Solid-state NMR Lineshapes

Figure 7.31 (a) 2H solid-state NMR lineshape of /j-f-butylcalix[4]arene with included toluene-c/8 as a... 

Figure 7.31 (a) solid-state NMR lineshape of p-f-butylcalix[4]arene with included toluene-dg as a function of temperature. The dotted lines are the theoretical fit for static aromatic rings (129 K), twofold flips of the aromatic ring (179 K), and fourfold rotation (337 K). (b) Improved, ordered X-ray crystal structure at low temperature showing the different toluene orientations, pinched cavity shape and different t-butyl group orientations (reproduced by permission of The Royal Society of Chemistry). 

Figure 2 shows 29Si solid state NMR data of high-silica ZSM-5 with 24 crystallographic Si positions, 15 of which are well enough resolved in the MAS NMR spectrum to be assigned to crystallographic positions. The CSA parameters are determined by simulation of the lineshapes of the powder pattern as obtained from the 2D experiment. 

In solid state NMR it turns out that, contrary to the situation described for C, Li spectra are affected by all three factors discussed above, albeit with varying importance. The lineshapes of Li solid state NMR spectra obtained from different species may thus be quite different, as Figure 3 demonstrates with three examples. 

As a consequence of the small quadrupole moment of Li, the quadrupolar interaction in solid state NMR spectra is much smaller for Li than for Li. This has been used to advantage for the determination of the Li chemical shift anisotropy from the Li static solid state powder spectrum of 2,4,6-tris(isopropyl)phenyllithium (see below) . Applying MAS up to 10 kHz, the CSA contributions to the lineshape can be completely ehminated in most Li spectra of organolithium compounds. If the measurement of the quadrupolar... 

It is a pleasure for me to introduce Volume 43 of Annual Reports on NMR Spectroscopy and to express my thanks to the reporters for their pellucid and refulgent accounts of NMR activities in a number of areas of molecular science. The volume commences with a report on Solid-State NMR Studies of Molecular Motion by M. J. Duer this is followed by a contribution from J. Higinbotham and I. Marshall on NMR Lineshapes and Lineshape Fitting Procedures the final chapter is on Recent Progress in Solid-State NMR of Low-7 Nuclei by M. E. Smith. My gratitude to the production staff at Academic Press (London) for their meticulous efforts in the realization of this, and other volumes in the series, is hereby recorded. 

We begin with the theoretical and computational progress in solid-state NMR, which includes calculations of the lineshapes and dynamic processes based on density matrix theory or computations of the interaction parameters based on quantum (statistical) mechanics. 

One way to obtain highly resolved, selective, solid state information plus uniquely defined information on the orientation-dependencies of spin interactions is to perform NMR experiments on oriented single crystals. However, for various reasons, such single crystal NMR experiments appear impractical in standard applications to organometallic chemistry. The vast majority of solid state NMR experiments on organometallic compounds are— and probably will be— performed on polycrystalline powder samples. In principle, also for polycrystalline powders, all relevant information on spin interactions is contained in the shape of the powder patterns obtained imder static conditions. The problem then is the extraction of well-defined single parameters from such lineshapes resulting from either a multitude of resonances and/or the simultaneous presence of multiple spin interactions. In practice, it turns out that only very rarely is this possible. 

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