Aluminum, Gallium, Indium, and Thallium

The elements below boron in Group IIIA of the periodic table include one of the most common and useful metals and three others that are much less important. Aluminum is the third most abundant element, and it occurs naturally in a wide variety of aluminosilicates, some of which will be described in more detail in Chapter 11. It also occurs in the minerals bauxite, which is largely AIO(OH), and cryolite, Na3AlF6. Although a few relatively rare minerals contain gallium, indium, and thallium, they are usually found in small quantities and are widely distributed. As a result, these elements are generally obtained as by-products in the smelting of other metals, especially zinc and lead. 

All of these metals exhibit a +3 oxidation state in many of their compounds, but there is an increasing tendency toward a stable +1 state in heavier members of the group. As in the case of the chlorides of Ag+ and Pb2+, T1C1 is insoluble in water and dilute HC1. In fact, the chemistry of thallium resembles that silver and lead in several respects. 

There is also a pronounced tendency for the Group IIIA metals to form metal-metal bonds and bridged structures. The electron configuration ns2 np1 suggests the possible loss of one electron from the valence shell to leave the ns2 pair intact. The electron pair that remains in the valence shell is sometimes referred to as an inert pair, and a stable oxidation state that is less than the group number by two units is known as an inert pair effect. The fact that oxidation states of +2, +3, +4, and +5 occur for the elements in Groups IVA, VA, VIA, VIIA, respectively, shows that the effect is quite common. Thus, it will be seen that the Group IIIA metals other than aluminum have a tendency to form +1 compounds, especially thallium. 

Aluminum was discovered in 1825 by Hans Christian Oersted. Its name comes from the Latin word alumen for alum. Gallium was discovered by P. Boisbaudran in 1875, and its name is derived from the Latin name for France, Gallia. The existence of eka-aiuminum  

Ga Sphalerite ZnS Canada, Mexico, Germany, United States (MO, KS, OK, Wl) 

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A. N. Nesmeyanov and R. A. SokoUk, The Organic Compounds of Boron, Aluminum, Gallium, Indium and Thallium, North-HoUand Publishing Co., Amsterdam, the Netherlands, 1967. 

For a discussion of the atomic properties of the group 13 metals see Downs AJ (1993) In Downs AJ (eds) Chemistry of aluminum gallium, indium and thallium. Blackie, London, Chapter 1... 

Metal-Nitrogen Bond Lengths and Torsion Angles between the Metal and Nitrogen Coordination Planes for Three-Coordinate Aluminum, Gallium, Indium, and Thallium Amides... 

Almond, M. J. Group 13 boron, aluminum, gallium, indium and thallium. J. Organomet. Chem. 2002, 30, 128-158. 

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... 

Homonuclear clusters of the heavier elements of the third main-group aluminum, gallium, indium and thallium having direct element-element interactions form a fascinating new class of compounds. As discussed in the previous Chapter 2.3, in some cases their structures resemble those known with the lightest element of that group, boron, while in other cases novel, metal-rich compounds were obtained which do not have any analogue in boron chemistry. 

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