ABSTRACT
Theoretically, separating the solids into two classes, diamagnetic and paramagnetic, is obvious. However, in practice, it is well known that the synthesis of materials, involving a number of various organic and inorganic reagents, generally leads to systems still containing paramagnetic impurities of a different nature. When concentrations of such impurities are small, they do not signiœcantly affect NMR parameters: isotropic chemical shifts, magnetic shielding anisotropy, and line shapes. The presence of the impurities can be detected only on the level of nuclear relaxation, occurring often via a speciœc relaxation mechanism, spin diffusion (see the following). We accept such systems as diamagnetic ones. At the same time, when the concentrations of paramagnetic centers become ≥0.5-1 wt%, such solids can show a speciœc NMR behavior and we accept these systems as paramagnetic.
