Single crystals chemical shift tensor

For line shift measurements with the eight-pulse cycle between 180°K and room temperature, the reference was acetyl chloride. Its frequency was measured relative to a spherical tetramethylsilane (TMS) sample at room temperature, and all results are reported relative to this TMS on the r scale, (r = a + 10 ppm, where a is the signed chemical shift used in solid state NMR.) At lower temperatures, the reference was a single crystal of Ca(OH)2, oriented in the magnetic field such that the major axis of its proton chemical shift tensor was parallel to the external field (19). Thus, it is assumed that the proton chemical snift of the Ca(OH)2 remained unchanged as the temperature was varied. 

Figure 4. The eight-pulse line shape and the peak locations of the Th4Hi5 (LP) powder sample as a function of temperature using a Ca(OH)2 single crystal as reference. The reference is oriented such that the major principal axis of the proton chemical shift tensor is parallel to the external magnetic field. A shift to the left signifies an increase in the value of

The origin of equations 1 and 2 was explained in more detail in (6). The calibration of the bond polarization parameters for, 3C chemical shift tensors for C(sp3/sp2)-C, C(sp3/sp2)-H, C(sp3/sp2)-0, and C(sp3)-N o-bonds as well as C(sp2)-C and C(sp2)-0 71-bonds was described in detail in (5). Structural data and tensorial single crystal, 3C NMR data of 20 crystalline substances including sugars, polycyclic aromatic compounds, and amino acids were used in this calculation. 

The resulting principal values of the 13C chemical shift tensors of the C60 carbons are 8n = 228 ppm, 822 = 178 ppm, and 833 = -3 ppm. Tycko et al reportet the experimental values 8n = 213 ppm, S22 = 182 ppm, and 833 = 33 ppm obtained from low temperature measurements of a powder pattern spectrum (18). However, the spectra have a low signal to noise ratio and a wide slope so that a larger error for the experimental value can be assumed. The chemical shift anisotropy of 217 ppm corresponds quite well with the spectral range of about 200 ppm reported by Kerkoud et al for low temperature single crystal measurements (19). 

M. Gee, R. E. Wasylishen, K. Eichele and J. F. Britten, Phosphorus chemical shift tensors for tetramethyldiphosphine a 31P single-crystal NMR, dipolar-chemical shift NMR and ab initio molecular orbital study.. Phys. Chem. A, 2000,104,4598-4605. 

Figure 15.4. The l3Cspectraofa single crystal of calcium formate in two orientations with respect to B(). In the top spectrum the crystal is oriented such that all eight distinguishable chemical shift tensors give different chemical shift values. In the lower spectrum the crystal is oriented such that Bo lies in a symmetry plane of the crystal structure, causing pairwise degeneracies of the chemical shift values.

Figure 15.6. Graphical representation of the l3C chemical shift tensor in calcium formate views from above and from within the OCO plane. (Reprinted with permission from Ackerman JL, Tegen-feldt J, Waugh JS. 13C chemical shielding anisotropies in single crystal calcium formate. J Amer Chem Soc. 1974 96 6843-6845. Copyright 1974 American Chemical Society.)...

Sastry DL, Thkegoshi K, McDowell CH (1987) Determination of the 13C chemical shift tensors in a single crystal of methyl a-D-glucopyranoside. Carbohydr Res 165 161-171... 

A single crystal XH NMR study of potassium hydrogen maleate has established the chemical shift tensors of all magnetically inequivalent XH nuclei in the unit cell [131]. 

A Se and NMR study of single-crystal K2Se04 has been used to elucidate the nature of the structural transition occurring in this compound at low temperatures (Topic et al. 1988). Measurement of the angular dependence of the Se line shifts allowed the chemical-shift tensor to be determined in the paraelectric phase of K2Se04. 

The principal values, 6n, 622, 633, of the chemical shift tensor were obtained for each form by CP/MAS NMR experiments. The orientation of the principal axes with respect to the molecular frame was investigated by P CP/single-crystal NMR for the complex with propan-2-ol. The principal axis 1 of both chemically equivalent phosphorus atoms is nearly parallel to the P-S bond and the principal axis 3 is very close to the P=S bond. The comparison of experimental P 6 parameters with theoretical data calculated by the DFT GIAO approach provided complementary information about the most sensitive NMR parameters, which best characterize the nature of the C-H -S contacts. 

A single-crystal 133Cs NMR study of Cs+(15-crown-5)2I yielded chemical shift tensor components and parameters for the quadrupolar interactions.28 A 133Cs NMR study has been carried out on the S = 1/2, quasi-two-dimensional ferromagnet Cs2CuBr4.29... 

Single crystal nmr spectra have been obtained for the resonance in K2Pt(CN)4Bro.3(H20)3, and the chemical shift tensor determined (565). The principal values (relative to the carboxyl carbon in acetic acid) have been reported as uu = 261 lOppm (parallel to the CN bond), <722 = — 48 10 ppm (perpendicular to the CN bond and Pt-Pt chain) and <733 = —10 5 ppm (parallel to the Pt-Pt chain). The primary effect on the chemical shift tensor of the cyanide bonding to the platinum and of the solid state structure is the nonzero asymmetry produced around the CN bond (565). 

It is apparent from Eq. (20.17) that in a rigid, solid sample the chemical shift will depend on its orientation with respect to the applied field. A sample having all like carbon nuclei with the same orientations—as in a single crystal—will exhibit chemical shifts that vary as the crystal is rotated in the applied magnetic field. In a powdered sample, all possible crystalline orientations are present, so the NMR spectrum will COTisist of the chemical shift tensor powder pattern. 

M.H. Sherwood, J.C. FaceDi, D.W. Alderman, D.M. Grant, Carbon-13 chemical shift tensors in polycyclic aromatic compounds. 2. Single-crystal study of naphthalene, J. Am. Chem. Soc. 113 (1991) 750. 

In the case of a single crystal, each carbon species yields an individual chemical shift tensor which depends on the molecular conformation. 

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