Singlet‐Triplet Transition in the C60 2− Dianion

Abstract

The C₆₀ complexes with decamethylcobaltocene: (Cp*₂Co)₂C₆₀(C₆H₄Cl₂, C₆H₅CN)₂ (1) and [K · (18‐crown‐6)]₂ · C₆₀ · (DMF)₄ (2) have been obtained as single crystals by the diffusion method. The IR‐ and UV‐VIS‐NIR‐spectra justify the formation of the C₆₀ ^2? dianions in these salts. EPR measurements show that the low temperature signals of 1 in the 4–140 K range and 2 in the 4–60 K range have intensity corresponding only to 0.4% and 3.5% from total C₆₀. Because of this, most of the complexes are EPR silent, and, consequently, C₆₀ ^2? has a diamagnetic singlet (S = 0) state in these temperature ranges. The appearance of a broad EPR signal in the spectum of 1 above 140 K and 2 above ～60 K is assigned to a thermal population of a close lying excited triplet (S = 1) state. The singlet–triplet energy gap for C₆₀ ^2? in solid 1 and 2 was estimated to be 730 ± 10 and 300 ± 10 cm^?1.     

Computer Simulation of Molecular and Electron Structure of C60 Fullerene Complexes with Twelve Half‐Sandwich Groups MC5H5 (M = Fe,Ru, Os)

Abstract

The C₆₀(MCp)₁₂ complexes of I _h ‐C₆₀ fullerene in which each of 12 MCp groups (M = Fe, Ru, Os; Cp = C₅H₅) is coordinated to one of the five‐membered cycles of C₆₀ via formation of η⁵–π‐bond are considered. Geometry and electron structure of these complexes are simulated by using of the PBE–DFT approach. Stability of complexes considered is evaluated. It is shown that energies of the M–C₆₀ bonds are increased in the sequence C₆₀(FeCp)₁₂, C₆₀(RuCp)₁₂, C₆₀(OsCp)₁₂.     

Synthesis,Spectral Investigations,and Thermal Stability of [60]Fullerene Complexes with TMTSF: 2(C60) · 2(TMTSF) · (C6H6), C60 · TMTSF · 2(CS2), and 2(C60) · 2(TMTSF) · (C6H5Cl)

Abstract

Molecular complexes of [60]fullerene with tetramethyltetraselenafulvalene (TMTSF): C₆₀ · (TMTSF) · 2(CS₂) (1), 2(C₆₀) · (2(TMTSF) · (C₆H₆) (2), and 2(C₆₀) · (2(TMTSF) · (C₆H₅Cl) (3) have been synthesized and their thermal stability and IR spectra vs. light polarization and temperature have been performed.     

A Novel Fullerene Hydroxamic Acid for the Liquid–Liquid Extraction,Separation, Preconcentration,and Spectrophotometric and ICP‐AES Determination of Vanadium

Abstract

A new reagent N‐phenyl‐(1,2 methanofullerene C₆₀)61‐formohydroxamic acid (PMFFA) is reported for extraction and trace determination of vanadium(V) in nutritional and biological substrates. The extraction mechanism of vanadium from 6 M HCl media is investigated. The influence of PMFFA, diverse ions, and temperature on the distribution constant of vanadium examined. The over all stability constant (log β₂ K _e ) and extraction constant (K _ex) are 20.89 ± 0.02 and 8.0 ± 0.02 × 10^?15, respectively in chloroform. The thermodynamics parameters are calculated and kinetics of vanadium transport is discussed. The system obeys Beer's law in the range of 3.2–64.0 ng mL^?1 of vanadium(V). The molar absorptivity is 7.96 × 10⁵ L mol^?1 cm^?1, at 510 nm. The PMFFA–vanadium(V) complex chloroform extract in chloroform was directly inserted into plasma for ICP‐AES measurement, which increases the sensitivity by 50 folds and obey Beer's law in the range of 50–1200 pg mL^?1 of vanadium(V). The method is applied for determination vanadium in real standard samples, sea water, and environmental samples.     

The New Method for the Synthesis of Fullerols Based on Radical Reaction

Abstract

The method for the synthesis of fullerols C₆₀(OH) _x was developed, allowing to obtain products with low number of hydroxy groups attached to fullerene molecule. At the first stage, product C₆₀(tert‐BuO) _x was obtained by the radical reaction of C₆₀ with tert‐butyl‐peroxide under heating or UV‐irradiation. At the second stage, fullerol C₆₀(OH) _x was synthesized after the elimination of tert‐butyl groups by acid treatment. Several samples C₆₀(OH) _x containing different numbers (x = 2–5) of hydroxy groups were obtained, the main product had x = 2. The structure of the fullerols was confirmed by UV‐ and Fourier‐transform infrared (FTIR)‐spectroscopy and MALDI‐TOF mass‐spectrometry.     

