Structure of the hydrated, hydrolysed and solvated zirconium(IV) and hafnium(IV) ions in water and aprotic oxygen donor solvents. A crystallographic, EXAFS spectroscopic and large angle X-ray scattering study

The tetrameric hydrolysis products of zirconium(IV) and hafnium(IV), the zirconyl(IV) and hafnyl(IV) ions, [M(4)(OH)(8)(OH(2))(16)(8+)], often labelled MO(2+).5H(2)O, are in principle the only zirconium(IV) and hafnium(IV) species present in aqueous solution without stabilising ligands and pH larger than zero. These complexes are furthermore kinetically very stable and do not become protonated even after refluxing in concentrated acid for at least a week. The structures of these complexes have been determined in both solid state and aqueous solution by means of crystallography, EXAFS and large angle X-ray scattering (LAXS). Each metal ion in the [M(4)(OH)(8)(OH(2))(16)](8+) complex binds four hydroxide ions in double hydroxo bridges, and four water molecules terminally. The M-O bond distance to the hydroxide ions are markedly shorter, ca. 0.12 A, than to the water molecules. The hydrated zirconium(IV) and hafnium(IV) ions only exist in extremely acidic aqueous solution due to their very strong tendency to hydrolyse. The structure of the hydrated zirconium(IV) and hafnium(IV) ions has been determined in concentrated aqueous perchloric acid by means of EXAFS, with both ions being eight-coordinated, most probably in square antiprismatic fashion, with mean Zr-O and Hf-O bond distances of 2.187(3) and 2.160(12) A, respectively. The dimethyl sulfoxide solvated zirconium(IV) and hafnium(IV) ions are square antiprismatic in both solid state and solution, with mean Zr-O and Hf-O bond distances of 2.193(1) and 2.181(6) A, respectively, in the solid state. Hafnium(IV) chloride does not dissociate in N,N'-dimethylpropyleneurea, dmpu, a solvent with good solvating properties but with a somewhat lower permittivity (epsilon= 36.1) than dimethyl sulfoxide (epsilon= 46.4), and an octahedral HfCl(4)(dmpu)(2) complex is formed.     

Application of zone-melting technique to metal chelate systems-XI Refining of tetrakis(di-n-propionylmethanato)zirconium(IV) from hafnium and trace amounts of some other metals

The zone-melting method was applied to purification of tetrakis(di-n-propionylmethanato)zirconium(IV) which contained copper(II), nickel(II), cobalt(II and III), iron(III) and hafnium(IV) in the forms of their chelates with the common ligand. All minor components having effective distribution coefficients < 1 in the zirconium(IV) chelate were concentrated toward the terminal end of the refining column. When an aqueous solution of zirconium(IV) containing zinC(II) and manganese(II) in addition to the metal contaminants above was treated with di-n-propionylmethane to precipitate the chelate complexes, only zinc, iron and hafnium were found in the precipitated zirconium chelate. The first two were ettectively removed by zone-melting. Though the separation of hafnium was poorer, the technique was efficient enough for practical purposes.     

Syntheses and X-ray crystal structures of zirconium(IV) and hafnium(IV) complexes containing monovacant wells-Dawson and Keggin polyoxotungstates

The syntheses and crystal structures of a series of zirconium(IV) and hafnium(IV) complexes with Dawson monovacant phosphotungstate [alpha2-P2W17O61](10-) and in situ-generated Keggin monovacant phosphotungstate [alpha-PW11O39](7-), which was obtained by a reaction of [alpha-PW12O40](3-) with Na2CO3, are described. K15H[Zr(alpha2-P2W17O61)2].25H2O (K-1), K16[Hf(alpha2-P2W17O61)2].19H2O (K-2), (Et2NH2)10[Zr(alpha-PW11O39)2].7H2O (Et2NH2-3), and (Et2NH2)10[Hf(alpha-PW11O39)2].2H2O (Et2NH2-4), being afforded by reactions in aqueous solutions of monolacunary Dawson and Keggin polyoxotungstates with ZrCl2O.8H2O and HfCl2O.8H2O followed by exchanging countercations, were obtained as analytically pure, homogeneous colorless crystals. Single-crystal X-ray structure analyses revealed that the Zr(IV) and Hf(IV) ions are in a square antiprismatic coordination environment with eight oxygen atoms, four of them being provided from each of the two monovacant polyanion ligands. Although the total molecular shapes and the 8-coordinate zirconium and hafnium centers of complexes 1-4 are identical, the bonding modes (bond lengths and bond angles) around the zirconium(IV) and hafnium(IV) centers were dependent on the monovacant structures of the polyanion ligands. Additionally, the characterization of complexes 1-4 was accomplished by elemental analysis, TG/DTA, FTIR, and solution (31P and 183W) NMR spectroscopy.     

