Gadolinium break

The stability constants show the same trend as with acetate having an extended region (Eu—Ho) of the gadolinium break. 

It will be noticed (Table 37) that the entropy of formation of the am oacid complexes are quite large and again on the basis of A/Sj values the complexes could be divided into two groups. Thus, at present, there seems to be no simple explanation of the gadolinium break. 

The extensive experimental analysis of the rare earth spectra in doped crystals has enabled us to deduce the Ft and X parameters for M3+ ions. These are presented in Table 42. It is interesting here to examine these values closely. Inspection of the Ft data reveals much irregularity throughout the series whereas 4/ shows a tendency to increase from Ce3+ to Yb3+. The author has tried to correlate the F2 and 4/ parameters with the polarizing power (e/r2) of the rare earth ions and obtained Fig. 21. The F2 parameter shows a linear increase up to Tb3+ followed by a decrease to Ho + and then another increase. However, the noteworthy aspect is the linear behaviour of 4/ with e/r2 having a small but distinct gadolinium break near the Gd—Dy region. 

The trend of log kn in glyoxylate complexes is more aimilar to that of the glycolate system than the acetate system. The gadolinium break... 

The stability constants for N/-(2-hydroxyethyl)ethylenediaminteri-acetic acid (HEDTA) [453], a closely related ligand to EDTA, and those of N, N -ethylenediaminediacetic acid (EDDA) [454] are compared in Table 34. A severe gadolinium break is observed in the case of both EDDA and HEDTA. 

In the case of a majority of ligands, the gadolinium complex is less stable than one would expect based on the simple electrostatic model. This has been known as the gadolinium break which cannot be explained in terms of steric hindrance since this anomaly is present even with ligands which offer no steric hindrance. 

Danilov and co-workers (20) studied the extraction of lanthanides with a,a -dialkylcarboxylic and hexanoic acids in n-heptane. The extracted species is invariably LnA3(HA)3. As is obvious from Table II, the gadolinium break is observed in the extraction constants. 

Keywords Lanthanide Sensor Sensitized luminescence Dipicolinate Macrocycle Ternary complex Bacterial spore Ancillary ligand Gadolinium break Catecholamine Salicylic acid Salicylurate. 

Although both Klemm and Noddack stuck to their respective diad and triad classifications of the lanthanides until the end of the discussion and later, it became, however, clear that a break do exist around the gadolinium region (not an experimental error, as many have supposed at that time), and that the gadolinium break is observed either (a) very weakly (or not at all) for some properties or (b) very pronounced for other properties of the lanthanide series. 

Thus the idea of gadolinium break and its association with the half-filled 4/-shell started to crystallized out around 1930. 

As more and more experimental results on the formation constants and the thermodynamic properties were obtained, it became positively clear that the region of the gadolinium break is not confined in gadolinium and that it may start as early as samarium and may extend upto dysprosium. This is exemplified in some representative plots of the formation constants in Fig. 3. It is obvious that in some cases severe gadolinium break has been observed. 

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