Semiempirical molecular dynamics studies of C60/C70 fullerene oxides: C60O, C60O2 and C70O

The spectral analysis indicates that all isomers of C₆₀O, C₇₀O and C₆₀O₂ have an epoxide-like structure (an oxygen atom bridging across a C–C bond). According to the geometrical structure analysis, there are two isomers of fullerene monoxide C₆₀O (the 5,6 bond and the 6,6 bond), eight isomers of fullerene monoxide C₇₀O and eight isomers of fullerene dioxide C₆₀O₂. In order to simulate the real reaction conditions at 300 K, the calculation of the different isomers of C₆₀O, C₆₀O₂ and C₇₀O fullerene oxides was carried out using the semiempirical molecular dynamics method with two different approaches: (a) consideration of the geometries and thermodynamic stabilities, and (b) consideration of the ozonolysis mechanism. According to the semiempirical molecular dynamic calculation analysis, the probable product of this ozonolysis reaction is C₆₀O with oxygen bridging over the 6–6 bond (C_2v). The most probable product in this reaction contains oxygen bridging across in the upper part of C₇₀ (6–6 bond in C₇₀O-2 or C₇₀O-4) an epoxide-like structure. C₆₀O₂-1, C₆₀O₂-3 and C₆₀O₂-5 are the most probable products for the fullerene dioxides. All of these reaction products are consistent with the experimental results. It is confirmed that the calculation results with the semiempirical molecular dynamics method are close to the experimental work. The semiempirical molecular dynamics method can offer both the reaction temperature effect by molecular dynamics and electronic structure, dipole moment by quantum chemistry calculation.     

Donor–acceptor interaction of fullerene C60 with triptycene in molecular complex TPC·C60

A molecular complex of fullerene C₆₀ with triptycene, TPC·C₆₀ is obtained. The complex has a three-dimensional packing of C₆₀ molecules. According to the IR spectra, the freezing of free rotation of C₆₀ molecules in the complex is maintained up to 360 K. The XP-spectra of TPC·C₆₀ show the suppression of π–π^* transitions of TPC phenylene rings. The separation of C₆₀ molecules by TPC ones in TPC·C₆₀ results in low intensity of the C₆₀ transitions in the 420–500 nm range in an optical spectrum. This absorption is assumed as that attributed to intermolecular transitions between adjacent C₆₀ molecules.     

Synthesis and crystal structures of (C8h8)Nd(C5H9C5H4) (THF)2 and [(C8H8)Gd(C5H9C4H4(THF)][(C8H8)GD(C5H9C5H4(THF)2]

LnCl₃ (Ln=Nd, Gd) reacts with C₅H₉C₅H₄Na (or K₂C₈H₈) in THF (C₅H₉C₅H₄ = cyclopentylcyclopentadienyl) in the ratio of 1 : to give (C₅H₉C₅H₄)LnCl₂(THF)_n (orC₈H₈)LnCl₂(THF)_n], which further reacts with K₂C₈H₈ (or C₅H₉C₅H₄Na) in THF to form the litle complexes. If Ln=Nd the complex (C₈H₈)Nd(C₅H₉C₅H₄)(THF)₂ (a) was obtained: when Ln=Gd the 1 : 1 complex [(C₈H₈)Gd(C_%H₉)(THF)][(C₈H₈)Gd(C₅H₉H₄)(THF)₂] (b) was obtained in crystalline form.

The crystal structure analysis shows that in (C₈H₈)Ln(C₅H₉C₅H₄)(THF)₂ (Ln=Nd or Gd), the Cyclopentylcyclopentadieny (η⁵), cyclooctatetraenyl (η⁸) and two oxygen atoms from THF are coordinated to Nd³⁺ (or Gd³⁺) with coordination number 10.

The centroid of the cyclopentadienyl ring (Cp′) in C₅H₉C₅H₄ group, cyclooctatetraenyl centroid (COTL) and two oxygens (THF) form a twisted tetrahedron around Nd³⁺ (or Gd³⁺). In (C₈H₈)Gd(C₅H₉C₅H₄)(THF), the cyclopentyl-cyclopentadienyl (η⁵), cyclooctatetraenyl (η⁸) and one oxygen atom are coordinated to Gd³⁺ with the coordination number of 9 and Cp′, COT and oxygen atom form a triangular plane around Gd³⁺, which is almost in the plane (dev. -0.0144 Å).     

