Evidence for C60 aggregation from solvent effects in [Ps-C60] molecular complex formation

Using a molecular probe positronium (Ps), Ps reaction rate constants (k) with C₆₀, a strong Ps acceptor, are determined for the formation of a donor-acceptor type molecular complex in solvents of varying surface tension (σ) and viscosity (η). Within the framework of Smoluchowski’s theory of diffusion, the calculated Stokes radius for C₆₀ in the different solvents deviated from the monomeric value, implying the existence of aggregated clusters in solution and using transmission electron microscopy, C₆₀ aggregation in carbon disulphide (CS₂) is observed with the formation of spherical fractal clusters of ∼90 nm size with aggregation number 1.7×10⁴ and a fractal dimension of 1.9 at a concentration of 0.5 mM. The fractal dimension of 1.9 revealed the mechanism of aggregation to proceed through a diffusion limited process with the estimated diffusion coefficient and the diffusion length of the aggregated cluster to be 2.27×10⁻⁶ cm²/s and 0.63 nm, respectively.     

Solid state studies of the C60. 2(CH3)CCl3 solvate

At room temperature, the hexagonal C₆₀. 2(CH₃)CCl₃ solvate (a = 10.13(1) Å, c = 10.84(1) Å), made of alternating layers of C₆₀ and solvent molecules, forms with a negative excess volume, and its desolvation enthalpy is virtually the same as the sublimation enthalpy of the pure solvent. Crystallographic and calorimetric studies vs temperature indicate that hexagonal C₆₀. 2(CH₃)CCl₃ changes at 211.7 K (1.3 kJ mol⁻¹ of solvate) into an intermediate triclinic phase which transforms at 189.7 K (4.1 kJ mol⁻¹ of solvate) into another triclinic phase.A crystallographic analysis in the series of hexagonal C₆₀. 2 YCCl₃ solvates (Y = H, Cl, Br, CH₃) reveals that: (i) the change in the unit-cell volume values is due to a change in axis c whose value depends on the size of Y, (ii) the molar volume of the solvates depends linearly on the molar volume of the solvents.Ageing studies at room temperature show that C₆₀. 2(CH₃)CCl₃ loses its solvent molecules within a few days or a few months, depending on storage conditions.     

Reaction rate coefficient of fullerene (C60) consumption by soot

The reaction of fullerene molecules with soot was studied by contacting sublimed C₆₀ fullerenes with commercially available carbon black particles at different temperatures in the range 1023-1273 K. Fullerene mass data collected both pre- and post-reaction were fit to a simple first-order kinetic model and yielded a temperature-dependent reaction rate expression. The calculated collision efficiency of the reaction is of the order 10⁻⁸ and the activation energy is ∼9.8 kcal mol⁻¹, which would be consistent with a surface diffusion reaction or a heterogeneous reaction. Simple extrapolation of the observed rate to the conditions of a fullerene forming flame would give a consumption rate six orders of magnitude too small to account for the rate of fullerene consumption observed in the post-flame zone of a fullerene-forming benzene/oxygen/argon flame. Extrapolation of the reaction rate to flame conditions also shows that the rate of consumption calculated here is too small to account for observed oscillations in the fullerene concentration profile which can be related to changes in the relative rates of consumption and formation. Calculation of activation energies required for the extrapolation of rates observed here to match those observed in flames yields significantly larger values than those obtained in the present study and are so large as to suggest that mechanisms other than those studied here control fullerenes consumption in flames. Other mechanistic possibilities for the consumption of fullerenes in flames include reactions of fullerenes with other flame species and fullerene-soot reactions in which soot reactivity depends on soot reactions with other flame species.     

C60 fullerene inclusions in low-molecular-weight polystyrene-poly(dimethylsiloxane) diblock copolymers

We have synthesized low-molecular-weight diblock copolymers of polystyrene-block-poly(dimethylsiloxane) with total molecular weights <12 kg/mol and PS volume fractions of ∼0.2. We have investigated the phase behavior of the PS-PDMS in its pure state and with up to 10 wt% of C₆₀ added. The C₆₀ was shown to selectively segregate into the PS phase only although its solubility limit is ∼1 wt%. Although the C₆₀ aggregates above 1 wt%, the cylindrical morphology observed in the pure copolymer bulk samples persists in the C₆₀-copolymer composites even up to 10 wt% C₆₀ loading. In thin films, the pure copolymer possesses a highly ordered morphology with grains hundreds of microns across. When C₆₀ is blended with the copolymer the high degree of order rapidly decreases due to increasing numbers of defects observed.     

