[en] The rotational correlation times for the nitrate and carbonate anions in dilute aqueous solution are determined by NMR spectroscopy, in the temperature range -4 to 80 ⁰C. Nitrogen-14 NMR spin-lattice relaxation times (T₁) yield rotational correlation times, tau/sub 2R/, for the end-over-end rotation of the C₃ axis in the nitrate ion, in fair agreement with Raman spectroscopic data. However, in contrast to the Raman study, the logarithm of tau/sub 2R/ is found to vary nonlinearly with the inverse of temperature. Oxygen-17 T₁ values for the nitrate and carbonate anions are used to probe the in-plane rotations of these ions. The results indicate that this motion is significantly slower than the end-over-end rotations of the C₃ axis. Furthermore, the in-plane rotations are slower for the carbonate than for the nitrate ion. These findings together with ²³Na NMR relaxation data support the claim of Perrot and co-workers that Na⁺ and CO₃^2- associate strongly in aqueous solution. 34 references, 3 figures, 4 tables

[en] ¹³C spin-lattice relaxation times and selected linewidths are reported for CBr₄ (natural abundance) as determined by conventional techniques in the liquid, solid I (fcc, 'plastic crystal') and solid II (monoclinic, 'rigid') phases. The linewidths are less than 50 Hz and the T₁'s are between 0.5 and 1.5s. Comments are made on the complexity of the relaxation of spin 1/2 nuclei by quadrupolar nuclei. (Auth.)

[en] Using ²H NMR, the dynamics of the cation in phenethylammonium bromide were studied in the two solid phases. Line shape and spin-lattice relaxation rate studies of the ammonium headgroups and the adajacent methylene groups indicate the onset of alkyl-chain motion prior to the first order phase transition. In the low-temperature phase the line shape and the spin-lattice relaxation rates of the -ND₃ groups are consistent with C₃ jumps and an activation energy of 54±4 kJ mol^-1. However, in the high-temperature phase the spin-lattice relaxation studies indicate the presence of small-angle diffusion of the -ND₃ groups around the C₃ symmetry axis. In this phase the -CD₂- groups show line shapes typical of large-amplitude two-site jumps occurring at a rate >10⁷ s^-1. In the low-temperture phase, at temperatures below 295 K, the -CD₂- ²H NMR line shapes indicate that the C-D bonds are essentially static. (orig.)

[en] A report is presented on the experimental value of ¹J(¹⁵N,¹³C) for hydrogen cyanide, and a deuterium isotope effect on this coupling constant is pointed out. (author)

[en] The ³¹P powder NMR line shapes of a number of solid mercury(II) phosphonates are analyzed in order to determine the anisotropies in both the ³¹P chemical shift and the ³¹P-¹⁹⁹Hg indirect spin-spin coupling. The magnitudes and orientation of the principal components of the ³¹P chemical shift tensor are determined for diethyl N-phenylphosphoramidate, (EtO)₂P(O)NHPh, by using dipolar-chemical shift NMR spectroscopy. Spectral simulations indicate that the most shielded component of the ³¹P chemical shift tensor lies along the P double-bond O plane. This information is used to interpret the ³¹P NMR line shapes for a series of mercury phosphonate complexes. These spectra indicate the presence of substantial anisotropies in the ³¹P-¹⁹⁹Hg indirect spin-spin (J) coupling, ranging from 1,500 to 2,700 Hz. The large anisotropies in J indicate that mechanisms other than the Fermi contact contribute to the electron-mediated communication between ³¹P and ¹⁹⁹Hg. 47 refs., 4 figs., 2 tabs

[en] The effect of successive deuterium substitution on the nitrogen-14 nuclear shielding constant and ¹J(¹⁴N,H) in the ammonium ion has been measured. Each additional replacement of hydrogen by deuterium resulted in an approximately 0.30 ppm increase in the nitrogen shielding. This is less than half that previously reported for liquid ammonia and approximately twice that reported for methane. These observations can be qualitatively accounted for by the theoretical model of Jameson. A measurable secondary deuterium isotope effect of ¹J(¹⁴N,¹H) was observed: on going from NH⁺₄ to NHD⁺₃ , ¹J(¹⁴N,¹H) decreased by 0.15 +- 0.03 Hz. The primary isotope effect on ¹J(¹⁴N,H) is less than 0.2 Hz

