The effect of bulk magnetic susceptibility on solid state NMR spectra of paramagnetic compounds

The effect of bulk magnetic susceptibility (BMS) on solid state NMR spectra of paramagnetic compounds was investigated theoretically and experimentally. The BMS shift was calculated for cylindrical and spherocylinderical containers with some ratios of the length L and the diameter D. The results show the best resolution can be obtained by using a long cylindrical sample container with L/D > 10 and by exciting only the region near the center of the container. The effect of the random orientations and distributions of crystallites in a powder sample was also calculated according to a model proposed by Schwerk et al. [J. Magn. Reson. A 119, 157 (1996)] with removing the Fermi contact term from their model. Static and the magic-angle spinning 13C NMR spectra were recorded on two paramagnetic compounds of Ln(C2D5SO4)3 . 8H2O where Ln = Pr, Yb. The modified theory predicts the BMS broadening of the experimental spectra very well. Copyright 1998 Academic Press.