Complexones metal complexes

Complexometric titrations, 2,782 Complexones, 2,777-791 applications, 2,790 macrocyclic, 2,789 metal complexes... 

Anderegg, G. Amaud-Neu, F. Delgado, R. Felcman, J. Popov, K. Critical evaluation of stability constants of metal complexes of complexones for biomedical and environmental applications. PureAppl. Chem. 2005, 77 (8), 1445-1495. 

MOLECULAR INCLUSION REACTIONS BETWEEN METAL COMPLEXES OF AZO COMPLEXONS AND a-CYCLODEXTRIN IN AQUEOUS SOLUTION... 

ABSTRACT. Kinetics of the molecular inclusion reactions of the azo complexons and their metal complexes with a- and 3-cyclodextrins (a- and 3-CD ) were studied in aqueous solution by means of a spectrophotometric and a stopped-flow method. The acid dissociation of the azo complexons was regulated by the inclusion with CD. Two-step process was observed for the interaction of a-cyclodextrin with LH species of the azo complexons and with the metal complexes. 

Fig. 2), were found to form 1 1 inclusion complexes with a- and 3-CD from the spectrophotometric measurements. Figure 3 shows the spectral change in the formation of the inclusion compound of NiLH - (R = Pr) with a-CD Table 1 shows the stability constants of the inclusion complexes of the azo complexons and their metal complexes with a- and 3-CD ... 

Table I. The Stability Constants of the Inclusion Complexes of the Azo Complexons and their Metal Complexes with o- and B-CO...

The method based on the precipitation of peroxometalate precursors enables to achieve additional purification during the process. Thus, the addition of complexonates, such as OEDP or EDTA, which form stable complexes with some polyvalent metals, prevents co-precipitation of the main impurities such as Fe, Co, Ni, Mn, Mg, etc., which in turn significantly increases the purity of the final product. Enhanced purification can also be achieved by recrystallization of the precursor. Particularly, the precipitation of ammonium peroxofluorometalates, such as ammonium peroxofluoroniobate ((NH4)3Nb04F4), as a primary precursor, leads to significant reduction of the titanium contamination. Ammonium peroxofluoroniobate, (NH4)3Nb04F4, is... 

Re-crystallization also leads to a significant reduction in the level of carbon and oxygen impurities however, the reduction of cationic impurities is usually not efficient. To prevent co-precipitation of complex fluorotantalates of polyvalent metals, some suitable complexonates are added to the solution. 

The availability of the trace metals is easily determined without any of the above risks, and the results used to assess both deficiencies and toxici-ties. The metals need to be removed from the sites where they are bound to the soil particles by use of an even stronger binding agent than the soil. This is achieved with two possible complexing reagents EDTA and DTPA. They are a class of chemicals known as complexones, which form complex molecules with metals in a cage-like structure called a chelate. 

Fe(Hedta), Na2Fe(edta) Zn2+, Mn2+, Mg2 edta complexes see Chapter 62.1) (iv) removal of poisoning or radioactive metal ions from the body (Cd2+ NaCa(edta) Pb2+ Na3Ca(dtpa) see Chapter 62.2). Complexones have been used in the form of " Tc complexes to obtain scintigraphic imaging of human organs in diagnostic nuclear medicine (see Chapter 65). 

The N,N-, N,0-, and 0,0-metal-cyclic structures can be found in these chelates. The first structures are characteristic for di- and triamine ligands (430a, 431), the second and third ones are formed in the complexes of all three types of ligand systems described above (429-431). In principle, the same situation as mentioned before (Sec. 2.2.4.2), for di- and triamine chelates, is observed for N,N-coordination. The 0,0-coordination is mostly present in structures formed only by carboxyl groups (compare with the data of Sec. 2.2.4.4). Here the most propagated structures in coordination compounds are 277, 279, and 280, for example, in complexonates of the triamine series [764], In the case of N,0-metal-binding, the most propagated structures are those with five (432) and six-member (433) metal-cycles [756-760,762-767] ... 

These complexones, as they are often called, form very stable water-soluble complexes with even the Gp. IIA metals (p. 263). With Gp. Ill metals the stability of the complexes is even more marked, indeed a pH of 13 can be reached without precipitating the rare earth oxides when (a) or (b) is present (p. 431). The stabilities are associated with the formation of chelate rings. 

The linkage of chemical processes in thermodynamic cycles arising from the definition of the state functions (the state of a system is independent on the way on which it was reached) is a great virtue that can immediately be exploited by calorimetry. In this sense, making use of the protonation properties is just a special case in the much broader field of competition analysis [25]. In fact, any molecular species that is expelled or taken up by the host as a result of binding, the guest of interest may serve as a probe in calorimetric determinations. Prominent examples include the binding or release of metal cations from proteins (e.g. Ca +, Mg +) which can be linked to their complexation by complexones (ethylenediaminetetra-acetic acid (EDTA) or similar). 

The direct method for determining traces of fluoride is based on the coloured ternary complex formed by fluoride with Alizarin Complexone and lanthanum or cerium(III). Fluoride ions form stable complexes with some multivalent metals, namely Zr, Th, Ti, Fe(III), and Al. The colour changes resulting from the reactions of fluoride with coloured complexes of these metals provide indirect methods for the determination of fluoride. Examples of these methods are the Eriochrome Cyanine R-zirconium method, and the (less sensitive) Fe(III)-sulphosalicylate method. 

Yellow Alizarin Complexone (AC) reacts with La or Ce(III) ions to form a red chelate, which, in turn, reacts with fluoride ions to give a blue ternary complex (Alizarin Fluorine Blue). The fluoride anion displaces the water molecule bound with the metal ion (formula 20.1) [19,20]. Other suggestions regarding the mechanism of this reaction have also been proposed [21,22]. 

---