Analytical chemical applications of high-resolution nuclear magnetic resonance spectroscopy of solids

Abstract

The basis of the combined cross-polarization-magic-angle spinning (c.p.-m.a.s.) experiment, which yields high-resolution n.m.r. spectra of solid materials, is described and the general applicability of the technique, including its quantitative reliability, discussed. Solid-state n.m.r. is in many ways complementary to X-ray diffraction, as shown by its application to amorphous systems in which diffraction methods cannot be used (for example resins, coals, glasses and surface-immobilized catalysts) and also by its application to crystalline materials where X-ray structural data are available but where, for various reasons, a fuller description of the structure may be obtained by n.m.r. Examples include zeolites and chemically exchanging solid systems. The technique also provides a bridge between the solid-state structures of conformationally mobile and charged species as determined by diffraction techniques and the structures of these species in solution. Quantitative reliability of the c.p.-m.a.s. technique has been evaluated for phenolic resins and coals.

31P solid-state nuclear magnetic resonance spectroscopy of aluminum phosphate minerals

“…These interactions can be probed by a variety of a 1p NMR experiments (Opella and Frey 1979, Maciel and Sindorf 1980, Fyfe et al 1982, Tropp et al 1983, Grimmer et al 1986). These experiments, especially the quantitative measurement of the cross-relaxation time, Tpn, represent the means for probing phosphate structure upon which we can rely with greatest confidence.…”

“…Among these are qualitative CP-MAS "interrupted decoupling" experiments (Opella and Frey 1979 and quantitative CP-MAS (Pines et al 1973, Schaefer andStejskal 1976) experiments where the cross-polarization relaxation time, Tpia, is measured (Maciel and Sindorf 1980, Fyfe et al 1982, Grimmer et al 1986). The former is a modified CP-MAS experiment in which a short time interval is inserted between the end of the spin-lock phase and reapplication of high-power proton decoupling (Figures 1 b and I c).…”

“…The rate at which resonance amplitude increases (typically from 50 Bs to 1 ms) is determined by the efficiency of cross-relaxation while the rate of amplitude decrease depends on the longitudinal relaxation rates of both the proton and the phosphorus nuclei, TlpH and Tlpp respectively (Maciel and Sindorf 1980, Fyfe et al 1982, Grimmer et al 1986). Measurement of T10n and Tlpp in separate experiments reveal whether or not the decay of signal amplitude in a contact-time experiment is dominated by Tips.…”

“…For instance, the material lacks sufficient long-range order to give a diffraction pattern suitable for least-squares structure refinement or because the material one is interested in occurs at an interface. High-resolution solid-state nuclear magnetic resonance (NMR) spectroscopy has proven extremely valuable for learning about structure under these circumstances (Andrew 1981, Fyfe et al 1982, Fyfe et al 1983, Oldfield and Kirkpatrick 1985, Nagy et al 1985.…”