Metal complexes formative constants

Reaction experiments were performed at the substrate to catalyst ratios between 250 and 5000 (Table 1). The immobilized catalyst showed a rather constant values of TOP and enantioselectivity in spite of the increase in the S/C ratio, even though these values were slightly lower than those of the homogeneous Ru-BINAP catalyst. After the reaction, the Ru content in the reaction mixture was measured by ICP-AES and was found to be under 2 ppm, the detecting limit of the instrument, indicating the at Ru metal didn t leach significantly during the reaction. These results show that the immobilized Ru-BINAP catalyst had stable activity and enantioselectivity and that the Ru metal complex formed a stable species on the alumina support. 

The stability constants of zinc(n) complexes of uracil, thymine, and cytosine have been reported.249 At 45 °C in 0.1M-KNO3, 1 1 complexes are formed. The 2 1 ligand metal complexes formed between thiosalicylic acid and zinc(n), mercury(n), cadmium-(n) and lead(n) have been isolated, and formation of the 1 1 complexes in solution has been characterized by pH-titration.250 With mercury, the 2 1 complex has been assigned the structure (7), while the other metals form complexes of general structure (8). This is thought to be a consequence of the order S—M11 bond strength being Hg > Zn > Cd > Pb. 

In the absence of such data, plots of stability constants for isostructural metal complexes formed with a common ligand against EN values for the metal ions are still useful. As shown in Figure 2, the stability of divalent metal complexes with HCO3 and S04 is practically independent of cation electronegativity, whereas the metal complexes formed with HP04 and 003 are increasingly dependent on EN, particularly for EN >1.5. Based on the relative solubilities of their salts, EN values for C0 2- ... 

As the free metal has no CD absorbance, and there is a measurable change in absorbance with increasing concentration of metal complex formed, we may utilise the Beer-Lambert law to calculate the concentration of the species present from the measured change in absorbance and thus calculate these constants. It was felt that iterative calculations as carried out by Freeman et al were not necessary due to the vast difference between the values of and... 

From the plots of the relative intensities of the metal complexes formed it could be seen that the formation of many zinc species was independent of the concentration of metal salt added. This was the case for all the doubly charged zinc complexes of patellamide C which, after an initial fast increase in their intensities, stabilised at around 1 equivalent of zinc added and remained more or less constant thereafter. This was also... 

The distribution coefficient may be expressed as a function of the metal association (stabihty) constants in the LM solution, the association constants of metal ions with solvent environment in the feed and in the strip solutions and partition coefficients of the carrier and metal ion. In this case, the separation factor can be determined by stability constants of the metal complexes, formed with functional groups of carrier, if we assume that the metal ions are predominantly present (a) as free ions in the acid solution, so that complex concentrations can be disregarded and (b) as complexes in the LM solutions, so that free ion concentrations can be disregarded. 

In addition to these two classes there are borderline elements which can show both characters. Since their character depends on the donor atoms, it may be interesting to study the stability of the complexes of the borderline elements and look for factors which effect the strength of metal-donor bonds. From this point of view the stability constants of some metal complexes formed with the ligands containing O, S, or Se as the donor atom were studied and their affinities towards bivalent metals were compared (2),... 

Bjerrum determined the stability constants of a large number of metal complexes forming in aqueous solutions. He described the stepwise formation of a series of metal complexes of the type ML, ML2---ML by the following equations ... 

Charles s and Gay-Lussac s law Relation stating that at constant P and n, the volume of a gas is directly proportional to its absolute temperature, 106-107, 111 Chelating agent Complexing ligand that forms more than one bond with a central metal atom the complex formed is called a chelate, 411-412 natural, 424-425 synthetic, 424-425 Chemical equation Expression that describes the nature and relative amounts of reactants and products in a reaction, 60-61. See also Equation, net ionic. 

A knowledge of stability constant values is of considerable importance in analytical chemistry, since they provide information about the concentrations of the various complexes formed by a metal in specified equilibrium mixtures this is invaluable in the study of complexometry, and of various analytical separation procedures such as solvent extraction, ion exchange, and chromatography.2,3... 

EDTA is a very unselective reagent because it complexes with numerous doubly, triply and quadruply charged cations. When a solution containing two cations which complex with EDTA is titrated without the addition of a complex-forming indicator, and if a titration error of 0.1 per cent is permissible, then the ratio of the stability constants of the EDTA complexes of the two metals M and N must be such that KM/KN 106 if N is not to interfere with the titration of M. Strictly, of course, the constants KM and KN considered in the above expression should be the apparent stability constants of the complexes. If complex-forming indicators are used, then for a similar titration error KM/KN z 108. 

In the pH range 7-11, in which the dye itself exhibits a blue colour, many metal ions form red complexes these colours are extremely sensitive, as is shown, for example, by the fact that 10 6 — 10 7 molar solutions of magnesium ion give a distinct red colour with the indicator. From the practical viewpoint, it is more convenient to define the apparent indicator constant K ln, which varies with pH, as ... 

Cathodic protection is a useful supplement to other forms of water treatment, as a general corrosion inhibiting device in HW boilers, or where specific design configurations can lead to inadequately protected localized metal in steam boilers. Where BW makeup demands are minimal and boiler output is fairly constant, cathodic protection devices can also provide some measure of protection against hardness scales. Calcium carbonate salt is formed as a floc-culant or soft sludge rather than a hard scale, due to the peptizing effects of a zinc hydroxide complex formed from zinc ions in alkaline BW. 

The resulting species is called a complex ion. The equilibrium constant for the formation of a complex ion is called its formation constant (itf). Tabulated values of Kf always refer to the equilibrium constant for the complex forming from the metal cation. Here, for example, is the reaction describing the complexation... 

For a complex-forming metal ion detectable by its own metal electrode, e.g. in the titration of Cu2+ with EDTA by means of a Cu electeode and a double junction calomel electrode, p/ curves are obtained of a nature comparable to those in Fig. 2.20 and with a Cu range of about 20 (cf., stability constant... 

Compartmental pyrazole ligands (14) can be used to form bimetallic complexes (15).157 This ligand enforces a separation distance between the metal ions. Stability constants were calculated showing a stability for both mononuclear and dinuclear compounds that was less than Cu11 but greater than Nin. 

Optical activity in metal complexes may also arise either if one of the ligands bound to the metal in the first co-ordination sphere is itself optically active or if the complex as a whole lacks a centre of inversion and a plane of symmetry. Thus all octahedral cts-complexes of the tris-or bis-chelate type have two isomeric forms related by a mirror plane, the d- and /-forms. These species have circular dichroism spectra of identical intensities but opposite in sign. The bands in the circular dichroism spectrum are, of course, modified if ligand exchange occurs but they are also exceedingly sensitive to the environment beyond the first co-ordination sphere. This effect has been used to obtain association constants for ion-pair formation. There also exists the possibility that, if such compounds display anti-tumour activity, only one of the mirror isomers will be effective. 

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