Metal-ligand stability

The metal-ligand stability constants in aqueous solutions for different metal ions, including Am(III) were determined262 using some neutral donors in combination with HTTA as the extraction agent for the uncomplexed metal ion. 

A linear relationship has been established414 between the pKa s and the metal-ligand stability constants for a series of VO24 complexes with substituted acetophenones. 

Pre-lab 7.4.b Potentiometric Titrations for Determining Ligand pKa Values and Metal Ligand Stability Constants19... 

Now equations 4.46 and 4.48 can be used to reexpress the equation for the metal-ligand stability constant, ATml> in a form that directly considers pH effects. It then becomes evident that, if the pH is raised to an alkaline value, the rise in OH activity and fall in H activity have opposing effects on metal complexation. The lowered metal ion activity, (M ), resulting from precipitation as the hydroxide, disfavors complexation. Conversely, the raised free ligand activity, (L ), resulting from dissociation at higher pH favors complexation. At extreme pH, complexation diminishes because of metal hydroxide precipitation (high pH) and association of the... 

Now we are ready to consider the practical application of metal-ligand stability constants to metal adsorption on organic matter. First we will take the case of a metal-humus system that is undersaturated with respect to the metal hydroxide. 

Agrawal YK and Patel DR, Thermodynamic proton-ligand and metal-ligand stability constants of some drugs, /. Pharm. Sci.,... 

The thermodynamic proton-ligand (pJ a) metal-ligand stability constants of clioquinol, clofibrate, nitrofurazone, and tetracycline with Cu", Zn, Mn", Mg" and Ca" have been determined at 35 °C in 50% ethanol-water media. An empirical pH correction for... 

USE Metal-ligand stability constants of complexes of 2-hydroxy-4-methylpro-piophenone,... 

Sohon G and Simon U 1995 A fasoinating new field in oolloidal soienoe small ligand stabilized metal olusters and their possible applioations in mioroeleotronies Coiioid Poiym. Sc/. 273 202... 

Conditional Metal—Ligand Formation Constants Recognizing EDTA s acid-base properties is important. The formation constant for CdY in equation 9.11 assumes that EDTA is present as Y . If we restrict the pH to levels greater than 12, then equation 9.11 provides an adequate description of the formation of CdY . for pH levels less than 12, however, K overestimates the stability of the CdY complex. 

EDTA Must Compete with Other Ligands To maintain a constant pH, we must add a buffering agent. If one of the buffer s components forms a metal-ligand complex with Cd +, then EDTA must compete with the ligand for Cd +. For example, an NH4+/NH3 buffer includes the ligand NH3, which forms several stable Cd +-NH3 complexes. EDTA forms a stronger complex with Cd + and will displace NH3. The presence of NH3, however, decreases the stability of the Cd +-EDTA complex. 

The ligand pATa values and transition metal chelate stability constants of arylisoxazoles were detected photometrically and the stability of the complexes studied (79JlCi25i). 

There is an interesting paradox in transition-metal chemistry which we have mentioned earlier - namely, that low and high oxidation state complexes both tend towards a covalency in the metal-ligand bonding. Low oxidation state complexes are stabilized by r-acceptor ligands which remove electron density from the electron rich metal center. High oxidation state complexes are stabilized by r-donor ligands which donate additional electron density towards the electron deficient metal centre. 

Abstract This chapter is devoted to phosphinous amides, a particular class of tervalent aminophosphanes. First, attention is focused on their stability and synthetic procedures. Reports dealing with their prototropic equilibrium and main group chemistry are also considered. Last but not least the really important applications of these species as metal ligands in the field of catalysis are reviewed, including asymmetric variants. 

The decomposition is significantly accelerated and the temperature of the first decomposition reaction is lowered to 120°C (Fig. 19.7). The decomposition rate is relatively low compared with other titanium-based dopants. The highest activity of a titanium catalyst used in alanate decomposition was observed for ligand-stabilized colloidal titanium metal [42]. 

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