Metal ions zirconium complexes

Zirconium and other nonmultivalent metal ions can act as promoters in some manner not currently clearly defined. For zirconium, the effect may be related to changes in monomer—dimer equitibria of Co(II) complexes (2,204,205). 

Since TCs form highly fluorescent chelates with metal ions at the appropriate pH value, their complexation with 5% zirconium chloride solution added postcolumn to the eluate from HPLC was used for fluorescence detection. The highest yield of fluorescence was observed at pH 2.0 therefore a pH adjustment of the mobile phases was necessary (25-27). Moreover, using a mobile phase of pH 2.0, the formation of both the C4 epimers and anhydroTCs are minimized. 

Catalysis by metal ions is reported for molybdenum and zirconium but not for a number of other cases. With chromium(III), where complexing is well established, a marked decrease in reaction rate occurs . 

To avoid interference by foreign ions in the reaction of fluoride with the Zr-ECR complex, preliminary distillation of fluoride is recommended. Sulphate, which complexes zirconium, and metal ions forming stable fluoride complexes, interferes. 

Zr has been separated from Hf with the use of TBP in 4 M HNO3 [21]. These metals can also be separated in thiocyanate medium with the use hexanone as extractant. Ion-pairs of thiocyanate complexes of Zr and Hf with antipyrine and DAM were separated by extraction (isoamyl alcohol, 1,2-dichloroethane) from other metals [22]. Zirconium can be extracted first with mesityl oxide from a 4 M solution (in HNO3 and NaNOs), then hafnium is extracted from 0.4 M HNO3 and 2 M NH4SCN medium [23]. 

Zirconium (and hafnium) have been separated from other metals by means of strongly acidic cation-exchangers, use being made of HCl [34], HCIO4 [35], and oxalic acid [36] media. In formic acid medium, metal ions form positive ions, except for Zr which produces anionic complexes [37]. Zirconium has been separated from hafnium on cation-exchangers by virtue of the differences in stability of their formate [38] and sulphate [39] complexes. Chelating resins have also been applied for separation of Zr and Hf [39]. 

The above reaction is also catalysed by several transition metal ions and metal complexes provided the coordination sphere is accessible for H Oj and/or HOj. In our laboratory catalytic activity of transition metal ions and metal complexes supported on various zirconium based inorganic ion exchangers has been studied in detail for the disproportionation of hydrogen peroxide ". 

When the organic complexing agent in the solvent is nearly all combined as extracted complexes, further increase in concentration of the complex-forming metal ions in the aqueous phase will cause the distribution coefflcient for metal extraction to decrease. This phenomenon has been observed for uranyi nitrate [G3, Ml, M2] and for zirconium and hafnium nitrates [H4] when extracted by TBP in kerosene. 

Cahnagite indicator gives a somewhat improved end point over Eriochrome Black T for the titration of calcium and magnesium with EDTA. It also has a longer shelf life. Xylenol orange is useful for titration of metal ions that form very strong EDTA complexes and are titrated at pH 1.5 to 3.0. Examples are the direct titration of thorium(IV) and bismuth(III), and the indirect determination of zirconium(IV)... 

The reaction of zirconium and hafnium with thiocyanate ion was studied spectrophotometrically 214) at thiocyanate concentrations over the range 0.002 to 0.18 M, free perchloric acid concentrations of 0.1 to 0.8 M, and at high metal ion concentrations. Experiments were interpreted to show that a series of complexes from MNCS + to M(NCS)4 were formed. At high thiocyanic acid concentrations, the zirconium is converted to an anionic species much more readily than the hafnium. 

A comparable constant for hafnium was not calculated owing to a lack of data for hydroxo and chloro complexing. A similar value has been obtained for the same constant by Ermako et al. (169, 170) by ion exchange techniques under vastly different conditions, namely, metal ion concentrations of 2 x 10 mole/liter and 0.23 M perchloric acid. Equilibrium constant values of logAz, = 20.8 and ogK = 20.3 were obtained. At high metal ion concentrations (0.01-0.1M) there is evidence for formation of a 2Zr NTA complex in which hydrolyzed zirconium atoms are bridged by the nitriloacetate ion (172). 

The reaction of zirconium(IV) with 5-sulfosalicylic acid has been studied by Babko (37) and Deich (142), with the latter concluding that only a highly dissociated species exists in solution. In contrast to these observations Sheka (284) reports that in a zirconium (hafnium) solution of 0.02 M metal ion and 6.1 M hydrochloric acid, a 1 1 complex is... 

Chromotropic acid (l,8-dihydroxynaphthalene-3,6-disulfonate) reacts with zirconium(IV) to form a 1 1 complex. The apparent equilibrium constant for this system at pH 2.0 and at a metal ion concentration of 5 X 10 M n 0. M KCl, was calculated to be logAzr = 3.63 (466). The initial report (98) of little or no reaction appears to be incorrect. A nitroso derivative of this ligand reacts with zirconium(IV) to give a red-violet precipitate in weak acid solution (535). 

Although alizarin-S (l,2-dihydroxyanthraquinone-3-sulfonate) has been used (162) for many years for the detection and estimation of zirconium and hafnium, the composition of the product formed in this system is still uncertain. Eecent studies on hafnium (43) and zirconium (317, 419) complex formation by spectrophotometric methods led to the conclusion that the zirconium 1 1 complex exists in the pH range 1.0-1.8 at a metal concentration of 1 x 10 M. Below that pH no complex could be observed and above that pH only suspensions were obtained. Hafnium, on the other hand, is said to form the 1 2 ligand complex at metal ion concentrations of (2 to 4) x 10 mole/liter over the pH range 1.0 to 4.0. A stability constant of 10.3 0.3 was reported for this species. The 1 1 complex of zirconium is extractable with i-butanol (149a). 

Equilibrium constants for the formation of nitrate complexes at hydrogen ion concentrations of 2 and 4 M and metal ion concentrations of 5 X 10 M or less, were determined using ion exchange techniques (353, 465) (Table XVIII). Activity coefficient data for aqueous zirconium and hafnium species are scarce, although there is one report (319) of activity coefficients for metal nitrate solutions as determined by the isopiestic method. 

Quantitative studies (464, 463) by ion exchange techniques on the complexing of the metal ions with sulfate ions, show that hafnium is less strongly complexed than zirconium (Table XIX). At lower hydrogen ion concentrations, the hydrogen ion dependence of the complexing is consistent with the reaction... 

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