WSOLIDS1: VAS, Dipolar-chemical shift (AB)

Description

This squeezed picture shows an example for the succesful simulation of a spectrum arising from the combined effect of chemical shift anisotropy and homonuclear indirect and dipolar coupling in a powder sample under fast variable-angle spinning. It is the ³¹P NMR spectrum of fac-(OC)₃(h²-phen)Mo(h¹-Ph₂P-PPh₂), and the results have been published in:

K. Eichele, G. Ossenkamp, R. E. Wasylishen, T. S. Cameron, J. F. Britten:
Phosphorus-31 Solid-State NMR Studies of Homonuclear Spin Pairs in Molybdenum Phosphine Complexes: Single-Crystal, Dipolar-Chemical Shift, Rotational-Resonance and 2D Spin-Echo NMR Experiments
Inorg. Chem. 1999, 38, 639-651.

Click on the picture to have a better look.

Background

In addition to the chemical shift anisotropy (CSA), the spectrum of a spin pair will also depend on the direct dipolar coupling and potentially the indirect spin-spin coupling between both nuclei. Because both, the CSA and dipolar interaction, are tensorial interactions, the actual line shape also depends on their relative orientation. Spinning the powder sample rapidly about an axis that forms an angle different from the magic angle with respect to the external magnetic field, the resulting lineshape will look like that of a static powder sample, but scaled by a factor that depends on the spinning angle. This scaling factor ranges from 1.0 (for spinning parallel to the field) to -0.5 (for spinning perpendicular to the magnetic field).