On the vibrational spectrum of C9, C11 and C13

The harmonic frequencies and infrared intensities of C₉, C₁₁ and C₁₃ have been calculated using SCF and complete active space SCF (CASSCF) methods. The ordering of the harmonic frequencies in C₉ is predicted wrongly unless at least the π HOMO and LUMO are included in the active space. Infrared intensities depend crucially on the size of the active space. For linear odd-numbered clusters C₁₃ and larger, the computed SCF spectrum is qualitatively wrong. The recent observation of a band near 1809 cm⁻¹ in the gas phase is explained using our CASSCF results on C₁₃.     

Effect of solvent polarity on the aggregation of fullerenes: a comparison between C60 and C70

Effect of solvent polarity on the aggregation behaviour of C₇₀ has been investigated in several mixed solvents using optical absorption, fluorescence, dynamic light scattering and scanning electron microscopic measurements and compared with those observed for the other fullerene analogue, C₆₀. It is seen that similar to C₆₀, aggregation of C₇₀ also requires the solvent polarity to exceed some critical value. In terms of solvent dielectric constant the critical solvent polarity, required for C₇₀ aggregation is found to be in the range of 27–31, which is much higher than that required for C₆₀ aggregation (12–14). The large difference in the critical solvent polarity required for C₆₀ and C₇₀ aggregation has been rationalized on the basis of the molecular shapes and the polarizabilities of two fullerene molecules.     

Surface-enhanced vibrational Raman spectroscopy of C60 and C70 on rough silver surfaces

The observation of the surface-enhanced vibrational Raman spectra of vapor-deposited C₆₀ and C₇₀ on rough silver films is reported. Both near-monolayer and multilayer films of pure C₆₀ and of C₆₀/C₇₀ mixtures are studied. The films are obtained by evaporating fullerene samples at temperatures of 683–875 K in ultra-high vacuum. Mixed fullerene samples were greatly enriched in C₇₀ by making use of the slightly different vapor pressures of the two major components at the low end of this temperature range. The spectra contain all the lines of the normal Raman spectra as well as several additional lines caused by a reduction in the stringency of the normal Raman selection rules. These results demonstrate the potential of this technique for detecting small quantities of fullerenes and obtaining their vibrational spectra.     

Theoretical studies on the BN substituted fullerenes C70−2x(BN)x (x=1–3)—isoelectronic equivalents of C70

The equilibrium structures and relative stabilities of BN-doped fullerenes C_70−2x(BN)_x (x=1–3) have been studied at the AM1 and MNDO level. The most stable isomers of C_70−2x(BN)_x have been found out and their electronic properties have been predicted. The calculation results show that the BN substituted fullerenes C_70−2x(BN)_x have considerable stabilities, though they are less stable than their all carbon analog. For C₆₈BN, the isomers whose BN is located in the most chemically active bonds of C₇₀ (namely B and A) are among the most stable species, of which B is predicted to be the ground state. The stabilities of C₆₈BN decrease and the dipole moments increase with increasing the distance between the heteroatoms. For C₆₆(BN)₂, the lowest energy species is the isomer in which the B–N–B–N bond is formed; For C₆₄(BN)₃, the most stable species should have three BN units located in the same hexagon to form B–N–B–N–B–N ring. The ionization potentials and the affinity energies of the most stable species of BN-doped C₇₀ are almost the same as those of C₇₀ because of the isoelectronic relationship. The ionization potentials and affinity energies depend on the relative position of the heteroatoms in C₆₈BN, the chemical reactivities of the isomers whose heteroatoms are well separated should differ significantly from their all carbon analog.     

Synthesis and characterization of hydroxo, pyrazolato and carboxylato derivatives of the PdR(PPh3)moiety (R = C6F5 or C6Cl5)

The hydroxo-complexes [{PdR(PPh₃)(μ-OH)}₂] (R = C₆F₅ or C₆Cl₅) have been obtained by reaction of the corresponding [{PdR(PPh₃)(μ-Cl)}2] complexes with NBu₄OH in acetone. In this solvent, the reaction of the hydroxo-bridged complexes with pyrazole (Hpz) and 3,5-dimethylpyrazole (Hdmpz) in 1:2 molar ratio leads to the formation of the new complexes [{Pd(C₅F₅)(PPh₃)(μ-azolate)}2] and [{Pd(C₆Cl₅)(PPh₃)}₂(μ-OH)(μ-azolate)] (azolate = pz or dmpz). The reaction of the bis(μ-hydroxo) complexes with Hpz and Hdmpz in acetone in 1:1 molar ratio has also been studied, and the resulting product depends on the organic radical (C₆F₅ or C₆Cl₅) as well as the azolate (pz or dmpz). The identity of the isomer obtained has been established in every case by NMR (¹H, ¹⁹F and ³¹P) spectroscopy. The reaction of the bis(μ-hydroxo) complexes with oxalic (H₂Ox) and acetic (HOAc) acids yields the binucle ar complexes [{PdR(PPh₃)}2(μ-Ox)] (R = C₆F₅ or C₆Cl₅) and [{Pd(C₆F₅)(PPh₃)(μ-OAc)}2], respectively. [{Pd(C₆F₅)(PPh₃)(μ-OH)}₂] reacts with PPh₃ in acetone in 1:2 ratio giving the mononuclear complex trans-[Pd(C₆F₅) (OH)(PPh₃)₂], whereas the pentachlorophenylhydroxo complex does not react with PPh₃, even under forcing conditions.     

