Selenium ring-chain equilibrium

Fig. 5.12. Average degree of polymerization (atoms per chain) as a function of temperature for liquid selenium (Warren and Dupree, 1980). Full curves, Nchain from resonance shift analysis tmd Eq. (5.7) assuming /. = 0 dashed curve, Nc am from magnetic susceptibility broken curve (ET), calculated from theory of ring-chain equilibrium by Eisenberg and Tobolsky (1960).

These results provide qualitative support for the validity of the ring-chain structural model for vitreous selenium implied by the Tobolsky-Eisenberg theory (1,2) of equilibrium polymerization. The establishment... 

Sulfur exhibits allotropy and its structure in all phases is quite complex. The common crystalline modification, rhombic sulfur, is in equilibrium with a triclinic modification above 96°C. Both have structures based on Sg-rings but the crystals are quite different. If molten sulfur is poured into water a dark red plastic form is obtained in a semielastic form. The structure appears to be a helical chain of S atoms. Selenium and tellurium both have a gray metal-like modification but sulfur does not have this form. 

---