Superconductivity in ZrB12 and LuB12 with Various Boron Isotopes

In BCS-type superconductors Zr ^N B₁₂ (T _C≈6 K) and Lu ^N B₁₂ (T _C≈0.42 K) heat capacity C(T) and magnetization measurements have been carried out on high quality single crystals with various boron isotopes (with N=10, 11, and with natural composition of ¹⁰B and ¹¹B). Parameters of the superconducting and normal states have been deduced from this study, allowing comparison between these two dodecaborides. It was shown that ZrB₁₂ is a type-II superconductor in which the Ginzburg–Landau parameter varies in the range κ=0.8–1.12. A detailed analysis of specific heat in the normal state of R¹⁰B₁₂, R¹¹B₁₂ and R^natB₁₂ (where R=Zr, Lu) has revealed three Einstein type vibration modes of Zr⁴⁺-ions in ZrB₁₂ with characteristic energies θ _E1(Zr ^N B₁₂)≈200 K and θ _E2,3(Zr ^N B₁₂)≈450 K, whereas only one quasi-local mode of Lu³⁺-ions in LuB₁₂ with θ _E1(Lu ^N B₁₂)≈160–170 K was detected. This difference of vibration spectra has been found to be the main reason for the dramatic change of T _C for ZrB₁₂ and LuB₁₂. Using strong coupling approximation, moreover, the Coulomb pseudopotential μ ^?, electron–phonon interaction constant λ ^? and logarithmic average frequency ω _ln were determined.     

Structural,spectral, quantum chemical and thermal studies on a new NLO crystal: guanidinium cinnamate

New organic non-linear optical (NLO) single crystals of guanidinium cinnamate were crystallized by solvent evaporation solution growth technique and the crystal and molecular structure were determined by single crystal X-ray diffraction. The crystal packing is dominated by classical N–H···O hydrogen bonding interactions. Due to deficiency of acceptor atoms compared to the donor sites, two unusual ring R₂ ¹(6) motifs are formed through two N–H···O hydrogen bonds. These ring motifs are further connected through chain C₂ ²(6) or C₂ ²(8) motifs along the b-axis of the unit cell. Further, these chain and ring motifs are cross-linked through another N–H···O hydrogen bond leading to classical ring R₂ ²(8) motif. These chain and ring motifs are interlinked with each other to form secondary ring R₆ ⁶(14)/R₆ ⁶(16) motifs. The molecular geometry of the asymmetric part of the unit cell was optimized theoretically by density functional theory using the B3LYP function with 6-311?+?+?G(d,p) basis set. The optimized molecular geometry and computed vibrational spectra are compared with experimental results which showed significant agreement. The intermolecular interactions of the title compound were analyzed by the Hirshfeld surfaces. The computed hyperpolarizability values showed that the compound is a good candidate for NLO applications. The chemical hardness, electro-negativity and chemical potential of the molecule were computed by HOMO–LUMO plot. The lower band gap of the frontier orbitals indicates the suitability of fabrication of the material for non-linear optoelectronic applications.     

Facile synthesis of Bi2S3 nanocrystalline-modified TiO2: Fe nanotubes hybrids and their photocatalytic activities in dye degradation

Interface-induced effects and large specific area of heteronanostructures are attracting much attention due to applications in photocatalysis. In this work, ultrafine bismuth sulfide (Bi₂S₃) nanocrystalline-modified Fe-doped TiO₂ nanotubes (NTs) were fabricated with facile methods. The effect of the ratio of Bi₂S₃ to the Fe-doped TiO₂ NTs on the microstructural, optical, and photocatalytic properties of the NTs and hybrids was studied. The NTs showed an actual Fe content of ～ 2.93 at.%. The optical bandgap of the NTs and hybrids was ～2.90 eV and ～2.46–2.88 eV, respectively, and decreased with increasing Bi₂S₃/NTs ratio. The specific surface area of the NTs was ～333 m² · g^?1; whereas the hybrids showed obviously larger specific surface area of ～ 527–689 m² · g^?1 than the NTs because of well-controlled formation process of Bi₂S₃ nanoparticles. The sunlight-excited degradation experiments of dyes in the water indicated that the photocatalytic activity of the hybrids was higher than that of the NTs and increased with increasing Bi₂S₃/NTs ratio. Moreover, the degradation rates of two dyes at different initial pH values were very different. The high photocatalytic activity of the hybrids was mainly ascribed to the narrow bandgap, large specific surface area, and effective heterojunction.     