Global minima of (C60)nCa, (C60)nF and (C60)nI clusters

Likely candidates for the lowest potential energy minima of (C₆₀)_nCa²⁺, (C₆₀)_nF⁻ and (C₆₀)_nI⁻ clusters are located using basin-hopping global optimisation. In each case, the potential energy surface is constructed using the Girifalco form for the C₆₀ intermolecular interaction, an averaged Lennard–Jones C₆₀–ion interaction, and a polarisation potential, which depends on the first few non-vanishing C₆₀ multipole polarisabilities. We find that the ions generally occupy the interstitial sites of a (C₆₀)_n cluster, the coordination shell being tetrahedral for Ca²⁺ and F⁻. The I⁻ ion has an octahedral coordination shell in the global minimum for (C₆₀)₆I⁻, however for 12  n  8 the preferred coordination geometry is trigonal prismatic.     

C2-symmetrical bis(camphorsulfonamides) as chiral ligands for enantioselective addition of diethylzinc to benzaldehyde

Purpose of the research was to determine the activity of chiral bis(sulfonamide) ligands derived from camphor in the addition of diethylzinc to benzaldehyde. Chiral bis(ketosulfonamides) and bis(hydroxysulfonamides), have been synthesized in a reaction of diamines with camphorsulfonic acid chloride. Their activity in a reaction of asymmetric addition of dialkylzinc to benzaldehyde in a presence of titanium(IV) tetraisopropoxide was determined. The bis(ketosulfonamide) ligands reveal low enantioselectivity, with the ee% not exceeding 12%. The bis(hydroxysulfonamides) reveal much higher asymmetric induction in the investigated ZnEt₂ addition. The best enantiomeric excess (62%) has been observed for bis(hydroxysulfonamide) obtained from 1,3-diaminepropane. The yields of the reaction obtained after 18 h are 92–96%. Crystal structures have been solved for bis(ketosulfonamide) ligands obtained from diamines based on C₂ to C₄ chain. The (2R) configuration in the rings systems of bis(hydroxysulfonamide) containing the C₃ bridge was also determined by the crystal structure analysis. The sulfonamides have been characterized by IR, ¹H and ¹³C NMR.     

Complexes of a bio-molecule and a C60 cage

C₆₀ is the most important fullerene cage and glycine is the simplest representative of a backbone unit of a protein. In this paper, the structures and the energies of glycine–C₆₀ complexes were calculated at the B3LYP/6-31G(d) level DFT. It was found that the binding of glycine to C₆₀ generated a slightly unstable complex via its amino nitrogen, a moderately unstable complex via its hydroxyl oxygen, and a very unstable complex via its carbonyl oxygen. This indicates that fullerene cages might be unable to form stable bindings to proteins via their amino nitrogen, hydroxyl oxygen and carbonyl oxygen active sites.     

Synthesis and characterization of (C5H9C9H6)2Yb(THF)2(II) (1) and [(C5H9C5H4)2Yb(THF)]2O2 (2), and ring-opening polymerization of lactones with 1

Reaction of YbI₂ with two equivalents of cyclopentylindenyl lithium (C₅H₉C₉H₆Li) affords ytterbium(II) substituted indenyl complex (C₅H₉C₉H₆)₂Yb(THF)₂ (1) which shows high activity to ring-opening polymerization (ROP) of lactones. The reaction between YbI₂ and cyclopentylcyclopentadienyl sodium (C₅H₉C₅H₄Na) gives complex [(C₅H₉C₅H₄)₂Yb(THF)]₂O₂ (2) in the presence of a trace amount of O₂, the molecular structure of which comprises two (C₅H₉C₅H₄)₂Yb(THF) bridged by an asymmetric O₂ unit. The O₂ unit and ytterbium atoms define a plane that contains a C_i symmetry center.     

