Hafnium compounds anion

Zirconium hydroxide is precipitated by bases at lower pH than the hafnium compound. Zr and Hf are obviously unable to form true hydroxides, and these compounds are more correctly formulated as MO2 XH2O. Amorphous hydrous zirconia and hafhia (a-phase) transform to microcrystalline forms (/f-phase) with noticeable heat evolution. They lose water up to the composition MO2 H2O at 140 °C (Zr) or 155 °C (Hf). Hydrous zirconia has excellent absorptive capacity, particularly for oxygen-containing anions. For example, the concentration of S04 anions over hydrous zirconia is so low that no precipitate forms on the addition of barium salts to the filtrate. While the hydroxides of composition M(OH)4 are not stable, in alkaline solutions, M(OH)s are present and even M(0H)6 anions have been reported in very concentrated alkalis. Salts of these anions, such as Na2Hf(OH)6, can be isolated. 

All salts of zirconium and hafnium tend to hydrolyze in aqueous solutions, though less so than those of titanium. In highly dilute solutions (<10 " M), Zr and Hf exist as the aqueous ions [M(OH) ] " " +, where n is pH-dependent. The hydration energies are 7001 and 7169kJ moU for Zr and Hf respectively. In chloride, perchlorate, and nitrate solutions, hafnium is less hydrolyzed than zirconium, while the reverse is true in sulfate solutions. This is connected with the lower solubility of hafnium compounds in sulfate solutions, even in only slightly acid media. It should be noted that the sulfate anion has a strong affinity for Zr and Hf... 

In a recent attempt we have reacted a TMEDA-adduct of tris(trimethylsilyl)silyl potassium with hafnium tetrachloride [8]. This represents the first example of a reaction of a silyl anion with a group 4 tetrahalide. The product obtained is tris(trimethylsilyl)silylhaMum trichloride, with one TMEDA molecule coordinated. With three potential leaving groups still present in the molecule, we hope that it might serve as a useful precursor for a number of differently substituted silyl hafnium compounds. 

A new compound of mixed oxidation state is the product from reduction of a mixture of BiCl3 and HfCl4 with metallic bismuth.783 Full identification was achieved only by an X-ray structure determination, which showed the composition to be Bi+Bi +(HfCI )3.140 The hafnium anions are distorted octahedral while the Big+ ion has C3h symmetry. Co-ordination of the Bi+ ion is unusual as it is co-ordinated to three chlorines from the anions. 

Compound (CsH4SiMe2NBut)TiCl2 has been synthesized and used as pre-catalyst for ethylene polymerization. The activities and the properties of the polymers have been compared to similar zirconium and hafnium derivatives.720 The consequences of anion-cation interactions on the activity of GGG group 4 metal complexes in olefin polymerizations have been explored for a series of zirconocene derivatives as well as the cationic species [(C5Me4SiMe2NBut)TiMe]+ with the sterically congested tris(perfluorobiphenyl)fluoroaluminate as the counteranion.721 The co-polymerization of ethylene and 1-butene by (CsMe iMe Bu TiC in the presence of... 

Tetrakis(acetylacetonato) complexes of zirconium and hafiiium were reported in 1904 and 1926, respectively, and a large number of j3-diketonate derivatives have been described subsequently (Table 10). These compounds are of the type [M(dik)4], [M(dik)3X], [M(dik)2X2], M(dik)X3 and [M(dik)3]Y (dik = -diketonate anion X = C1, Br, I, NO3, or alkoxide Y = [FeCU], [AuCU], [PtCU] or 2[Zr(S04)3]). Additional j3-diketonate compounds include the anionic complex [NEt4][Zr(bzbz)F4] (bzbz = dibenzoylmethanate) and the 1 1 ZrCU-diketone adducts [ZrCl4(MeCOCR2COMe)] (R = H or Me). " Early work on zirconium and hafnium jS-diketonates has been reviewed by Larsen, Bradley and Thornton, Fackler and Mehrotra et al. ... 

Formation of zirconium and hafnium complexes with polyhydroxyaromatic compounds in aqueous solution has been studied by potentiometric, spectrophotometric and ion exchange methods. Much of this work has been reviewed by Larsen. A potentiometric and lightscattering study of the zirconium(IV)-Tiron (Tiron = disodium l,2-dihydroxybenzene-3,5-disulfonate) system provides evidence for mixed hydroxo-Tiron chelates at Tiron/Zr " ratios less than 2.5, but at higher Tiron/Zr ratios the unhydrolyzed complexes [Zr2L5] and [ZrL4] (L = tetranegative anion of l,2-dihydroxybenzene-3,5-disulfonic acid) are present. ... 

Layer intercalation compounds of ZrSj and HfSj with NH3, N2H4, and RNHNHMe (R = H or Me) have been obtained and the corresponding layer expansions determined. The non-stoicheiometric zirconium and hafnium ditelluride phases ZrTe, (x = 1.74—1.45) and HfTei 94 have been characterized by X-ray diffraction studies. The non-stoicheiometry of the latter compound appears to be in the anion sub-lattice. ... 

It is interesting that the salt (NH4)3(HfF7) is actually (NH4)2[HfF6] + NH F this is one of the few clear-cut distinctions between the chemistries of zirconium and hafnium—the zirconium compound contains the [ZrF7]" anion. 

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