Catenation sulfur

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... 

The sulfur analog of hydrogen peroxide also exists and is an example of a polysulfane, a catenated molecular compound of composition HS—S —SH, where n can take on values from 0 through 6. The polysulfide ions obtained from the polysulfanes include two ions found in lapis lazuli (Fig. 15.15). 

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]. 

The characteristic strong tendency of sulfur and its heavier congeners to catenate is reflected in the wide range of polychalcogenide ions, i.e., reduced forms of the elements, that may be discrete in highly ionic salts or dissolved in polar solvents. 

The 0=0 and S=S bond energies are 498 and 431 kj mol-1, respectively, and the 0-0 and S-S bond energies are 142 and 264. Explain why it is reasonable to expect structures containing sulfur that have extensive catenation but such structures are not expected for oxygen. 

Because of the tendency of sulfur toward catenation, solutions containing sulfides react with sulfur to give polysulfides, which can be represented as SnJ (see Chapter 15). Sulfides of the group IA and IIA metals can also be produced by reducing the sulfates with carbon at high temperature. 

As a result of the tendency toward catenation, sulfur reacts with solutions of sulfides to produce polysulfides. 

Whereas the variously catenated modifications of elemental sulfur can be satisfactorily treated by the MM method (207), organic sulfides and other sulfur-containing molecules suffer from the same polarization problem as do oxygen-containing molecules. Thus,... 

Sulfur is a rather exceptional element for several aspects. It can assume various oxidation states [1] and in these oxidation states it exists in a great number of different chemical forms. Sulfur is a constituent of a large number of industrial products (H2SO4, rubber vulcanization, for instance) and is also at the origin of a major pollutant (SO2) [2]. Sulfur can exist in more than ten allotropic forms at room temperature, that is, in a variety not found with any other element [3-5]. Orthorhombic sulfur is the most stable form at room temperature. It contains crown-shaped Sg molecules, which are stacked in a complex array. It can also be mentioned that the liquid and gaseous phases of sulfur are very complex [6, 7]. Undoubtedly, the existence of catenated species is a general feature of sulfur chemistry and is the basic reason for its complexity. 

This review has shown the complexity of the chemistry and the electrochemistry of sulfur, polysulflde ions, and sulfur cations. This complexity originates from the ability of sulfur to form catenated species, which leads to disproportionation and dissociation equilibria. 

Aromatic cyclic chains are more stable than aliphatic catenated carbon chains at elevated temperatures. Thus linear phenolic and melamine polymers are more stable at elevated temperatures than polyethylene, and the corresponding cross-linked polymers are even more stable. In spite of the presence of an oxygen or a sulfur atom in the backbones of polyphenylene oxide (PPO), polyphenylene sulfide (PPS), and polyphenylene sulfone, these polymers are... 

The propensity of sulfur, selenium and tellurium to catenate is illustrated by the formation of an extensive series of polyanions for all three chalcogens. The structures of these polyanions exhibit interesting trends within the series in which the ability of tellurium and, to a lesser extent, selenium to adopt... 

Sulfur is usually only divalent, unless oxidized, and its catenation chemistry is therefore more limited and less familiar than that of carbon. Solid a-sulfur contains very stable eight-membered crown like rings, Ss,... 

The catenation of sulfur is discussed in more detail in Section 10.1. 

Fluorinated Compounds that Contain Catenated Oxygen, Sulfur or Nitrogen Atoms Kirchmeier, R.L. Shrecvc. J.M. Verma, R.D. Coord. Chem. Rev. 1992, 112, 169-213. 

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