Surface diffusion in reversed-phase liquid chromatography using silica gels bonded with C1 and C18 ligands of different densities

Surface diffusion in reversed-phase liquid chromatography (RPLC) using silica gels bonded with C₁ and C₁₈ alkyl ligands of different densities was studied from the viewpoints of two extrathermodynamic relationships, i.e., enthalpy-entropy compensation (EEC) and linear free energy relationship (LFER). First, according to the four methods proposed by Krug et al., the values of surface diffusion coefficient (D_s) were analyzed to confirm that an actual EEC resulting from substantial physico-chemical effects takes place for surface diffusion. Then, it was also demonstrated that a LFER is observed between surface diffusion and the retention equilibrium. The establishment of EEC and LFER suggests a mechanistic similarity of molecular migration by surface diffusion, irrespective of the alkyl chain length and the densities of C₁ and C₁₈ ligands. Finally, a thermodynamic model for the LFER based on the real EEC was used to estimate D_s values under various RPLC conditions. The D_s values can be estimated with a mean square deviation of about 25–30%. The agreement between the D_s values estimated and those experimentally measured suggests that the total mass flux by surface diffusion consists of the two contributions due to C₁ and C₁₈ ligands and that the contribution of each ligand is proportional to the ligand density.     

Homo- and hetero-bridged mixed-valence dinuclear complexes which contain the fragment ‘Rh(C6F5)3’

The reaction of the anionic mononuclear rhodium complex [Rh(C₆F₅)₃Cl(Hpz)]^t- (Hpz = pyrazole, C₃H₄N₂) with methoxo or acetylacetonate complexes of Rh or Ir led to the heterodinuclear anionic compounds [(C₆F₅)₃Rh(μ-Cl)(μ-pz)M(L₂)] [M = Rh, L₂ = cyclo-octa-1,5-diene, COD (1), tetrafluorobenzobarrelene, TFB (2) or (CO)₂ (4); M = Ir, L₂ = COD (3)]. The complex [Rh(C₆F₅)₃(Hbim)]⁻ (5) has been prepared by treating [Rh(C₆F₅)₃(acac)]⁻ with H₂bim (acac = acetylacetonate; H₂bim = 2,2′-biimidazole). Complex 5 also reacts with Rh or Ir methoxo, or with Pd acetylacetonate, complexes affording the heterodinuclear complexes [(C₆F₅)₃Rh(μ-bim)M(L₂)]⁻ [M = Rh, L₂ = COD (6) or TFB (7); M = Ir, L₂ = COD (8); M = Pd, L₂ = η³-C₃H₅ (9)]. With [Rh(acac)(CO)₂], complex 5 yields the tetranuclear complex [{(C₆F₅)₃Rh(μ-bim)Rh(CO)₂}₂]₂₋. Homodinuclear Rh^III derivatives [{Rh(C₆F₅)₃}₂(μ-L)₂]^·- [L₂ = OH, pz (11); OH, S^tBu (12); OH, SPh (13); bim (14)] have been obtained by substitution of one or both hydroxo groups of the dianion [{Rh(C₆F₅)₃(μ-OH)}₂]²⁻ by the corresponding ligands. The reaction of [Rh(C₆F₅)₃(Et₂O)_x] with [PdX₂(COD)] produces neutral heterodinuclear compounds [(C₆F₅)₃Rh(μ-X)₂Pd(COD)] [X = Cl (15); Br (16)]. The anionic complexes 1–14 have been isolated as the benzyltriphenylphosphonium (PBzPh₃⁺) salts.     

Formation of [C60C5H5] adduct cations and theoretical study of the isomers

We study here the reactions between C₆₀ and planar C₅H₅⁺ cations that lead to the formation of [C₆₀C₅H₅]⁺ adduct cations in the chemical ionization source of the mass spectrometer. The structures, stabilities and charge locations of some possible isomers of [C₆₀C₅H₅]⁺: σ-adduct, π-complex, [1,4]- and [l,2]-addition cations, are studied by AM1 semiempirical molecular orbital calculations. We find that the most stable is the σ-addition cation. Another interesting and stable structure is the π-complex cation which is bonded by the electrostatic interaction at the inter-ring distance of 1.589 Å with the C_5v symmetry. The C₅H₅⁺ cyclopentadienium cation seems to be an “inverted umbrella” sitting on a five-membered ring of the C₆₀ cage.     

