Stability constants of complexes

A significant achievement of Anatoly K. Babko was in the area of systematic physicochemical research of complex compounds in solution based on their photometric properties. Anatoly K. Babko showed the stability constants of complexes to be highly important, and demonstrated the relevance of the stepwise character of the dissociation of complex compounds. 

Some of these divalent cations form part of the Irving-Williams series Mn, Fe, Co, Ni, Cu and Zn. Irving Williams (1953) examined the stability constants of complexes of a number of divalent ions and found that the order... 

Another factor that affects trends in the stability constants of complexes formed by a series of metal ions is the crystal field stabilization energy. As was shown in Chapter 17, the aqua complexes for +2 ions of first-row transition metals reflect this effect by giving higher heats of hydration than would be expected on the basis of sizes and charges of the ions. Crystal field stabilization, as discussed in Section 17.4, would also lead to increased stability for complexes containing ligands other than water. It is a pervasive factor in the stability of many types of complexes. Because ligands that form tt bonds... 

The stability constant of complexes between /1-cyclodextrine and p-nitroaniline is higher than that of aniline because the resonace charge delocalization (and London dispersion interactions) is an important factor influencing the stability of these complexes62. This behaviour parallels that of corresponding phenols. 

The measurement of stability constants of complexes of yttrium, lanthanide, and actinide ions with oxalate, citrate, edta, and 1,2-diaminocyclohexanetetra-acetate ligands has revealed that there is a slight increase in the stability of complexes of the /-electron elements, relative to the others. A series of citric acid (H cit) complexes of the lanthanides have been investigated by ion-exchange methods and the species [Ln(H2cit)]", [Ln(H2cit)2] , [Ln-(Hcit)], and [Ln(Hcit))2] were detected. Simple and mixed complexes of dl- and jeso-tartaric acid have been obtained with La " and Nd ions, and the stability constants of lactate, pyruvate, and x-alaninate complexes of Eu and Am " in water have been determined. 

Stability constant of complexes, measurement by chomatography, 276 Stack configuration, 137 Standard deviations, 3 Stetionary phases, bonded hydrocaibona-ceous, 121... 

The equilibrium potentials of saturated zinc amalgam were determined [94] as a function of concentration of free ethylene-diamine in the solutions of pH 9.5, 10.5, and 11.5. The stability constants of complexes with different compositions, which were formed, have been estimated. 

Rudd, T., Sterritt, R. M. Lester, J. N. (1984b). Formation and conditional stability constants of complexes formed between heavy metals and bacterial extracellular polymers. Water Research, 18, 379-84. 

Pyridines are also well known as ligands in transition metal complexes, and if the equilibrium constants for the formation of such complexes can be related to base strength, it is expected that such constants would follow the Hammett equation. The problem has been reviewed,140 and a parameter S, formulated which is a measure of the contribution of the additional stabilization produced by bond formation to the stabilization constants of complexes expressed in terms of a.141 The Hammett equation has also been applied to pyridine 1 1 complexation with Zn(II), Cd(II), and Hg(II) a,/3,y,<5-tetraphenylporphins,142 143 the a values being taken as measures of cation polarizing ability. Variation of the enthalpy of complexation for adducts of bis(2,4-pentanediono)-Cu(II) with pyridines plotted against a, however, exhibited a curved relationship.144... 

In the presence of excess TC, soft acidic Cd2+ forms tetra-thiocyanato complexes in which four TC coordinate to Cd2+ with their soft basic S atoms as expected from the high stability constant of complex formation. 

The coordination of 9-hydroxy-4//-pyrido[1,2- ]pyrimidin-4-one with Ni(II), Zn(II), Co(II), and Cd(II) ions was studied by potentiometric and polarographic methods. Stability constants of complexes were also determined (93MI25). 

Van den Berg, C.M.G., 1984. Determination of the complexing capacity and conditional stability constants of complexes of copper (II) with natural organic ligands in seawater by CSV of copper-catechol complex ions. Mar. Chem., 15 1-18. 

Table 1 Stability constants of complexes of (3-cyclodextrin and tetrahelicenes...

