Constant instability

The reverse of the association or formation reactions would represent the dissociation or instability constant for the systems, i.e., —log Kj, = log TsTjjjstji,. 

It should be apparent that the larger the equilibrium constants for these reactions, the more unstable the complexes. Consequently, the equilibrium constants for these reactions are called dissociation or instability constants. One must remember that the first step in the dissociation of ABm corresponds to the reverse of the last step in the formation of the complex. Thus, if we represent the instability constants as fc and a total of six steps are involved, the relationships between the fe, and K values are as follows. 

Nalidixic acid and sodium nalidixate form a strong colored complex with iron III. The maximum of absorbance of the complex is 410 nm and Beer s Law is obeyed from 10 to 250 yg of nalidixic acid per ml(33)5 and from 0.43 to 17.05 mg iron III per ml.(34) Nalidixic acid complexes through the oxo-group on C-4 and the carboxylic acid group on C-3. Three moles of nalidixic acid complex with one mole of iron III. The instability constant of the complex was calculated to be 2.11 x 10 8 by Dick and Murgu.(34)... 

K B. Yatsimirksii, V. P. Vasil ev, Instability Constants cf Complex Compounds, Pergamon, New York, 1960. 

Vasilev, V. P. Influence of ionic strength on the instability constants of complexes. Russ. J. Inorg. Chem., 1962, 7, 8, 924 927. 

The value of the instability constant (i.e., the concentration, indicated in brackets) ratios for the preceding is... 

Cl Br H2O Pd q- redox potentiometric method Instability constants are greater for Pd than Pt. c... 

Yatsimirksii KB, Vasil ev VP (1960) Instability constants of complex compounds. Pergamon, New York... 

The equilibrium constant for the formation of a metal complex is known as its stability constant. (Some authors, however, present the datum as its reciprocal, the instability constant of the complex, by analogy with the dissociation of a weak acid.) There are two kinds of stability constants stepwise (Ad, Ad, Ad,..., Kn) and overall (/ ). We will assume that there are six aqua ligands to be replaced by some other unidentate ligand Xx, in an aqueous solution of Mm+ ... 

The hydroxo complex ions formed in this way have instability constants, just as ammine or other complexes do. These instability constants are somewhat special, in that one of the products of the equilibrium is the insoluble amphoteric hydroxide. Thus, for aluminum hydroxide,... 

The [A1(OH)3(s)] is omitted, as usual, because it is a solid. Because the solids are part of the equilibrium, the instability constants of these hydroxyl complex ions can be applied only to solutions that are saturated with respect to the solid. 

As the complex becomes more stable, the formation constant becomes larger. The reciprocal of the formation constant is called the instability constant. 

With ascorbic add, silver was reduced to metallic silver although at room temperature the reaction was slow enough for a measurement of the instability constant (A = 2.2 0.2 x 10 4 hence log j8i = 3.66 0.04).265... 

Often the logerithms of kn values are reported in the literature. Some workers prefer to report the instability constants, A jnst, rather than formation constants, where fcinst is the reciprocal of the formation constant. 

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