The foam separation of zirconium(IV) from aqueous solutions

Summary The foam separation of zirconium(IV) from chloride solutions has been investigated over the 1.8–12 pH range using sodium lauryl sulphate or cetyl(trimethyl)ammonium bromide as collectors. The effects of gas flow rate, bubbling time, collector and zirconium(IV) concentrations, ageing of the metal ion, and ionic strength have been studied and the results are discussed in relation to the hydrolytic behaviour of zirconium(IV). Under optimum conditions,ca. 99.5% removal can be achieved.     

Hafnium(IV)-nitrilotriacetate and hafnium(IV)-fluoride complexes investigated using an ion-selective electrode

Models of plutonium solution chemistry in vivo require formation constants which are difficult to obtain but hafnium(IV) is biochemically similar t     

Sol-Gel Technique for Production of Spherically Granulated Zirconium(IV) Phosphate

A sol-gel technique for production of spherically granulated zirconium(IV) phosphate of Termoksid-3A brand is described. The method includes the following main stages: electrolysis of a zirconium(IV) chloride solution to give a sol of zirconium(IV) hydroxide, drop dispersion of the sol into an ammonia solution, conversion of gel-spheres of zirconium(IV) hydroxide into zirconium(IV) phosphate, and washing and drying of gel-spheres. The physicochemical and ion-exchange properties of the product obtained were studied.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 2, 2005, pp. 229–234.Original Russian Text Copyright © 2005 by Sharygin, Kalyagina, Borovkov.     

Preparation of Globular Zirconium(IV) Hydroxide by Sol-Gel Process

The sol-gel process of the preparation of globular zirconium(IV) hydroxide is described, which involves formation of zirconium(IV) hydroxide sol by electrolysis of zirconium(IV) chloride solution in a one-compartment cell to a Cl/Zr atomic ratio of less than 0.6, gelation of sol droplets in aqueous ammonia, treatment of gel spheres to remove electrolytes, and drying.     

Dynamic adsorption of uranium(VI) and zirconium(IV) on silica gel

Adsorption of uranium(VI) and zirconium(IV) from aqueous nitric acid solution on silica gel has been investigated under dynamic conditions. The influence of temperature, nitric acid concentration (pH), and solution flow rates was studied. If the nitric acid concentration in the solution is higher than 0.05 mol/l, then it is possible to achieve separation of uranium(VI) and zirconium(IV) by passing the solution through a column filled with silicagel.     

Spectrofluorimetric determination of titanium,zirconium and hafnium and their binary mixtures with biacetylmonoxime nicotinylhydrazone

The synthesis, characteristics and analytical applications of biacetylmonoxime nicotinylhydrazone are described. This compound forms fluorescent complexes with titanium(IV) (λ_ex = 430, λ_em = 540 nm), zirconium (λ_ex = 415 nm, λ_em = 505 nm) and hafnium (λ_ex = 400, λ_em = 500 nm) in an acidic medium. Titanium forms a 1:2 metal:ligand complex, whereas zirconium and hafnium form 1:2:1 metal:ligand:sulphate ternary complexes. Highly selective spectrofluorimetric methods for titanium (20–100 ng ml^?1), zirconium and hafnium (5–100 ng ml^?1) are proposed, and procedures for the analysis of binary mixtures of these ions are described.     

Synthesis of nanosized group IV borides in ionic melts of anhydrous sodium tetraborate

The preparation of nanosized Group IV metal diborides by reacting powdery titanium, zirconium, and hafnium with fine-grained boron in Na₂B₄O₇ ionic melts in the temperature range 600–850°C has been studied. Nanosized titanium, zirconium, and hafnium diborides are formed at temperatures of at least 750°C.     

A rapid procedure for the simultaneous determination of zirconium and hafnium in high-temperature alloys by means of a spectrophotometric masking approach

Data are presented for a refined spectrophotometric procedure for the simultaneous determination of zirconium and hafnium based on the combined effects of hydrogen peroxide, sodium sulphate, and excess of zirconium ion on the hafnium and zirconium complexes with Xylenol Orange in 0.2M perchloric acid. Isolation procedures for the hafnium/zirconium content of complex high-temperature alloys which result in an ionic substrate compatible with the spectrophotometric masking method were devised.     

