Thallium oxidation states

The exhibition of variable valency is indeed a characteristic of transition metals. Main group metal ions such as those of groups 1 or 2 exhibit a single valence state. Other main group metals may show a number of valencies (usually two) which are related by a change in oxidation state of two units. This is typified by the occurrence of lead(iv) and lead(ii) or thallium(iii) and thallium(i). However, all the transition metals exhibit a range of valencies that is generally not limited in this manner. 

During oxidation of tin(II) ions by hydrogen peroxide, iodine, bromine, mercury(ir) and thallium(III) the induced reduction of cobalt(in) complexes cannot be observed. Therefore, it was concluded that these reactions proceed by 2-equivalent changes in the oxidation states of the reactants. 

Thallium may be described as a relativistic alkali metal the downshift in energy of the 65 orbital, due to a combination of relativity and shell structure effect, favours the oxidation state I over III (see 4.2.22). The stability of the oxidation state +1... 

Thallium occurs in soils in both -p3 and -pl oxidation states. Tl + behaves much like Al +, but hydrolyses even more readily and insoluble Tl(OH)3 is formed... 

Other metah—a classification given to seven metals that do not fit the characteristics of transition metals. They do not exhibit variable oxidation states, and their valence electrons are found only on the outer shell. They are aluminum, gallium, indium, tin, thallium, lead, and bismuth. 

Two examples of compounds in thallium +1 and +3 oxidation states follow ... 

Of the metals that form luminescent supramolecular entities with gold, that for which most complexes are known is thallium in its +1 oxidation state. As described below, in recent years the contributions of several laboratories have been reported. Nevertheless, in some cases, the papers also report similar reactions with other metals, leading to similar structures. In order to maintain a congruent synthetic description, those examples will be discussed together as they appear in the original work. 

For A, the nitrogen coordination is invariably planar because of a low to zero inversion barrier which facilitates possible overlap of the M and N p-orbitals. The n-overlap in B is facilitated by a linear geometry. However, a further consideration in the case of B is the increasing stability of the lower oxidation state of the metal when descending the group. This effect is most prominent in thallium and it implies an increasing stability of the monovalent unit R-M which may lead to destabilization or distortion of structure B. 

One of the classical properties of the main group elements is that the stability of the lower oxidation states increases with atomic number, and the chemistry of thallium is a good example of this effect. In aqueous solution, the Tl+ ion is stable with respect to oxidation by the solvent and there is accordingly an extensive chemistry of this oxidation state. The similarities between Tl+ and the corresponding alkali metal cations have resulted in much interest in the use of this ion as a probe in biochemical systems, and the ease with which 205T1 NMR spectra can be recorded has also had an impact on such studies.277,278... 

The analogous selenium and tellurium chemistry has not been explored. The [Tl2Te2]2-anion has been obtained by reacting KTITe with [2.2.2]cryptate in ethylenediamine to give [K([2.2.2]crypt)]2[Tl2Te2]2- en, in which the anion is butterfly-shaped with a 50° fold.328 The assignment of oxidation numbers is somewhat arbitrary in such systems (cf. Section 25.2.6.1.2), but it seems clear that thallium is in a low oxidation state. 

The oxidizing properties of thallium(III) in both aqueous and non-aqueous media obviously preclude the existence of a number of compounds analogous to those found for aluminum, gallium and indium in this oxidation state. Thus, while there is much richer chemistry for thallium in the +1 state, there is a concomitant decrease in the detailed information on thallium(III) coordination chemistry. 

Thallium has two stable oxidation states, + f and +3. Use the Kapustmskii equation to predict the lattice energies of TIF and TIF. Predict the enthalpies of formation of these compounds. Discuss. 

Finally, the heavier posttransition metals have group number oxidation states corresponding to < 10 configurations indium(lll), thallium(III), tin(IV), lead(lV), anti-mony(V). bismuth(V), etc. However, there is an increasing tendency, termed the inert pair effect," for the metals to employ p electrons only and thus to exhibit oxidation states two less than those given above (see Chapter 18). 

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