Thermodynamic 6s inert pair effect

A number of related Ga-containing cages are known, as well as a few Tl—N clusters, e.g. Tl2(MeSi)2(N Bu)4,12.37. However, in the latter and related compounds, the Tl atoms do not carry terminal substituents, another manifestation of the thermodynamic 6s inert pair effect (see Box 12.3). 

The preference for the - -2 over -1-4 oxidation state increases down the group, the change being due to the thermodynamic 6s inert pair effect (Box 12.3). Whereas members of the GeX4 family are more stable than GeX2,... 

Cyclopentadienyl complexes illustrate the increase in stability of the M(I) oxidation state as group 13 is descended, a consequence of the thermodynamic 6s inert pair effect (see Box 12.3). Cyclopentadienyl derivatives of Ga(III) which have been prepared (equations 18.35 and 18.36) and structurally characterized include Cp3Ga and CpGaMe2. 

The general trend in decreasing values of IE and IE2 down the group (see Section 1.10) is broken by the increase in going from Ba to Ra, attributed to the thermodynamic 6s inert pair effect (see Box 13.3). 

CHEMICAL AND THEORETICAL BACKGROUND Box 13.3 The thermodynamic 6s inert pair effect... 

Finally, we must consider the effect of varying M down a group. In general, ionization energies (see Appendix 8) and lattice energies of compounds decrease as atomic and ionic radii (see Appendix 6) increase. It is where there is actually an increase in ionization energies, as is observed for the valence electrons of Tl, Pb and Bi, that we get the clearest manifestations of the thermodynamic 6s inert pair effect. Where covalent bond formation is involved, a really satisfactory discussion of this inert pair effect is not yet possible, but the attempt at formulation of the problem can nevertheless be a rewarding exercise. 

On descending group 13, the trend in IE2 and lE shows increases at Ga and Tl (Table 13.1), and this leads to a marked increase in stabUity of the 4-1 oxidation state for these elements. In the case of Tl (the only salt-like trihalide of which is TIF3), this is termed the thermodynamic 6s inert pair effect (see Box 13.4), so called to distinguish it from the... 

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