Sodium ion complexes with ethylenediaminetetraacetic acid

Abstract

The crystal structures of tetrasodium (1,2-ethanediyldinitrilo)tetraacetate pentahydrate and disodium dihydrogen (1,2-ethanediyldinitrilo)tetraacetate dihydrate have been determined. Na ions prefer to act as bridges between different edta ligands and only in the tetrasodium salt is the edta ligand hexadentate to one Na ion. Na ions display seven-coordination, when coordinated to one edta ligand (distorted pentagonal bipyramid), and six-coordination, when linked to several edta ligands (from distorted octahedral to trapezoidal bipyramidal geometry). An Na ion in the tetrasodium salt shows five-coordination, because the sixth site is blocked by the edta ligand. H atoms in the disodium salt are linked to amine groups. Only these two salts can be obtained on varying the pH of an aqueous solution containing Na ÷ and ethylenediaminetetraacetic acid. The first is obtained around pH 2-5 and the second around pH 12. CommentThe chelating capacity of the ethylenediaminetetraacetato (edta) ligand has attracted widespread interest and the literature contains a large number of Acta Crystallographica Section C ISSN 0108-2701 ©1993REGULAR STRUCTURAL PAPERS 1453 studies on the crystal structures of metal complexes with this ligand, as well as spectroscopic and electrochemical studies (Hughes & Martell, 1953;Martell & Plumb, 1952;Scharzenbach & Freitag, 1951), aimed at determination of the behaviour of edta. Crystal structure studies of edta complexes with Na have been carried out (Solans, Font-Altaba & Garcia-Oricain, 1984; Nassimbeni, Wright, van Niekerk & MacCullum, 1979;Templeton, Templeton, Zalkin & Ruben, 1982; Templeton, Templeton & Zalkin, 1985;Solans, Gali, Font-Altaba, Oliva & Herrera, 1988;Lee, 1967;Porai-Koshits, Novozhilova, Polyniva, Filippova & Martynenko, 1973;Pozhidaev, Polynova, Porai-Koshits & Dudakov, 1974), but always on complexes containing a second metal. It is the second metal that is coordinated to the edta ligand in all the crystal structures determined. In this paper we report the behaviour of the Na ion when it is alone with the edta ligand, in order to contribute to the understanding of the chemistry of NanHmedta 4-n-m complexes. The Na salts of ethylenediaminetetraacetic acid are interesting in the biochemical and medical field in spite of their toxic effects.The syntheses of the title compounds were carried out in aqueous solutions of Na2CO3 and Haedta at controlled pH; the acidity of the solutions was controlled by addition of HC1 or piperazine. Within the pH range 0.5-14, only two compounds were obtained. Neither of the dry crystalline products obtained decomposes detectably on exposure to laboratory air. From pH-meter analysis we conclude that only the disodium and tetrasodium salts can be obtained from ethylenediaminetetraacetic acid in aqueous solution. This result disagrees with those of Palaty (1963) and does not support the existence of a commercial product with formula Hedta.Na3. Powder diffraction analysis of the commercial product shows that it is an equimolar mixture of the dis...

New coordination modes in potassium edta salts: K2[H2edta]·2H2O, K3[Hedta]·2H2O and K4[edta]·3.92H2O

“…4). The overall conformations of the anions in (III) are comparable with those of the corresponding Y 4À anion in Na 4 [edta]Á5H 2 O (Font- Bardia et al, 1993) and of the HY 3À ion in (II), although the analogous acetate arms are not arranged in exactly the same manner. Both edta anions in compound (III) chelate K + via six ligating atoms (two N and four carboxylate O atoms), which results in the formation of five-membered rings at both K1 and K2, similar to the metal-organic compounds m268 Krawczyk and Lis Three K + -edta hydrates Acta Cryst.…”

“…This anion is also found in Rb 2 [H 2 edta]Á2H 2 O (Cotrait, 1970) and Na 2 [H 2 edta]Á2H 2 O (Font- Bardia et al, 1993). The H 2 Y 2À ion in (I) has a different overall conformation in relation to the relevant anions in the dirubidium and disodium edta salts (Cotrait, 1970;Font-Bardia et al, 1993), in which NCH 2 CH 2 N units adopt an antiperiplanar conformation and the acetate arms have a different geometry. However, the anion in (I) has similar overall geometry to the Y 4À ligand in complexes such as Li (Lind et al, 1964;Weakliem & Hoard, 1959;Pozhidaev et al, 1973;Barnett & Uchtman, 1979).…”

“…Another anionic form of edta is H 2 Y 2À reported in salts of Na, K and Rb (Font-Bardia et al, 1993;Cotrait, 1969Cotrait, , 1970. Therefore, it seemed an attractive idea to obtain and structurally characterize crystalline potassium edta salts, especially the tripotassium edta salt, (II), which is an example of a new coordination mode of this edta anion to a metal centre, and tetrapotassium edta, (III), which is analogous to the Na 4 YÁ5H 2 O salt (Font-Bardia et al, 1993). Potassium edta salts are used as anticoagulants for haematologic examinations of human and animal blood (Balakrishnan et al, 2006;Hekimsoy et al, 2004;Vatn et al, 2000;Olsen et al, 2001;Sanchez-Migallon Guzman et al, 2008).…”

A Comparative Study of [CaEDTA]2– and [MgEDTA]2–: Structural and Dynamical Insights from Quantum Mechanical Charge Field Molecular Dynamics

“…10,23 Even a seven-fold coordination has been reported in the case of Ca(II), Mg(II), Na(I), Co(III) and Fe(III), where EDTA adapts a six-fold coordination and an additional water molecule is present in the coordination sphere of the metal. [12][13][14]18,19,24 Regarding the EDTA complexes of Ca and Mg generally a hexadentate six-fold coordination of EDTA with a distorted octahedral conformation has been reported. 7,15 Nevertheless, seven-fold coordination spheres adopting a pentagonal bi-pyramidal conformation have been mentioned in the literature.…”

“…2,30 Because of the manifold ways EDTA is used on a daily basis, it is important to investigate the structural and dynamical properties of EDTA complexes in the aqueous medium. In fact, many studies have been carried out so far to characterise metal chelating EDTA in the solid 5,[10][11][12][13][14][15][18][19][20]23,31 and liquid phase [6][7][8][9]16,17,[20][21][22]24,25,32 using a number of different experimental methods including NMR, IR/RAMAN, X-RAY and EXAFS/XANES spectroscopy. It was concluded that the coordination behaviour of EDTA strongly depends on the nature of the complexed metal as well as on the pH value of the medium.…”