Spin-Polarized Structures and Solid-State NMR Spectroscopy of Paramagnetic Compounds

摘要

Solid-state NMR spectroscopy of paramagnetic compounds has a long standing tradition. Scientists such as McConnell, Fermi, or Van Vleck made important contributions more than half a century ago. Notably, it is impossible to distinguish different fields of science in this area because EPR and NMR spectroscopy, magneto chemistry, and quantum mechanics merge creating a new unit. High-resolution solid-state NMR spectroscopy offers a special view of the spin structure of solid matter, because, unlike magnetic-susceptibility measurements, very small spin densities can be traced on an atomic scale. Such spin-density measurements are well documented, for example 1H NMR spectroscopy of organic radicals, organometallic compounds, or inorganic coordination complexes. Paramagnetic compounds are also used as chemical-shift thermometers in NMR spectroscopy because the isotropic chemical shift has a rather simple dependency on temperature. Li NMR spectroscopy allowed different Li environments to be distinguished according to their coordination number in materials serving as electrodes. The class of cyano metallates of the type [Me(CN)_6]~(n-) have attracted considerable interest, among them the compounds Cd3[Fe/ Co(CN)6]2·H2O by Lescouezec et al. highlighted herein. It is to be expected that the spin density of the spin center Fe~(III) is distributed to the surrounding atoms. Lescouezec et al. were able to clarify by ~(13)C, ~(15)N, (113)Cd NMR spectroscopy how much spin density is distributed away from the spin center, the static disorder of the sample structure, and if spin-polarization mechanisms are active over three bonds.