(C5Me5). The yttrium center in (1‐Me‐3,5‐tBu2−C5H3E)(μ‐Me)Y(2,4‐dtbp) readily forms adducts with neutral Lewis bases like 4‐DMAP (4‐dimethylaminopyridine), PMe3, DMPE (1,2‐bis(dimethylphosphino)ethane), and DME (1,2‐dimethoxyethane). In stark contrast, addition of TMEDA (N,N,N’,N’‐tetramethylethylenediamine) results in methyl/pentadienyl exchange between aluminum and yttrium resulting in (1‐(2,4‐dtbp)‐1‐Me‐3,5‐tBu2−C5H3Al)Y(Me)(tmeda). The bonding features of the newly synthesized complexes are analyzed by single‐crystal X‐ray diffraction (SCXRD) and heteronuclear (89Y, 31P) NMR spectroscopy.
The gallabenzene‐type yttrium complex (1‐Me‐3,5‐tBu2−C5H3Ga)(μ‐Me)Y(2,4‐dtbp) (A) is readily formed from one‐pot‐reactions using mixtures YMe3n/GaMe3/K(2,4‐dtbp) (2,4‐dtbp=2,4‐di‐tert‐butyl‐pentadienyl), while the remaining pentadienyl ligand gets easily displaced by pentamethylcyclopentadienyl affording B, showcasing the strong interaction of the heterobenzene ligand with the rare‐earth‐metal center. Distinct ligand bonding is revealed by 89Y NMR chemical shifts.
NHCs go nano: Ruthenium nanoparticles were formed from (cyclooctadiene)(cyclooctatriene)ruthenium(0) and stabilized by N‐heterocyclic carbenes (NHCs). Solid‐state NMR spectroscopy revealed both the ...coordination of the NHC ligands on the surface of the particles and their surface reactivity.
NMR Signatures of the Active Sites in Sn-β Zeolite Wolf, Patrick; Valla, Maxence; Rossini, Aaron J. ...
Angewandte Chemie (International ed.),
September 15, 2014, Letnik:
53, Številka:
38
Journal Article
Recenzirano
Odprti dostop
Dynamic nuclear polarization surface enhanced NMR (DNP‐SENS), Mössbauer spectroscopy, and computational chemistry were combined to obtain structural information on the active‐site speciation in Sn‐β ...zeolite. This approach unambiguously shows the presence of framework SnIV‐active sites in an octahedral environment, which probably correspond to so‐called open and closed sites, respectively (namely, tin bound to three or four siloxy groups of the zeolite framework).
Open and closed: The Sn‐β zeolite spectroscopic signatures obtained from 119Sn Mössbauer and DNP‐SENS NMR spectroscopy combined with DFT calculations on a T site model indicate that the active sites correspond to two types of octahedral SnIV sites: one with two water molecules coordinated to the framework Sn atom (closed site) and one where an Sn‐O‐Si bridge was opened by one of the water molecules (open site).
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