Overall stability constants

Speciation diagrams resulting from metal-ligand titrations, with the concentration profiles of the various MLn species throughout the process of successive addition of the ligand identified. At left is the pH-dependent formation of vanadyl complexes with the acetylacetonate anion at right is the chloride ion concentration-dependent formation of chloromercury(II) species. 

We can represent the sequential substitution steps for formation of MLX by a series of equilibria (5.18)  

For each step, a stepwise stability constant can be written of the form (5.19)  

The overall reaction occurring through combination of the above steps can be written as (5.20)  

This overall stability constant simply defines the formation of the overall or final complex, where all of one ligand (here, water) can be considered replaced by another it does not infer anything about the mechanism of the process. Actual examples have appeared earlier in Equations (5.9) and (5.10). 

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MA( , ) + A. MA n-[MA( , )][A] Ky, Kfy being called the step-wise stability constants. Overall stability constants, designated may be evaluated by multiplication of the individual stability constants, e.g. 

The equilibrium constants pi,p2,...,p are called the overall stability constants and are related to the stepwise stability constants by the general expression... 

It can be shown from a consideration of the overall stability constants of the ions [Ni( CN)4] 2 " (1027) and [ Ag( CN)2 ] (1021) that the equilibrium constant for the above ionic reaction is 1015, i.e. the reaction proceeds practically completely to the right. An interesting exercise is the analysis of a solid silver halide, e.g. silver chloride. 

In this part we shall use the nomenclature of Si lien and Martel 1 (76) to define stability constants, medium and experimental techniques. We shall only deal with overall stability constants of the cation M with the ligand L according to reaction (25)... 

For obvious reasons, we tend to use the simpler form, although we will discuss some of the limitations shortly. We may also consider overall stability constants, (5 (Eq. 8.3). 

Thus, the overall stability constants for the various steps, [3-v can be expressed in terms of the product of several stepwise stability constants, Kt (e.g., [32 = Kiff2 P4 = K1K2K3K4). 

The overall stability constants are given as the products of the stability constants for all steps up to the one being considered. These are represented as A and they are related to the K values by the equations... 

However, Eqs. (14) and (15) can be combined with the proton independent overall stability constant of the FeL complex to give an overall stability constant for the FeLH complex, /iin. 

Alternately, they are indicated by overall stability constants as shown in equations 1.4-1.6 ... 

The equation relating the stepwise and overall stability constants is indicated by equation 1.7 ... 

The bisanthraceno-crown ether E-l (Figure 10.26) exhibits a fluorescence spectrum composed of the characteristic monomer and excimer bands. Gradual addition of sodium perchlorate to a solution in methanol induces a decrease in the monomer band and an increase in the excimer band. Complexation is indeed expected to bring closer together the two anthracene units, which favors excimer formation. A 2 1 (metabligand) complex is formed with Na+ in methanol and acetonitrile with a positive cooperative effect (see Appendix B). Interestingly, the overall stability constant obtained from absorption data was found to be lower than that... 

Oudeman law physchem The law that the molecular rotations of the various salts of an acid or base tend toward an identical limiting value as the concentration of the solution is reduced to zero. od-a-man, I6 ) outer orbital complex phys chem A metal coordination compound in which the d orbital used in forming the coordinate bond is at the same energy level as the s and p orbitals. aud-or 6rb-od-3l kam.pleks) overall stability constant analychem Reaction equilibrium constant for the reaction... 

It is common to use the overall stability constant, where p = number of metal, q = number of hydrogens (for protonated species), and r = number of ligands. The value of q is negative for hydroxo species. For the reaction to form ML,... 

If a sexidentate ligand were to coordinate to Mm+, fin would just be fii = Ad, with units L mol-1. Consequently, we cannot compare fix for formation of a sexidentate ligand with the overall stability constant fie for six comparable unidentate ligands because the units are incompatible. 

Raymond. K- N. Mtiller, G. Malzankc, B. F. Top. Curr. Chart. L9K4. r J,49. Enierohuclm is the most powerful iron(MI) chelator known with an overall stability constant of K, UV" (Loomis, L. D. Raymond. K. N. Inorg. Client. 1991, JO, 906). 

Clearly the position of the homogeneous reaction (la) will depend on the concentration of the free metal ions which can be modified by an auxiliary complexing (or masking) agent (see Section 10.3). It will move increasingly to the right as the (overall) stability constant of the complex, ML , increases and to the left as the solution becomes more acidic. Increase of pH should lead to more complete reaction but since this implies a concomitant increase in hydroxyl ion concentration there will now be increasing competition between the tendencies of IT and OH- to coordinate to the cation basic species and even metal hydroxides may form and precipitate. 

Hydrolysis constants for Pu(IV) have been determined in aqueous solutions at many pH values and ionic strengths. In 1MNaQ04 solution the first three Pu(IV) — OH- complexes and overall stability constants are (105) as follows ... 

The overall stability constants of several metals in solution have been determined by many workers34 employing Bjerrum s technique, pH titration and distribution and potentiometric methods. It has been shown by Irving and Williams,35 as well as by Mellor and Maley,36 that the stability of chelates of bivalent 3d metals increases regularly from Mn2+ to Cu2+ and decreases from... 

BPEI (6) respectively, have been studied to examine the chelating ability of poly(ethyleneimine)s having different microstructures. From the overall stability constant for Co2+, Ni2 +, Cu2+, Zn2 +, Cd2+, and UO + ions, the chelating ability of LPEI was estimated to be ca 10 times less than that of BPEI for all but U02 +. The branched structure gives a more favorable complexation than the linear structures 22). 

Receptor 60 possesses similar ion-pair sensing properties to its [Ru(bpy)3]2+ analogue 47 [38]. The neutral receptor naturally showed lower overall stability constants for halides, but the anion binding enhancement observed on the addition of Li+ or Na+ was increased, with a 60-fold enhancement in the stability constant for bromide in the presence of Li+. 

The dissociation constant, Kd, is the reciprocal of the overall stability constant, Ks. Other symbols commonly used in texts and tables of data are... 

From data in Table 19-1, calculate the overall stability constant, Ks, of [Ag(S203)2]3 at 25°C. 

In the case of Ag+, only two imidazolyl groups participate in complex formation, and the overall stability constant is log p2 = 8.00, about one order of magnitude larger than the overall formation constant of the Ag/imidazole complex (log p2 = 6.84). Complexes of Cu2 + with poly 4(5)-vinyl-imidazole, poly(N-vinyl-imidazole), and... 

Studies on the formation of chlorocomplexes when Ln = Pr, Sm, Nd, by UV-Vis and I spectroscopy in propylene carbonate [113] showed the formation of [MC1]2+ and [MCI2] with the following values for the overall stability constants. 

Overall stability constants for the formation of lanthanide chloro- and bromo-complexes in anhydrous methanol, ethanol, and propanol, as determined by spectrophotometry. 

These values reflect moderate interaction between Ln(III) and the chloride ion. The overall stability constants for the formation of chloro and bromo complexes of lanthanides (y6(MX)2+ and (MXj)) are given in Table 4.7. 

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