Metal ligand constant

The equilibrium constant for a reaction in which a metal and a ligand bind to form a metal—ligand complex K ). 

The formation of a metal-ligand complex is described by a formation constant, K. The complexation reaction between Cd + and NH3, for example, has the following equilibrium constant... 

The formation constant for a metal—ligand complex in which only one ligand is added to the metal ion or to a metal—ligand complex Ki). 

Stepwise and cumulative formation constants for selected metal-ligand complexes are given in Appendix 3C. 

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. 

The equilibrium formation constant for a metal-ligand complex for a specific set of solution conditions, such as pH. 

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. 

Molecular absorption, particularly in the UV/Vis range, has been used for a variety of different characterization studies, including determining the stoichiometry of metal-ligand complexes and determining equilibrium constants. Both of these examples are examined in this section. 

In the slope-ratio method two sets of solutions are prepared. The first set consists of a constant amount of metal and a variable amount of ligand, chosen such that the total concentration of metal, Cm, is much greater than the total concentration of ligand. Cl- Under these conditions we may assume that essentially all the ligand is complexed. The concentration of a metal-ligand complex of the general... 

The shift in the voltammogram for a metal ion in the presence of a ligand may be used to determine both the metal-ligand complex s stoichiometry and its formation constant. To derive a relationship between the relevant variables we begin with two equations the Nernst equation for the reduction of O... 

Very slight changes in wave numbers observed when moving within the same group, from Mo to W, from Nb to Ta and from Zr to Hf (see Fig. 46), indicate that the contribution of the change in the central atom s mass is compensated for by respective changes in the metal-ligand force constant. 

It is possible to obtain fairly reliable values for many complexes of 1 1 (metal ligand) stoichiometry by using an extended empirical equation in which the dielectric constant is dependent on the cationic charge (21). For the complexation reaction ... 

A quantum-mechanical description of spin-state equilibria has been proposed on the basis of a radiationless nonadiabatic multiphonon process [117]. Calculated rate constants of, e.g., k 10 s for iron(II) and iron(III) are in reasonable agreement with the observed values between 10 and 10 s . Here again the quantity of largest influence is the metal-ligand bond length change AR and the consequent variation of stretching vibrations. 

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