Solid state NMR studies of transition metal compounds
This thesis is concerned with a systematic study of phosphine-containing transition metal complexes and cluster compounds by high resolution solid state nmr spectroscopy, using the techniques of magic angle spinning and cross polarisation. Previous work has indicated the potential of the solid state nmr technique to investigate a variety of materials: this is considered in the introduction to this thesis, and the reasons for choosing to study transition metal phosphine compounds are discussed. The analysis of spinning sidebands to obtain the principle values of the shielding tensor is examined to determine how well the calculated values represent the true values. Simulations of slow MAS spectra are proposed as a means of testing and refining the calculated tensor components before attempting to correlate the shielding with structural parameters. The results of a study of a series of crystalline phosphine-containing complexes and clusters are presented. The spectra are interpreted on the basis of the known crystal structures: in some cases separate resonances can be resolved in the solid state spectra from the distinct phosphine environments of a cluster framework, and from inequivalent sites in the unit cell. Information is obtained from the isotropic shifts, scalar couplings and the chemical shift anisotropy. Many of the compounds are fluxional in solution, some even at low temperature: whereas a number of these are found to be rigid in the solid state at room temperature, some of the crystalline compounds retain their fluxionality. Investigations of the species formed when transition metal carbonyl clusters are anchored to oxide supports were carried out. These show the presence of several distinct phosphorus-containing species, some of which are not consistent with the simple attachment of the cluster to the surface. The unique importance of the solid state technique is demonstrated in the study of these supported species.