Mixed stability constants

Other forms of stability constant can be derived from the fundamental definition given in Eq. 2. For example, if one of the reagents is the hydrogen ion activity can be measured with a suitable electrode, and this will give rise to a mixed stability constant when the other species are represented by concentrations. 

The complexation of other mixed oxa aza macrocycles has been studied, and protonation and stability constants of the zinc complexes of macrocycles l,4,10,13-tetraoxa-7,16-diazacycloocta-decane-7,16-bis(malonate), the -7-malonate derivative and -7,16-bis(methylacetate) derivative have been determined by potentiometry at a 1 1 ligand-to-metal ratio.730... 

Solution equilibria of Fe(III)/Cr(III) in methionine and Fe(III)/Cr(III) in methio-nine/penicillamine complex systems were studied by paper electrophoresis and were reported by Tewari [38]. The formation of 1 1 1 mixed ligand complexes is inferred, and the stability constants of the complexes at 35 °C and 0.1 M ionic strength were 6.80 0.09 (Fe(III) methionine penicillamine) and 4.60 0.16 (Cr(III)-methionine-penicillamine), respectively. 

An electrophoretic method was described by Srivastava et al. [40] to study equilibria of the cited mixed ligand complex systems in solution. Stability constants of the Zn(II) and Cd(II) complexes were 5.36 and 5.18 (log K values), respectively, at an ionic strength of 0.1 and a temperature of 35 °C. 

An ionophoretic method was described by Tewari [41] for the study of equilibria in a mixed ligand complex system in solution. This method is based on the movement of a spot of metal ion in an electric field with the complexants added in the background electrolyte at pH 8.5. The concentration of the primary ligand (nitrilo-triacetate) was kept constant, while that of the secondary ligand (penicillamine) was varied. The stability constants of the metal nitrilotriacetate-penicillamine complexes have been found to be 6.26 0.09 and 6.68 0.13 (log K values) for the Al(III) and Th(IV) complexes, respectively, at 35 °C and an ionic strength of 0.1 M. 

In order to co clarify the role of complex formation, the new data on stability constants should be accumulated, being collected at strictly similar conditions. It should be also mentioned that any analysis of equilibrium in solutions involving anions of polybasic hydroxy carboxylic acids requires the data on the deprotonation constants of the acid in question. This information would be crucial for conclusions regarding the presence and stability of mixed complexes in the system. Valuable knowledge about the structure of complex compounds present in solutions (and in precursors as well, see later) may be gained by means of vibrational spectroscopy (IR and Raman spectra) and nuclear magnetic resonance. 

These equilibria have been studied by various methods of which potentiometry and 51V NMR spectroscopy proved to be particularly useful for the identification of species and the determination of stability constants (8-10,13-16,18,20,22,24). Values obtained for stability constants by different research groups under the same conditions usually show good agreement, e.g., for 0.60 M NaCl medium (Table II). In some cases so-called Bronsted (or mixed) constants (25) are... 

Structures known to form with either metal also form with the entire intermediate range of mixed-metal combinations 180). Both molybdenum and tungsten form the heptametalate [M7O24]6 in aqueous solution. The existence of mixed heptametalates has been shown by the application of 170 NMR 182) and 183W NMR spectroscopy 180). In fact, molybdenum can replace any or all of the tungsten atoms in [W7O24]6 so that at least 19 mixed-metal structures can be observed 180). Approximate relative stability constants have been determined for the intermediate species in the series... 

The stepwise stability constants for V complexes with glutamic, aspartic, W -ethylenediaminedisuccinic, and W -ethylenediamine-bis-(a-glutaric acid) have been reported.The 1 1 oxovanadium(iv) complex of 5-nitrosalicylic acid has been characterized = 710 nm), and the mixed species formed between vanadium(iv) with protocatechuic acid (H3L ) or gallic acid (H L ) and 4-aminoantipyrine (aant) have been identified spectroscopically as the 1 1 1 and 1 2 2 HL (HL ) aant complexes. The species present in solutions of and tartaric acid below pH 2 have been identified as [VO-... 