Electrochemical and chemical redox doping of fullerene (C60) peapods

Different types of redox doping of C₆₀@SWCNT were monitored by Raman spectroscopy. Chemical doping was carried out by gaseous potassium, liquid potassium amalgam and gaseous fluorine diluted with argon. Electrochemical doping was investigated by in situ Raman spectroelectrochemistry in LiClO₄ + acetonitrile solution and in 1-butyl-3-methylimidazolium tetrafluoroborate (ionic liquid). The peapods exhibit characteristic and complex feedback to chemical as well as to electrochemical doping. In contrast to chemical p-doping by F₂, the Raman scattering of intratubular fullerene is selectively enhanced during electrochemical p-doping. Similar selective enhancement is traced at chemical n-doping with gaseous potassium. Doping by gaseous potassium causes deep reduction of intratubular C₆₀ to , which is not fully re-oxidizable upon contact to air. On the other hand, doping with liquid potassium amalgam causes reduction of intratubular C₆₀ to , and complete re-oxidation to neutral fullerene occurs spontaneously upon contact to air. In general, the doping chemistry of peapods is significantly dependent on the applied redox potential, charge-compensating counterions and on the actual doping technique used. A critical review of the current data is provided.     

C60(Cg) and C70(g): A computational study of the pressure and temperature dependence of their populations

Equilibrium mixtures of pure carbon gas-phase aggregates, C_n(g). are treated combining all available observational as well as computational thermodynamical data for n = 1, 2, 3, 4, 5, 60 and 70. A considerable sensitivity to temperature and pressure is pointed out, showing that there are both regions of a higher relative population of C₆₀(g) as well as of C₇₀(g). There can be significant competition between the formation of small and large clusters. Relations between the full-equilibrium situation (i.e., including graphite), gas-phase equilibrium, and the nonequilibrium situation are discussed.     

Samarium Coordinated Polymer: Structural, Vibrational and Thermal Studies of [Sm2(C3H2O4)3(H2O)6]n

The title compound, [Sm₂(C₃H₂O₄)₃(H₂O)₆]_, was investigated by X-ray diffraction. It crystallizes in the monoclinic space group C2/c with cell parameters a = 17.1650(8) ?, b = 12.3010(5) ?, c = 11.1420(4) ?, β = 127.5161(10)°, Z = 4 and V = 1866.04(14) ?³. The Sm atom lies on a two-fold axis and has nine-coordination with six oxygen atoms from carboxylate groups and three water molecules. The compound forms a layer-type polymeric structure. The layers are formed by samarium and one independent malonate group to give a three-dimensional framework. The extensive network of hydrogen bonds and bridge bonds observed in this structure enhances the structural stability. The thermal dehydration of the compound was investigated by thermogravimetric analysis.     

The effects of fullerene (C60) crystal structure on its electrochemical capacitance

The electrochemical properties of different types of fullerene crystals (x-C₆₀), having hollow-long cylindrical (C-C₆₀), hollow-long square (S-C₆₀), and thick solid-short hexagonal (H-C₆₀) shapes were investigated. The prepared x-C₆₀ samples had specific dimensions with respect to aspect ratio (12.0, 6.7, and 1.5) and lattice spacing distance (1.12, 1.04, and 1.00 nm). Interestingly, it was possible to control the aspect ratio and lattice spacing distance by adjusting the molecular ratio of C₆₀ to the aromatic solvent (m-xylene) used in the preparation. In addition, the number of m-xylene molecule in the x-C₆₀ crystal structure increased with decreasing ratio of x-C₆₀ to m-xylene in the solution, corresponding to ca. C₆₀·0.83m-xylene (for C-C₆₀), C₆₀·0.39m-xylene (for S-C₆₀), and C₆₀·0.36m-xylene (for H-C₆₀). A more ordered arrangement of m-xylene molecules resulted in an improved electrochemical capacitance of x-C₆₀. Importantly, in the case of the regular structure (C-, S-, H-C₆₀), when m-xylene was assembled in the x-C₆₀ structure, the large lattice spacing distance increased. This explains why the C-C₆₀ sample had the largest electrochemical capacitance, compared to the S- and H-C₆₀ samples. Such a configuration would allow for a high charge accumulation and the formation of a donor-acceptor complex, which would permit an easier charge transfer.     

Electrochemical characterization of self-assembly process of nano-scaled polyoxomolybdate (NH4)42[Mo72Mo60O372(CH3COO)30(H2O)72]·ca.300H2O

Cyclic voltammetry and electrochemical admittance were used to characterize the self-assembly process of nano-scaled spheres of polyoxomolybdate (NH₄)₄₂[Mo^VI₇₂Mo^V₆₀O₃₇₂(CH₃COO)₃₀(H₂O)₇₂]·ca.300H₂O·ca.10CH₃COONH₄) or {Mo₁₃₂}. Cyclic voltammetry indicated that the self-assembly process could be detected after 8 h and completed after one day. Electrochemical admittance showed that the molybdenum species in the CH₃COONH₄-CH₃COOH buffer (pH 4.46) were totally different from those in the pure (NH₄)₆Mo₇O₂₄ solution (pH 5.54) and the (NH₄)₆Mo₇O₂₄ solution (pH 4.21) acidified by hydrochloric acid. However, the molybdate species in the latter two solutions should be mixtures of non-protonated and/or protonated [Mo₇O₂₄]⁶⁻ and [Mo₈O₂₆]⁴⁻ anions. Detailed analysis of admittance results could support the existence of the molybdate species related to the {Mo^VI₆} fragment which was one of the components of {Mo₁₃₂} clusters. Admittance results on the self-assembly process were coincident with those from cyclic voltammetry.     

