Arnd-Rüdiger Grimmer

Influence of Magic Angle Spinning on Sample Temperature

Magic angle spinning at sufficiently high rates dramatically changes the sample temperature. A method is described for calibrating a probe head for the thermal effects encountered during magnic angle spinning experiments. Using Sm2Sn2O7 as a chemical shift thermometer, the overlapping effects of ‘external’ heating or cooling by the bearing gas and ‘internal’ heating by friction on the actual sample temperature were studied. The empirical expression

19F-NMR solid state investigations of monovalent alkali metal fluorides and tetra-alkylammonium fluorides

Abstract The 19 F -NMR chemical shifts of the alkali metal fluorides and of monovalent tetra-alkylammonium fluorides were measured under strictly anhydrous conditions. For reducing the line widths of the broad resonance signals, conventional and ultrafast MAS at 32xa0kHz rotational frequency as well as CRAMPS (combined rotation and multiple-pulse spectroscopy) techniques were used. Averaging the strong homonuclear dipolar interactions of fluorine by MAS, the dependence of line width on the frequency of sample rotation is given for (CH3)4N+ F−. The data obtained are compared with CRAMPS results. The broad distribution in shielding of the fluorine nucleus in the cubic alkali fluorides in the column from LiF to CsF is discussed in terms of cation–anion polarization effects, creating a partial covalent bond. The experimental chemical shift values were correlated with the Allred–Rochow electronegativities and with the polarizabilities of ions in the alkali fluoride crystals. The linear fit of both gave R-values better than 0.96. From the latter, a chemical shift of the “free F-ion” at −293xa0ppm, referred to CCl3F, was extrapolated.

29Si chemical shift tensors of silyl silicate cages

Static and 29Si CP MAS spectra (spinning rates of 2000 and 500 Hz) of six silyl silicate cages are analyzed by deconvolution and simulation. The principal values of the various 29Si chemical shift tensors provide information about the point symmetry of the Si sites. The intensities of the signals correspond sufficiently well with the stoichiometries.

Donorstabilized Monometaphosphates and Phosphonates- Structure, Bonding, and Reactivity

Abstract Previoudy we reported on the preparative use of donorstabilized monometaphosphates, Py.PO2Cl and Py.PS2Cl[1]. 3P MAS investigations as well as X-ray single crystal analysis have been carried out. The isotropic chemical shift of the sulfur compound shows the typical downfield shift (106 ppm) with respect to the oxygen compound The chemical shift anisotropy gives additional information. The relative large spans ω (Py.PO2Cl: 401 ppm, Py.PS2Cl: 461 ppm) [2] reveal strong deviations from tetrahedral symmetry (ω = 0 ppm) in agreement with the structural data. The values of the skew parametem K (0.64 and 0.71 resp.) reflect the trend to axial symmetry (k = ± l). X-ray diffraction and NMR data suggest a structural model corresponding to a concentration of double bond character on the two P-X bonds. This model is consistent with the extremely short P-X bond length (1.449 A and 1.921 A rasp.) as well as the large P-X-P bond angles (126.4°and 123.7° resp.).

Solid-state high-resolution NMR K2PO3F·KF

Abstract In melts of potassium monofluorophosphate and potassium fluoride the new compound K 2 PO 3 F.KF is formed at 850 °C. According to x-ray powder diffraction data this compound and K 2 SO 4 .KF [1] are isostructural. Only one mole fluoride per mole monofluorophosphate reacts. Solid-state high-resolution 19F NMR spectroscopy shows that different types of fluorine atoms exist in the investigated samples. In solid-state NMR spectra natural broadening due to strong direct dipolar F-F interactions masks the chemical shift and indirect spin-spin coupling. To overcome this obstacle we used the multipulse technique (four pulse cycle WHH 4 with γ = 4,1 μs). The shape of the resulting high-resolution 19F NMR spectra of polycrystalline samples is dominated by the F-P coupling tensor as well as the 19 F chemical shift tensor. On the basis of the tensor data it is possible to differentiate the covalent bonded fluorine atoms from the ionic bonded ones and to get new insights into the structure of the title compound.

Salts of sulfane-α,ω-bis(fluorodithiophosphoric acids)

Abstract In aqueous medium P4S10 reacts with sodium fluoride yielding sodium difluoropentathiodiphosphate, Na2[P2S5F2][1]. It was found that in acetonitrile sulfur-rich phosphorus sulfides (the S:P ratio varying from 11:4 to 16:4) react with fluoride under formation of alkali sulfane-α,ω-bis(fluorodithiophosphates) of the general formula 1 The higher the sulfur content of the sulfur-rich phosphorus sulfides the higher are the yields of sulfane derivatives. These sulfane-α,ω-bis(fluorodithiophosphates) are identified by 19 F and 31 P NMR spectroscopy. For the trisulfane derivative 2 long range couplings over six bonds are observed. These results may be explained by the assumption of a substitution of S-atoms in the P-S-P bridges of the adamantane-like P4S10 molecule by Sn-units in the sulfur-rich phosphorus sulfides. On the other side solutions of alkali pentathiodifluorodiphosphates in CH3CN react with sulfur also to a mixture of compounds of type 2 . Therefore the nucleophilic degradation of P4S10+m(m=1−5) with fluorides do not allow definite conclusions about the molecular structure of the starting compounds.