ABSTRACT
IV. Methods for Preparing Carbyne A. Oxidative Dehydropolycondensation of Acetylene.
Discovery of Carbyne B. Polycondensation of Carbon Suboxide with
Bis(bromomagnesium) Acetylide c. Chemical Transformations of Polymers D. Carbyne in Nature E. High-Energy Modification of Carbon Materials
v. Electronic Structure of Carbyne VI. IR and Raman Spectroscopy of Carbyne
VII. Crystal Structure of Carbyne A. First Crystal Models of Carbyne B. Kinked-Chains Model of Carbyne c. Alternative Model of the Carbyne Crystal D. Improved Crystal Structure Model of Carbyne
VIII. Properties of Carbyne 53 A. Physicochemical Properties of Carbyne 53
IX. Conclusion
References
I. INTRODUCTION
Elemental carbon is widely encountered in nature in two well-known allotropic forms-diamond and graphite, which exist in several polymorphous modifications [1]. Until the sixties the allotropy of crystalline carbon was considered to be limited to these two forms. For a long time, a third form, namely amorphous carbon, was included among the simple forms. Currently, all forms of amorphous carbon (various carbon blacks, soots, cokes, etc.) are assigned to the so-called transitional forms of carbon [2], whose structure approaches that of graphite to various degrees. Recently, a family of spherical carbon molecules (called fullerenes) was discovered and was set apart by researchers as an independent allotropic form of carbon [3]. Thus, in how many allotropic forms can elemental carbon exist, and what is the criterion to distinguish them from the multitude of carbon materials? The most convenient and correct classification scheme for carbon materials is their division according to the type of chemical bonds [4], i.e., according to the type of hybridization of the valence orbitals (Fig. 1). It is well known that carbon can exist in three valence states, which correspond to sp 3-, sp 2-, and sp-hybridization of the atomic orbitals. According to the classification mentioned above, there are three pure carbon allotropes corresponding to each valence state. The first state (sp 3 ) corresponds to the three-dimensional (spatial) polymer of carbon, diamond. The second state (sp 2 ) corresponds to the two-dimensional (planar) polymer of carbon, graphite. Finally, the third valence state (sp) corresponds to the one-dimensional (chainlike) polymer called carbyne. Notice that this classification is closely related to a very illustrative scheme developed recently for carbon materials by Heimann et al. [5].
