Nitriloacetate complexes

In the case of nitriloacetate complexes, the changes in enthalpy have been explained in terms of the consequences of lanthanide contraction (i) increasingly exothermic complexation with decreasing crystal radius and (ii) decreasing exothermic complexation with decreasing hydration of the cation [22]. In the case of dipicolinates and diglycolates these effects become small as the coordination sphere loses water molecules. Thus AH3 and A S3 vary more regularly than A Hi and A Si. 

Trott, T., R. W. Henwood, and C. H. Langford. 1972. Sunlight photochemistry of ferric nitriloacetate complexes. Environ. Sci. Technol. 6, 367-368. 

Various complexes of transition metals and nitriloacetic acid Various diols and diacids 186... 

The composition of I, and possibly its structure, may be deduced by identifying Q. Certain examples from peroxide chemistry will illustrate the scope of the method. The reactions of ferrous(nitriloacetate) and ferrous(ethylenediamine-N,N -diacetate) with hydrogen peroxide are complicated processes.1 A particular scavenger T did indeed divert the reaction at high concentrations of T. The required levels of T were, however, much higher than those that would have been needed to trap the hydroxyl radical, HO. It is thereby ruled out. With this and with spectroscopic evidence, a reactive hypervalent iron complex was suggested as the intermediate. 

Precipitation of Fe(IIl) compounds from acid solutions as the pH increases above 2.2 is a particular problem. Complexing agents that have been used include 5-sulfosalicylic acid and citric acid (136) dihydroxymaleic acid (137) ethylenediaminetetraacetic acid (138) lactic acid (138) blends of hydroxylamine hydrochloride, citric acid, and glucono-delta-lactone (139) nitriloacetic acid blends of citric acid and acetic acid lactic acid and gluconic acid (140). 

Citric acid and nitriloacetic acid (NTA) lanthanide complexes were used in the earliest ion exchange separations of lanthanides from fission product mixtures (Kf = 3.2 for Ce(H3 Cit.)3 and Kf = 10.8 for CeNTA2) (Sillen and Martell, 1964). More recently such polyamino-polycarboxylic acids as ethylenediaminetetraacetic acid (EDTA), 1,2-diaminocyclohexaneacetic acid (DCTA), and diethylenetriaminepentaacetic acid (DTPA) have been prepared. Their lanthanide complexes are very stable (Table 3) and have been widely used in analysis and separation of lanthanide mixtures. They have also been used experimentally to remove internally-deposited 144Ce and other radioactive lanthanide nuclides from animals and man (Foreman and Finnegan, 1957 Catsch, 1962 Balabukha et al., 1966 Palmer et al., 1968 among others). 

Kinetics and activation parameters for NO reactions with a series of iron(II) aminocarboxylato complexes have been obtained (Table II) in aqueous solution (31). Rate constants for these reactions ranged from 105 to 108M-1s-1 for the series of iron(II) complexes studied. The reactions of NO with Fen(edta) (edta = ethylenediaminetetraacetate) and Fen(Hedtra) (Hedtra = hydroxyethylenediaminetriacetate) yielded activation volumes of +4.1 and +2.8 cm3 mol-1, respectively and were assigned to a dissociative interchange (Id) mechanism (31b). All of the iron(II) aminocarboxylato complexes studied followed a similar pattern with the exception of the Fen(nta) (Nta = nitriloacetic acid) complex which gave a AV value of —1.5 cm3 mol-1. The reaction of this complex with... 

In common with other sequential extraction procedures, the BCR scheme suffers from a degree of non-specificity (Whalley and Grant, 1994 Coetzee et d., 1995) and redistribution of analytes during extraction (Raksasataya et d., 1996). Some success in limiting lead redistribution by addition of cryptand 2.2.2 or nitriloacetic acid to the acetic acid in Step 1 has been reported, but the effectiveness of the complexing agent was found to be strongly dependent on the bulk composition of the model soil system studied (Raksasataya et d., 1997). 

The interference caused by chloride ion, Fe(III), and Cu(II) in the determination of nitriloacetic acid and EDTA in natural waters was removed by pre-treating samples (pH > 4) with cation exchangers. Some samples required additional treatment with an anion exchanger (pH 1). The analytes were complexed with Bi (III) before being determined by differential pulse anodic stripping voltammetry at the hanging mercury drop electrode (vs. Ag/AgCl. The detection limit was 0.1 pg/L for EDTA. 

Such experiments show that oxalate, tartrate, and citrate give fairly strong complexes, and indeed these mixtures do not suffer quite such rapid oxidation as the other systems (57, 70). Stability constants for the complexing of U(III) by acetate, 2-hydroxy-2-methylpropionate, nitriloacetate, trans-cyclohexyl-1,2-diaminotetraacetate, ethylenedi-amine tetraacetate, and diethylenetriamine pentaacetate have been reported, but no pure compounds have been isolated (71). Thiocyanate also accelerates oxidation of the uranium, but the blue complex that is formed can be extracted with triethyl phosphate, tributyl phosphate, or better, trioctyl phosphine oxide the organic extract decomposes only slowly (45, 72). 

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). 

Triethylenetetraaminehexaacetic acid forms (MH2L)°, and tetra-ethylenepentaminepentaacetic acid forms (MH4L ), in 0.5-2 M HCIO4. These complexes are about as stable as the nitriloacetic acid complex (171). The stability constant for the 1 1 complex with 2-hydroxytri-methylene-l,3-bis(iminodiacetic) acid is logA = 23.58 with (2,2 -diaminodiethyl ether)-A,A,A, A -tetraacetic acid [2,2 -oxybis(ethyl-... 

Intorre and Martell (237) have also studied the formation of mixed chelate species in which the zirconium 1 1 complex with the hexa-dentate chelating ligands, ethylenediaminetetraacetic acid, iV-hydroxy-ethylethylenediaminetriacetic acid, and m7 s-cyclohexanediaminetetra-acetic acid, are shown to take up one mole of the bidentate ligands, l,2-dihydroxybenzene-3,5-disulfonate l,8-dihydroxynaphthalene-3,6-disulfonate 8-hydroxyquinoline-5-sulfonate, and acetylacetone (except ZrHEDTA), to form 8-coordinate 1 1 1 species. At least for the zir-conium-EDTA-l,2-dihydroxybenzene-3,5-disulfonate species, there is evidence for dimerization (230). Additionally, the Zr EDTA complex reacts with one mole of the bidentate ligands, 5-sulfosalicyclic acid, alizarin sulfonate, citric acid, and lactic acid to form 1 1 1 complexes tartaric acid and pyrophosphate ions form complexes which could not be identified. The zirconium-nitriloacetic acid complex in the presence of two moles of oxalic acid or l,2-dihydroxybenzene-3,5-sulfonate also forms 1 1 1 complexes in solution. 

Both types of oxidation are reported for oxidation by "OH of the first-row bivalent metal complexes containing ethylenediaminetetra-acetatc (edta) or nitriloacetate (nta) ligands. For M = lSIi i, Cu or Fe the metal centre is oxidized directly, whereas for M = Zn, Mn or Co hydrogen-atom abstraction from the ligand occurs. With [Co (edta)] partial oxidation of the metal centre is observed. All these reactions have rate constants in the range (2—5)xl0 M-is- ... 

The second approach is to disperse Co and Ni on the particular sites of M0O2. In practical catalysts, EDTA (ethylenediaminetetraacetic acid), NTA (nitriloacetic acid) complexing agents can be applied to prevent interaction of Co(Ni) ions with the AI2O3 surface. 

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