Is fullerene C60 large enough to host a multiply bonded dimetal?

Some dimetal fullerenes M 2@C 60 (M = Cr, Mo, W) have been studied with computational quantum chemistry methods. The transition metal diatomic molecules Cr 2, Mo 2, W 2 form exohedral complexes with C 60, while U 2 forms a highly symmetric endohedral compound and it is placed in the center of the C 60 cavity. This highly symmetric structure is an artifact due to the small size of the C 60 cavity, which constrains U 2 at the center. If a larger cavity is used, like C 70 or C 84, U 2 preferentially binds the internal walls of the cavity and the U-U bond no longer exists.     

Electrochemical conversion of dinitrogen to ammonia mediated by a complex of fullerene C60 and gamma-cyclodextrin

We report on an electrochemical conversion of N2 to NH3 at ambient pressure and 60 degrees C, which is mediated by reduced C(60) inside the molecular cavity of gamma-cyclodextrin.     

Preferential trapping of C60 in nanomesh voids

Surface nanotemplate-assisted molecular assembly offers great potential in the "bottom-up" construction of addressable molecular architectures for device miniaturization. Here, we report the fabrication of an extended 2D C60 nanomesh featuring a well-ordered nanocavity array by controlling the binary molecular phases of C60 and pentacene on Ag(111). Using low-temperature scanning tunneling microscopy, we demonstrate that the C60 nanomesh can serve as an effective template to selectively accommodate guest C60 molecules at the cavity sites, thereby leading to the formation of an ordered 2D C60 array.     

Modulation of the photophysical properties of C60 by electronic confinement effect

This research work reports on the incorporation of fullerene C60 in diverse inorganic and organic matrixes and how these different environments induce changes on the photophysical properties of the molecule depending on the cavity dimensions of the host. Indeed the fluorescence emission band of C60 experiences a progressive bathochromic shift with respect to C60 in solution as the cavity dimensions of the host decrease in going from the mesoporous material MCM41 to UTD-1 and Na-Y zeolites. This experimental observation, which has been documentarily confirmed by theoretical predictions and recent experimental results, is a reflection of the confinement effect imposed by the host. However, the most striking result reported in this work is that the fluorescence range accessible to this occluded species can be extraordinarily extended by confinement inside the neutral cages of a "dendritic box". The ability of the dendritic shell to create a microenvironment, modifying the properties of its functional core, allows the emission bands of C60 incorporated into a dendrimer to be effectively red-shifted with respect to their emission in solution, and, contrarily to other confined spaces of considerable hardness such as zeolites or the high surface material MCM41, the magnitude of this shifting is maximum and can be modulated under appropriate experimental conditions. This phenomenon has an enormous relevance since it can be exploited in future technological applications.     

An M2L4 molecular capsule with an anthracene shell: encapsulation of large guests up to 1 nm

A new M(2)L(4) molecular capsule with an aromatic shell was prepared using two Pd(II) ions and four bisanthracene ligands. The self-assembled capsule possesses a cavity with a diameter of ~1 nm that can encapsulate medium-sized spherical and planar molecules as well as a very large molecule (C(60)) in quantitative yields. The encapsulated guests are fully segregated and shielded from the external environment by the large anthracene panels.     

(6,17-Dimethyl-8,15-diphenyldibenzo[b,i][1,4,8,11]-tetra-aza[14]annulenato)nickel(II) in solids: two guest-free polymorphs and inclusion compounds with methylene chloride and fullerene (C(60))-carbon disulfide

