Thermodynamic > 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. 

R. S. Drago, /. Phys. Chem., 62, 353 (1958). Thermodynamic Evaluation of the Inert Pair Effect. 

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... 

Cadmium is chemically very like Zn, and any differences are attributable to the larger sizes of the Cd atom and Cd ion versus Zn. Among the group 12 metals, Hg is distinct. It bears some resemblance to Cd, but in many respects is very like Au and Tl. It has been suggested that the relative inertness of Hg towards oxidation is a manifestation of the thermodynamic 65 inert pair effect (see Box 13.4). 

Use standard reduction potentials to determine the AG° of the reaction of T1 (r) and H (ay) to produce (a) Tl (ay) and H2( ) and b) TP (ay) and H2( ). Which reaction is more thermodynamically spontaneous under standard-state conditions Comment on the results relative to the inert-pair effect. 

The fact that SFs does not react with water is not due to thermodynamic stability. Rather, it is because there is no low-energy pathway for the reaction to take place (kinetic stability). Six fluorine atoms surrounding the sulfur atom effectively prevent attack, and the sulfur atom has no unshared pairs of electrons where other molecules might attack. In SF4, not only is there sufficient space for an attacking species to gain access to the sulfur atom, but also the unshared pair is a reactive site. As a result of these structural differences, SF6 is relatively inert, whereas SF4 is very reactive. 

Sulfur hexafluoride sublimes at -64 °C to produce a dense gas (6.14 g L-1). Under a pressure of 2 atm, the melting point is -51 °C. The molecule has the expected octahedral structure and a dipole moment of zero. The compound is so inert that it is used as a gaseous insulator, and rats allowed to breathe a mixture of SF6 and oxygen show no ill effects after several hours of exposure. This inertness is a result of the molecule having no vacant bonding site or unshared electron pairs on sulfur to initiate a reaction and the fact that six fluorine atoms shield the sulfur atom from attack. Consequently, there is no low-energy pathway for reactions to occur, and the compound is inert even though many reactions are thermodynamically favored. 

Another commonly observed decomposition pathway involves C-H bond activation. For example, the reaction of (l,3-But2Gp)2ZrMe2 with B(C6F5)3 yields a C-H activated 77s,771- tuck-in cation 710 (Scheme 173), which is inert with respect to ethylene polymerization. There are also significant metal-alkyl group effects on the thermodynamic stability and stereochemical mobility of the B(C6F5)3-derived Zr and Hf metallocenium ion pairs.538... 

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