Hafnium halides

Hafnium Halides. Hafnium tetrafluoride, HfF, can be prepared by careful thermal decomposition of ammonium fluorohafnate in an... 

Hafnium-free zirconium alloys, 26 6351 Hafnium halides, 73 91-93 Hafnium hydride, 73 93 Hafnium hydroxide chloride heptahydrate, 13 92... 

Preparation of Zirconium (Hafnium) Bromide (Iodide). To prepare a zirconium (hafnium) halide, use a multisection tube made from refractory glass with a test tube and offtake fused to it (Fig.123). 

Zirconiumf iv) and Hafnium(. Halides and Oxyhalides. Raman spectroscopic measurements260 on LiF-NaF-ZrF4 mixtures at 650°C have identified a six-co-ordinate environment for zirconium in a 31-36-33 mol % LiF-NaF-ZrF4 melt. The... 

NIS] Nisel son, L. A., Fusion diagrams of the binary systems of zirconium and hafnium halides, Russ. J. Inorg. Chem., 7, (1962), 354-355. Cited on pages 172, 175. 

Samples of TI1F4 and ThCfi were heated to 1475 and 950 K respectively to observe their infrared spectram. The observed values of the stretching frequencies were 520 and 335 cm respectively. The values for the zirconium and hafnium halides agreed closely with earlier measurements. The frequencies of the bending vibration, also active in the infrared, were lower than the cut-off ca. 200 cm ) of the Csl prism used in the spectrometer. 

Reduction. Hafnium oxide can be reduced using calcium metal to yield a fine, pyrophoric metal powder (see Calciumand calciumalloys). This powder contains considerable oxygen contamination because of oxygen s high solubility in hot hafnium, and caimot be consoHdated into ductile metal. To obtain low oxygen ductile hafnium, the feed must be an oxygen-free halide compound such as hafnium tetrachloride or potassium hexafluorohafnate [16871-86-6]. 

Monovalent Halides. Zirconium monochloride [14989-34-5], ZrCl, was discovered during electrorefining studies of zirconium in a SrCl2—NaCl—ZrCl4 melt intended to produce pure ductile hafnium-depleted zirconium from cmde zirconium anodes (180—181). The monochloride is also called Zirklor. It is obtained as black flakes with a graphite sHp-plane behavior and was proposed as a lubricant (182,183). 

H+], calculation of, 192, see also Hydrogen ion Haber, Fritz, 151 Haber process, 140, 150 Hafnium, oxidation number, 414 Haldane, J. B. S., 436 Half-cell potentials effect of concentration, 213 measuring, 210 standard, 210 table of, 211, 452 Half-cell reactions, 201 Half-life, 416 Half-reaction, 201 balancing, 218 potentials, 452 Halides... 

Hydrogen reduction has a major advantage in that the reaction generally takes place at lower temperature than the equivalent decomposition reaction. It is used extensively in the deposition of transition metals from their halides, particularly the metals of Groups Va, (vanadium, niobium, and tantalum) and Via (chromium, molybdenum, and tungsten). The halide reduction of Group IVa metals (titanium, zirconium, and hafnium) is more difficult because their halides are more stable. 

In this table, the free energy of formation, AGf of the chloride of these metals is listed for four different temperatures. As can be seen, the values are more negative than that of hydrogen chloride. These metals can be used to reduce the halides of titanium, zirconium, or hafnium, whereas hydrogen, as mentioned above, cannot do so readily. In order to be useful in CVD, the by-product chloride must be volatile at the deposition temperature. This may rule out the use of sodium or potassium, which evaporate above 1400°C. 

As shown in Table IV, the highest catalytic activity of metal halides used as Lewis acid for the alkylation reaction of ferrocene with 2 was observed in methylene chloride solvent. Among Lewis acids such as aluminum chloride, aluminum bromide, and Group 4 transition metal chlorides (TiCl4, ZrCU, HfCU), catalytic efficiency for the alkylation decrea.ses in the following order hafnium chloride > zirconium chloride > aluminum chloride > aluminum bromide. Titanium chloride... 

In contrast to the zirconium compounds the chromium halides are less active than pure Cr(allyl)3 Cr (allyl) Cl2 seems to be completely inactive. The only other element known in which halide substitution of the corresponding allyl compound results in activation is hafnium, suggesting the effect may be confined to group IVa. 

Hafnium tetrabenzyl, preparation and catalytic activity of, 23 277-279 Halides... 

Friedel-Crafts acylation generally involves reaction of an acyl halide and Lewis acid such as AICI3, SbF5, or BF3. Bismuth(III) triflate is also a very active acylation catalyst.40 Acid anhydrides can also be used in some cases. A combination of hafnium(IV) triflate... 

Hafnium tetrachloride combines with molten sodium chloride, potassium chloride, or other alkali halides to form addition products such as 2NaCl HfCl4, which decompose at higher temperatures. 

Only a small number of zirconium(III) and hafnium(III) complexes are known. Nearly all of these are metal trihalide adducts with simple Lewis bases, and few are well characterized. Just one zirconium(III) complex has been characterized structurally by X-ray diffraction, the chlorine-bridged dimer [ ZrCl PBu,) ]- Although a number of reduced halides and organometallic compounds are known in which zirconium or hafnium exhibits an oxidation state less than III, coordination compounds of these metals in the II, I or 0 oxidation states are unknown, except for a few rather poorly characterized Zr° and Hf° compounds, viz. [M(bipy)3], [M(phen)3] and M Zr(CN)5 (M = Zr or Hf M = K or Rb). 

Zirconium(IV) and hafnium(IV) halides form adducts with a variety of monodentate and polydentate amines. Typical complexes are listed in Table 3. In general, these compounds are air- and moisture-sensitive white solids (yellow when the halide is iodide), thermally stable and insoluble in most organic solvents. 

Table 3 Complexes of Ziiconium(lV) and Hafnium(IV) Halides with Amines...

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