D. Anibal Garcia-Hernandez

A new route to graphene starting from heavily ozonized fullerenes: Part 1—thermal reduction under inert atmosphere

It is shown that heavily ozonized C60 or C70 fullerenes (known also as “fullerene ozopolymers”) are suitable substrates for the preparation of graphene or nanographene in place of graphite oxide (GO) by thermal reduction in inert atmosphere. TGA-FTIR study shows that the release profile of CO2 and CO from fullerene ozopolymers in the temperature range between 25°C and 900°C is comparable to that shown by GO. Furthermore, the FT-IR spectral evolution of fullerene ozopolymers from room temperature to 630°C under inert atmosphere is once again strikingly comparable to that observed on GO under the same conditions.

Determination of the Integrated Molar Absorptivity and Molar Extinction Coefficient of Hydrogenated Fullerenes

The integrated molar absorptivity (Ψ) and the molar extinction coefficient (ε) of each infrared transition of the hydrogenated fullerenes (known as fulleranes) C60H36, C70H38 and a mixture of fulleranes generally referred as 77% of C60Hx and 22% C70Hy with x ≈ y > 30 were determined. These data are useful for the search, identification and quantitative determination of fulleranes in space after the recent discovery that their parent molecules C60 and C70 are present in certain planetary nebulae and in the interstellar medium. It is shown that the C-H stretching band of fulleranes C60H36, C70H38 and their mixture at about 2905 and 2820 cm−1 are the most useful for the identification of these molecules because their Ψ and ε values are unique in terms of strength overcoming by far the typical Ψ and ε values of reference molecules like adamantane and docosane as well as typical ε literature data for aliphatic molecules.

Sonochemical Synthesis of Fullerene C60/Anthracene Diels-Alder Mono and Bis-adducts

The sonication of a mixture of C60 fullerene and anthracene in benzene yields the trans-1 bis-adduct C60(anthracene)2 in 52% yield. The bis-adduct is accompanied by the monoadduct C60(anthracene) in 26% yield. The reaction products of the sonochemical synthesis were identified by FT-IR and electronic absorption spectroscopy. The composition of adducts and their thermal stability was studied by thermogravimetric analysis (TGA) and by differential thermal analysis (DTA). The advantages of the sonochemical synthesis in terms of yields and regioselectivity toward the highly symmetric trans-1 bis-adduct C60(anthracene)2 are outlined.

About the iron carbonyl complex with C60 and C70 fullerene: [Fe(CO)4(η2C60)] and [Fe(CO)4(η2C70)]

ABSTRACT The iron carbonyl complexes with C60 and C70 fullerenes were synthesized in high yield by photochemical irradiation of solutions of C60 and C70 in presence of Fe(CO)5. The resulting complexes were studied by FT-IR, Raman and electronic absorption spectroscopy. All the data are consistent with the structures [Fe(CO)4(η2C60)] and [Fe(CO)4(η2C70)]. The thermal stability and decomposition reaction of the two complexes were studied by TGA-FTIR and Differential Scanning Calorimetry (DSC). Both complexes decompose at moderate temperatures releasing CO and Fe(CO)5 in the vapor phase leaving a residue of metallic iron and free C60 or C70 fullerenes that can be recovered by solvent extraction of the decomposition residue.

A new route to graphene starting from heavily ozonized fullerenes: Part 3 – an electron spin resonance study

ABSTRACT It is shown that graphite oxide (GO) and both heavily ozonized C60 and C70 fullerenes, known as “fullerene ozopolymers,” are paramagnetic materials with a very strong electron spin resonance (ESR) signal at room temperature. When thermally annealed, the paramagnetic centers are gradually lost in large part. This occurs at 350°C in the case of GO, while for fullerene ozopolymers, a higher temperature is required, reaching the same results in the end. The half-width of ESR signal is linked to the distribution of paramagnetic centers. Once again, striking analogies were found in the half-width of the ESR signal measured on GO and fullerene ozopolymers, at least in the temperature range of 25–450°C. Similarly, the same g-factor values, which are diagnostic for understanding the chemical nature of paramagnetic centers, were found on both GO and fullerene ozopolymers in all ranges of temperature considered.