UV and IR absorption spectra of C3 embedded in solid para-hydrogen

This paper presents the UV and IR absorption spectroscopy of small carbon molecules of C₃ observed using a high-resolution Fourier-transform spectrometer. The C₃ molecules were produced by irradiation of dimers or larger clusters of acetylene with an ArF laser (λ=193 nm). Sharp UV absorption features with multiple structures were observed in the electronic transition of C₃. The sharp UV absorption demonstrates the potential of solid para-hydrogen as a matrix for high-resolution spectroscopy of UV–vis electronic transitions.     

A new route to complexes containing the tetracarbon (C4) ligand

Pyrolysis of a solution of {Ru₃(CO)₁₁}₂(μ-bdpp) (bdpp = bis(diphenylphosphino)butadiyne) yielded the complex {Ru₃(μ-PPh₂)(CO)₉}₂(μ₆-C₄), which contains a μ₆-C₄ ligand symmetrically bridging two Ru₃(μ-PPh₂)(CO)₉ clusters. When the complex {Fe(CO)₄}₂(μ-bdpp) was heated in the presence of Fe₂(CO)₉ another example of a C₄ complex, {Fe₂(μ-PPh₂)(CO)₆}₂(μ-C₄), was obtained. Both complexes were characterised by X-ray structure determinations; the C₄ ligand behaves as a buta-1,3-diyne-1,4-diyl system.     

Synthesis and crystal structure of the complex [MoW(OEt)(μ-CH2){μ-C(C6H4Me-4)C(Me)O}(η-C7H7)(η-C2B9H10Me)]

The complex [MoW(μ-CC₆H₄Me-4)(CO)₂(η⁷-C₇H₇)(η⁵-C₂B₉H₁₀Me)] reacts with diazomethane in Et₂O containing EtOH to afford the dimetal compound [MoW(OEt)(μ-CH₂){μ-C(C₆H₄Me-4)C(Me)O}(η⁷-C₇H₇)(η⁵-C₂B₉H₁₀Me)]. The structure of this product was established by X-ray diffraction. The Mo---W bond [2.778(4) Å] is bridged by a CH₂ group [μ-C---Mo 2.14(3), μ-C---W 2.02(3) Å] and by a C(C₆H₄Me-4)C(Me)O fragment [Mo---O 2.11(3), W---O 2.18(2), Mo---C(C₆H₄Me-4) 2.41(3), W---C(C₆H₄Me-4) 2.09(3), Mo---C(Me) 2.26(3) Å]. The molybdenum atom is η⁷-coordinated by the C₇H₇ ring and the tungsten atom is η⁵-coordinated by the open pentagonal face of the nido-icosahedral C₂B₉H₁₀Me cage. The tungsten atom also carries a terminally bound OEt group [W---O 1.88(3) Å]. The ¹H and ¹³C-{¹H} NMR data for the dimetal compound are reported and discussed.     

Direct dynamic study on the hydrogen abstraction reaction C2(Πu)+H2 → C2H+H

The ab initio direct dynamics method at the G2//UQCISD/6-311 + G(d,p) level is employed to study the hydrogen abstraction reaction C₂(³Π_u)+H₂ → C₂H+H over a wide temperature range 100–4650 K. The barrier heights obtained for the forward and reverse reactions are 7.78 and 17.53 kcal/mol, respectively. Comparing with one recent experiment, the calculated forward rate constants over the temperature range 2580–4650 K are about 4.4–13.5 times greater and show a steeper temperature-dependent effect. This indicates that further experimental investigation on this simple radical reaction may still be desired. Finally, G2//UQCISD/6-311 + G(2df,2p) calculations are performed to test the reliability of the G2//UQCISD/6-311 + G(d,p) results.     

Theoretical investigation on the two-photon absorption of C60

We present a theoretical study on the two-photon absorption (TPA) properties of C₆₀. On the basis of the equilibrium geometry optimized by B3LYP/6-31G method, we employ the ZINDO method combined SOS formula to investigate the second hyperpolarizability and TPA cross section of C₆₀. The calculated result of the real part of the second hyperpolarizability of C₆₀ is in good agreement with the previous calculation and the experimental observation. In the 400–1000 nm range of TPA wavelength, we calculated TPA cross sections corresponding to all two photon allowed states. As a result, we find that there is only a TPA cross section maximum—995.7×10⁻⁵⁰ cm⁴ s/photon at 518 nm. Another interesting phenomenon is that C₆₀ possesses the distinct TPA process in contrast to other conjugated molecules in terms of three-state approximation. This paper provides a theoretical basis of further studying TPA properties of C₆₀.