Complexes stepwise formation constant

Stepwise formation constants have been determined in the system Hg2+/Cl-/diethylenetriamine (dien) and related systems by potentiometry. Thermodynamic parameters have been calculated and the contribution of the entropy term to complex stability discussed.208... 

The thermodynamic stability of a complex ML formed from an acceptor metal ion M and ligand groups L may be approached in two different but related ways. (The difference between the two approaches lies in the way in which the formation reaction is presented.) Consistent with preceding sections, an equilibrium constant may be written for the formation reaction. This is the formation constant Kv In a simple approach, the effects of the solvent and ionic charges may be ignored. A stepwise representation of the reaction enables a series of stepwise formation constants to be written (Table 3.5). 

In Chapter 3 we described how an uncharged metal complex MA is formed from a metal ion central atom) through a stepwise reaction with the anion A (ligand) of a monobasic organic acid, HA, defining a stepwise formation constant k , and an overall formation constant (3 , where... 

The average ligand number can be used to obtain approximate equilibrium constants, as described by [65], assuming that at half integer -values the two adjacent complexes dominate e.g., at = 0.5 the species and MA dominate, while at il = 1.5 MA and MA dominate, etc.. The following expression for the stepwise formation constant is approximately valid at... 

Ki stepwise formation constant for ith complex (e.g., MLj) overall extraction constant... 

Gregor et al66 reported the Cu-complex formation of poly(methacrylic acid) (PMA) resins crosslinked with 1% or 9% divinylbenzene. The formation constants of the Cu complexes with the resins were smaller than that of noncrosslinked PMA. The stepwise formation constants decreased from Ki to KA in the resin system, which was the opposite of the noncrosslinked PMA system. The rigidity of the polymer-ligand chain was considered to hinder chelate formation. Formation constants of the PMA resin were also reported by Gustafson era/.67. The formation constant of the noncrosslinked PMA decreased for various metal ions ... 

Formation constants are the equilibrium constants for complex ion formation. The stepwise formation constants, designated K, are defined as follows ... 

Thiosalicylic acid forms a green 2 1 complex with V02+ in aqueous ethanol442 (log K1 = 10.24, log K2 = 8.39). Addition of pyridine causes a more than 10-fold increase in the molar extinction coefficient and a yellow shift affording a chloroform extractable complex which can be used for the analysis of vanadium. The thermodynamic parameters for the 2 1 complex of furfurylmercaptan and V02+ are (35 °Q log K, 8.18 AH° = - 8.18 kcal mol"1, AG°, - 23.31 kcal mol"1 AS°, + 49.12 e.u 443 Stepwise formation constants of the V02+ complex of p-(mercaptoacetamide)chloro-benzene have been determined.444... 

The larger the value of the constant is, the more stable the complex (Table 12.11). The metal-ammine formation constants Ksl and Kst are known as stepwise formation constants. Stepwise formation constants1 could be used to estimate overall formation constants. For example,... 

The data for bromo complexes were obtained in aqueous methanolic solutions and outer-sphere bromo complexes with K = 1.3-1.9 were obtained for Pr, Nd, Sm, which are larger than the values of Ho (0.97) and Er (0.70). Chloro and bromo complex formation in dimethyl formamide studied by titration calorimetry [122] showed the evidence for MC12+, MCC. MCI3, and MCI4 species in solutions. In the case of bromide, monobromo and dibromo inner sphere complexes have been detected. The stepwise formation constants could not be determined for iodo complexes due to the small value of enthalpies of reaction. The stability constants data obtained in DMF are given in Table 4.8. 

Larson and Iwamoto determined the interaction of small amounts of water in nitror methane with by voltammetric studies. The dependence of the half-wave potential for the Cu /Cu wave on water concentration was analysed to deduce the stepwise formation constants Kj of the complex species [Cu(H20)j] " . The constants are in good agreement with those evaluated from spectroscopic measurements. 

Studies on ionic hydration and complex formation reactions in solution in the 1960 s quite actively proceeded in Europe, especially in northern Europe. J. Bjerrum, a son of N. Bjerrum in Denmark, established a method for determination of stepwise formation constants of complexes with simple monodentate ligands in solution by the spectrophotomeffic method, which was soon modified to the method by potentiometry. Sillen in Sweden extended the method to polynuclear complex formation reactions and Schwartzenbach in Switzerland, who is a pioneer of chelate chemistry, applied this method to multidentate ligand complexes... 

If the successive formation constants of ML, are known, the value of m be calculated from (12-47), and the electrode potential can be calculated from (12-49). Conversely, from measurements of the electrode potential at various concentrations of complexing agent L, the value of aM can be determined for each value of L. If sufficient data are available, the values of the stepwise formation constants Ki, K, ..., A, can be evaluated. If there are q such values, we need q equations these are available from q determinations of E. 

After determining the simplified equation 9, Ventry (23) postulates that Ires Iq where d is related to the residual and initial fluorescence intensity. Manipulation of mass balance and stepwise formation constant relationships, and application of a similar derivation procedure used in the nonlinear model, yields equation 10. Equation 10, like the nonlinear model equation, relates observed changes in FA fluorescence intensity I, to total metal, with a conditional stability constant (for the metal ion and FA) and the degree of complexation of the FA. The modified Stem-Volmer equation is ... 

The equilibrium constants for complex formation reactions are generally written as formation constants, as discussed in Chapter 9. Thus, each of the Reactions 17-1 through 17-4 is associated with a stepwise formation constant, K through K. For example, Ki = [ML]/[M][L], Kj = [ML2]/[ML][L], and so on. We can also write the equilibria as the sum of individual steps. These have overall formation constants designated by the symbol jS,. Thus,... 

In Appendix 4, we find that the logarithms of the stepwise formation constants for the four zinc complexes with ammonia are 2.21,2.29, 2.36, and 2.03. Thus,... 

To parameterize and solve the total metal and total ligand equations for a given solution, we also need to know the formation constants of the complexes. The stepwise formation constants of mononuclear complexes are usually defined as follows (cf. Beck, 1970)... 

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