Lanthanide propionate complexes

In Fig. 7.30 log Ln is plotted against log K for the trans-cis isomerization of the oxalato complex. Here Ln refers to catalytic rate constants and K is the complex formation constant for lanthanide propionate complexes. The linear free energy relationship holds... 

Fig. 7.30. log-log plot of the catalytic rate constants for the lanthanide ion catalyzed trans-cis isomerization of trans-bis(oxalato)diaquochromate(III) (25°C, / = 1.5 M adjusted with NaN03) vs. the formation constants for the lanthanide/propionate complexes (25°C, I = 2.0 M) [84]. 

Fig. 18. Variation of the enthalpy (AH ) and the entropy (AS) of formation of the propionate (-----) and the isobutyrate (----) complexes (26) with the L-values of the trivalent lanthanides.

The decomplexation of trivalent lanthanide complexes of l,10-diaza-4,7,13,16-tetraoxacyclooctadecane-JV-acetic acid (K22MA) and l,10-diaza-4,7,13,16-tet-raoxacyclooctadecane-iV,N -di-i3-propionic acid (K22DP) (which are diaza crown ethers with one and two carboxylic acid pendant arms attached to the diaza nitrogens, respectively) has been studied by a spectrophotometric SF method, and is characterized by the rate law (64). When the diaza crown ether is K22MA, fcd = 0.88, 0.25, and 3.99 s respectively, for La ", Eu, and Lu and -1.42 X lO and 4.93 x 10 dm moP s for La and Eu and when the diaza... 

Figure 9 Examples of a Z plot (a) and an inclined W plot (b) for log Ki for lanthanide complexes with propionate...

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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