共查询到20条相似文献,搜索用时 0 毫秒
1.
Wiegand T Eckert H Grimme S Hoppe D Ruck M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(31):8739-8748
The (31)P MAS NMR spectrum of Hittorf's phosphorus has been measured and assigned to the 21 crystallographically distinct phosphorus atoms based on two-dimensional dipolar correlation spectroscopies. Application of such 2D techniques to phosphorus-based networks is particularly challenging owing to the wide chemical shift dispersions, rapid irreversible decay of transverse magnetization, and extremely slow spin-lattice relaxation in these systems. Nevertheless, a complete assignment was possible by using the combination of correlated spectroscopy (COSY) and radiofrequency-driven dipolar recoupling (RFDR). The assignment is supported further by DFT-based ab initio chemical shift calculations using a cluster-model approach, which gives good agreement between experimental and calculated chemical shift values. The (31)P chemical shifts appear to be strongly correlated with the average P-P bond lengths within the P(P(1/3))(3) coordination environments, whereas no clear dependence on average P-P-P bond angles can be detected. Calculations of localized Kohn-Sham orbitals reveal that this bond-length dependence is reflected in energy variations in the corresponding localized p-p-σ orbitals influencing the paramagnetic deshielding contribution in Ramsey's equation. In contrast, the contributions of the lone pairs to shielding differences are small and/or do not vary in a systematic manner for the different crystallographically distinct phosphorus sites. The combined spectroscopic and quantum chemical approach applied here and the increased theoretical understanding of (31)P chemical shifts will facilitate the structural elucidation of other phosphorus-based clusters and networks. 相似文献
2.
Svetlana A. Kondrashova Fedor M. Polyancev Shamil K. Latypov 《Molecules (Basel, Switzerland)》2022,27(9)
In this study, comparative analysis of calculated (GIAO method, DFT level) and experimental 31P NMR shifts for a wide range of model palladium complexes showed that, on the whole, the theory reproduces the experimental data well. The exceptions are the complexes with the P=O phosphorus, for which there is a systematic underestimation of shielding, the value of which depends on the flexibility of the basis sets, especially at the geometry optimization stage. The use of triple-ζ quality basis sets and additional polarization functions at this stage reduces the underestimation of shielding for such phosphorus atoms. To summarize, in practice, for the rapid assessment of 31P NMR shifts, with the exception of the P=O type, a simple PBE0/{6-311G(2d,2p); Pd(SDD)}//PBE0/{6-31+G(d); Pd(SDD)} approximation is quite acceptable (RMSE = 8.9 ppm). Optimal, from the point of view of “price–quality” ratio, is the PBE0/{6-311G(2d,2p); Pd(SDD)}//PBE0/{6-311+G(2d); Pd(SDD)} (RMSE = 8.0 ppm) and the PBE0/{def2-TZVP; Pd(SDD)}//PBE0/{6-311+G(2d); Pd(SDD)} (RMSE = 6.9 ppm) approaches. In all cases, a linear scaling procedure is necessary to minimize systematic errors. 相似文献
3.
《Magnetic resonance in chemistry : MRC》2002,40(6):406-411
Numerous alkenylsilanes with silyl and boryl groups in cis ‐positions at the C?C bond were studied for the first time by 29Si NMR with regard to isotope‐induced chemical shifts Δ10/11B(29Si). Such effects are transmitted across an Si—X—B bridge (X = H, OR, SR, Cl) most efficiently if the interactions in this bridge are weak. In the absence of an Si—X—B bridge, 3Δ10/11B(29Si) effects were not observed. In such cases, where, depending on the substituents, both weak and strong B—X bonding are possible, the 2Δ10/11B(29Si) effects were readily observed only for weak B—X interactions (except for X = Cl), whereas for strong B—X bonding the effects were small or not detectable. Thus, the 2Δ10/11B(29Si) values provide another tool for probing weak interactions which are not clearly reflected by other NMR data. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
4.
Resolving the different silicon clusters in Li12Si7 by 29Si and (6,7)Li solid-state NMR spectroscopy
Köster TK Salager E Morris AJ Key B Seznec V Morcrette M Pickard CJ Grey CP 《Angewandte Chemie (International ed. in English)》2011,50(52):12591-12594
Structural signatures: The analysis of Si-Si and Si-Li connectivities by solid-state NMR spectroscopy allows the different types of silicon clusters to be discriminated in the model lithium silicide compound Li(12)Si(7) (see picture, Si clusters red and blue, Li ions gray). The results provide new NMR spectroscopic strategies with which to differentiate and study the structures formed in silicon-based electrode materials. 相似文献
5.