New Molecular Complex of Fullerene C60 with Porphyrin Dimer [FeTPP]2O: Synthesis and Crystal Structure

Abstract

New molecular complex of C₆₀ with covalently linked (Fe^IIITPP)₂O · C₆₀ dimer has been obtained. The complex has isolated packing of fullerenes in which fullerene molecule is embraced in a pocket built by porphyrins. (Fe^IIITPP)₂O preserves its initial geometry in the complex. The Fe···C(C₆₀) contacts are in the 3.239–3.513 Å range indicating the absence of Fe–C₆₀ coordination. This results in the similarity of the EPR spectra of the complex and parent (Fe^IIITPP)₂O.     

Nonlinear Optical Characteristics of C60 Thin Films

Abstract

The results of investigation of the real and imaginary parts of third‐order nonlinear susceptibility (χ⁽³⁾) of C₆₀ thin films (～100 nm) at the wavelength of Nd: YAG laser radiation (532 nm, τ = 55 ps) are presented using Z‐scan technique. Our studies show that the sign of Reχ⁽³⁾ changes from negative, at pulse repetition rate of 2 Hz to positive, at 0.5 Hz. Sign variations of the real part of the third‐order susceptibility were attributed to the influence of the thermal lens.     

Synthesis and Complex Study of Water‐Soluble Polymer Derivatives of C60 Fullerene

Abstract

The water‐soluble composites with fullerene content up to 5 wt% based on poly‐(N‐vinylpyrrolydone) (PVP) were obtained. The higher fullerene content is achieved by means of introducing tetraphenylporphyrine (TPP) and KBr into composites. The synthesis includes the formation of C₆₀–TPP complex and its further interaction with polymer. The formation of C₆₀–TPP complex was confirmed by ¹³C NMR, SANS, and translational diffusion. The hydrodynamic and electrooptical studies of C₆₀–TPP–PVP complexes indicate the higher symmetry of the polymer coil in the complex as compared to PVP. The C₆₀–PVP–KBr composites were also obtained by the solid state interaction under vacuum, KBr promoting the destruction of fullerene aggregates.     

Equilibrium Phase Diagram of Polymerized C60 and Kinetics of Decomposition of the Polymerized Phases

Abstract

Equilibrium phase diagram (T=0–1000 K; p=0–8 GPa) of pressure‐temperature polymerized C₆₀ has been constructed. It included rhombohedral; orthorhombic and tetragonal polymerized phases of C₆₀ along with fcc monomeric phases of C₆₀. The isothermal kinetics of depolymerization (T=373–513 K) of the O‐, R‐, T‐ and D‐phases was studied by means of the IR‐spectroscopy. The isothermal rate of decomposition goes up along the series: (T‐)<(O‐)<(R‐)<(D‐).     

Trifluoromethylated [60]Fullerenes: Synthesis and Characterization

Abstract

The high temperature reaction of C₆₀ with silver(I) trifluoroacetate followed by 500°C sublimation and HPLC purification has led to the characterization of the trifluoromethyl‐[60]fullerenes 1,4‐C₆₀(CF₃)₂, C _s‐C₆₀(CF₃)₄, C ₁‐C₆₀(CF₃)₄, and C ₁‐C₆₀(CF₃)₆ by EI‐MS and ¹⁹F NMR. The compounds C ₁‐C₆₀(CF₃)₄ and C ₁‐C₆₀(CF₃)₆ were obtained with 90+% compositional purity. A sample of C₆₀(CF₃)₂ also contained ca. 15–20% of a C _s‐symmetry isomer of C₆₀(CF₃)₄. The structural assignments are based on calculations at the AM1 and DFT levels of theory.     

