Glycolate complexes stability constants

The enthalpies and entropies of formation of mono-mandelato-complexes have been determined and, in comparison with other hydroxycarboxylic acid complexes, the enthalpy order of stabilization is lactate > a-hydroxyiso-butyrate mandelate > glycolate, whereas the entropy order of stabilization is glycolate > a-hydroxyisobutyrate > mandelate > lactate. The stability constants and enthalpy of formation of mono- and di-malonate complexes have also been measured.The mono-1,1-cyclopentanedicarboxylato-complexes are less stable than the corresponding malonate species. 

The glycolate Cr(C2H303)2-H20,213 salicylate Cr(C6H4(0)C02)-3H20 and tartrate Cr(C02CH0HCH0HC02)3 have been prepared. Stability constants have been determined for complexation of Cr11 with salicylate and 5-sulfosalicylate (Table 39). 

Recently, Grenthe [407] compared the stability constants for the acetate, glycolate and thioglycolate (mercaptoacetate) complexes of Eu3+ and Am3+ (fi — 0.5 at 20° C), and obtained the following log k values... 

Table 28. Stability constants of some rare eartha glycolate complexes [406]...

Absorption spectra in the f-f region are in general not very sensitive to the ligand environment unlike the transition metal ions. In spite of this difficulty, the absorption spectroscopic method has been used in the determination of stability constants of Er(III) acetate [197] and Nd(III) glycol ate complexes [198]. For complexes of low stability, a... 

Examination of Table 8.9 reveals that aminopolycarboxylic adds complex Am(iii) more strongly than do either hydroxycarboxylic or aminoalkylpolyphos-phoric adds (e.g. ethyIenediaminebis(methyIene)phosphonic add). Keller [3] observes that in the series of a-hydroxycarboxylic adds (e.g. glycolic and lactic) the stability of the ameridum complex decreases with increasing number of carbon atoms. The logarithm of the stability constant of the complexes of Am with aminopolycarboxylic adds increases linearly (Fig. 8.9) with the number of bound donor atoms of the ligand. 

A practical application of the spectral intensity of hypersensitive transitions in lanthanide ions is the determination of stability constants. Bukietynska et al. (1977, 1981a,b) have evaluated the stability constants of lanthanide complexes from the changes of the oscillator strength of hypersensitive transitions as a function of the ligand concentration. The method was applied to acetate, propionate, glycolate, lactate and a-hydroxyisobutyrate complexes of Nd ", Ho and Er +. Bukiet5mska et al. claim that this spectrophotometric method is superior to the potentiometric method, since the best results for the latter method can be obtained only for the first complexation steps. The stability constants evaluated at several temperatures have been used also to calculate the thermodynamic quantities AG, AH and AS. 

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