Atom catenation

On the other hand, formates are less stable. This seems to be related to the H-CO-S atomic catenation in which 2 is an oxygen or chlorine atom. Nevertheless, with esters, the presence of a base as well as a high temperature and pressure are necessary. In the presence of sodium methoxide in a small quantity (0.5%), at 100°C and under 70 bar, methyl formate decomposes according to the reaction below the violent release of carbon oxide creates a dangerous overpressure in the apparatus ... 

An important property of sulfur is its ability to form chains of atoms, catenation. The -S-S-links that connect different parts of the chains of amino acids in proteins are an important example. These disulfide links contribute to the shapes of proteins (see Chapter 19). 

All Group IV elements form tetrachlorides, MX4, which are predominantly tetrahedral and covalent. Germanium, tin and lead also form dichlorides, these becoming increasingly ionic in character as the atomic weight of the Group IV element increases and the element becomes more metallic. Carbon and silicon form catenated halides which have properties similar to their tetrahalides. 

The structures of metal-rich borides can be systematized by the schematic arrangements shown in Fig. 6.6, which illustrates the increasing tendency of B atoms to catenate as their concentration in the boride phase increases the B atoms are often at the centres of trigonal prisms of metal atoms (Fig. 6.7) and the various stoichiometries are accommodated as follows ... 

Figure 6.6 Idealized patterns of boron catenation in metal-rich borides. Examples of the structures (a)-(f) are given in the text. Boron atoms are often surrounded by trigonal prisms of M atoms as shown in Fig. 6.7.

The ability of C to catenate (i.e. to form bonds to itself in compounds) is nowhere better illustrated than in the compounds it forms with H. Hydrocarbons occur in great variety in petroleum deposits and elsewhere, and form various homologous series in which the C atoms are linked into chains, branched chains and rings. The study of these compounds and their derivatives forms the subject of organic chemistry and is fully discussed in the many textbooks and treatises on that subject. The matter is further considered on p. 374 in relation to the much smaller ability of other Group 14 elements to form such catenated compounds. Methane, CH4, is the archetype of tetrahedral coordination in molecular compounds some of its properties are listed in Table 8.4 where they are compared with those of the... 

Some metahrich silicides have isolated Si atoms and these occur either in typical metallike structures or in more polar structures. With increasing Si content, there is an increasing tendency to catenate into i.solated Si2 or SU, or into chains, layers or 3D networks of Si atoms. Examples are in Table 9.3 and further structural details are in refs. 24, 26 and 27. 

Some of the alkali metal-group 15 element systems give compounds of stoichiometry ME. Of these, LiBi and NaBi have typical alloy stmc-tures and are superconductors below 2.47 K and 2.22 K respectively. Others, like LiAs, NaSb and KSb, have parallel infinite spirals of As or Sb atoms, and it is tempting to formulate them as M+ (E )" in which the (E )" spirals are iso-electronic with those of covalently catenated Se and Te (p. 752) however, their metallic lustre and electrical conductivity indicate at least some metallic bonding. Within the spiral chains As-As is 246 pm (cf. 252 pm in the element) and Sb-Sb is 285 pm (cf. 291 pm in the element). 

Sulfur has a striking ability to catenate, or form chains of atoms. Oxygen s ability to form chains is very limited, with H202, 03, and the anions 02, 022-, and OG the only examples. Sulfur s ability is much more pronounced. It appears, for instance, in the existence of Ss rings, their fragments, and the long strands of plastic sulfur that form when sulfur is heated to about 200°C and suddenly... 

Polysilanes (or polysilylenes) consist of a silicon-catenated backbone with two substituents on each silicon atom. The two groups attached to the silicon chain... 

Metal polysulfido complexes have attracted much interest not only from the viewpoint of fundamental chemistry but also because of their potential for applications. Various types of metal polysulfido complexes have been reported as shown in Fig. 1. The diversity of the structures results from the nature of sulfur atoms which can adopt a variety of coordination environments (mainly two- and three-coordination) and form catenated structures with various chain lengths. On the other hand, transition metal polysulfides have attracted interest as catalysts and intermediates in enzymatic processes and in catalytic reactions of industrial importance such as the desulfurization of oil and coal. In addition, there has been much interest in the use of metal polysulfido complexes as precursors for metal-sulfur clusters. The chemistry of metal polysulfido complexes has been studied extensively, and many reviews have been published [1-10]. 

Carbon atoms bond to each other to form chains, a process known as catenation. Open chains ... 

Carbon atoms have the ability to bond to themselves to a greater extent than those of any other element. Known as catenation, this ability gives rise to the several allotropic forms of the element. The most common form of elemental carbon is graphite, which has the layered structure shown in Figure 13.11. 

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