Speciation and interconversion mechanism of mixed halo and O,O- and O,N-bidentate ligand complexes of zirconium

[摘要] English: The aim of this project is to find significant chemical differences between the fluorinated O,O-bidentate ligand complexes of zirconium and hafnium which would allow the separation and purification of these metals. In the present investigation of zirconium complexes, different ratio's of bidentate ligands (L,L') have been used in synthesis, to study the variation in activity and selectivity of coordination of L,L' to zirconium halides, where L,L' = tfacacH, hfacacH and oxH. Different synthetic procedures and characterization methods of these complexes are discussed. Optimal reaction conditions have been found for different substituted L,L'- bidentate halo-zirconium complexes. The crystallographic characterization of tetrakis(1,1,1-trifluoroacetylacetonato-κ2-O,O') zirconium(IV) toluene solvate and tetrakis(quinolinolato-κ2-N,O)zirconium(IV) N,N-dimethyl-formamide solvate is presented and compared with literature. The former crystallizes in a monoclinic crystal system while the latter is triclinic. Both crystal structures were found to have solvent molecules as part of the basic molecular unit, though these solvent molecules are shown to not have a great impact on the steric packing for either basic organometallic group (consisting of the respective bidentate ligands coordinated to zirconium). It was also found that these structures show square anti-prismatic coordination polyhedra, with a small distortion towards a dodecahedral geometry in both cases. This is however not uncommon for zirconium-bidentate ligand structures. A discussion of the principles of the kinetic approach employed is also included as well as experimental results. Specific reference is made to the advancement in setting standards for identifying reaction steps and defining reaction mechanisms. New conclusions about the coordination mechanism with regard to these systems are drawn from new observations made during the synthesis, characterization and IXpreliminary kinetic studies. The initial coordination mechanism is postulated for the four observed steps of zirconium chelating reactions individually identified and analyzed with bidentate ligands. A step-wise substitution mechanism is proposed and discussed for this coordination reaction scheme, yielding interesting results concerning the theoretical assumptions for such a reaction proceeding to full coordination of zirconium, studied by time resolved stopped flow and slower UV/Vis spectroscopy. Other than traditional square-planar coordination reactions, this system proved to be independent of solvent effects, as also evident by the independence of crystallographic characterized structures shown to have no influence from steric effects of solvent molecules present in the formula unit.

[发布机构] University of the Free State