Structural studies on high oxidation state nickel complexes and their nickel (II) precursors using EXAFS spectroscopy

Perry, Richard John (1991) Structural studies on high oxidation state nickel complexes and their nickel (II) precursors using EXAFS spectroscopy. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

Octahedral nickel(III) complexes [Ni(L-L)₃]X₃ (L-L = diamine; X = Cl, Br) have been prepared by oxidation of the corresponding nickel(II) species with halogen in carbon tetrachloride under anhydrous conditions. The structures of the more stable products and all the precursors where investigated using nickel K-edge EXAFS spectroscopy and their Ni-N and Ni..C_backbone interatomic distances were determined. The ability of this technique to detect substituents beyond the second coordination sphere was also investigated. Tetragonal nickel(III) complexes (Ni(L-L)₂X₂0D (L-L = diamine, N-methyl substituted diamine; X = Cl, Br) have also been synthesised by halogen oxidation of the appropriate nickel(II) precursors. The structures of the starting materials were probed using nickel and bromine K-edge EXAFS data, and these were shown to have either a trans or a cis geometry, depending upon the degree of N-methyl substitution and the presence of aquo ligands. The more stable oxidation products have also been structurally characterized. Octahedral nickel(II), F₄-diars and diphos have been prepared and their structures elucidated using a combination of nickel, bromine and arsenic K-edge EXAFS data. The interatomic distances obtained for [Ni(F₄-diars)₂Br₂]BF₄ have been compared with those determined by X-ray crystallography and were found to be in excellent agreement. Some Class II mixed-valence nickel(II)/(IV) linear chain complexes have been prepared and a structure re-investigated using XAS. The preliminary findings of a model study for these systems using some platinum and mixed-metal analogues are reported.