Chalcogen Group

Scheme 4.2 Possible mechanistic paths for the displacement of a chalcogen group (R X, where X = S or Se) by (TMS)3Si radicals...

Polonium exhibits the allotropy of the lower members of the chalcogen group, having a low-temperature, cubic form, a-polomum. and a high-temperature, ihombohedial form, /1-polonium. 

Tris(trimethylsilyl)silane is found to be an efficient reducing agent for a variety of functional groups. In particular, the reduction of halides, chalcogen groups, thiono esters and isocyanides are the most common ones. The efficiency of these reactions is also supported by available kinetic data. The rate constants for the reaction of (TMS)3Si radicals with a variety of organic substrates are collected in Table 2. 

Scheme 5-32. Compounds containing a ferrocenyl chalcogenate group, Fc-E (E = O, S, Se, Te),...

Rate constants for chalcogen group transfer in bimolecular substitution reac-... 

The chalcogen group of elements includes oxygen and sulfur, important elements for life, as well as selenium, tellurium, and polonium. The name stems the Greek word chalkos, meaning bronze or ore, and genes, which means bom. ... 

All of the chalcogens form chalcogenide 2 anions such as oxides, sulfides, selenides, and tellurides. Selenium is used in photocopiers, it makes the electrostatic charge on the paper that directs where the ink sticks. Polonium is the most unique element in this period since it is a metal. Keep reading to find out the important properties of oxygen and sulfur, two very important chalcogen group elements. 

Much of our discussion in this chapter will focus on sulfur, which we ll treat as paradigmatic of the chalcogen group. As for the remarks by Pauling quoted above, selenium and tellurium compounds are indeed toxic. With good laboratory practices, however, they can be safely handled. We will see that selenium reagents allow some unique transformations... 

In the same way, the valence states are -2, 0, 2,4, and 6 in the chalcogen group (O, S, Se, Te, Po) and -1, 0, 1, 3, and 5 in the halogen group (F, Cl, Br, I, At). The number of valence shell electrons is the same for all elements in a group. The number of electrons in a shell or subshell is most important to determine the chemical properties. Missing valence numbers are of interest in electron transfer since single electrons cannot easily be traded between ions of the same element. In this case, the electrons appear in pairs and behave as pairs. 

We will first treat ionic crystals formed by positive ions from the first (alkali) and second (alkaline earth) group in the periodic table, together with negative ions from the sixth (chalcogen) group and seventh (halogen) group in the periodic table. 

Since chalcogen groups are also potential redox-active sites, we have studied the coordination polymers constructed by bridging ligands with chalcogen sites. For the syntheses of coordination polymers with sulfide and disulfoxide sites, 4-pyridylthioacetate (pyta), 4,4 -sulfonyldibenzoate... 

The redox behaviors of these compounds have been characterized by the solid-state CV (Figure 13). Compound 8 showed irreversible oxidation wave at 2529 mV (vs SCE), which is ascribed to the oxidation of sulfide. On the other hand, 9 and 10 showed irreversible reduction waves ascribed to the reduction of disulfoxide at —1765 and —1760 mV (vs SCE), respectively. These results demonstrate that the coordination polymers into which chalcogen groups are incorporated are useful for the creation of flexible redox-active coordination polymers. 

---