Chemical Thermodynamics Applied to the Diels–Alder Reaction of C60 Fullerene with Polyacenes

The Diels–Alder addition reactions of a series of acenes (anthracene, 9,10-dimenthylanthracene, tetracene and pentacene) to C60 fullerene are next to equilibrium reactions and were analyzed using a classic chemical thermodynamics approach using group increment calculations. In the case of the C60/anthracene adducts and C60/dimethylanthracene adducts the calculations results were compared with experimental thermochemical data and found in fair agreement. The calculations showed a progressive reactivity of the acenes with C60 following the sequence pentacene ≥ tetracene >> anthracene. The thermochemical calculations show also that both naphthalene and 1,2,3,4-tetramethylnaphalene are not reactive with C60 and no adducts are expected for these two acenes. The temperature field of existence of the C60/acenes adducts where disclosed with the thermochemical calculations and compared with experimental data. In general the C60/acenes adducts are stable at low or moderately high temperatures. The most stable appear to be the C60/tetracene and C60/pentacene adducts which decompose at about 608 K.

On the C60 Fullerene Adduct with Pentacene: Synthesis and Stability

C60 fullerene and pentacene were reacted under mild conditions in toluene, yielding the monoadduct, which was characterized by electronic absorption and Fourier transform infrared (FT-IR) spectroscopy. The C60/pentacene adduct was studied by thermogravimetric analysis and its experimental composition was found in line with the theory for a 1:1 molar adduct. The decomposition temperature of the C60/pentacene monoadduct was found to be 404°C. The decomposition implies a retro Diels–Alder reaction, yielding back C60, which was recognized by FT-IR spectroscopy, while pentacene underwent decomposition and vaporization at 404°C. When an equimolar mixture of C60 and pentacene was heated in a differential scanning calorimeter in absence of solvents, the formation of monoadduct occurred at 380°C, but above 400°C it was decomposed back to reactants.

A new route to graphene starting from heavily ozonized fullerenes: Part 2—oxidation in air

ABSTRACT Graphite oxide (GO) and heavily ozonized C60 and C70 fullerenes known as “fullerene ozopolymers” were studied by TGA-FTIR (Thermogravimetry coupled with FT-IR spectroscopy), DTG (Differential Thermogravimetry) and DTA (Differential Thermal Analysis) in air flow. It was found that GO burns at 70°C higher temperature than the fullerene ozopolymers. This different behavior toward the thermal oxidation of GO is due to the size of the oxidized and staked graphene layers which are expected to be significantly larger than those of the fullerene ozopolymers. Furthermore, the latter should necessarily have a buckybowl shaped structure which should favor their reactivity with oxygen.

A review on carbon-rich molecules in space

We present and discuss carbon-rich compounds of astrochemical interest such as polyynes, acetylenic carbon chains and the related derivative known as monocyanopolyynes and dicyanopolyynes. Fullerenes are now known to be abundant in space, while fulleranes - the hydrogenated fullerenes - and other carbon-rich compounds such as very large polycyclic aromatic hydrocarbons (VLPAHs) and heavy petroleum fractions are suspected to be present in space. We review the synthesis, the infrared spectra as well as the electronic absorption spectra of these four classes of carbon-rich molecules. The existence or possible existence in space of the latter molecules is reported and discussed.

Charge-transfer interaction between C60 fullerene and alkylnaphthalenes

ABSTRACT A series of alkylnaphthalenes, namely 1,4-dimethylnaphthalene, 2,6-diethylnaphthalene, 2-ethylnaphthalene and pure naphthalene are not able to form Diels-Alder adducts with C60 fullerene but produce a series of 1:1 charge-transfer complexes (CTC) where the aromatic compounds act as donor and C60 as acceptor. The spectrophotometric analysis of these CTC has permitted to determine the equilibrium constants of the CTC formation at four different temperatures and the relative enthalpies and entropies of formation. The C60-alkylnaphthalenes and C60-naphthalene were identified as weakly bound CTC. Using the Mulliken theory of the CTC also the degree of charge transfer α was determined, confirming the results already suggested by the equilibrium constants, i.e., the weakly interaction between the donor and the acceptor considered.