Stability constant, thermodynamics

It should be noted that some data on complexation of transuranium elements with various N-donor ligands, such as azide ion, isothiocyanate ion, amine-N-polycarboxylic and heterocyclic acids, 8-hydroxyquinoline and its derivatives, were published as early as 1950-1970 [42-77], The quantitative parameters of complexation (number and composition of complexes, stability constants, thermodynamic parameters) were determined using accessible at that time methods (spectrophotometry, potentiometry, ion exchange, solvent extraction). It was shown that transuranium elements in different oxidation states can form complexes with N-donor ligands. However, only presumptive conclusions regarding structure of complexes were drawn at that time,... 

Marin, D. Mendicuti, F. Polarographic Determination of Composition and Thermodynamic Stability Constant of a Complex Metal Ion, /. Chem. Educ. 1988, 65, 916-918. 

Table 3. Thermodynamic and Stability Constant Data for Selected Aqueous Cadmium Complexes ...

Stability. The thermodynamic stabiUty of coordination compounds in solution has been extensively studied (12). The equiUbrium constants may be reported as stabiUty or formation constants. 

Table 19.1 Stability constants and thermodynamic functions for some complexes of Cd at 25°C...

Complexes with the Fluoride Ion. For the compilation of stability constants (Table IV) of complexes with F , we have used, when needed, thermodynamic parameters (K, AH) pertaining to the dissociation of hydrofluoric acid as given by Smith and Martell (77) or extrapolated from their selection. 

In spite of well identified deficiencies, the status of the existing thermodynamic data on solid halides and related compounds is rather satisfactory. By contrast, the data on aqueous halogeno-complexes are fragmentary, sometimes contradictory and in most cases limited to stability constants in such a context, recommendation of best values can be made for a few species only. 

The physical nature of the sulfate complexes formed by plutonium(III) and plutonium(IV) in 1 M acid 2 M ionic strength perchlorate media has been inferred from thermodynamic parameters for complexation reactions and acid dependence of stability constants. The stability constants of 1 1 and 1 2 complexes were determined by solvent extraction and ion-exchange techniques, and the thermodynamic parameters calculated from the temperature dependence of the stability constants. The data are consistent with the formation of complexes of the form PuSOi,(n-2)+ for the 1 1 complexes of both plutonium(III) and plutonium(IV). The second HSO4 ligand appears to be added without deprotonation in both systems to form complexes of the form PuSOifHSOit(n"3) +. ... 

The stability of a complex is conveniently expressed in terms of the thermodynamic stepwise stability constant K as defined in Eq. (8.1). 

In the introductory chapter we stated that the formation of chemical compounds with the metal ion in a variety of formal oxidation states is a characteristic of transition metals. We also saw in Chapter 8 how we may quantify the thermodynamic stability of a coordination compound in terms of the stability constant K. It is convenient to be able to assess the relative ease by which a metal is transformed from one oxidation state to another, and you will recall that the standard electrode potential, E , is a convenient measure of this. Remember that the standard free energy change for a reaction, AG , is related both to the equilibrium constant (Eq. 9.1)... 

The reaction of [Ir(H20)6]4+ with Cl- ions has been studied at various temperatures, giving stability constants and the thermodynamic parameters A/7°, AG°, and AS° for the substitution reactions.49... 

The above account of selectivity of inorganic plus organic chemistry in synthesis is given rather extensively to stress three points. All the four (Mg, Fe, Co and Ni) porphyrin products came from one source, the synthesis of uroporphyrin. The basis of selection is very different from that in primitive centres which use thermodynamic stability constant selectivity based on different donor atoms for different metal ions. Here, all ion complexes have the same donor atoms, nitrogen, the most constrained being the coordination of Mg2+ by five nitrogens exactly as is seen for Fe in haemoglobin. Hence, there also has to be a new control feedback to ensure that the appropriate quantities of each metal cofactor is produced in a balanced way, that is synthesis from uroporphyrin has to be divided based upon... 

The thermodynamic stability of an ML complex is expressed by the equilibrium constant of the formation reaction, A1ML, called the the stability constant ... 

Batch adsorption experiments by Yee and Fein (2002) using aqueous Cd, B. subtilis, and quartz as a function of pH showed that the thermodynamic stability constants, determined from binary systems, could successfully describe the distribution of Cd between the aqueous phase and the bacterial and mineral surfaces. The constants could also be used to estimate the distribution of mass in systems, and construct a surface complexation model. 

Borrok et al. (2004a) used potentiometric titration to measure Cd sorption by different bacterial consortia, and a surface complexation approach to determine thermodynamic stability constants. When the data were modeled by adopting a single set of stability constants, a similar sorption behavior was shown by a wide range of bacterial species. Further, current models that rely on pure strains of laboratory-cultivated bacterial species appear to overestimate the extent of metal biosorption in natural systems. 

Thermodynamic aspects of the interaction of metal ions with macrocyclic ligands have been well studied. In many instances such studies have involved a comparison of the behaviour of cyclic ligand systems with that of their open-chain analogues. In this manner, information concerning the thermodynamic consequences arising from the cyclic nature of the macrocyclic ligand has been obtained. Frequently these studies have been restricted to stability constant (log K) measurements and, for such studies, a variety of techniques has been employed (Izatt etal., 1985). 

In the preceding chapter, thermodynamic aspects of macrocycle complexation were treated in some detail. In this chapter, kinetic aspects are discussed. Of course, kinetic and thermodynamic factors are interrelated. Thus, in terms of a simple complexation reaction of the type given below (charges not shown), the stability constant (/CML) may be expressed directly as the ratio of the second-order formation constant (kf) to the first-order dissociation rate constant (kd) ... 

This conditional stability constant, K, is related to the thermodynamic stability constant (KM]J by (133) ... 

The identity of the hard donor group and how it is incorporated in a molecular structure has a bearing on the affinity of a siderophore for iron(III). An analysis of siderophore structure and its relationship to iron(III) binding affinity as expressed by the thermodynamic stability constant is useful in understanding structure/function relationships and in the design of siderophore mimics for specific applications. 

Thermodynamic Stability Constants for Iron(III)-Siderophore Complexes,... 

---