Magnetism in C60 Charge Transfer Complexes

Abstract

This article summarises current activities in the field of magnetism in C₆₀ charge transfer complexes. The main theoretical concepts and the most important representative of this interesting class of C₆₀ compounds is presented in detail.     

Bromination of [60]Fullerene. II. Crystal and Molecular Structure of [60]Fullerene Bromides, C60Br6, C60Br8, and C60Br24

The crystal and molecular structures of the bromofullerene solvates C₆₀Br₆·0.5C₆H₅Cl·0.5Br₂, C₆₀Br₈·1.5(o-C₆H₄Cl₂), C₆₀Br₈·Br₂, C₆₀Br₈·0.5C₆H₅Br·0.5Br₂, and C₆₀Br₂₄·2Br₂ have been determined by single crystal X-ray diffraction. The molecular species C₆₀Br₆, C₆₀Br₈, and C₆₀Br₂₄ which have idealized C_s, C_2v , and T_h symmetries, respectively, have several different types of C-Br and C-C bonds. A comparison between different solvates of the same bromofullerenes revealed a larger stability of the packing modes for the C₆₀Br₆ and C₆₀Br₂₄ solvates, whereas the C₆₀Br₈ solvates showed different packing motifs dependent on the nature and amount of the solvent molecules.     

Bromination of [60]Fullerene. II. Crystal and Molecular Structure of [60]Fullerene Bromides,C60Br6, C60Br8, and C60Br24

Abstract

The crystal and molecular structures of the bromofullerene solvates C₆₀Br₆·0.5C₆H₅Cl·0.5Br₂, C₆₀Br₈·1.5(o‐C₆H₄Cl₂), C₆₀Br₈·Br₂, C₆₀Br₈·0.5C₆H₅Br·0.5Br₂, and C₆₀Br₂₄·2Br₂ have been determined by single crystal X‐ray diffraction. The molecular species C₆₀Br₆, C₆₀Br₈, and C₆₀Br₂₄ which have idealized C _s , C _2v  , and T _h symmetries, respectively, have several different types of C?Br and C?C bonds. A comparison between different solvates of the same bromofullerenes revealed a larger stability of the packing modes for the C₆₀Br₆ and C₆₀Br₂₄ solvates, whereas the C₆₀Br₈ solvates showed different packing motifs dependent on the nature and amount of the solvent molecules.     

Charge Transfer Complex of TTF-Carbon Nanotubes

The charge transfer complex of multi-walled carbon nanotubes (MWNTs) and tetrathiafulvalene (TTF) was prepared and characterized by x-ray photoelectron spectroscopy (XPS), and electron spin resonance (ESR) spectrometer. The results demonstrated that MWNTs could act as electron acceptors in the formation of charge transfer complex.     

Bromination of [60]Fullerene. I. High-Yield Synthesis of C60Brx (x=6, 8, 24)

The systematic study of the bromination of C₆₀ was performed under various experimental conditions. Application of some chloroarenes as reaction media resulted in the high-yield (70-96%) selective synthesis of C₆₀Br₆ and C₆₀Br₈. Direct bromination of fullerene yielded either C₆₀Br₈, C₆₀Br₁₄, or C₆₀Br₂₄ depending on the reaction time. Possible pathways of bromination of C₆₀Br₈ were analyzed using semiempirical (AM1) calculations, two most probable molecular structures are conjectured for the first isolated C₆₀Br₁₄.     

Tumor-inhibitory effect and immunomodulatory activity of fullerol C60(OH)x

The tumor-inhibitory effect of C60(OH)x was tested on the murine H22 hepatocarcinoma model. Doses of 0.2 and 1.0 mg kg(-1) body weight both showed significant antitumor activity with tumor inhibition rates of 31.9 and 38.4%, respectively, when mice were treated for 17 consecutive days. The damnification of liver was prominently reduced. Furthermore, histological examination indicated that an envelope of fibroblasts and lymphocytes was formed surrounding tumor tissues in the C60(OH)x-treated group, which inhibited the infiltration of tumor to the neighboring normal skeleton muscle tissues. To understand the antitumor mechanism, the immunomodulatory activity of C60(OH)x was investigated. The results indicate that C60(OH)x enhances the phagocytosis of peritoneal macrophages and elevates the activity of arginase and acid phosphatase in vivo. The tumor necrosis factor alpha production of C60(OH)x-treated macrophages also increases in vitro. These results suggest that C60(OH)x can enhance the innate immunity of tumor-bearing mice, and therefore inhibits growth of the tumor.     

Density functional calculations on the thermodynamic properties of a series of nitrosocubanes having the formula C8H8-x(NO)x)x=1-8

Recent studies have suggested that octanitrocubane and heptanitrocubane may be two of the most powerful non-nuclear high-energy materials currently known. Progressive substitution of the hydrogen atoms on cubane for nitroso groups is expected to also produce a new potential high-energy material, which should have thermodynamic properties similar to nitrocubane. In this study we predict optimized structures, vibrational frequencies, enthalpies of formation, and specific enthalpies of combustion for a series of nitrosocubanes ranging from mononitrosocubane to octanitrosocubane. Our results indicate, on the basis of the specific enthalpies of combustion alone, that mononitrosocubane should make the best new high-energy material; however, we speculate that the velocity of detonation of octa- and heptanitrosocubane will make them better high-energy materials.     