Prof. Jochen Autschbach Kiplangat Sutter Dr. Lionel A. Truflandier Dr. Erica Brendler Dr. Jörg Wagler 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(40):12803-12813
New members of a novel class of metallasilatrane complexes [X‐Si‐(μ‐mt)4‐M‐Y], with M=Ni, Pd, Pt, X=F, Cl, Y=Cl, Br, I, and mt=2‐mercapto‐1‐methylimidazolide, have been synthesized and characterized structurally by X‐ray diffraction and by 29Si solid‐state NMR. Spin‐orbit (SO) effects on the 29Si chemical shifts induced by the metal, by the sulfur atoms in the ligand, and by heavy halide ligands Y=Cl, Br, I were investigated with the help of relativistic density functional calculations. Operators used in the calculations were constructed such that SO coupling can selectively be switched off for certain atoms. The unexpectedly large SO effects on the 29Si shielding in the Ni complex with X=Y=Cl reported recently originate directly from the Ni atom, not from other moderately heavy atoms in the complex. With respect to Pd, SO effects are amplified for Ni owing to its smaller ligand‐field splitting, despite the smaller nuclear charge. In the X=Cl, Y=Cl, Br, I series of complexes the Y ligand strongly modulates the 29Si shift by amplifying or suppressing the metal SO effects. The pronounced delocalization of the partially covalent M←Y bond plays an important role in modulating the 29Si shielding. We also demonstrate an influence from the X ligand on the 29Si SO shielding contributions originating at Y. The NMR spectra for [X‐Si‐(μ‐mt)4‐M‐Y] must be interpreted mainly based on electronic and relativistic effects, rather than structural differences between the complexes. The results highlight the sometimes unintuitive role of SO coupling in NMR spectra of complexes containing heavy atoms. 相似文献
6.
In this paper, we presented new J-oriented basis sets, pecJ-n (n = 1, 2), for phosphorus and silicon, purposed for the high-quality correlated calculations of the NMR spin–spin coupling constants involving these nuclei. The pecJ-n basis sets were generated using the modified version of the property-energy consistent (PEC) method, which was introduced in our earlier paper. The modifications applied to the original PEC procedure increased the overall accuracy and robustness of the generated basis sets in relation to the diversity of electronic systems. Our new basis sets were successfully tested on a great number of spin–spin coupling constants, involving phosphorus or/and silicon, calculated within the SOPPA(CCSD) method. In general, it was found that our new pecJ-1 and pecJ-2 basis sets are very efficient, providing the overall accuracy that can be characterized by MAEs of about 3.80 and 1.98 Hz, respectively, against the benchmark data obtained with a large dyall.aae4z+ basis set of quadruple-ζ quality. 相似文献
7.
The reaction of amino acids and phosphorus trichloride in THF was studied by 31P NMR tracing and ESI‐MS/MS. A series of hydridophoranes and cyclic dipeptides were obtained. The reaction presented interesting diversity and the reaction mechanism was proposed. The mechanism suggests that phosphorus plays an important role in the synthesis of amino acid hydridophorane and cyclic dipeptides. The results also show that 31P NMR and ESI‐MS/MS are useful tools for the investigation of reaction mechanism. 相似文献
8.
Ahmed Dkhissi 《International journal of quantum chemistry》2008,108(5):996-1003
Several developed exchange‐correlation functionals in density functional theory have been systematically applied to describe the geometries and electronic properties of small silicon (Sin+1, n < 5) and doped silicon (CuSin) clusters. The performance of the various approaches is done with their critical comparison with B3LYP and available high level wave function methods. Our calculations indicate that all functional give reasonable results. Further, OLYP/6‐311+G* approach generally agrees with B3LYP results. The good performance of OLYP is of significant interest knowing that the hybrid functionals are computationally more demanding than nonhybrid schemes. So, we recommend OLYP/6‐311+G* approach for studying the doped silicon clusters and understanding the electronic properties of silicon by the presence of doped metal impurities. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 相似文献
9.
10.
Sam Smet Pieter Verlooy Fadila Saïdi Francis Taulelle Johan A. Martens Charlotte Martineau-Corcos 《Magnetic resonance in chemistry : MRC》2019,57(5):224-229
The 1H–29Si multiple-contact cross polarization (MC-CP) MAS NMR experiment is evaluated for the class of silicate-siloxane copolymers called POSiSils, that is, polyoligosiloxysilicones. It proves a reasonably good solution to tackle the challenge of recording quantitative 29Si NMR data in experimental time much reduced compared with single pulse acquisition. In a second time, we report 29Si–29Si MC-CP double-quantum single-quantum (MC-CP-DQ-SQ) NMR experiment, which provides information about the through-space proximities between all silicon species despite the high degree of heterogeneity of this material. This work furthers the NMR tools for NMR crystallography for inorganic polymers, as it covers flexible polymers with different dimensionalities and long or heterogeneous relaxation characteristics at low 29Si natural abundance. 相似文献
11.
