A spectroscopic mechanistic study on zirconium(iv) and hafnium(iv) complexes

[摘要] English: The aim of this study was to synthesize M(L,L')4 type complexes of zirconium(IV) and hafnium(IV) using N,N'-diamine and O,O'-bidentate ligands. The synthesized complexes were characterized and a kinetic study of the formation of the respective complexes was performed.Characterization of the successfully synthesized complexes, tetrakis(thenoyltrifluoro-acetylacetone) zirconium(IV) monohydrate ([Zr(tta)4].H2O) and tetrakis(thenoyltrifluoroacetylacetonato) hafnium(IV) ([Hf(tta)4]) was done by infrared (IR), ultraviolet and visible spectroscopy (UV/Vis) and 1H and 19F nuclear magnetic resonance (NMR) spectroscopy. The structure of [Zr(tta)4]∙H2O was successfully characterized by single crystal X-ray diffraction while its hafnium counterpart was unsuccessful due to poor crystal quality.[Zr(tta)4].H2O crystallized in the orthorhombic space group Pca21 with Z = 4. The structure of [Zr(tta)4].H2O consists of a zirconium(IV) metal centre coordinated to eight oxygen atoms of four O,O'-bidentate ligands, with an average Zr-O bond distance of 2.18(7) Å and an average bite angle of 107(8)˚. Unlike common alternating CF3 groups with respect to the coordinating ligand, the CF3 groups of this structure were clustered in the plane of the molecule. In contrast to a similar structure the thenoyl rings of this structure were connected by a water molecule.In the kinetic investigations the formation reaction between zirconium(IV) and hafnium(IV) with the Na(tta) ligand at varying metal to ligand ratios were followed by 19F and 1H-NMR. Competition studies were also performed between the two metals and Na(tta). In both the studies the a general observation was made that the formation reaction consisted of two reactions: a fast first reaction and a slow second reaction.In the individual metal studies it was determined that the observed rate constants for the hafnium(IV) system were ~ 2 times faster than the zirconium(IV) system for the first fast reaction and ~ 7 times faster for the second slow reaction.In the competition studies between zirconium(IV) and hafnium(IV) integration values of the final spectra showed that more of [Zr(tta)4].H2O was formed compared to [Hf(tta)4] was formed. The observed rate constants for both the fast and the slow reaction were comparable in each case and didn't reflect the observations that were made for the individual metal kinetic runs.

[发布机构] University of the Free State