Two guest-free polymorphs and two inclusion compounds of the macrocyclic title complex [NiL] have been isolated and characterized with single-crystal and/or powder XRD, solid-state (13)C NMR, and other methods. The inclusion compound with methylene chloride, [NiL](CH(2)Cl(2)), is stable in air and thermally stable up to approximately 128 degrees C. Its crystal structure is consistent with van der Waals packing of the host [NiL] and guest CH(2)Cl(2) molecules. The host complex has square-planar coordination of the nickel(II) center with four nitrogen atoms of the macrocycle with an average Ni-N distance of 1.86 A. The molecule has a saddle-shaped conformation with the guest molecule located between one phenylene and two phenyl rings of the host molecule. Isostructural compounds with chloroform and 2-chloropropane form only as mixtures along with a guest-free host polymorph. The inclusion compound with C(60) has a composition 3[NiL]*(C(60))*2(CS(2)) and here also the crystal structure is consistent with a van der Waals type of packing. Three crystallographically inequivalent [NiL] molecules have geometries similar to that in the inclusion compound with methylene chloride. The concave surfaces of the complex molecules form a spherical cavity for the C(60) molecule. At -100 degrees C the C(60) molecule is disordered over two orientations centered at the same site. (13)C NMR studies at room temperature show that the C(60) molecule is undergoing rapid pseudo-isotropic rotation. The stability and other properties of the title and related complexes are discussed.     

Nanosized ball joints constructed from C60 and tribenzotriquinacene sockets: synthesis, component self-assembly and structural investigations

The formation of supramolecular host-guest complexes of fullerene (C(60)) and two novel tribenzotriquinacene based hosts (5 a and 5 b) was investigated in solution and in the solid state. Stability constants for 1:1 and 2:1 complexes were obtained from spectroscopic (UV/Vis, (1)H NMR) titration experiments. Association constants of K(1)=(2908+/-360) L mol(-1) and K(2)=(2076+/-300) L mol(-1) for C(60)/5 a, and K(1)=(5608+/-220) L mol(-1) and K(2)=(673+/-160) L mol(-1) for C(60)/5 b were obtained. Single crystal X-ray structural analysis of compound C(60) subset5 b3 toluene revealed that a molecule of C(60) was located at short van der Waals contact distances in the open pre-organised cavity of the rigid host. The supramolecular complex created resembles an engineered nanosized ball joint and represents the first member for a future nanomechanics construction kit.     

A BPTTF-based self-assembled electron-donating triangle capable of C60 binding

A kinetically stable self-assembled redox-active triangle is isolated. The resulting electron-donating cavity, which incorporates three BPTTF units, exhibits a remarkable binding ability for electron-deficient C(60), supported by a favorable combination of structural and electronic features.     

“Helix‐in‐Helix” Superstructure Formation through Encapsulation of Fullerene‐Bound Helical Peptides within a Helical Poly(methyl methacrylate) Cavity

A one‐handed 3₁₀‐helical hexapeptide is efficiently encapsulated within the helical cavity of st‐PMMA when a fullerene (C₆₀) derivative is introduced at the C‐terminal end of the peptide. The encapsulation is accompanied by induction of a preferred‐handed helical conformation in the st‐PMMA backbone with the same‐handedness as that of the hexapeptide to form a crystalline st‐PMMA/peptide‐C₆₀ inclusion complex with a unique optically active helix‐in‐helix structure. Although the st‐PMMA is unable to encapsulate the 3₁₀‐helical peptide without the terminal C₆₀ unit, the helical hollow space of the st‐PMMA is almost filled by the C₆₀‐bound peptides. This result suggests that the C₆₀ moiety can serve as a versatile molecular carrier of specific molecules and polymers in the helical cavity of the st‐PMMA for the formation of an inclusion complex, thus producing unique supramolecular soft materials that cannot be prepared by other methods.     

A supramolecular oscillator composed of carbon nanocluster C(120) and a rhodium(III) porphyrin cyclic dimer

A rhodium(III) porphyrin cyclic dimer (1) included carbon nanocluster C120 (2) to form a pi-electronic supramolecular complex (1 superset2), in which 2 oscillated back and forth within its cavity. Spectroscopic titration of 1 with 2 and line shape analysis on variable-temperature 1H NMR spectral profiles of 1 superset2 and reference inclusion complexes in toluene-d8, chlorobenzene-d5, and dichlorobenzene-d4 indicated that the association constant (Kassoc) of 1 superset2 and oscillation activity of included 2 are both larger as the affinity of the solvent toward fullerenes is smaller. The DeltaS values for the oscillation were all positive, indicating that the oscillation of 2 involves desolvation of a protruding C60 moiety of included 2 from the host cavity.     

