Coordinating compounds naturally produced

In summary, it is now agreed that coordination concepts are valuable in explaining a wide variety of inorganic phenomena of theoretical and practical nature, such as the stabilization of unusual oxidation states, analytical implications of metal complexes, and the industrial use of com-plexing agents. Aside from the ammines and the hydrates, discussed mostly by Werner, there are many important types of coordination compounds, such as complex cyanides of heavy metals, metal carbonyls (formed in the catalysis of petroleum products and used to produce metals), and others. 

The directional nature of secondary bonds on a metal ion can act as a template to hold specific configurations (see the example from evolution in Figure 3.4) and to produce isomers which may be optically active. Such coordination compounds have given our evolution a great boost and added a whole new dimension to life s biochemistry. 

The main oxides are the dioxides. In fact, Ti02 is by far the most important compound formed by the elements of this group, its importance arising predominantly from its use as a white pigment (see Panel, p. 959). It exists at room temperature in three forms — rutile, anatase and brookite, each of which occurs naturally. Each contains 6-coordinate titanium but rutile is the most common form, both in nature and as produced commercially, and the others transform into it on heating. The rutile... 

Tetravalent silicon is the only structural feature in all silicon sources in nature, e.g. the silicates and silica even elemental silicon exhibits tetravalency. Tetravalent silicon is considered to be an ana-logon to its group 14 homologue carbon and in fact there are a lot of similarities in the chemistry of both elements. Furthermore, silicon is tetravalent in all industrially used compounds, e.g. silanes, polymers, ceramics, and fumed silica. Also the reactions of subvalent and / or low coordinated silicon compounds normally lead back to tetravalent silicon species. It is therefore not surprising that more than 90% of the relevant literature deals with tetravalent silicon. The following examples illustrate why "ordinary" tetravalent silicon is still an attractive field for research activities Simple and small tetravalent silicon compounds - sometimes very difficult to synthesize - are used by theoreticians and preparative chemists as model compounds for a deeper insight into structural features and the study of the reactivity influenced by different substituents on the silicon center. As an example for industrial applications, the chemical vapor decomposition (CVD) of appropriate silicon precursors to produce thin ceramic coatings on various substrates may be mentioned. 

In the broadest sense, coordination chemistry is involved in the majority of steps prior to the isolation of a pure metal because the physical properties and relative stabilities of metal compounds relate to the nature and disposition of ligands in the metal coordination spheres. This applies both to pyrometallurgy, which produces metals or intermediate products directly from the ore by use of high-temperature oxidative or reductive processes and to hydrometallurgy, which involves the processing of an ore by the dissolution, separation, purification, and precipitation of the dissolved metal by the use of aqueous solutions. 4... 

The reactive nature of compound 22 is illustrated by the series of transformations shown in Scheme 7.12, in which its Zr—C bond reacts selectively with electrophilic reagents to produce a-haloboronates 36—38. Compound 22 also catalyzes the polymerization of styrene. The polymers thus obtained had weight-average molecular masses in the range 75000—100000 with polydispersities of 1.8—2.1. An X-ray analysis of 22 confirmed it to be a four-coordinate Zr complex with two cyclopentadienyl rings, chlorine, and the aliphatic C-l carbon atom as the ligands (Fig. 7.4). 

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