Anionic NbO-type copper organic framework decorated with carboxylate groups for light hydrocarbons separation under ambient conditions

Light hydrocarbons are important raw materials for industrial products and fine chemicals. The storage and separation of C₁–C₃ hydrocarbons are vital to their practical use. Here, we report efficient C₁–C₃ hydrocarbon adsorption and separation with a NbO-type anionic copper metal–organic framework with uncoordinated –COO^? groups ([Cu₂(L)·(H₂O)₂]·2H₂O·3DMA·(CH₃)₂NH₂) (1). Complex 1 exhibited large C₂H₂ (190 cm³ g^?1), C₂H₄ (147 cm³ g^?1), C₂H₆ (156 cm³ g^?1), C₃H₆ (170 cm³ g^?1), and C₃H₈ (173 cm³ g^?1) uptakes and high selectivities for C₂H₂/CH₄ (32.3), C₃H₆/CH₄ (152), and C₃H₈/CH₄ (127) under ambient conditions. The excellent cycling performance of the material was reflected by only 9.2 and 10.9% losses of the C₂H₂ and C₃H₆ storage capacities even after ten cycles of adsorption–desorption tests. First-principles calculations and Grand canonical Monte Carlo simulations further revealed that not only the open metal sites but also the –COO^? groups played a key role in the high C₂–C₃ hydrocarbon uptakes. The results obtained in this study suggest that anionic 1 is a promising candidate for light hydrocarbon adsorption and natural gas purification at room temperature.     

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.     

Ion–Ion Collisions Involving Fullerene Ions

Abstract

Fullerenes are a direct link between atoms with discrete electronic energy levels and solids with a band structure and a well defined surface. In collision experiments, both between energetic ions or electrons and neutral C₆₀ molecules [Walch, B.; Cocke, C.L.; Voelpel, R.; Salzborn, E. Electron capture from C₆₀ by slow multiply charged ions. Phys. Rev. Lett. 1994, 72, 1439–1442; Scheier, P.; Hathiramani, D.; Arnold, W.; Huber, K.; Salzborn, E. Multiple ionization and fragmentation of negatively charged fullerene ions by electron impact. Phys. Rev. Lett. 2000, 84, 55–58; Hathiramani, D.; Aichele, K.; Arnold, W.; Huber, K.; Salzborn, E.; Scheier, P. Electron‐impact induced fragmentation of fullerene ions. Phys. Rev. Lett. 2000, 85, 3604–3607], as well as between charged fullerene ions and neutral targets [Hvelplund, P.; Andersen, L.; Haugen, H.; Lindhard, L.; Lorents, D.C.; Malhotra, R.; Rouff, R. Dynamical fragmentation of C₆₀ ions. Phys. Rev. Lett. 1992, 69, 1915–1918; Hvelplund, P.; Andersen, L.; Brink, C.; Yu, D.; Lorents, D.C.; Rouff, R. Charge transfer in collisions involving multiply charged C₆₀ molecules. Z. Phys. D 1994, 30, 323; Rohmund, F.; Campbell, E.E.B. Resonant and non‐resonant charge transfer in C₆₀ ⁺ + C₆₀ and C₇₀ ⁺ and C₆₀ collisions. J. Phys. B: At. Mol. Opt. Phys. 1997, 30, 5293–5304; Shen, H.; Hvelplund, P.; Mathur, D.; Barany, A.; Cederquist, H.; Selberg, N.; Lorents, D.C. Fullerene–fullerene collisions: fragmentation and electron capture. Phys. Rev. A 1995, 52, 3847–3851], the fundamental processes of electron transfer, ionization, and fragmentation have been studied extensively. Here we report on our experiments on electron transfer in the collision systems C₆₀ ⁺ + ³He²⁺ → C₆₀ ²⁺ + ³He⁺ and C₆₀ ⁺ + C₆₀ ²⁺ → C₆₀ ²⁺ + C₆₀ ⁺. For the latter system we also report on an upper level for the fragmentation probability.     

Influence of a Weak Magnetic Field on Photoconductivity Spectrum of C60 Single Crystal

Abstract

Comparative research of the excitation photoconductivity spectra (quantum light energy 2–5 eV) of C₆₀ single crystal in and out of magnetic field at the temperature T = 250–350 K has been carried. The spectral evolution at this temperature range is described. It is shown that the spectra changes abrupt at temperature T ₁ ～ 260 K and T ₂ ～ 315 K. An increase in the photoconductivity up to 15% was observed in the magnetic field (B = 0.4 T) within the photon energy range 2.5–4.5 eV. Local photoconductivity peak's appearances in the magnetic field have been proven that the charge transfer excitons take part in a photoconductivity.     

