Chelate formation constants

Other arsenic-containing ligands reported include mixed donor species with S212 or N213,214 as the other donor atom. The ligand bis(carboxymethyl)(o-methylthiophenyl)arsine (24) contains S and As donors in a position suitable for chelation. Formation constants for its complexes with Ag1 are given in Table 30. The silver complexes of the m and p derivatives were insoluble under the conditions used and no data could be collected.212... 

The complexing ability of iminodiacetic acid type chelating agents, e.g. benzyl-aminediacetic acid (BDA) (8), was found to be enhanced considerably in aqueous solution by the use of a polymeric analogue such as (vinylbenzylamine diacetic acid)-co-(sodium styrenesulfonate) (PBDA) (9) 23). The chelate formation constants for... 

Table 1. Chelate formation constants of Co2 +, Ni2+ and Cu2+ with PBDA or BDA at ionic strength (I) = 0.1 and 25 Ca...

TABLE II. log kj METAL CHELATE FORMATION CONSTANTS IN 50% v/v AQUEOUS DIOXANE. 

Whatever the actual mechanism in anion-exchange distributions of rare earths between an aminopolycarboxylate-charged resin and an aqueous solution of the same (or different) aminopolycarboxylate anion, the Ln distribution curve (log Ka VS. Z) peaks at (or near) the same Z as does the second step chelate formation constant. For example in the case of -HjfEDTAl /HzfEDTA) , Minczewski et al. (1962) found the Ka a maximum at about Z = 63 (Eu), corresponding rather well with the K2 value maximum observed by Brucher et al. (1975) at Z = 62 (Sm). 

The first identified complexes of unsubstituted thiazole were described by Erlenmeyer and Schmid (461) they were obtained by dissolution in absolute alcohol of both thiazole and an anhydrous cobalt(II) salt (Table 1-62). Heating the a-CoCri 2Th complex in chloroform gives the 0 isomer, which on standirtg at room temperature reverses back to the a form. According to Hant2sch (462), these isomers correspond to a cis-trans isomerism. Several complexes of 2,2 -(183) and 4,4 -dithiazolyl (184) were also prepared and found similar to pyridyl analogs (185) (Table 1-63). Zn(II), Fe(II), Co(II), Ni(II) and Cu(II) chelates of 2.4-/>is(2-pyridyl)thiazole (186) and (2-pyridylamino)-4-(2-pyridy])thiazole (187) have been investigated. The formation constants for species MLr, and ML -" (L = 186 or 187) have been calculated from data obtained by potentiometric, spectrophotometric, and partition techniques. 

In common with other hydroxy organic acids, tartaric acid complexes many metal ions. Formation constants for tartaric acid chelates with various metal ions are as follows Ca, 2.9 Cu, 3.2 Mg, 1.4 and Zn, 2.7 (68). In aqueous solution, tartaric acid can be mildly corrosive toward carbon steels, but under normal conditions it is noncorrosive to stainless steels (Table 9) (27). 

Table 2. Concentration Formation Constants of Metal Chelates...

If the metals or ligands involved in a displacement reaction form chelates where type formulas are different, the exchange equiUbrium constant is the simple ratio of the formation constants of the chelates. Rather, for the reaction... 

In the equation for pM, log K appears instead of piC because iCis a formation constant, the reciprocal of the chelate dissociation constant, which is analogous to the acid dissociation constant K. ... 

The log function of the ratio of chelated metal ions to free-metal ions is expressed as the stabiUty constant or formation constant as shown in Table 6. The higher the stabiUty constant the greater the percentage of metal ions that are chelated (11). 

Formation constants and thermodynamic parameters have been measured for the Fe(II) chelates of 3-chloro-2-quinoxalinecarboxylic acid and 3-oxo-3,4-dihy-dro-2-quinoxalinecarboxylic acid. ... 

The complexation constant for copper(II) is particularly high and Wall Gill (1954) have suggested that chelate formation takes place with two carboxyl groups ... 

The complex Cu(II)2(0-BISTREN) is much more acidic than the free Cu2+ ion, by a factor of more than three log units. This is primarily due to the presence of two Cu(II) ions, because the formation constant of the Cu2(OH)+ complex is not much less than that for the Cu2(0-BISTREN) complex with hydroxide. This is not a good indication of how well two free Cu2+ ions would bind hydroxide compared to the Cu2(0-BISTREN) complex, however, since one must take into account the dilution effect operative in the chelate effect to make the comparison more realistic (90). Thus, the formation constant for the Cu2OH+ complex above applies for the standard reference state of 1 M Cu2 +. In contrast, in 10 6 M Cu2+, for example, the pH at which Cu2(OH) + would form is raised from pH 5.6 to 11.6, ignoring the fact that Cu(OH)2(s) would precipitate out long before this pH as reached. By comparison, the acidity of the Cu2(0-BISTREN) complex is not affected by dilution and would still form the hydroxide complex at pH 3.9 if present at a 10"6 M concentration. 

EDTA salts are used for the treatment of heavy metal poisoning. Roosels and Vanderkeel142) were able to extract lead from urine in the presence of EDTA with dithizone by adding calcium to presumably release the lead from EDTA. In view of the fact that the formation constant of the lead-EDTA chelate is 20,000,000 times larger than that of the corresponding calcium chelate, it is doubtful that the calcium actually releases the EDTA from the lead. 

The hydrated metal ion M(HzO), reacts with the reagent anion R to form the neutral chelate MR, (formation constant K ), i.e. 

It can be seen from equation (4.25) that the value of P is determined by the formation constants and distribution coefficients of the two chelates, i.e. 

Barium(II), concentration formation constant of chelates, 5 717t Barium 2-ethylhexanoate, 3 362 Barium acetate, 3 355 Barium acetate monohydrate, 3 355 Barium alloys, 3 344 Barium-aluminum evaporation getters, 3 349... 

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