Science of Synthesis

Braverman, S.; Cherkinsky, M.; Birsa, M. L., Science of Synthesis, (2005) 18, 247.

As previously mentioned, carbon diselenide exhibits a great tendency to polymerize, especially under basic conditions. In many respects, carbon diselenide behaves like carbon disulfide. However, carbon disulfide can be polymerized only under high pressure and at high temperature, e.g. 3.4 × 107 Torr at over 175°C. Carbon diselenide yields a black solid at a rate of about 1% per month at room temperature. The obtained solid is presumed to have a linear polymeric structure that is similar to poly(carbon disulfide). When a solution of carbon diselenide in dioxane or dichloromethane is pressurized at about 3.8 × 106 Torr and heated at 100°C for 20 h, a black solid is obtained in 95% yield. At 160°C, this solid undergoes a structural rearrangement to another solid material which is stable up to 300°C.[‌1119‌] The polymerization mechanism seems to take place stepwise, the first solid being the trimerization product, poly(1,3,5-triselenan-2,4,6-triselenone). The second step appears to be analogous to the solid-state polymerization of S2N2, into the well-known inorganic polymer superconductor (SN)x,[‌1120‌] when poly(carbon diselenide) is obtained with a proposed linear chain structure or two-dimensional structure.[‌1121‌] At first sight, the polymerization of carbon diselenide seems to be less effective for synthetic goals. However, the crystalline poly(carbon diselenide) has been revealed to be a highly conductive material.[‌1122‌] Further investigations have indicated that, contrary to the previously proposed one- or two-dimensional polymerization structure, metallic poly(carbon diselenide) has a rather complex structure that is composed of crystalline hexagonal selenium, graphite, and some amorphous parts. Thus, the high conductivity and the diamagnetism of the crystalline solid at ambient pressure seem to originate from the graphite part and the superconductivity seems to come from the hexagonal selenium part.[‌1123‌]

References

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