Noncovalent complexes of Ih−C80 fullerene with phthalocyanines

The noncovalent interactions of I_h?C₈₀ fullerene with free-base and 3d transition M(II) phthalocyanines (where M = Mn, Fe, Co, Ni, Cu, Zn) were studied at the PBE-D/DNP level of density functional theory. The optimized complex geometries, formation energies and electronic parameters were analyzed and compared to those reported previously for similar dyads with C₆₀. In the complexes with I_h?C₈₀, the central metal atom (as well as one H atom of H₂Pc) is always coordinated to a C_6:6:6 atom of C₈₀ cage, exhibiting only one general interaction pattern. The shortest M^…C_C80 and N^…C_C80 distances are notably longer than in dyads with C_60, and the distortion of Pc macrocycle is less significant. In none of C₈₀-based dyads the formation of new coordination bonds by metal atoms was observed. The bonding strength for Pc–C₈₀ dyads varies approximately to the same degree of 20 kcal/mol as for their Pc–C₆₀ analogues, however negative formation energies for Pc–C₈₀ dyads are on average by 5–6 kcal/mol lower than for their C₆₀ analogues. While in closed-shell Pc–fullerene systems HOMO is usually found totally on Pc molecule, in the case of C₈₀-based dyads only a minor HOMO fraction can be detected for some dyads on Pc, with the major one always distributed over fullerene cage. As a result, the calculated HOMO-LUMO gap energies turn to be very low, around 0.1 eV. Analysis of spin density plots revealed that H₂Pc+C₈₀, NiPc+C₈₀ and ZnPc+C₈₀ dyads behave as closed-shell systems, like similar noncovalent complexes of Pcs with C₆₀.     

A Bent Tb2C2 Cluster Encaged in a CS (6)-C82 Cage: Synthesis,Isolation and X-ray Crystallographic Study

Terbium (Tb)-based dimetallofullerene, Tb₂C₈₄, has been synthesized and isolated by multistep HPLC. According to the UV-vis-NIR spectroscopic characterization and comparison with the reported analogous M₂C₈₄ (M = Sc, Y) metallofullerenes, the molecular structure of Tb₂C₈₄ is proposed to be Tb₂C₂@C_s (6)-C₈₂ featuring a metal carbide clusterfullerene (CCF) structure, which is unambiguously confirmed by X-ray crystallographic study. A detailed analysis of the crystal structure of a cocrystal of Tb₂C₂@C_s (6)-C₈₂·Ni^II(OEP)·2C₆H₆ (Ni^II(OEP) = nickel (II) octaethylporphyrin) reveals that a bent Tb₂C₂ carbide cluster is encaged rigidly inside a C_s (6)-C₈₂ cage. The C-C bond within the encaged Tb₂C₂ carbide cluster behaves as a typical C-C triple bond. The asymmetric unit in Tb₂C₂@C_s (6)-C₈₂·Ni^II(OEP)·2C₆H₆ contains two fullerene sites, for which the encaged Tb₂C₂ carbide cluster however locates at nearly the same position with one Tb atom being beneath a hexagon and another Tb atom pointing to the conjunction of two adjacent hexagons.     

A methyl parathion electrochemical sensor based on Nano-TiO2, graphene composite film modified electrode

A methyl parathion electrochemical sensor based on nano-TiO₂ and graphene composite film modified glassy carbon electrode has been developed. The electrochemical behavior of MP at the sensor was investigated by cyclic voltammetry and linear sweep voltammetry. Scanning electron microscopy was used to characterize the surface morphology of nano-TiO₂ and graphene composite film. Compared with a bare glassy carbon electrode or a mono-film modified electrode, the redox peak currents of methyl parathion on the composite film modified electrode improved greatly, indicating that the sensor showed good catalytic effects. The optimal experimental condition was obtained. The results indicated that the linear sweep voltammetry responses of methyl parathion, in pH 5.2 acetate buffer solution with open-circuit accumulation for 2 min, were linear with concentrations of methyl parathion in two ranges of 0.002～5 μM and 5～100 μM. The linear equations were i_Pc(μA) = 0.0136 + 4.965c_MP(μM) (R₁² = 0.9911) and i_Pc(μA) = 21.87 + 0.8206c_MP(μM) (R₂² = 0.9914), respectively. The detection limit was 1.0 nM (S/N = 3). The sensor exhibited high sensitivity and good reproducibility as well as certain anti-interference ability. It was applied to the determination of residual MP in fresh apple sample with the recovery of 92%～102%. The result was satisfactory.