Gadolinium compounds Gd

Gadolinium texaphyrin (Gd-tex Figure 4.8) is reported to be an effective radiation sensitizer for tumour cells, whilst the corresponding lutetium compound, which absorbs light in the far-red end of the visible spectrum, is in Phase II trials for photodynamic therapy for brain tumours and breast cancer. 

The Pr ion can be used succesfully as a sensitizer in luminescent materials based on gadolinium compounds 112-115). However, this is only possible if the Afbd state of Pr " " decays radiatively. Otherwise the nonradiative return to the Af configuration occurs more rapidly than the Pr " " - Gd + transfer. 

As the data in Table 11.1 illustrate, the most promising nuclei for NCT are B and Gd atoms, which are stable isotopes with large thermal neutron capture cross sections. Gadolinium is toxic, while boron exhibits low toxicity. Gadolinium compounds tend to be chemically unstable, and must be stabilized by chemical procedures such as chelation. 

The unsuitability of non-gadolinium(III) lanthanide(III) ions has been demonstrated empirically by Zheng et al. [32]. The isostructural pair of compounds [Ln(III)8Co(II)8(OH)4(N03)4(03PtBu)8(02CtBu)16], where Ln(III) is either Gd(III) or Dy(III), are 3d-4f phosphonates, with the core structure shown in Figure 9.10. See the comprehensive review in [32] from whence Figure 9.10 is taken for a huge study of lanthanide-cobalt-phosphonate compounds. 

For the Gd(III) compound -ASf is 21.4Jkg 1 K 1 (AH = 0 — 7T, 3K), whereas for Dy(III) this is only 11.6 J kg-11<-1. This is accounted for by the lower spin of Dy(III), but what is interesting is the fact that - ASM has already passed through a maximum at 4I<, compared to the Gd(III) plot, which is still rising at 3K, which is qualitatively in line with the work of Evangelisti and Brechin [13] for 3d metals. From this, we can say that the best lanthanide(III) for low-temperature MCE is gadolinium(III) indeed, there are only a handful of compounds using Dy(III) reported for this application. 

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