Magnetic anisotropy nuclear spin states

NMR spectroscopy is a powerful technique to study molecular structure, order, and dynamics. Because of the anisotropy of the interactions of nuclear spins with each other and with their environment via dipolar, chemical shift, and quadrupolar interactions, the NMR frequencies depend on the orientation of a given molecular unit relative to the external magnetic field. NMR spectroscopy is thus quite valuable to characterize partially oriented systems. Solid-state NMR... 

PAC atomic probes (e.g., mIn or mHf) possess a nuclear quadrupole moment and a magnetic dipole. Even if no field acts on the PAC nucleus, the successive emission of the y-photons through an intermediate state exhibits an appreciable angular anisotropy between the emission directions. If the (isolated) nucleus is then brought into a perturbing field (e.g., on a specific lattice site which is next to a vacancy), the angular anisotropy becomes time-dependent due to the precession of the nuclear spin. For example, if the PAC nucleus in the crystal is exposed to a (static) electric... 

MAS is routinely used in solid-state NMR spectroscopy for eliminating the effects of chemical shift anisotropy, heteronuclear dipolar interactions and first-order quadrupolar interactions. In this method the sample is rotated about the axis inclined at 54.74° with respect to the external magnetic field Bq, so that the average of the geometric term in nuclear spin interactions (3 cos 0 — 1) = Except... 

The aim of this section is to provide an overview about the development and application of solid state NMR spectroscopic techniques for the study of molecular structures and dynamics on the molecular and intermolecular length scale (lA-lOA). In particular, anisotropic magnetic nuclear spin interactions like chemical shielding anisotropy (CSA), magnetic dipolar interaction and quadrupolar interaction are used as probes for interatomic distances and orientations of molecular groups, i.e. structures, and changes of these interactions are monitored and used as a measure of dynamic processes inside the system. 

A 13C nuclear magnetic resonance (NMR) study in solution and in the solid state has been reported for three thermochromic spirooxazines, 29-31.32 From a quantitative analysis of I3C cross-polarization/magic-angle-spinning (CP-MAS) NMR spectra shielding anisotropies were estimated and a correlation of these characteristics with thermochromic activity was suggested. 

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