The effects of interplay between quadrupolar, dipolar and shielding tensors on magic-angle spinning NMR spectra: Shapes of spinning sidebands

The shapes of spinning sidebands for C-13 magic-angle spinning spectra of solids affected by residual dipolar splittings to N-14 are found to be spinning-speed dependent. Simple theory for the case of co-axial tensors indicates that centreband splittings at low spinning speeds yield values of chi D (chi and D are quadrupolar and dipolar coupling constants respectively) directly. The case of the cyanide carbon resonances for the coordination polymer [{(CH3)(3)Pb}Ru-4(CN)(6)](infinity) is considered in detail. Computer simulations of the sideband bandshapes fit the experimental results well. The quadrupole coupling constants for the three cyanide nitrogen sites lie in the range -1.9 to -2.5 MHz. The shielding anisotropy for the cyanide carbon giving the highest-frequency resonance is found to be Delta sigma = +/- 350 ppm.