Hafnium acetylacetonate

Hafnia can also be deposited by the pyrolysis of a metallo-organic such as hafnium acetylacetonate, ( 511702)3, at 400-750°C, or hafnium trifluoro-acetylacetonate, Hf(C5H402F3)4, at 500-550°C with helium and oxygen as carrier gases. 

Zirconium acetylacetonate was first prepared by Biltz and Clinch by the reaction of zirconyl nitrate and sodium acetylacetonate in water solution. The compound was crystallized as the 10-hydrate from a slightly acid solution and dehydrated by several crystallizations from alcohol. Von Hevesy and Logstrup later developed a method for the preparation of hafnium acetylacetonate that has been found applicable to the synthesis of the zirconium compound and this forms the basis of the present procedure. 

Zirconium acetylacetonate 10-hydrate effloresces in air and may be completely dehydrated in a vacuum of 0.1 mm. The anhydrous salt sublimes slowly with some decomposition in vacuo at about 140° and melts at 194.5 to 195° with decomposition. The acetylacetonate reacts with alcohol. Its solubility at 25° per liter in other organic solvents is as follows carbon disulfide, 30 g. carbon tetrachloride, 47 g. acetylacetone, 56 g. ethylene dibromide, 44 g. benzene, approximately 200 g. Both the hydrate and the anhydrous compound give a red color with carbon disulfide on standing. This is also true of hafnium acetylacetonate but not of the thorium compound. 

A key issue in studies of thermolysis kinetics in hitherto unexplored systems, including Hf-containing polymers, is the optimization of the experimental procedure. Preliminary thermodynamic analysis of the Hf-C-H-0 system offers the possibility of establishing the temperature stability limits of HfC and HfO. Earlier, thermodynamic studies of the Hf-C-H-O system were carried out in relation to hafnium acetylacetonate, which is used to prepare HfC [33]. The most convenient approach to producing hafnium-containing nanocomposites with the aim of... 

Thenoyltrifluoroacetone(TTA), C4H3S,CO,CH2,COCF3. This is a crystalline solid, m.p. 43 °C it is, of course, a /1-diketone, and the trifluoromethyl group increases the acidity of the enol form so that extractions at low pH values are feasible. The reactivity of TTA is similar to that of acetylacetone it is generally used as a 0.1-0.5 M solution in benzene or toluene. The difference in extraction behaviour of hafnium and zirconium, and also among lanthanides and actinides, is especially noteworthy. 

Also increasingly common, as CVD precursors, are many halogen-acetylacetonate complexes, such as trifluoro-acetylacetonate thorium, Th(C5H4F302)4, used in the deposition of thoriated tungsten for thermionic emitters, the trifluoro-acetylacetonates of hafnium and zirconium and the hexafluoro-acetylacetonates of calcium, copper, magnesium, palladium, strontium, and yttrium. 

Also, the rates of exchange of zirconium and hafnium trifluoroacetyl-acetonate or acetylacetonate, respectively, with the free ligand have been studied (3). Rates for acetylacetone exchange in benzene and chlorobenzene are faster for zirconium than for hafnium however, for the trifluoroacetyl-acetone ligand, the exchange rates are essentially the same for both metals. The exchange for thorium is faster than for zirconium or hafnium regardless of solvent. 

The refractory carbides NbC and TaC and the nitride NbN, each with the sodium chloride structure, are also similar to the corresponding zirconium and hafnium compounds. Finally, it may be noted that the same group of complexing agents form complexes with Nb(V) and Ta(V) as with Zr(IV) and Hf(IV) (for example, fluoride, hydrogen peroxide, acetylacetone, and 1,2-dihydroxybenzene). 

Only recently Colonna et al. reported that in PBT synthesis, the nse of mixtures of titanium(lV) tetrabutoxide and Hafnium(lV) acetylacetonate as catalysts in the presence of metal phosphates as co-catalysts improved the thermal stability of the polymers. [24] Unfortunately these interesting results have not received significant attention and no hypothesis has been formnlated about the relationships between the improved stability and the catalyst composition. 

Electron diffraction and vibrational spectroscopic data for hafnium and zirconium tetra(acetylacetonate) have been analysed together to give the molecular structures." " The structures adopted are tetragonal antiprisms, having... 

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