Thermal properties of hafnium(IV) and zirconium(IV) β-diketonates

Five volatile hafnium(IV) and zirconium(IV) β-diketonates: hafnium(IV) acetylacetonate, hafnium(IV) trifluoroacetylacetonate, hafnium(IV) pivaloyltrifluoroacetonate, hafnium(IV) 2,2,6,6-tetramethylheptane-3,5-dionate and zirconium(IV) 2,2,6,6-tetramethylheptane-3,5-dionate were obtained, purified and identified. Thermal behavior of solid compounds was investigated by thermogravimetry (TG) and differential scanning calorimetry (DSC) in helium atmosphere and in vacuum. DSC method was also used for definition of thermodynamic characteristics of melting processes. Using the static method with quartz membrane zero-manometer and the flow method the temperature dependencies of saturated vapor pressure for hafnium(IV) complexes was obtained. The standard thermodynamic characteristics ΔH _T⁰ and ΔS _T⁰ of sublimation and evaporation processes were calculated from the temperature dependences of saturated vapor pressure.     

The study of the Cd(NH3) 4 2+ /Cd*(NH3) 4 2+ exchange reaction in hydrous oxides of zirconium(IV), silicon(IV) and tin(IV)

Kinetics of the exchange reaction of cadmium(II)-ammine complex ion using radio-active isotope¹¹⁵Cd in the same chemical form in hydrous oxides of zirconium(IV), silicon(IV) and tin(IV) has been studied. It has been found that the major contribution in the overall exchange process is from the surface of the exchanger particles. It has also been found that the rate of exchange follows the order: hydrous ZrO₂>hydrous SnO₂>hydrous SiO₂     

Solvent extraction of hafnium(IV) by N-benzoyl-N-phenylhydroxylamine

The extraction of hafnium(IV) tracer by N-benzoyl-n-phenylhydroxylamine (BPHA) from 1M perchloric acid has been investigated and stability constants have been calculated for the complexes Hf(BPHA)(i)((4-i)+) (i = 1cdots, three dots, centered4). It was found that variation of perchlorate concentration in the range 0.5-2.0M at constant acidity has no effect on the distribution of hafnium.     

Selective transport of zirconium (IV) and niobium (V) from hydrochloric media through a bulk liquid membrane

The selective transport of zirconium/niobium from hydrochloric medium has been investigated through a bulk liquid membrane (BLM) using tri-n-butyl-phosphate (TBP), tri-n-octylamine and dibenzo-18-crown-6 (DBC-6) as the extractants (carriers). The Optimization studies have been carried out by scrutinizing the effect of variables such as the hydrochloric acid concentration in the feed solution, membrane type and hydrochloric acid concentration in the strip solution using the Taguchi approach. The Quantitative transport of zirconium/niobium has been observed by 30% (v/v) TBP in 1200 min from the feed composed of a 9.0 M hydrochloric acid solution of Zr(IV), Nb(V) and lanthanide cations, while the transport of other cations, which have been presented along with Zr/Nb are less than 3% during the same time. Moreover, the possible mechanism of Zr(IV)/Nb(V) ion transport through the BLM has also been discussed and the results show a consecutive, irreversible second-order reaction at the interfaces. Transfer kinetics studies show that niobium transfer process exhibits slightly faster kinetics than zirconium.     

Titrimetric assay of ofloxacin in pharmaceuticals using cerium(IV) sulphate as an oxidimetric reagent

Two titrimetric methods which are simple, rapid, cost-effective and eco-riendly are described for the determination of ofloxacin (OFX) in bulk drug and in tablet formulations based on the oxidation of OFX by Ce(IV) sulphate. In direct titrimetry (method A), the acidified solution of OFX is titrated directly with Ce(IV) sulphate using ferroin as indicator, and indirect titrimetry (method B) involves the addition of known excess of Ce(IV) sulphate to an acidified solution of OFX followed by the determination of unreacted oxidant by back titration with ferrous ammonium sulphate (FAS) using the same ferroin indicator. In both the methods, the amount of Ce(IV) sulphate reacted corresponds to OFX concentration. Method A and method B permit the determination of OFX over the concentration range of 1.5?C15 mg in both the methods and the quantitation is based on a 1: 5 reaction stoichiometry (OFX: Ce (IV) sulphate). The methods were statistically evaluated by calculating percent relative error (% RE) for accuracy and percent relative standard deviation (% RSD) for precision, and were applied successfully to the determination of OFX in tablets with mean recoveries in the range of 96.50?C98.42%. No interference was observed from common additives found in pharmaceutical preparations. The accuracy and reliability of the methods were further ascertained by performing recovery tests s standard-addition technique.     

