Zirconyl compounds

Zirconyl pyrophosphate, (ZrO)2P207, mp = 2070°C, p = 3.88 g/cc, is stable up to about 1600 C, and calcium orthophosphate, Ca3(P04)2 which melts at 1820°C, can be used for some purposes at temperatures up to 1600°C. The zirconyl compound, which loses P2O5 above 1600°C, has potential use as a low-expansion ceramic, although its strength is rather limited [3]. Up to llOO C the net expansion is <1.7 x 10 C (Table 12.27). Zirconyl pyrophosphate is a good electrical insulator and its dielectric constant is similar to that of alumina [4]. Solid solutions of composition Ca Sr,. Zr4(P04)g and Zr 2-Nx i show almost zero thermal expansion over a considerable temperature range, and are promising materials for future application (see below). 

Starting from alkynes, hydrozirconation reactions lead to alkenyl zirconyl compounds that in turn can be cross-coupled with halides to give enynes. The total synthesis of the polyenyne xerulin is a showcase of this reaction sequence (Scheme 5-111). 

Douglas investigated heats of formation of dimethyl sulphoxide (and also of the sulphone) and proposed in a footnote that it could be determined by 5-min reaction with potassium permanganate/sulphuric acid, then adding excess iron(II) sulphate and finally titrating with permanganate. The same principle was used by Krishnan and Patel to determine dimethyl sulphoxide in various complexes (with perchlorates of titanyl, zirconyl and thorium), and by Krull and Friedmann to determine the same compound but using only dilute sulphuric acid and 5-min reaction. 

They include the hydrolysis to form the (i-dioxo dimer 49, and the products derived from the formal insertion of nitriles, ketones, and Bu NC into the Zr-C ct bonds. In the case of hydrolysis, butenes have been identified. The occurrence of the zirconyl ( Zr=0 ) group in a monomeric zirconium compound remains... 

Zirconyl chloride is used to make pigment toners and improve properties of color lakes of acid and basic dyes. Also, it is used to prepare body deodorants and antiperspirant, water repellant, dye precipitant, catalysts, and many zirconium compounds. 

Very little X-ray data is available for zirconium or hafnium complexes that contain oxo ligands. The only X-ray evidence for the existence of the zirconyl or hafnyl group, M=Oz+, comes from a structural study of K2Zr03.157 This compound contains chains of Zr05 square pyramids that share basal edges. The Zr—O distance to the apical oxygen atom (1.92 A) is appreciably shorter than the sum of ionic radii (2.20 A), the sum of the covalent radii (2.22 A)... 

Treatment of a hot methanol solution of appropriate zirconyl salts with 1,10-phenanthroline mono-Af-oxide (phenNO) yields the oxozirconium(IV) complexes [ZrO(phenNO)X2] (X = Cl, Br, N03 or NCS), [ZrO(phenNO)2]I2 or [Zr0(phenN0)3][Q04]2.697 These compounds are analogues of the 2,2 -bipyridine-l,l -dioxide complexes discussed in Section 32.4.4.1. 

Separation of hafnium from zirconium. In a zirconium-hafnium separation process developed by Eldorado Nuclear, a mixture of sodium zir-conate and hafnate can be obtained by fusing zircon sand with NaOH and dissolving the product in water. Acidification with nitric acid then gives aqueous zirconyl (ZrO +, or hydrolyzed Zr + ) and hafnyl (HfO " ") nitrates. Extraction with TBP then gives an extract containing mainly [Hf0(N03)2(TBP) ], but most of the ZrO " " remains in the aqueous phase and can be recovered on evaporation as essentially Hf-free Zr0(N03)2(s). The effectiveness of this process can be ascribed to compounding of factors... 

Zirconium (Zr, at. mass 91.22) occurs in its compounds exclusively in the IV oxidation state it is similar to titanium in its properties. In HNO3 and HCIO4 solutions, zirconium Zr and zirconyl ZrO ions occur. They tend to polymerize as the concentration increases. Hydrolysis of zirconium ions begins at pH 1-1.5. Zr(OH>4 has no amphoteric properties. Zirconium forms stable complexes with fluoride, EDTA, and hydroxy acids. 

With sulfur a compound of the formula ZrS2 is produced by the action of CS2 on zirconia at red heat. It forms steel-gray crystals which are not decomposed by water nor most acids, but HN03 oxidizes the zirconium and precipitates the sulfur. The zirconyl sulfide ZrOS is obtained when the anhydrous sulfate is heated to red heat in a stream of EbS. It is a bright yellow powder which ignites readily in the air. 

Aqueous solutions of zirconium or hafnium compounds may be obtained by dissolving the conesponding hydrous dioxide in the appropriate strong acid. Because zirconium and hafnium oxides are such weak bases, these aqueous solutions tend to hydrolyze, with formation of zirconyl salts such as Zr0(N03)2. 

The use of zirconyl chloride octahydrate (ZrOCl2 8H2O) as an intestinal phosphate binder in place of aluminum compounds has also been reported (Graff and Bumel 1995). 

Clearfield [64CLE] reviewed the structural aspects of zirconium chemistry. One of the important findings of this review was the substantial amount of evidence that was presented for the absence of the zirconyl (ZrO ) ionic structure in aqueous solution and in solids. Even in monoclinic zirconium oxide, Zr-O-Zr bonds are present rather than the Zr=0 double bond. Many compounds in both aqueous solution and the solid state contain hydroxo-zirconium bridges (see Section V.2.2). Clearfield presented evidence of the moiety [Zr4(0H)g(H20)i6] occurring in both aqueous solution and the solid state and argued that measurements by Zielen and Connick [56Z1E/CON] to determine the stability of polymeric zirconium hydrolysis species confirmed the existence of this species in aqueous solution. 

These authors measured the solubility of zirconium phosphate in hydrochloric acid solutions. Analysis of the compound used in the experiments was found to have the composition ZrH4P209, which the authors believed to be Zr0(H2P04)2, although they did acknowledge that the formula Zr(HP04)2-H20 was equally possible. They believed that the former compound formed when the zirconyl ion, ZrO, reacts with the phosphate ion. However, [56CLE/VAU] provided clear evidence for the absence of the zirconyl... 

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