WSOLIDS1: VAS, Dipolar-chemical shift (A2, AX)

Description

This squeezed picture shows an example for the succesful simulation of a spectrum arising from the combined effect of chemical shift anisotropy, and heteronuclear indirect and dipolar coupling in a powder sample under fast variable-angle spinning. It is the ³¹P NMR spectrum of a cadmium phosphine complex.

Click on the picture to have a better look.

From version 1.21 and higher, this model also includes the calculation of spinning sidebands:

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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).

Examples

The SVG images shown below were produced using the following tools: my own SpecPlot to plot the spectra, Platon or Ortep 3 for Windows to plot the molecular structures from X-ray data, and Inkscape to compose the picture.

P-31 NMR CP/VAS NMR spectrum of Ac2Cd-PCy3: this example uses two isotopologues, with indirect spin-spin and direct dipolar coupling to Cd-113/Cd-111 and the uncoupled P-31. Because the magnetogyric ratios and natural abundancies of Cd-113 and Cd-111 are very similar, both are lumped together to 25%. The values of D and J are the average values then. Note that the line shapes of the individual satellites and the central peak deviate from each other, due to the effect of the coupling. For spinning angles much greater than 65° the satellites and the central peak will overlap each other. You can download a zip file of the WSolids1 document: (ZIP) or have a look at the report generated from the WSolids1 document: (XML)