Analysis of mixtures of hafnium and zirconium by the methylthymol blue-hydrogen peroxide method

The reaction of hydrogen peroxide with the zirconium(IV) and hafnium(IV) Methylthymol Blue complexes (MeMTB) has been investigated. The conditional stability constants of the Zr(IV) and Hf(IV) complexes with hydrogen peroxide [K'(Me(H(2)O(2)))] were determined spectrophotometrically. The K'(Me(H(2)O(2))) values found, which depend on the acidity, are 3.91 x 10(2) 3.24 x 10(2), 2.63 x 10(2) at [HCl] = 0.2, 0.3, 1.0M respectively for Me = Zr(IV) and 0.828, 0.523, 0.319 for Me = Hf(IV). The ratios of the conditional stability constants, K'(Me(H(2)O(2)))/ K'(MeMTB), are: 5.52 x 10(-4), 5.79 x 10(-4), 8.23 x 10(-4) for Me = Zr(IV) and 2.08 x 10(-6), 2.74 x 10(-6), 1.48 x 10 (-5) for Me = Hf(IV) at the three acidities. The maximum of the ratio of the relative conditional stability constants is obtained in 0.2M hydrochloric acid. The conditions which should be complied with for the determination of hafnium in the presence of zirconium are discussed. The results were compared with those obtained by the Xylenol Orange-hydrochloric acid method. They are superior for samples containing less than 20 mole% of hafnium in admixture with zirconium.     

Adsorption of anions to zirconium(IV) and titanium(IV) chemically immobilized on gel-phase

Adsorption behaviors of 25 anions to zirconium(IV) and titanium(IV) chemically immobilized on a gel-phase were studied by ion chromatography and by batch adsorption experiments. The affinities of Zr(IV) to iminodiacetate as an anchoring group and to anions as a sample are much stronger than those of Ti(IV). On a Zr(IV) column, fourteen anions showed no retention, four anions showed pH-dependent retention in a low pH region, and seven anions were irreversibly adsorbed at pH <7. In the last group, fluoride was adsorbed both by the ligand exchange mechanism and the addition mechanism, while phosphate, arsenate and selenite were only by the ligand exchange mechanism. The structures of the adsorbed species are discussed.     

Spectrophotometric determination of hafnium(IV) with 1-(2-pyridylazo)-2-naphthol

Summary The red complex formed between hafnium(IV) and 1-(2-pyridylazo)-2-naphthol (1 2) at pH 4.0 is used for Spectrophotometric determination of hafnium., the absorbance being measured at 545 nm. Beer's law is obeyed for hafnium concentration of 0.2 to 3.6g per ml. Molar absorptivity is 3.86×10⁴ and Sandell sensitivity is 0.0046g per cm². Hafnium has been determined in the presence of 6-fold amounts of zirconium. The relative standard deviation is ± 1.0%.

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Zusammenfassung Der rote, bei pH 4,0 sich bildende Komplex mit 1-(2-Pyridylazo)-2-naphthol (1 2) dient zur Bestimmung von Hafnium (IV). Seine Extinktion wird bei 545 nm gemessen. Zwischen 0,2 und 3,6g Hf/ml ist das Beersche Gesetz gültig. Hafnium läßt sich in Gegenwart der sechsfachen Menge Zirkonium bestimmen. Die relative Standardabweichung beträgt ± 1,0%.

     

Adsorption behavior of Zr, Hf, Nb, Ta and Pa on macroporous anion exchanger in NH4SCN/HClO4 and NH4SCN/HF media

The possible use of thiocyanate and ammonium thiocyanate-hydrofluoric acid mixtures for quantitative anion exchange separation of zirconium from hafnium and niobium from tantalum and protactinium has been investigated. Distribution coefficients of zirconium(IV), hafnium(IV), niobium(V), tantalum(V) and protactinium(V) on macroporous BIO-RAD AGMP1 resin over a wide range of SCN and SCN/HF concentrations have been determined. The simultaneous presence of these two complexing agents causes a strong decrease of the adsorption phenomena.