Theoretical study of endohedral C36 and its dimers

It is found that atoms of lithium and carbon can be encapsulated in C(36) on the basis of the calculation of their encapsulation energies using density functional theory. Specifically, they can be encapsulated in C(36) better than in C(60) despite the smaller (70%) cavity size of the former. In C@C(36), the encapsulated carbon atom forms covalent bonds with the carbon atoms of the cage, which is in contrast with the case of N@C(60.) Two isomers are expected to be in an equilibrium which involves spin quenching and generation. Li@C(36) and C@C(36) are expected to exist in the form of dimers with nonendohedral fullerenes, i.e., as Li@C(36)-C(36) and C@C(36)-C(36). Three stable isomers were found for the former (A, B, and C). Equilibrium between A and C as well as that between B and C is accompanied by spin transfer between two fullerene units, while that between A and B is not. The two stable isomers in C@C(36)-C(36) form an equilibrium accompanied by spin quenching and generation, allowing the dimer to be potentially useful for molecular devices.     

Effect of Chemical Composition of Fullerenes on the Structure and Internal Rotation Barrier of Encapsulated Ammonia Borane Molecule

Russian Journal of General Chemistry - Investigation of the structure and conformational properties of ammonia borane molecule in the cavity of C60, C12B24N24, B36N24, C70, B41N29, C80, C14B33N33,...     

Relative partial cross sections for single, double, and triple photoionization of C60 and C70

Partial cross sections for the photoion formation from C(60) and C(70) were determined from the yields of singly, doubly, and triply charged ions which were measured by mass spectrometry combined with tunable synchrotron radiation at hnu = 25-120 eV. The dependence of the detection efficiencies on the mass-to-charge ratio was evaluated by using the formula proposed by Twerenbold et al. Corrections of the detection efficiency were found to be critical for obtaining accurate partial cross sections for photoionization of fullerenes. Revisions were made of the partial cross-section curves for single and double photoionization of C(60) and C(70). The curve for triple photoionization of C(70) was newly proposed. The ratios between the cross sections for double and single photoionization increase with hnu and reach saturated values of 0.78 at 85 eV for C(60) and approximately 1.3 at 100 eV for C(70). In contrast, the ratios at 120 eV between the cross sections for triple and single photoionization of C(60) and C(70) amount to 0.14 and approximately 0.38, respectively. The formation mechanism of multiply charged fullerene ions was discussed in terms of valence-electron excitation to antibonding unoccupied orbitals and/or spherical standing waves inside the cavity of a fullerene. This excitation could be followed by Spectator Auger processes and transmission of the excess electronic energy among numerous vibrational degrees of freedom.     

Different methods for β-cyclodextrin/triclosan complexation as antibacterial treatment of cellulose substrates

Two different production ways of antibacterial cotton fabrics by means of triclosan inclusion into a β-cyclodextrin cavity have been compared. On the one hand, triclosan has been dissolved into an aqueous solution of a β-cyclodextrin derivative with the aim of including the antibacterial agent into the cavity before grafting the β-cyclodextrin on a cotton fabric. On the other hand, the same β-cyclodextrin derivative has been grafted onto cotton and, subsequently, the fabric has been immersed into a triclosan water–ethanol solution to allow the inclusion complex formation. The antibacterial properties have been evaluated according to AATCC Test Method 100–1993 before and after two washing cycles at 60 °C. It has been shown that the durability of the antibacterial finishing depends on the production method, obtaining a more durable antibacterial action in case of prior triclosan inclusion followed by grafting. This suggests that the immobilization onto the fiber has affected the cyclodextrin cavity accessibility.     