Trihydroxyglutaric acid forms a 1 1 complex with chromium(iii) which has a stability constant of 0.9 x 10. In the presence of copper(n) a mixed complex is formed and dark bluish-green crystals of Na3[CuCrCioH70i4],5H20 have been isolated. The substituted benzoic acid complexes (60) have been prepared by heating a mixture of CrCL,6H20 and RCgH4C02H in Pr OH. The... 

The stability constants of yttrium tartrates have been determined and a mixed copper-yttrium tartaric (T) acid species, Y2CuT3H q unknown), was detected. ... 

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. 

KP and v can, in contrast to kp, not be determined via the concentration gradient for binary and ternary mixed micelles, because for the calculation of the Nemstian distribution a constant CMC and an almost constant partial molar volume must be assumed. The calculation of aggregation constants of simple bile salt systems based on Eq. (4) yields similar results (Fig. 8b). Assuming the formation of several concurrent complexes, a brutto stability constant can be calculated. For each application of any tenside, suitable markers have to be found. The completeness of dissolution in the micellar phase is, among other parameters, dependent on the pH value and the ionic strength of the counterions. Therefore, the displacement method should be used, which is not dependent on the chemical solubilization properties of markers. For electrophoretic MACE studies, it is advantageous for the micellar constitution (structure of micelle, type of phase micellar or lamellar) to be known for the relevant range of concentrations (surfactant, lipids). 

Given the structure of InF3-3H20 (see above) and the tendency of indium(III) to be six-coordinate with hard ligands, it is reasonable that the mixed fluoro/aqua anionic complexes should also be [InF4(H20)2] and [InF5(H20)]2. This is compatible with the evidence from aqueous solution chemistry, where stability constants and thermochemical results indicate a series of [In(H20)6-nFn]l3 n)+ species.9 These complexes still await detailed systematic structural investigation. 

The pseudohalides and related compounds have been investigated by a number of workers. Thallium(I) cyanate and thiocyanate are both known, and the latter has been shown to be ionic in the solid state 288 differing values have been reported for the stability constants in the T1/NCS system in aqueous or mixed water/non-aqueous systems, but the overall evidence is that the complexes are extremely weak.289 The ionic selenocyanate has been reported, but the chemistry has not been investigated.1... 

Table 46 Stability Constants /SVOAL of Some Mixed-Ligand Chelates of Oxovanadium(IV)a...

Extension of the principle to more complex equilibria of the type OL(, and of mixed ligand complexes, etc. is straightforward. In conclusion, the stability constants of such complexes can be determined by means of any electrochemical technique that allows to determine E, 2. ... 

Mixed ligand complexes of Zn2+ with en and monoethanolamine (mea) in H20-MeOH systems have been investigated.192 At <20% MeOH, the presence of the complexes [Zn(en) —(mea)3 ]2+ (n = 0-3) and the complexes [Zn(en)2]2+ and [Zn(mea)2]2+ is indicated. At >20% MeOH, only the tris complexes (n = 0 or 3) are found. Stability constants for mixed complexes of Zn2+ with en and glycine in mixed aqueous solutions of methanol, dioxane, acetonitrile and DMF have been determined.193 In general, the stability constants increase with increasing composition of the co-solvent in the order H20 < MeOH < MeCN < DMF < dioxane. 

Measurement of stability constants for complex formation between Zn2+ and the Schiff bases derived from salicylaldehyde (sal) and either en or 1,3-diaminopropane indicate terdentate coordination by two nitrogen atoms and one oxygen atom. Zn2+ also promotes formation of these Schiff bases, and the rate constants are consistent with a mechanism which involves the preequilibrium formation of a mixed [(sal)Zn(diamine)]+ complex.1216... 

The stability constants for 1 1 complexes between 2,2 -thiodiethanol, tetrahydrothiophene, diethyl sulfide and Hgn were detected in H20 and mixed aqueous solvent systems.384... 

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