TWO-DIMENSIONAL DEUTERIUM MAGIC-ANGLE-SPINNING NUCLEAR MAGNETIC RESONANCE OF PARAMAGNETIC COMPOUNDS - SEPARATION OF PARAMAGNETIC AND QUADRUPOLE INTERACTIONS

摘要

A new two-dimensional H-2 magic-angle-spinning NMR experiment to study paramagnetic compounds is presented. It can be carried out by the two-pulse sequence (90 degrees)-(t(1))-(180 degrees) -(t(2), acquisition) or the three-pulse sequence (90 degrees)-(t(1))-(54.7 degrees)-(tau)-(125.3 degrees)-(t(2), acquisition). The latter has the advantages over the former in that pure-absorption spectra can be obtained, and also finite pulse-width effects are less apparent. The intensities of the two-dimensionally spread sidebands are calculated as a function of the paramagnetic and the quadrupole coupling parameters, the time-evolution of the spin system during the rf pulse being involved. The method is applied to paramagnetic coordination compounds with selectively deuterated acetate groups: Mn2O(O2CCD3)(2){(C3H3N2)(2)BH}(2) and Pr(O2CCD3)(3) . H2O. The principal values of the two interaction tensors can be separately estimated from the projections of the two-dimensional spectrum onto the corresponding diagonals. These values are further refined by simulations of the two-dimensional spinning sideband pattern, which also allows us to determine the mutual orientation of the two tensors. The paramagnetic shift tensors are calculated on the basis of the crystal structures and are compared with those obtained by the experiments. The effect of the bulk magnetic susceptibility on the observed paramagnetic shift tensor is discussed. Some methods to remove this effect are suggested. (C) 1997 American Institute of Physics. [References: 56]