Highly efficient oxidation of organic halides to aldehydes and ketones with H5IO6 in ionic liquid [C12mim][FeCl4]

A simple, mild, and efficient procedure for the oxidation of organic halides to aldehydes and ketones with H₅IO₆ in ionic liquid [C₁₂mim][FeCl₄] has been developed. The oxidation reactions afford the target products in good to high yields and no overoxidation was observed. The products can be separated by a simple extraction with organic solvent, and the catalytic system can be recycled and reused without loss of catalytic activity.     

Diplatinum(III) [Cl2(μ2-amidinate)4] compound derived from air oxidation of mononuclear cis-[Pt(NH3)2(amidine-κ)2] complex

The dinuclear platinum(III) complex [Pt₂Cl₂{μ₂-N(H)C(Et)N(H)}₄] (2) has been prepared by heating cis-[Pt(NH₃)₂{NHC(NH₂)Et}₂](Cl)₂ (cis-1) under aeration conditions in an EtOH/H₂O mixture at 70 °C for 2 d and it was characterized by elemental analyses (C, H, N), ESI⁺-MS, IR, ¹H and ¹³C NMR spectroscopies and also by X-ray diffraction. Complex 2 represents the second Pt^III dimer stabilized by the amidinate ligand ever known and it has a lantern-type structure with four amidinate ligands bridging two Pt^III centers with Pt–Pt distance of 2.4809(2) Å.     

Solid solution between Al-ettringite and Fe-ettringite (Ca6[Al1 − xFex(OH)6]2(SO4)3·26H2O)

The solid solution between Al- and Fe-ettringite Ca₆[Al_1 − xFe_x(OH)₆]₂(SO₄)₃·26H₂O was investigated. Ettringite phases were synthesized at different Al/(Al + Fe)-ratios (= X_Al,total), so that X_Al increased from 0.0 to 1.0 in 0.1 unit steps. After 8 months of equilibration, the solid phases were analyzed by X-ray diffraction (XRD) and thermogravimetric analysis (TGA), while the aqueous solutions were analyzed by inductively coupled plasma optical emission spectroscopy (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS). XRD analyses of the solid phases indicated the existence of a miscibility gap between X_Al,total = 0.3-0.6. Some of the XRD reflections showed two overlapping peaks at these molar ratios. The composition of the aqueous solutions, however, would have been in agreement with both, the existence of a miscibility gap or a continuous solid solution between Al- and Fe-ettringite, based on thermodynamic modeling, simulating the experimental conditions.     

Microwave-induced decomposition of nitrogen-rich iron salts and CNT formation from iron(III)-melonate Fe[C9N13]

Two nitrogen-rich iron salts, ferric ferrocyanide (Fe₄[Fe(CN)₆]₃, Prussian Blue, “PB”) and iron melonate (Fe[C₆N₇(NCN)₃], “FeM”), were thermally decomposed. A household microwave oven was used to heat a molybdenum wire after being coated with the precursor and protected from ambient atmosphere. The nanostructured products obtained were characterised with FTIR- and Raman-spectroscopy, XRD, SEM, EDX, EELS and TEM. While the PB-precursor did not give any nanotube-containing products, the FeM-precursor furnished tubular carbon nanostructures in a reproducible manner. This result may be due to the graphite-like nature of the [C₆N₇(NCN)₃]³⁻-anions present in FeM. The C₆N₇-unit is aromatic and completely planar, while the cyanide anions in PB do not provide similar structures. Another significant difference is the high Fe:C-ratio in PB, which might prevent CNT-formation when this precursor is used. The nitrogen content of the tubes was found to be below the detection limit of EELS. This indicates that the synthesis temperatures were too high resulting in complete evaporation of all nitrogen present in the FeM-precursor forming volatile species such as N₂ or (CN)₂.     

The Synthesis and Characterization of Triorganotin Carboxylates of 2-Mercapto-4-methyl-5-thiazoleacetic Acid: X-ray Crystal Structures of Polymeric Me3Sn[O2CCH2(C4H3NS)S]SnMe3 and Ph3Sn[O2CCH2(C4H3NS)S]SnPh3

The triorganotin carboxylates of 2-mercapto-4-methyl-5-thiazoleacetic acid (1), R₃Sn[O₂CCH₂- (C₄H₃NS)S]SnR₃ (R=Me 2, n-Bu 3, Ph 4 PhCH₂ 5), have been synthesized and characterized by IR, ¹H and ¹³C NMR spectroscopy. Among them, complexes 2 and 4 were also characterized by X-ray crystallography diffraction analysis, which revealed that both 2 and 4 showed a one-dimensional polymeric structure in which the geometries of the tin atoms are different: one was a distorted tetrahedron and the other was trigonal bipyramidal with the axial positions occupied by oxygen atoms.