[en] The principal components of the carbon, nitrogen, and selenium chemical shift (CS) tensors for several solid selenocyanate salts have been determined by NMR measurements on stationary or slow magic-angle-spinning powder samples. Within experimental error, all three CS tensors are axially symmetric, consistent with the expected linear geometry of these anions. The spans (ω) of the carbon and selenium CS tensors for the selenocyanate anion (SeCN^-) are approximately 300 and 800 ppm, respectively, much less than the corresponding values for carbon diselenide (CSe₂). This difference is a consequence of the difference in the CS tensor components perpendicular to the C_∞ symmetry axes in these systems. Ab initio calculations show that the orbital symmetries of these compounds are a significant factor in the shielding. For CSe₂, efficient mixing of the sigma and pi orbitals results in a large paramagnetic contribution to the total shielding of the chemical shielding tensor components perpendicular to the molecular axis. Such mixing is less efficient for the SeCN^-, resulting in a smaller paramagnetic contribution and hence in greater shielding in directions perpendicular to the molecular axis. (author)

[en] Mercury-199 spin-lattice relaxation times are reported for several mercury(II) compounds at 5.875 and 9.40 T. From the field dependence of T¹ in Hg(CN)², Hg(CH³)², and Hg(C⁶H⁵)², ₁₉₉Hg chemical shielding anisotropies of 3800, 5820, and 5800 ppm are calculated. The errors in these of estimates of δσ are at least 10%. Some implications of the large δσ(₁₉₉Hg) values in high field nmr studies are discussed

[en] Arsenic and antimony hexafluoride salts have played an important role in the history of both solution and solid-state NMR spectroscopy. Here, solid polycrystalline KAsF₆ and KSbF₆ have been studied via high-resolution variable temperature ¹⁹F, ⁷⁵As, ¹²¹Sb, and ¹²³Sb solid-state NMR spectroscopy at high magnetic field (B₀ = 21.14 T). Both KAsF₆ and KSbF₆ undergo solid-solid phase transitions at approximately 375 and 301 K, respectively. We use variable temperature NMR experiments to explore the effects of crystal structure changes on NMR parameters. C_Q(⁷⁵As) values for KAsF₆ at 293, 323, and 348 K are -2.87 ± 0.05 MHz, -2.58 ± 0.05 MHz, and -2.30 ± 0.05 MHz, respectively, the sign determined via DFT calculations. In the higher temperature cubic phase, C_Q(⁷⁵As) = 0 Hz, consistent with the crystal symmetry at the arsenic nucleus in this phase. In contrast, C_Q values for ¹²¹Sb and ¹²³Sb in the cubic phase of KSbF₆ are nonzero. E.g., at 293 K, C_Q(¹²¹Sb) = 6.42 ± 0.10 MHz, and C_Q(¹²³Sb) = 8.22 ± 0.10 MHz. In the higher temperature tetragonal phase (343 K) of KSbF₆, these values are 3.11 ± 0.20 MHz and 4.06 ± 0.20 MHz, respectively. CASTEP calculations performed on the cubic and tetragonal structures support this trend. Isotropic indirect spin-spin coupling constants are ¹J(⁷⁵As,¹⁹F) = -926 ± 10 Hz (293 K) and -926 ± 3 Hz (348 K), and ¹J(¹²¹Sb,¹⁹F) = -1884 ± 3 Hz (293 K), and -1889 ± 3 Hz (343 K). Arsenic-75 and antimony-121,123 chemical shift values show little variation over the studied temperature ranges. (author)

[en] Variable-temperature solid-state ³¹P, ¹⁵N, and ²H NMR spectroscopy, X-ray diffraction, and differential scanning calorimetry studies of the 1:1 adduct of silver nitrate and triphenylphosphine (AgNO₃·PPh₃) reveal a solid-solid phase transition at 300 K. The principal components of the phosphorus and nitrogen chemical shift tensors for both phases are determined from NMR spectra of MAS and stationary samples. In addition, the indirect spin-spin coupling between phosphorus and the naturally occurring isotopes of silver (¹⁰⁷Ag and ¹⁰⁹Ag) are resolved. Experimental ²H NMR line shapes for silver nitrate perdeuterated triphenylphosphine are those characteristic of rigid phenyl groups at temperatures above and below the phase-transition temperature. Powder and single-crystal X-ray diffraction data for AgNO₃·PPh₃ obtained at 193, 295, and 313 K are reported; data obtained at 193 and 295 K are almost identical, but are significantly different from those obtained at 313 K and from an earlier single-crystal X-ray diffraction investigation performed at 298 K. All X-ray studies found that AgNO₃·PPh₃ crystallizes in the monoclinic form, space group P2₁lc. (author)