M.V. Korobov

New solid solvates of C60 and C70 fullerenes: The relationship between structures and lattice energies

The goal of this study was to establish the relationship between the X-ray and the thermodynamic data on fullerene’s solvated crystals. X-ray diffraction study of 12 solid solvates of C60 and C70 with different aromatic solvents have been performed. It has been demonstrated that the solid solvates under consideration were typical van-der-Waals complexes with the negative excess volumes, packing coefficients from 0.72 to 0.78, stable due to the formation of the fullerene to solvent bonds, reasonably described by six to 12 Lennard–Jones potentials. The atom–atom potential method has been used to describe both the crystal structures and the thermodynamics of the solid solvates. The minimization of the lattice energy with respect to the cell and rigid body parameters (T=0 K) has led to the crystal structures very close to the experimental ones. The minimum energies found have reasonably reproduced the calorimetric lattice energies of the solvates. The theory has also demonstrated its ability to account for the trends in thermodynamic stability of solid solvates, e.g., has predicted correctly the low stability of the hypothetical monoclinic solvate C60·2C6H14.

Sublimation of hydrofullerenes C60H36 and C60H18

Abstract Thermal behavior of two hydrofullerenes, C 60 H 36 and C 60 H 18 , was studied by means of Knudsen cell mass-spectrometry and infrared spectroscopy. Vapor pressures and enthalpies of sublimation at T =550–685 K were measured. Sublimation of the hydrofullerenes was accompanied by partial loss of hydrogen. Decomposition of C 60 H 36 was confirmed to be a stepwise process with formation of C 60 H 18 as an intermediate product. The material of the Knudsen cell strongly affected the partial pressures and mass-spectra of the hydrofullerene vapor species.

Improving the dispersity of detonation nanodiamond: differential scanning calorimetry as a new method of controlling the aggregation state of nanodiamond powders

Detonation nanodiamond (ND) is a suitable source material to produce unique samples consisting of almost uniform diamond nanocrystals (d = 3-5 nm). Such samples exist in the form of long stable aqueous dispersions with narrow size distribution of diamond particles. The material is finding ever increasing application in biomedicine. The major problem in producing monodispersed diamond colloids lies in the necessity of deagglomeration of detonation soot and/or removing of clusters formed by already isolated core particles in dry powders. To do this one must have an effective method to monitor the aggregation state or dispersity of powders and gels prior to the preparation of aqueous dispersions. In the absence of dispersity control at various stages of preparation the reproducibility of properties of existing ND materials is poor. In this paper we introduce differential scanning calorimetry (DSC) as a new tool capable to distinguish the state of aggregation in dry and wetted ND materials and to follow changes in this state under different types of treatment. Samples with identical X-ray diffraction patterns (XRD) and high resolution transmission electron microscopy (HRTEM) images gave visibly different DSC traces. Strong correlation was found between dynamic light scattering (DLS) data for colloids and DSC parameters for gels and powders of the same material. Based on DSC data we improved dispersity of existing ND materials and isolated samples with the best possible DSC parameters. These were true monodispersed easily dispersible fractions of ND particles with diameters of ca. 3 nm.

Effect of the age of the C60/N-methyl-2-pyrrolidone solution on the structure of clusters in the C60/N-methyl-2-pyrrolidone/water system according to the small-angle neutron scattering data

Fullerene clusters in the C60/N-methyl-2-pyrrolidone (NMP)/water system have been investigated by small-angle neutron scattering. It is shown that the scattering cross section corresponding to the size range 10–100 nm depends on the water content in the mixture. Addition of water to a C60/NMP solution in an amount exceeding 40% leads to a sharp increase in the average scattering cross section. This effect depends on the interval between the times of preparation of a C60/NMP solution and its dilution with water: the size of the clusters formed as a result of adding water increases with increasing the age of the initial solution. The reasons for this effect are discussed.

Solvatochromism and Fullerene Cluster Formation in C60/N-methyl-2-pyrrolidone

UV-Vis spectroscopy and small-angle neutron scattering experiments are performed on the cluster solution of fullerene C60 in N-methyl-2-pyrrolidone before and after dilution of the system with pure solvent. Some changes in the UV-Vis spectra showing solvatochromism at dilution are observed, while the neutron scattering signal does not change. The effect is discussed with respect to the relation between solvatochromism and cluster formation for fullerene solutions in nitrogen-containing solvents.

The electron affinity of platinum hexafluoride

Abstract The effusion method has been applied to the study of equilibria of molecular negative ions. The heats of the charge-exchange reactions between platinum tetra- and hexa- fluorides and their negative ions have been determined and the electron affinity of PtF6 calculated as 8.0 ± 0.3 e V.

TERNARY SYSTEM OF C60 AND C70 WITH 1,2-DIMETHYLBENZENE

Differential scanning calorimetry, X-ray, and solubility measurements were used to study phase equilibria in the ternary system C60-C70-1,2-dimethylbenzene up to the boiling point of the solvent. Formation of the two ternary phases was confirmed. Partial solubilities of C60 and C70 were measured and calculated.

Thermal behaviour of the crystals formed in the buckminsterfullerene-toluene, o-xylene and bromobenzene systems

Abstract Unusual solubility versus temperature dependence for C 60 fullerene in toluene and several other solvents is due to the formation of solid solvates. Temperature Maximum of Solubility (TMS) in toluene coincides with the incongruent melting point of the solvate with the mole ratio of C 60 to toluene 1:1.8 ± 0.5. Similar results were obtained in the system C 60 -bromobenzene, C 60 -o-xylene, where solvates with the mole ratio 1:2 were found. Stoichiometry of the solvates of C 60 with the aromatic solvents are discussed in terms of incongruent melting.

Electron affinity of rhodium tetrafluoride

Knudsen-cell mass spectrometry was used for the investigation of ion-molecule equilibria in the gas phase of some fluoride systems. The combined ion source used allows the partial pressures of negative ions and neutral molecules to be measured within the scope of one experiment. By the third law of thermodynamics the following quantities at T = 298.15 K have been determined: FeF4−(g)=FeF3(g)+F−(g); ΔrHm°=(456.1±13.7)kJ·mol−1 ; MnF4−(g)=MnF3(g)+F−(g); ΔrHm°=(421.0±13.0)kJ·mol−1 ; RhF4−(g)=RhF3(g)+F−(g); ΔrHm°=(400.8±14.4)kJ·mol−1 ; RhF4−(g)=RhF3(g)+F(g); ΔrHm°=(248.0±15.0)kJ·mol−1 ; ΔfHm°(FeF4−,g)=−(1475.2±15.2)kJ·mol−1 ; ΔfHm°(MnF4−,g)=−(1462.7±60.0)kJ·mol−1 ; (EaRhF4)=(482±19)kJ·mol−1 ;

Structure and toxicity of aqueous fullerene C60 solutions

In this paper, two types of fullerene C60 solutions are compared with respect to their structural features and toxic properties. The results are discussed in terms of their potential in medical and biological applications. The fullerene cluster state at the nanoscale in these solutions is analyzed by small-angle neutron scattering. Experiments on the cytotoxicity of these systems on Chinese-hamster V-79 cells showed no toxic effects of the solutions.