Sulfur cyclo allotropes

A new allotrope of sulfur, cyclo-Su, has been isolated as yellow rod-like crystals (mp 113°C) from the reaction of [(tmeda)ZnSe] (tmeda = N,N,N,N/-tetra-methylethylenediamine) with SsCl2. The bond distances vary from 204.7 to 206.1 pm, the bond angles from 104.0° to 109.3°, and the torsion angles in the... 

An extensive series of sulfur allotropes cyclo-S (n = 6-24) (Section 12.1) is obtained as an inseparable mixture from the reaction of SCI2 with potassium iodide. The challenge of making an individual allotrope can be surmounted by employing a cyclocondensation reaction between a cyclic metallopolysulfide and a dichlorosulfane, e.g. in the formation of cycloheptasulfur [eqn (2.1)]. This reaction is also used to prepare other cyclic sulfur allotropes by using... 

The synthesis of specific sulfur allotropes is achieved by reactions of titano-cene pentasulfide Cp2TiSs with dichlorosulfanes S Cl2 ( = 2, 4, 6) or sulfuryl chloride SO2CI2 [see eqns (2.1) and (6.1)]. The X-ray structures of many of these cyclic sulfur allotropes have been determined (see Figure 6.2 in Section 6.1). In general, they adopt puckered molecular conformations, e.g. the crown-shaped cyclo-Sg, which minimise repulsions between non-bonding electron pairs on... 

SioO from the corresponding cyclic sulfur allotropes [eqn (12.4)]. Interestingly, the use of an excess of CF3CO3H for the oxidation of cyclo-Sg results in ring contraction to give the dioxide... 

The most common allotrope of sulfur is orthorhombic a-Ss. At about 95.3°C, ct-Ss transforms to monoclinic such that the packing of Ss molecules is altered and their orientation becomes partly disordered. This leads to a lower density of 1.94 to 2.01 g cm-3, but the dimensions of Ss rings in the two allotropes are very similar. Monoclinic y-Ss also comprises cyclo-Ss molecules, but the packing is more efficient and leads to a higher density of 2.19 g cm-3. It reverts slowly to a-Ss at room temperature, but rapid heating gives a melting point of 106.8°C. 

R. Steudel, O. Schumann, J. Buschmann and P. Luger, A new allotrope of elemental sulfur convenient preparation of cyclo-Sj4 from Sg. Angew. Chem. Int. Ed. 37, 2377-8 (1998). 

Sulfur. The S atom s ability to bond to itself over a wide range of bond lengths and angles makes sulfur the aUotrope champion of the periodic table, with more than 10 forms. The most stable is orthorhombic a-Sg, a crown-shaped ring of eight atoms, also called cyclo-Sg (Figure 14.11) all other S allotropes eventually revert to this one. 

---