Carbon clusters

Key point: Fullerenes are formed when an electric arc is discharged between carbon electrodes in an inert atmosphere.Metal and nonmetal cluster compounds have been known for decades, but the discovery of the soccer-ball shaped C60 cluster in the 1980s created great excitement in the scientific community and in the popular press. Much of this interest undoubtedly stemmed from the fact that carbon is a common element and there had seemed little likelihood that new molecular carbon structures would be found.When an electric arc is struck between carbon electrodes in an inert atmosphere, a large quantity of soot is formed together with significant quantities of C60 and much smaller quantities of related fullerenes, such as C₇₀, C₇₆, and C₈₄. The fullerenes can be dissolved in a hydrocarbon or halogenated hydrocarbon and separated by chromatography on an alumina column. The structure of C60 has been determined by X-ray crystallography on the solid at low temperature and electron diffraction in the gas phase. The molecule consists of five- and six-membered car bon rings, and the overall symmetry is icosahedral in the gas phase (3).Fullerenes can be reduced to form [60] fulleride salts, C₆₀ⁿ (n=1 to 12). Fullerides of alkali metals are solids having com positions such as K₃ C₆₀. The structure of K3 C60 consists of a

face-centred cubic array of C60 ions in which K ions occupy the one octahedral and two tetrahedral sites available to each C60 3 ion (Fig. 14.5). The compound is a metallic conductor at room temperature and a superconductor below 18 K. Other Supercon ducting salts include Rb2 CsC₆₀, which has a superconducting transition temperature (Tc) of 33 K, and Cs₃ C₆₀, with Tc 40 K. The conductivity of E₃C₆₀ compounds can be explained by con sidering that the conduction electrons are donated to the C₆₀ molecules and are mobile because of overlapping C₆₀ molecular orbitals (Section 24.21).Some of the most interesting consequences of fullerene re search have been the identification of carbon nanotubes. Carbon nanotubes consist of one or more concentric cylindrical tubes formed of graphene sheets in which the ends may be closed by fullerene-like caps containing six five-membered rings of atoms. The preparation of nanotubes has stimulated much research and the compounds could ultimately find a wide range of practical applications such as hydrogen storage and catalysis.Graphene has very high electrical conductivity, opacity, and strength and is being investigated for use in electronic devices, bat teries, and for gas storage. It is currently very expensive and it is very difficult to produce perfect layers that give the best electronic performance. The method that produces the cleanest graphene surface is exfoliation, where the surface is mechanically ripped from a graphite crystal. This can be achieved quite simply by using sticky tape, but separating the useful thin flakes from the graph ite debris is time-consuming. A simple and inexpensive route to graphene could revolutionize its use. A step in this direction is a new method that has been developed which can produce gram

Figure 14.5 The structure of K₃C₆₀ . The full cell is face-centred cubic. (The structure of solid C60 itself is shown in Fig. 3.16.)quantities by a simple chemical process: sodium metal is heated with ethanol for three days before being heated rapidly. The result ing solid consists of fused graphene sheets which are then washed and dried to separate them. The quality of the sheets is not as good as those produced by exfoliation, but this may be the first step to large-scale production of perfect graphene flakes.

اخر الاخبار

اخبار العتبة العباسية المقدسة

قسم شؤون المعارف ينظم دورة متقدمة في تحقيق المخطوطات لملاكاته

قسم الشؤون الفكرية يصدر العدد العشرين من مجلة دراسات إفريقية

المجمَع العلمي يكرم الأساتذة المشاركين في مشروع الدورات القرآنية الصيفية في كربلاء

العتبة العباسية المقدسة تختتم فعاليات البرنامج المركزي الأسبوعي لمنتسبيها

المزيد

الآخبار الصحية

تحذير من "عدوى بكتيرية" تسبب نوبات قلبية

ماذا يحصل لجسمك عند التوقف عن استخدام الزيت في الطهي؟

الأمل في كبسولة.. "فيتامين شهير" يبطئ التقدم في العمر

اشتهاء أطعمة بشكل مفاجئ.. ناقوس خطر للسرطان ؟!

المزيد

الآخبار التكنلوجية

زلزال أفغانستان يحصد أكثر من ألف قتيل.. ويدمر آلاف المنازل !

ناجٍٍ وحيد من انزلاق أرضي.. دمّر قرية سودانية بأكملها !

نهر الفرات.. مورد مائي بين الندرة والتقاسم

ما السر وراء مشية إيلون ماسك الغريبة والسريعة ؟

المزيد

مواضيع ذات صلة

Partially crystalline carbon

Fullerene metal complexes

Diamond and graphite

Simple compounds

Occurrence and extraction

Thermodynamic considerations

The atom and its ions

Oxidation states

Occurrence

Enthalpies of atomization

Electronegativity

Ionization energies and electron affinities