Electronic gallium compounds

Most gallium compounds are toxic, particularly the metal gaUium arsenide. When forms of gallium are used in the electronics industry, great care must be taken to protect workers. 

We could show that the hypersilyl substituent is a very useful group in the synthesis of low valent gallium compounds. Not only the steric demand of this group but also its electronic properties, as theoretical studies have confirmed, contribute to its cluster stabilizing ability [18]. 

Table 4.1- -65 Effective masses of electrons ( ) and holes (mp) for gallium compounds (in units of the electron mass mo) ...

Table ft.1-67 Electron and hole mobilities /Xn and /Xp of gallium compounds... 

The principal characteristic that distinguishes the Group 3A elements from the rest of the representative elements is the existence of electron-deficient compounds. You may recall earlier references, in this book and elsewhere, to compounds of this type. It is not unusual for boron, aluminum, gallium, and occasionally beryllium and lithium to form compounds in which the metal is surrounded by less than an octet of electrons. One should of course be wary of such phrases as electron-deficient. It seems to imply that there is something wrong with such compounds. In fact, it is... 

Electron-deficient compounds are formed by boron, aluminum, gallium, and indium as well as lithium, beryllium, and magnesium. Such compounds are... 

G for gallium. These values (see also in the next section) are consistent with the unpaired electron residing in a Ti-orbital. The stability of these compounds was attributed to the large size and electronic properties of the Si(f-Bu)3 substituents [26-28]. Computational data for the aluminum compound indicate an Al—Al distance of 2.537 A and a wide Al—Al-Si angle of 174.90° [26]. The longer distance for the aluminum species is a result of the larger covalent radius for this metal [18]. 

KT1 does not have the NaTl structure because the K+ ions are too large to fit into the interstices of the diamond-like Tl- framework. It is a cluster compound K6T16 with distorted octahedral Tig- ions. A Tig- ion could be formulated as an electron precise octahedral cluster, with 24 skeleton electrons and four 2c2e bonds per octahedron vertex. The thallium atoms then would have no lone electron pairs, the outside of the octahedron would have nearly no valence electron density, and there would be no reason for the distortion of the octahedron. Taken as a closo cluster with one lone electron pair per T1 atom, it should have two more electrons. If we assume bonding as in the B6Hg- ion (Fig. 13.11), but occupy the t2g orbitals with only four instead of six electrons, we can understand the observed compression of the octahedra as a Jahn-Teller distortion. Clusters of this kind, that have less electrons than expected according to the Wade rules, are known with gallium, indium and thallium. They are called hypoelectronic clusters their skeleton electron numbers often are 2n or 2n — 4. 

The 3IP NMR chemical shifts, shown in Table IV, should be a useful indicator of the electronic environment at phosphorus. Almost all the 3IP chemical shifts are upfield (negative 8 values) in contrast to the boron-phosphorus compounds where downfield shifts (positive 8 values) are observed. This can be interpreted in terms of weak gallium-phosphorus it-... 

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. 

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