Carbone acétylénique linéaire

Linear acetylenic carbon (LAC), also known as carbyne or Linear Carbon Chain (LCC), is an allotrope of carbon that has the chemical structure as a repeat unit, with alternating single and triple bonds. It would thus be the ultimate member of the polyyne family. This polymeric carbyne is of considerable interest to nanotechnology as its Young's modulus is 32.7TPa – forty times that of diamond; this extraordinary number is, however, based on a novel definition of cross-sectional area that does not correspond to the space occupied by the structure. Carbyne has also been identified in interstellar space; however, its existence in condensed phases has been contested recently, as such chains would crosslink exothermically (and perhaps explosively) if they approached each other. The first claims of detection of this allotrope were made in 1960 and repeated in 1978. A 1982 re-examination of samples from several previous reports determined that the signals originally attributed to carbyne were in fact due to silicate impurities in the samples. Absence of carbyne crystalline rendered the direct observation of a pure carbyne-assembled solid still a major challenge, because carbyne crystals with well-defined structures and sufficient sizes are not available to date. This is indeed the major obstacle to general acceptance of carbyne as a true carbon allotrope. The mysterious carbyne still attracted scientists with its possible extraordinary properties. During the past thirty five years an increasing body of experimental and theoretical work has been published in the scientific literature dealing with the preparation of carbyne and the study of its structure, properties and potential applications. In 1968 a silver-white new mineral was discovered in graphitic gneisses of the Ries Crater (Nordlingen, Bavaria, Germany). This material was found to consist entirely of carbon and its hexagonal cell dimensions matched those reported earlier for carbine by Russians scientists.