Thermodynamic properties, fullerene

Thermodynamic Properties of Fullerene Hydrides C60H2n and Equilibria of Their Reactions... 

The most effective way for investigation of thermodynamic properties for fullerene hydrides is a combination of the experimental methods, the quantum-chemical calculation of molecular characteristics, the statistical thermodynamic calculation of thermodynamic... 

Equations 4.2 and 4.3 are simplified for C60H2n because internal rotation does not occur in these molecules. As it was demonstrated for the C60 fullerene, the electronic contributions to its thermodynamic properties may be neglected at T < 1,000 K (Diky and Kabo 2000). The same is expected for fullerene hydrides. 

Since fullerene C60 is one of the participants of reaction (4.4) one may suppose that all the conjugation effects in a fullerene cage are properly considered. The values of thermodynamic properties for fullerene C60, cyclohexane and adamantane have been... 

Thermodynamic Properties of Fullerene Hydrides and Equilibria of Their Reactions 81 Table 4.13 Thermodynamic characteristics of reaction (4.16) with C cr)... 

Comprehensive investigation of thermodynamic properties for fullerene hydrides is actual for optimization of the conditions of their synthesis, chemical functionalization, justification of their technical application. The structure, spectra, isomeric compositions for the samples of fullerene hydrides seriously affect their thermodynamic properties. So, the thermodynamic investigations will favor solution of many theoretical problems of chemistry and physics of fullerene hydrides. Taking into account the difficulties in synthesis and separation of individual fullerene hydrides of high purity, one should suppose that the theoretical evaluation of their physicochemical properties is the most effective tool for their investigation. 

Diamond, graphite, and the fullerenes differ in their physical and chemical properties because of differences in the arrangement and bonding of the carbon atoms. Diamond is the densest (3.51 vs 2.22 and 1.72 g cm-3 for graphite and Cw, respectively), but graphite is more stable than diamond, by 2.9 kJ mol-1 at 300 K and 1 atm pressure it is considerably more stable than the fullerenes (see later). From the densities it follows that to transform graphite into diamond, pressure must be applied, and from the thermodynamic properties of the two allotropes it can be estimated that they would be in equilibrium at 300 K under a pressure of —15,000 atm. Of course, equilibrium is attained extremely slowly at this temperature, and this property allows the diamond structure to persist under ordinary conditions. 

Davydov et al. [46] used IGC to determine several adsorption thermodynamic properties (equilibrium constants and adsorption heats) for the adsorption of organic compounds on C q crystals, and compared them with those obtained for graphitized carbon black. The adsorption potential of the surface of fiillerene crystals was much lower than that of a carbon black surface. The dispersive interaction of organic molecules with C q is much weaker than with carbon black. The adsorption equilibrium constant for alkanes and aromatic compounds is therefore lower in the case of fullerenes. Aliphatic and aromatic alcohols as well as electron-donor compounds such as ketones, nitriles and amines were adsorbed more efficiently on the surface of fiillerene crystals. This was taken as proof that fiillerene molecules have electron-donor and electron-acceptor properties, which is in agreement with the results of Abraham et al. [44]... 

The heat of formation of fullerene would also be a desirable quantity to know experimentally, as a test for the accuracy of various theoretical calculations, as well as studies on aromaticity. Some thermodynamic properties of fullerene will be discussed in Chapter 11. 

Solid carbon exists as graphite, diamond, and other phases such as the fullerenes, which have structures related to that of graphite. Graphite is the thermodynamically most stable of these allotropes under ordinary conditions. In this section, we see how the properties of the different allotropes of carbon are related to differences in bonding. 

Cationic species of fullerenes have long been considered to be difficult to prepare, based on the well-known resistance of C , toward oxidation. However, reliable methods are now available for the preparation of alkylated fullerene cations RC60+ and RC70+ as long-lived species, allowing their structures and properties to be investigated in detail. Precise evaluation of their thermodynamic stabilities revealed that these cations have stabilities comparable to the terf-butyl cation. 

It is therefore the right time to give a first comprehensive overview of fullerene chemistry, which is the aim of this book. This summary addresses chemists, material scientists and a broad readership in industry and the scientific community. The number of publications in this field meanwhile gains such dimensions that for nonspecialists it is very difficult to obtain a facile access to the topics of interest. In this book, which contains the complete important literature, the reader will find all aspects of fullerene chemistry as well as the properties of fullerene derivatives. After a short description of the discovery of the fullerenes all methods of the production and isolation of the parent fullerenes and endohedrals are discussed in detail (Chapter 1). In this first chapter the mechanism of the fullerene formation, the physical properties, for example the molecular structure, the thermodynamic, electronic and spectroscopic properties as well as solubilities are also summarized. This knowledge is necessary to understand the chemical behavior of the fullerenes. 

---