Spectrophotometric data for the stability constants of complexes of Me3SnCl with substituted pyridine JV-oxides in acetonitrile show (76) that these constants correlate linearly with the [Pg.81]

The formation and stability constants of complexes between Pd (Pt. Rh, Ir, Os, Ru) and o-coumaric acid have been determined by pH titration.31 The results indicate that a 1 2 complex is formed with Pd. 

Obviously one could measure the pH of a known concentration of a weak acid and obtain a value of its hydronium ion activity, which would permit a direct evaluation of its dissociation constant. However, this would be a one-point evaluation and subject to greater errors than by titrating the acid halfway to the equivalence point. The latter approach uses a well-buffered region where the pH measurement represents the average of a large number of data points. Similar arguments can be made for the evaluation of solubility products and stability constants of complex ions. The appropriate expression for the evaluation of solubility products again is based on the half-equivalence point of the titration curve for the particular precipitation reaction [AgI(OH2)2h represents the titrant] ... 

For multistep complexation reactions and for ligands that are themselves weak acids, extremely involved calculations are necessary for the evaluation of the equilibrium expression from the individual species involved in the competing equilibria. These normally have to be solved by a graphical method or by computer techniques.26,27 Discussion of these calculations at this point is beyond the scope of this book. However, those who are interested will find adequate discussions in the many books on coordination chemistry, chelate chemistry, and the study and evaluation of the stability constants of complex ions.20,21,28-30 The general approach is the same as outlined here namely, that a titration curve is performed in which the concentration or activity of the substituent species is monitored by potentiometric measurement. 

This value of K can be identified with the solubility product—the differences that arise in relation to tabulated values of Ksp are due to differences in the solution conditions. In the same way we can calculate stability constants of complexes. 

ET-AAS with graphite furnace tubes constituted the analytical support for the speciation analysis of Al and the concomitant determination of Al (III) in tea infusions, as described by Alberti and coworkers [141], Lvov platforms incorporated into the graphite furnace atomizers enabled the authors to attain an LoD of 2 xg l-1 Al. The determination was not impaired by the relatively high solid contents. Adsorption of Al on ion Chelex-100 resin was employed to estimate the free metal content and the concentration and stability constants of complexed Al species. The metal is reported to be present in total concentrations from 0.09 to 0.26 mM, but mainly linked to strong complexes. Strong complexation is demonstrated by the inability of Chelex-100 to dissociate the complexes. These results are considered by the authors as an explanation of the low toxicity of the Al associated with tea infusions. The concentration of free Al was found to be very low (at the nM level). No structural or chemical information about the ligands was obtained from the method. 

Stability constants of complexes may be determined by (i) kinetic and (ii) equilibrium methods. In the present discussion, attention will be focused on mononuclear complexes and the fact that the activity coefficients of all the species can be held effectively constant by using suitable ionic media. The kinetic approach is applicable when (i) the rates of formation and dissociation of a complex are sufficiently slow and (ii) accessible to experimental measurement by suitable techniques. Using the law of mass equation... 

It is necessary Cmr should be low and kept constant so that equation (3.34) with constant l and lo can be used within a concentration range of [A-] that is large enough for the calculation of stability constants of complexes. In order to calculate Cmr and the following equation is used... 

The second chapter deals with quantum chemical considerations, s, p, d and f orbitals, electronic configurations, Pauli s principle, spin-orbit coupling and levels, energy level diagrams, Hund s mles, Racah parameters, oxidation states, HSAB principle, coordination number, lanthanide contraction, interconfiguration fluctuations. This is followed by a chapter dealing with methods of determination of stability constants, stability constants of complexes, thermodynamic consideration, double-double effect, inclined w plot, applications of stability constant data. 

Luca C, Barboiu M, Supuran CT (1991) Stability constant of complex inhibitors and their mechanism of action. Rev Roum Chim 36(9-10) 1169-1173... 

Stability constants of complexes can be found in the commercial databases mentioned earlier, Gd(m) constants were reviewed <2000CCR309>, and constants for DOTA and TETA were critically evaluated <2005PAC1445>. 

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