Section 16. Gallium, Indium, Thallium

The discussion of the main group 3-5 and 3-6 compounds in the previous sections was limited to examples in which the group 3 element E is three-coordinate, so that an empty p-orbital on E is available for overlap with a lone pair on the group 5 or 6 atom. For the same reason, the discussion here will focus on those compounds with three-coordination at gallium, indium, or thallium. In the case of the transition metal derivatives, it is transition metal -electrons that are available to overlap with the empty p-orbital on E to form the potential ir-bond, as illustrated in Fig. 26. 

This section will focus on homonuclear neutral or anionic clusters of the elements aluminum, gallium, indium, and thallium, which have an equal number of cluster atoms and substituents. Thus, they may clearly be distinguished from the metalloid clusters described below, which in some cases have structures closely related to the allotropes of the elements and in which the number of the cluster atoms exceeds the number of substituents. The compounds described here possess only a single non-centered shell of metal atoms. With few exceptions, their structures resemble those of the well-known deltahedral boron compounds such as B4(CMe3)4 [30], B9CI9 [31] or [B H ]2 [32]. The oxidation numbers of the elements in these... 

The elements in group 13 - boron, aluminium, gallium, indium and thallium - show a wide variation in properties B is a non-metal, A1 is a metal but exhibits many chemical similarities to B, and the later elements essentially behave as metals. The diagonal relationship between aluminium and beryllium was discussed in Section 11.10. Although the M(III) oxidation state is characteristic for elements in group 13, the M(I) state occurs for all elements except B, and for T1 this is the more stable oxidation state. Thallium shows similarities to elements outside those in group 13, and can be compared to the alkali metals, Ag, Hg and Pb, an observation that led Dumas to describe it as the duckbill platypus among elements . 

This section contains references other than those in the main Report, which have been abstracted during the literature search, and are considered relevant to the chemistry described in this Chapter. The references are arranged according to whether they are aluminium, gallium, indium, or thallium organo-metals and then in alphabetical order according to the name of the first author. Where the information has been obtained from Chemical Abstracts, only the abstracts reference number is given. 

Hi) Gallium, indium, and thallium. Most of the organic chemistry of gallium, indium, and thallium that merits inclusion in this book is included in the section below on co-ordination compounds. Here are mentioned only lower oxidation states and the instability of hydrides. 

Studies of the pyrolysis of these three alkyls may conveniently be discussed in a combined section. The decompositions were carried out in a conventional toluene carrier flow system using contact times of 1-2 sec120,122,123. The conditions used satisfy both plug flow and thermal equilibrium requirements68,69. Toluene to alkyl ratios greater than 50 in the trimethyl gallium system and greater than 200 in the trimethyl indium and thallium studies were required to obtain first-order dependence in terms of the alkyl concentration. Under these conditions methane and ethane are produced by the reactions... 

Thallium(III)(CF3)3T1.2L (L = DMF,DMSO,py) have been prepared from TIX3 (X = Cl,OAc,O2CCF3) and (CF3)2Cd in aprotic, coordinating solvents, as described earlier for the gallium and indium analogues (Section 1.1). With excess (CF3)2Cd, nmr... 

---