Catalytic Preparation and Characterization of C60Br24

In this paper the procedure for catalytical bromination of C₆₀ with elementary bromine with FeBr₃ as a catalyst is described. In this procedures only one reaction product - C₆₀ Br₂₄ is obtained. The twenty four bromine atoms are symmetrically distributed over the C₆₀ sphere, which was confirmed by thermogravimetric analysis. The yield of bromine derivative in this reaction is 98%.     

Catalytic Preparation and Characterization of C60Br24

Abstract

In this paper the procedure for catalytical bromination of C₆₀ with elementary bromine with FeBr₃ as a catalyst is described. In this procedures only one reaction product - C₆₀ Br₂₄ is obtained. The twenty four bromine atoms are symmetrically distributed over the C₆₀ sphere, which was confirmed by thermogravimetric analysis. The yield of bromine derivative in this reaction is 98%.     

Normal-incidence reflectance of crystalline K(6)C(60), Rb(6)C(60), and Cs(6)C(60)

The structure factors and normal-incidence reflectances of the alkali-metal-doped fulleride crystals M(6)C(60) (where M = K, Rb, or Cs) were calculated, and the peak reflectances are in the 2-20% range for incident wavelengths of 9-17 ?, which indicates that C(60) may be a promising transmissive (spacer) material for normal-incidence mirrors that have relatively high normal-incidence reflectance in the x-ray region.     

Raman Spectra of Chlorinated C60 and C70 Fullerenes

Raman spectra of chlorinated C₆₀ and C₇₀ fullerenes prepared by photochlorination have been reported and discussed. The Raman lines suggest structural analogies with already fully characterized brominated fullerenes. Intense laser light irradiation cause a decomposition of fullerene chloro-derivatives leading to the formation of C₆₀ polymer.     

Raman Spectra of Chlorinated C60 and C70 Fullerenes

Abstract

Raman spectra of chlorinated C₆₀ and C₇₀ fullerenes prepared by photochlorination have been reported and discussed. The Raman lines suggest structural analogies with already fully characterized brominated fullerenes. Intense laser light irradiation cause a decomposition of fullerene chloro-derivatives leading to the formation of C₆₀ polymer.     

Studies of the System C60-Pb by Tunneling Spectroscopy

In the present work we report tunneling experiments on junctions of the type Al-oxide-C₆₀-Pb, and Pb-oxide-C₆₀-Pb. At low temperatures we observed a well defined and narrow semiconducting gap with a magnitude of the order of 6-7 meV. This gap corresponds to the semiconductor formed by C₆₀ doped with Pb.     

B3LYP calculations on the thermodynamic properties of a series of nitroxycubanes having the formula C8H8-x(NO3)(x) x=1-8

Recent studies have suggested that octanitrocubane and heptanitrocubane are two of the most powerful non-nuclear high-energy (HE) materials currently known. In this study, we suggest for consideration as new possible HE materials a series of nitroxycubanes, in which the hydrogen atoms on cubane have been progressively substituted for nitrate groups. We hypothesize that these molecules will be good HE materials due to their high nitrogen content and high density, the same reasons nitrocubanes are good high-energy materials. In this study, we predict optimized geometries, vibrational frequencies, enthalpies of formation, and specific enthalpies of combustion. Our results indicate that the enthalpies of formation decrease as the number of nitrate groups increases, which is in direct opposition to what calculations have shown occurs for both the nitroso and the nitrocubane series. Given the difficulty in synthesis of octanitrocubane, octanitroxycubane may still be a more viable candidate for use as a new potential high-energy material.     

Preparation and Characterization of a New Complex of C60 with 7714AS-Dimethyltetrathiodiazafulvalene (DMTTDF)

A new charge transfer complex based on C₆₀ was synthesized, and characterized elementarily by element analysis, FT-IR spectrum, Raman spectrum, and X-ray diffraction method. the magnetic properties of the complex were measured by ESR and a SQUID-magnetometer.     

Preparation and Characterization of a New Complex of C60 with 7714AS-Dimethyltetrathiodiazafulvalene (DMTTDF)

Abstract

A new charge transfer complex based on C₆₀ was synthesized, and characterized elementarily by element analysis, FT-IR spectrum, Raman spectrum, and X-ray diffraction method. the magnetic properties of the complex were measured by ESR and a SQUID-magnetometer.     

Modelling of C(2) addition route to the formation of C(60)

To understand the phenomenon of fullerene growth during its synthesis, an attempt is made to model a minimum energy growth route using a semi-empirical quantum mechanics code. C(2) addition leading to C(60) was modelled and three main routes, i.e.?cyclic ring growth, pentagon and fullerene road, were studied. The growth starts with linear chains and, at n = 10, ring structures begins to dominate. The rings continue to grow and, at some point n>30, they transform into close-cage fullerenes and the growth is shown to progress by the fullerene road until C(60) is formed. The computer simulations predict a transition from a C(38) ring to fullerene. Other growth mechanisms could also occur in the energetic environment commonly encountered in fullerene synthesis, but our purpose was to identify a minimal energy route which is the most probable structure. Our results also indicate that, at n = 20, the corannulene structure is energetically more stable than the corresponding fullerene and graphene sheet, however a ring structure has lower energy among all the structures up to n≤40. Additionally, we have also proved that the fullerene road is energetically more favoured than the pentagon road. The overall growth leading to cage closure for n = 60 may not occur by a single route but by a combination of more than one route.