EDTA tetraanion

The introduction of conditional stability constants permits us, from a theoretical standpoint, to treat a complexation equilibrium to which are superimposed other equilibria of any nature as if it were alone, at least in some conditions. Conditional stability constants were introduced by G. Schwarzenbach 1957 to take into account acido-basic phenomena occurring simultaneously with complexation phenomena. The first case for which conditional stability constants were inuoduced concerned the titration of some metallic ions with EDTA tetraanion. The scope of their application scope was extended to other parasitic phenomena by A. Ringbom 1959. 

In a typical titration of a metal cation with EDTA tetraanion, the solution in the reaction vessel, among other species, contains the formed complex [MEDTA] " +, free remaining metallic ions M +, hydroxo complexes resulting from their hydrolysis, and some complexes formed with a possibly present buffer. Usually, the latter are those formed with ammonia and with acids-alcohols (see Chap. 28). 

Vanadium(V) oxide is amphoteric, dissolving in alkali to give salts of tetrahedral VO " anion, and in acid to give V02. The latter cation is almost certainly cis-[V02(H20)4]+, as in [V02(ox)2]3- and [V02(edta)]3 (ox = oxalate dianion edta = ethylenediamine tetraacetate tetraanion). All dioxo complexes of d° metals have cis configurations, an arrangement that maximizes dji-pjt interactions. 

The tetraanion of EDTA, (—OOCCH2)2NCH2CH2N(CH2COO—)z, is an especially effective complexer in that it can form five five-membered chelate rings with a single metal ion by coordination through the electron-pair donors of the four (or sometimes... 

One of the best known podand-type ligands is EDTA which, in its tetraanionic form, is an extremely conunon chelate... 

The best known chelating agent, with wide applications in several fields is edta, or the tetraanion of ethylenedi-aminetetraacetic acid (Scheme 19a). Its high efficiency in sequestering metal ions has led to a number of applications. On the other hand, the conformational flexibility of its aliphatic skeleton makes it a less than ideal building block for supramolecniar architectures. Edta can arrange... 

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