Cyclooctasulfur monoclinic /3-sulfur

Three of the polymorphs of cyclooctasulfur are firmly established orthorhombic a-sulfur, monoclinic j8-sulfur, and monoclinic y-sulfur. Their structure, along different axes, is shown in Fig. 6. Over a dozen of... 

Alpha cyclooctasulfur or the alpha-sulfur is yellow orthorhombic crystalline solid refractive index 1.957 density 2.07 g/cm at 20°C stable at ordinary temperatures converts to monoclinic beta form at 94.5°C. 

Gamma-sulfur is a second monoclinic form of cyclooctasulfur pale-yellow amorphous solid density 1.92 g/cm melts around 120°C. 

Sulfur crystallizes as a monoclinic polymorph which on cooling to room temperature inverts to an orthorhombic form. The most characteristic molecule is an eight-membered, crown-shaped ring (Sx or S8R — cyclooctasulfur), but solids composed of hexatomic sulfur and numerous... 

Cyclooctasulfur exists as three main crystalline forms (allotropes) the most stable allotrope at 25°C is orthorhombic sulfur (Sa) (m.p. 112.8°C), found as large yellow crystals in volcanic deposits. When Sa is heated slowly to 95.5°C, it is converted to the high temperature monoclinic form (Sp) (m.p. 119.5°C), which also contains S8 rings but differently arranged. Another monoclinic form of sulfur (Sy) (m.p. 106.8°C) can be prepared by the slow crystallisation of sulfur from ammonium polysulfide. When sulfur... 

Figure 17.5 summarizes the major sulfur allotropes that exist in the solid, liquid, and gaseous phases. The most stable form is a (or rhombic) sulfur, which is composed of the Sg crown-type molecules shown in Figure 17.6a. Heating to 95°C produces the somewhat more disordered f3 or (monoclinic) phase, also composed of Sg rings. Sulfur in rings is sometimes called cyclosulfur and Sg, more specifically, cyclooctasulfur.

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