Dr. Erica Brendler Thomas Heine Wilhelm Seichter Jörg Wagler Raiker Witter 《无机化学与普通化学杂志》2012,638(6):935-944
29Si NMR shielding tensors of a series of triphenylsilanes Ph3SiR with R = Ph, Me, F, Cl, Br, OH, OMe, SH, NH2, SiPh3, C≡CPh were determined from 29Si CP/MAS spectra recorded at low spinning rates. In addition the principal components of the shielding tensor were calculated employing the DFT‐IGLO method. For most silanes experimental and calculated values are in good accordance. Larger differences were observed for systems with hydrogen bridge forming substituents and the halides bromide and chloride. In some of the spectra the shielding information interfered with residual dipolar couplings. The different contributions of the various substituents to the principal components of the shielding tensor and the orientation of the tensor within the molecules are discussed and compared for the compounds under investigation. 相似文献
12.
Corrigendum: Intact P4 Tetrahedra as Terminal and Bridging Ligands in Neutral Complexes of Manganese
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
M. Sc. Sebastian Heinl Dr. Eugenia V. Peresypkina Prof. Dr. Alexey Y. Timoshkin Prof. Dr. Piero Mastrorilli Dr. Vito Gallo Prof. Dr. Manfred Scheer 《Angewandte Chemie (International ed. in English)》2014,53(25):6296-6296
13.
14.
15.
16.
Lithium Ion Mobility in Lithium Phosphidosilicates: Crystal Structure, 7Li, 29Si,and 31P MAS NMR Spectroscopy,and Impedance Spectroscopy of Li8SiP4 and Li2SiP2
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Lorenzo Toffoletti Holger Kirchhain Johannes Landesfeind Dr. Wilhelm Klein Prof. Dr. Leo van Wüllen Prof. Dr. Hubert A. Gasteiger Prof. Dr. Thomas F. Fässler 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(49):17635-17645
The need to improve electrodes and Li‐ion conducting materials for rechargeable all‐solid‐state batteries has drawn enhanced attention to the investigation of lithium‐rich compounds. The study of the ternary system Li‐Si‐P revealed a series of new compounds, two of which, Li8SiP4 and Li2SiP2, are presented. Both phases represent members of a new family of Li ion conductors that display Li ion conductivity in the range from 1.15(7)×10?6 Scm?1 at 0 °C to 1.2(2)×10?4 Scm?1 at 75 °C (Li8SiP4) and from 6.1(7)×10?8 Scm?1 at 0 °C to 6(1)×10?6 Scm?1 at 75 °C (Li2SiP2), as determined by impedance measurements. Temperature‐dependent solid‐state 7Li NMR spectroscopy revealed low activation energies of about 36 kJ mol?1 for Li8SiP4 and about 47 kJ mol?1 for Li2SiP2. Both compounds were structurally characterized by X‐ray diffraction analysis (single crystal and powder methods) and by 7Li, 29Si, and 31P MAS NMR spectroscopy. Both phases consist of tetrahedral SiP4 anions and Li counterions. Li8SiP4 contains isolated SiP4 units surrounded by Li atoms, while Li2SiP2 comprises a three‐dimensional network based on corner‐sharing SiP4 tetrahedra, with the Li ions located in cavities and channels. 相似文献
17.
Lantto P Jackowski K Makulski W Olejniczak M Jaszuński M 《The journal of physical chemistry. A》2011,115(38):10617-10623
Ab initio values of the absolute shielding constants of phosphorus and hydrogen in PH(3) were determined, and their accuracy is discussed. In particular, we analyzed the relativistic corrections to nuclear magnetic resonance (NMR) shielding constants, comparing the constants computed using the four-component Dirac-Hartree-Fock approach, the four-component density functional theory (DFT), and the Breit-Pauli perturbation theory (BPPT) with nonrelativistic Hartree-Fock or DFT reference functions. For the equilibrium geometry, we obtained σ(P) = 624.309 ppm and σ(H) = 29.761 ppm. Resonance frequencies of both nuclei were measured in gas-phase NMR experiments, and the results were extrapolated to zero density to provide the frequency ratio for an isolated PH(3) molecule. This ratio, together with the computed shielding constants, was used to determine a new value of the nuclear magnetic dipole moment of (31)P: μ(P) = 1.1309246(50) μ(N). 相似文献
18.
19.
20.
《Magnetic resonance in chemistry : MRC》2002,40(9):563-565
The 33S NMR signal of gaseous carbonyl sulfide (COS) was monitored as a function of density for the first time. An extrapolation to the zero‐density limit permitted the measurement of nuclear magnetic shielding of an isolated COS molecule. An improved 33S shielding scale was established taking the value of 817(12) ppm as the absolute shielding of COS. The new 33S shielding scale is certainly more accurate than any previous estimation and contains some reference standards, e.g. an isolated SF6 molecule, a saturated solution of (NH4)2SO4 in D2O, 2 M aqueous Cs2SO4 solution or liquid SF6, CS2 and SO2. The latter results can be applied for the easy estimation of sulfur shielding available from all the measurements of 33S NMR chemical shifts. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献