NMR of solid phosphorus-containing compounds

Abstract

Solid-state NMR techniques have been applied to the structure and dynamic characterisation of a range of phosphorus-containing compounds. Comparisons have been made within several series of compounds as well as studies of individual molecules with interesting NMR properties, whether dynamic, structural or magnetic. Spectral features such as shielding anisotropy, the high sensitivity of phosphorus and its large chemical shift range are extensively utilised in this work. Triple-channel, fluorine-observe and variable-temperature spectrometer facilities at different magnetic field strengths have been explored to give as much complementary information as possible. For both chlorinated and fluorinated diazadiphosphetidines, motional properties have been examined and the indirect spin-spin and dipolar interactions, together with shielding have been studied. Spectra from the NMR-active nuclei in these cyclic dimers have been used to compare effects of differing substituents on NMR properties. The bowl-shaped' molecules, calix[4] resorcinols with phosphorus functionality modifying the upper rim, constitute the other major group of compounds studied. These are of interest in inclusion chemistry. As well as simple one-dimensional NMR characterisation of solid-state calix[4]resorcinol compounds, interesting two-dimensional correlation results have helped with the assignment and conformational conclusions. A qualitative and quantitative study of a co-crystal of triphenylphosphine oxide and phenol was made to establish the nature of the disorder observed, but undefined, in an X-ray structural investigation of the hydrogen-bonded network. Complementary NMR techniques were used to extend the temperature range over which the rate of any motion can be characterised. Bandshape analysis, Tip measurement and selective polarisation inversion experiments have proved to be accurate in different regions of a variable temperature study. Other compounds explored were those which showed interesting solid-state NMR results, for example, the complexities of cross-polarisation dynamics between two abundant spins in inorganic phosphates, and compounds with potential solid-state applications. These include (i) phosphorus-containing compounds with chlorine and fluorinated aromatic substituents and (ii) complexes with transition metals. Comparison with single-crystal and powder X-ray diffraction has also been exploited. In some cases, data have been produced, and in others the applicability of a theoretical approach has led to other conclusions.