WSOLIDS1: Static, 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 dipolar coupling in a powder sample. It is the ³¹P NMR spectrum of pentacarbonyl molybdenum [bis(diphenylphosphino) methane], shown as absorption and first derivative spectrum, 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. In contrast to the A2 and AX first-order spin systems, the line shape of a general homonuclear AB spin system may also depend on the relative orientations of the two chemical shift tensors.

Examples

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

P-31 CP NMR spectrum of a powder sample of [Mo(CO)5(dppm)]: this example uses the simulation of absorption and first derivative mode in separate spectrum windows. It is the spectrum shown in the description above. You can download a zip file of the WSolids1 document: (ZIP) or have a look at the report generated from the WSolids1 document: (XML)

P-31 CP NMR spectrum of a powder sample of [Ru2(CO)6(μ-PPh2)2]: this is an example with pronounced second order effects that are quite sensitive to the mutual orientation of the two chemical shift tensors. This example has been published in J. Am. Chem. Soc. 2002, 124, 1541-1552. You can download a zip file of the WSolids1 document: (ZIP) or have a look at the report generated from the WSolids1 document: (XML)