Spinning sidebands in slow-magic-angle-spinning NMR spectra arising from tightly J-coupled spin pairs

Complex spinning sidebands are observed in magic-angle-spinning (MAS) NMR spectra arising from isolated tightly J-coupled spin pairs under slow spinning conditions. Such spinning sidebands are sensitive to the magnitude and relative orientation of the chemical-shift tensors, the dipolar-coupling tensor, and the sign of the indirect spin-spin (J) coupling. We show that it is possible to extract information concerning such NMR parameters from an analysis of the observed spinning sidebands. As an example, numerical simulations are carried out to reproduce observed 31P MAS NMR spectra of a phosphole tetramer (1) and o-bis(diphenylphosphino)benzene (2), so that invaluable information concerning the orientations of the phosphorus chemical-shift tensors and the sign of J(31P, 31P) can be deduced. Simulations are carried out by numerically evaluating the spin-density matrix of the spin system.