Ethylenediaminetetraacetate ion EDTA

Let Y denote the ethylenediaminetetraacetate ion EDTA. With a metal ion M, it can form a complex MY, a protonated complex MHY, a hydroxo complex MY(OH)n, and a mixed complex MYX, where X is a monodentate ligand. The complexation reactions involved are... 

The ethylenediaminetetraacetate ion, [EDTA] , is an important polydentate ligand that has six donor atoms. It can wrap around a metal ion using all six donor atoms, as shown in FIGURE 23.12, although it sometimes binds to a metal using only five of its donor atoms. 

Ethylenediaminetetraacetate ion (EDTA) is a ligand that bonds through six of its atoms. 

Some ligands, called polydentate ligands, can donate even more than two electron pairs (from more than two atoms) to the metal. The most common polydentate ligand is the ethylenediaminetetraacetate ion (EDTA" ) shown below. 

The utility of complexation titrations improved following the introduction by Schwarzenbach, in 1945, of aminocarboxylic acids as multidentate ligands capable of forming stable 1 1 complexes with metal ions. The most widely used of these new ligands was ethylenediaminetetraacetic acid, EDTA, which forms strong 1 1 complexes with many metal ions. The first use of EDTA as a titrant occurred in... 

The lanthanides form many compounds with organic ligands. Some of these compounds ate water-soluble, others oil-soluble. Water-soluble compounds have been used extensively for rare-earth separation by ion exchange (qv), for example, complexes form with citric acid, ethylenediaminetetraacetic acid (EDTA), and hydroxyethylethylenediaminetriacetic acid (HEEDTA) (see Chelating agents). The complex formation is pH-dependent. Oil-soluble compounds ate used extensively in the industrial separation of rate earths by tiquid—tiquid extraction. The preferred extractants ate catboxyhc acids, otganophosphoms acids and esters, and tetraaLkylammonium salts. 

Chromium (ITT) can be analy2ed to a lower limit of 5 x 10 ° M by luminol—hydrogen peroxide without separating from other metals. Ethylenediaminetetraacetic acid (EDTA) is added to deactivate most interferences. Chromium (ITT) itself is deactivated slowly by complexation with EDTA measurement of the sample after Cr(III) deactivation is complete provides a blank which can be subtracted to eliminate interference from such ions as iron(II), inon(III), and cobalt(II), which are not sufficiently deactivated by EDTA (275). 

Knabe has introduced mercuric acetate plus ethylenediaminetetraacetic acid (EDTA) as an oxidizing agent for tertiary amines (74). The solvent employed is 1 % aqueous acetic acid. In this system, the complexed mercuric ion is reduced to elemental mercury. Knabe s studies have centered on the... 

Ligands bite at one or more points. Chelants bite at two or more points, so all ligands are not necessarily chelants. Chelants forming water-soluble complexes with metal ions are called sequestrants (but not all sequestrants are chelants). The most commonly employed BW chelant, ethylenediaminetetraacetic acid (EDTA) produces coordination complexes with four points of attachment and is termed a tetraden-tate ligand. 

The oxidation of ethylenediaminetetraacetic acid (EDTA) by Pu02 and Np02 to give the quinquevalent metal ions in perchlorate media is first-order in both oxidant and substrate and the stoichiometry, d[M(VI)]/ A [EDTA], is 6 in both cases. The Np(VI) oxidation shows a fractional dependence on acidity and has parameters E = 23.0 kcal.mole , AS — 12.3 eu. 

Okemgbo A.A., Hill H.H., Metcalf S.G., and Bachelor M., Metal ion interferences in reverse polarity capillary zone electrophoretic analysis of Hanford Defense Waste for ethylenediaminetetraacetic acid (EDTA) and N-hydroxy-ethylethylenediaminetriacetic acid (HEDTA), Anal. Chim. Acta, 396,105,1999. 

In most systems, K2 < K[. Otherwise (e.g. the first two dissociation steps for ethylenediaminetetraacetic acid—EDTA) the first hydrogen ion capable of dissociation is stabilized by the presence of the second one and can dissociate only when the second begins to dissociate. As a result both hydrogen ions dissociate in one step. 

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). 

A common reagent used in complexometric titrations is ethylenediaminetetraacetic acid (EDTA). It is often used to determine the concentration of metal ions present in a solution. 

Numerous d cobalt(III) complexes are known and have been studied extensively. Most of these complexes are octahedral in shape. Tetrahedral, planar and square antiprismatic complexes of cobalt(lII) are also known, but there are very few. The most common ligands are ammonia, ethylenediamine and water. Halide ions, nitro (NO2) groups, hydroxide (OH ), cyanide (CN ), and isothiocyanate (NCS ) ions also form Co(lII) complexes readily. Numerous complexes have been synthesized with several other ions and neutral molecular hgands, including carbonate, oxalate, trifluoroacetate and neutral ligands, such as pyridine, acetylacetone, ethylenediaminetetraacetic acid (EDTA), dimethylformamide, tetrahydrofuran, and trialkyl or arylphosphines. Also, several polynuclear bridging complexes of amido (NHO, imido (NH ), hydroxo (OH ), and peroxo (02 ) functional groups are known. Some typical Co(lll) complexes are tabulated below ... 

Radium in hydrochloric acid solution may be separated effectively by ion exchange methods using cation exchange-resin columns. A weak HCl solution is passed through the column. The absorbed metals on the ion-exchange column are eluted with ethylenediaminetetraacetic acid (EDTA) at pH 6.25 or with ammonium citrate at pH 7.8. With either eluant, radium is eluted last, after removing barium and then lanthanum, calcium, magnesium, and other metals. 

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