Electron spin resonance of some low spin d7 transition metal complexes.

The principles and experimental techniques of electron spin resonance (esr) are outlined in the early chapters. A general investigation of low spin cobalt (II) complexes, in Chapter 3, indicates how the esr parameters are related to electronic and molecular structure. In Chapter 4, a solid state esr study of the paramagnetic pentacyanocobaltate (II) ion, in various alkali metal halide hosts, confirms a(dz,)1 configuration for this d7 ion and mixing of 4s atomic orbital is invoked to explain the esr data. The extent of mixing of 4s orbitals is also estimated for other low spin cobalt (II) complexes. In this study, some new halogenated cobaltous complexes were formed by thermal substitution of lattice halide ions. In the second half of the chapter, an investigation of the paramagnetic adduct of the pentacyanocobaltate (II) ion and phenyl nitroxide involved both liquid and solid state analyses. A novel method for linking data for the two phases is utilised to allow analysis of the complex powder spectra. The results are used to discuss the bonding in the molecule. In Chapter 5 the paramagnetic species to be discussed are produced by 8-irradiation. Several d6 transition metal complex cyanides are irradiated and d7 species showing nitrogen hyperfine structure are observed. This hyperfine structure is shown to arise from a "bent" cyanide ligand, rather than an inverted cyanide (isocyanide) ligand as previously thought. The discovery of many more halogenated d7 species led to an analysis of the electronic structure of these complexes and the differences in spin density distribution in the 3d and 4d series are discussed. An esr study of the hexanitritocobaltate (II) ion is reported in Chapter 6. The magnitude of the hyperfine couplings to cobalt and nitrogen are discussed and the radiation damage of the hexanitritocobaltate (II) ion is interpreted in relation to the damage of the analagous hexacyanide complex.