Metalloid structures

A possible explanation for the formation of this planar ladder structure can be found in the close geometrical similarity of 7 to (3-gallium. The relative positions of the Ga atoms in 7 are comparable to those found in (3-gallium (see Fig. 18), but as expected, the Ga-Ga distances in 7 are all shorter than in (3-gallium due to a more molecular kind of bonding. This means that in 7 the formation of metalloid structures is preferred over the formation of polyhedral structures, which results in the unusual arrangement of the Ga atoms. 

The relationship of the wheel-rim-type structure of 62 to the metal can be demonstrated by a 30° rotation of the two centered Alg rings followed by a shift of the six rings towards each other (cf. Figure 2.3-13) [92], The other possibility of the formation of an Al14 polyhedron with point symmetry by displacement of the two naked central atoms in the direction of a polyhedral entity has been shown to be energetically unfavorable by quantum chemical calculations i.e., the observed metalloid structure (Figure 2.3-13) is favored over the anticipated polyhedral structure as described by Wade-Mingos [5, 96] (see Chapter 1.1.2). 

Some physical properties of the elements are compared in Table 10,2. Germanium forms brittle, grey-white lustrous crystals with the diamond structure it is a metalloid with a similar electrical resistivity to Si at room temperature but with a substantially smaller band gap. Its mp, bp and associated enthalpy changes are also lower than for Si and this trend continues for Sn and Pb which are both very soft, low-melting metals. 

Several nonmetallic elements and metalloids have a network covalent structure. The most important of these is carbon, which has two different crystalline forms of the network covalent type. Both graphite and diamond have high melting points, above 3500°C. However, the bonding patterns in the two solids are quite different... 

Boron forms perhaps the most extraordinary structures of all the elements. It has a high ionization energy and is a metalloid that forms covalent bonds, like its diagonal neighbor silicon. However, because it has only three electrons in its valence shell and has a small atomic radius, it tends to form compounds that have incomplete octets (Section 2.11) or are electron deficient (Section 3.8). These unusual bonding characteristics lead to the remarkable properties that have made boron an essential element of modern technology and, in particular, nan otechn ol ogy. 

Regardless of their possible metallic properties, metal-rich Zintl system or phases are defined here as cation-rich compounds exhibiting anionic moieties of metal or metalloid elements whose structures can be generally understood by applying the classical or modern electron counting rules for molecules. 

There are distinct structural types of organic compounds containing metals and metalloids. The first contain covalent carbon-metal bonds and are strictly organometallic compounds, for example, the alkylated compounds of Hg, Sn and Pb, and of Li, Mg, and A1 (and formerly Hg), which have been extensively used in laboratory organic synthesis, and A1(C2H5)3 that is a component of the... 

Krebs, Robert E. The history and use of our earth s chemical elements a reference guide. Westport (CT) Greenwood P, 1998. ix, 346p. ISBN 0-313-30123-9 A short history of chemistry — Atomic structure The periodic table of the chemical elements — Alkali metals and alkali earth metals - Transition elements metals to nonmetals — Metallics and metalloids - Metalloids and nonmetals — Halogens and noble gases - Lanthanide series (rare-earth elements) — Actinide, transuranic, and transactinide series... 

The isolation methods and the structures of the metalloid aluminum clusters discussed here have shown the particular suitability of the ligand N(SiMe3)2 for... 

This short description of the various elementary modifications of gallium shows its high structural variety, which also includes structural elements that are atypical for metals. This variety is also reflected in the inner composition of the metalloid gallium clusters, as discussed below. 

The Gag[C(SiMe3)3]6 8 cluster, which occurs as an intermediate during the formation of the Gai 9 cluster (see above), includes the most extraordinary arrangement of gallium atoms in the cluster core of all structures of metalloid gallium clusters... 

Consequently, there is a direct relation to the metalloid In Rs (see Section III, B) cluster whose inner frame contains metallic partial structures.47... 

The more molecular character of 9 in comparison to 8-gallium is responsible for a decrease of the bond lengths by about 25 pm. These results prove that 9, considering its synthesis as well as the electronic structure, has to be classified in between polyhedral gallium clusters such as the square antiprismatic cluster GajjiCnHcih2- 72 and metalloid clusters. 

The compound [Gai9 C(SiMe3)3 6F[Li2Br(THF)6]+ contains 11, the smallest metalloid gallium cluster with a shell-like structure discussed here. The gallium core of 11 contains 19 gallium atoms, 6 of which are connected to a trisyl ligand... 

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