Solid-State NMR has become an important method in zeolite research. Numerous new developments and applications of solid-state NMR techniques have evolved. Just to name a few of the more important ones: multidimenional methods to correlate different NMR lines with each other can unravel connectivity patterns and solve ambiguities in assignments, high-resolution techniques for quadrupolar nuclei make a wealth of elements much more accessible, and powerful double-resonance methods enable the study of spatial neighborhood and interatomic distances. Last but not least, multiple-quantum techniques offer a wide range of applications.
All available NMR methods are aiming at the exploration of the important "NMR interactions" which contain the information wanted. Simply speaking: these interactions provide the framework how the experimental and analytical strategies of NMR can be structured. These fundamental interactions are:
a) The dipole interaction is a magnetic interaction between two or more nuclei. This effect is transmitted through space which means that it is not restricted to chemical bond connectivities. The strength of the dipole interaction is a function of the interatomic distance, and the dipole coupling constant, D, contains direct distance information.
b) The chemical shift interaction (chemical shift, δcs) is still the most popular NMR parameter used. The isotropic chemical shift provides insight into the chemical surroundings of a nucleus, e.g. bonding partners, coordination number, and bond angles. If the chemical surrounding is anisotropic, then, in principle, the chemical shift interaction has an anisotropic component which can be measured and analyzed.
c) The quadrupole interaction is an interaction between the nuclear quadrupole moment of nuclei with a spin quantum number of I > 1/2 and the local electric field gradient. It contains information on the local charge-distribution. With the quadrupole coupling constant, Cq, information can be obtained on the local symmetry: For ideal cubic, octahedral or tetrahedral coordination (high symmetry), Cq is zero.
d) The indirect spin-spin coupling is a magnetic interaction between at least two NMR nuclei which is transmitted by bonding electrons. This interaction (sometimes also called J coupling) is only effective, when there is a chemical bond connectivity. This interaction is of lesser importance in solids, because the effect is usually too small to be resolved.
Most parameters are not directly understood in structural or dynamical terms, and the interpretation must be (or must have been in the past) developed by model studies. Such model studies are usually performed by the investigation of a large number of model compounds (e.g. to establish a chemical shift scale), or by physical model calculations (prediction of parameters for a given reference structure). The dipole interaction is special in that it does not require a model to translate the dipole coupling into structural information, since it is a direct function of spatial ordering and distances. The presentation will show how the dipolar interaction can be extracted using tailor-made NMR techniques.