Selective extraction of higher fullerenes using cyclic dimers of zinc porphyrins

Higher fullerenes (>/=C76) were selectively extracted from a fullerene mixture obtained from a combustion-based industrial production source by cyclic dimers of beta-unsubstituted porphyrin zinc complexes 2C5-2C7 with C5-C7 alkylene spacers as host molecules. Results of single extraction of the fullerene mixture with 2C5-2C7 together with a beta-substituted analogue of 2C6 (1C6) and spectroscopic titration of 2C6 and 1C6 with C60, C70, and C96 indicated that the host selectivity toward higher fullerenes is much dependent on the structure of the porphyrin units and the size of the host cavity. Sequential three-stage extraction of the fullerene mixture with the best-behaved 2C6 resulted in considerable enrichment in very rare fullerenes C102-C110 (<0.1 abs %) up to 82 abs % (C76-C114, 99 abs %) (356 nm) of total fullerenes.     

Synthesis, structure, fullerene-binding and resolution of C3-symmetric cavitands with rigid and deep cavities

An efficient palladium-catalyzed Suzuki-Miyaura coupling method involving the reaction between CTV-Br(3) and a variety of aryl and heteroaryl boronic acids in the presence of indolyl phosphane ligands has been developed. This reaction procedure provided a series of C(3)-symmetric aryl-extended rigid cavitands for the first time. X-ray crystal structure analysis revealed that the phenyl substituted cavitand 5a has much larger rim edges and cavity height. This macrocyclic host adopts a linear head-to-tail "hand-shake" self-inclusion arrangement in the crystalline state. The fluorescence of 5a was considerably quenched upon the addition of C(60), with a binding constant of 78,700 ± 2300 dm(3) mol(-1) and a 1:1 stoichiometry according to the Job's plot. The interaction of C(60) with 5a in the excited state is stronger than that with CTV, which could be attributed to more binding sites in the extended arms of 5a. Moreover, optically active C(3)-symmetric cavitands (+)- and (-)-6 were easily obtained with high efficiency through chemical resolution.     

Inhibition of the beta-cyclodextrin catalyzed dediazoniation of 4-nitrobenzenediazonium tetrafluoroborate. blocking effect of sodium dodecyl sulfate

We have investigated the effects of sodium dodecyl sulfate, SDS, on the reaction between 4-nitrobenzenediazonium, 4NBD, ions and beta-cyclodextrin, beta-CD, under acidic conditions at T = 60 degrees C by employing a combination of spectrophotometric, chromatographic, and conductometric techniques. Previous studies under acidic conditions indicate that the secondary -OH groups of beta-CD solvate 4NBD ions, which are included in the beta-CD cavity, leading to the formation of a highly unstable transient diazo ether complex that undergoes homolytic fragmentation with an observed rate constant about 1700 times higher than that in pure aqueous acid solution (t(1/2) = 6 h at T = 60 degrees C) when [beta-CD]/[4NBD] = 40. Addition of SDS to a 4NBD/beta-CD system makes the k(obs) values decrease up to its value in a SDS micellar solution, which is similar to that in aqueous acid solution. Dediazoniation product distribution is significantly affected; the reaction between 4NBD and beta-CD ([beta-CD]/[4NBD] = 40), in the absence of SDS, proceeds exclusively through a homolytic mechanism leading to the quantitative formation of nitrobenzene, ArH, but addition of SDS turns over the mechanism by promoting the heterolytic mechanism. In addition, mixtures of 4-nitrophenol, ArOH, and ArH dediazoniation products are formed; their relative yields depend on the amount of added SDS so that at very high [SDS(T)], the heterolytic mechanism becomes the predominant one. Results are consistent with conductometric measurements showing that addition of beta-CD to an aqueous surfactant solution inhibits micelle formation and elevates CMC(app) values because CD encapsulation of surfactant monomers competes with the micellization process and are interpreted in terms of SDS monomers blocking the beta-CD cavity by forming a nonreactive complex, releasing 4NBD to the bulk solution.     

Property control of new forms of carbon materials by fluorination

Multiwall carbon nanotubes (MWNTs) based on the template carbonization technique were fluorinated in a temperature range 323-473 K by elemental fluorine. The fluorination of the carbon nanotubes results in functionalization and modification of pristine nanotubes with respect to adsorption and electrochemical properties. Selective fluorination of the inner surface of the carbon nanotubes, brings about a decrease in the surface free energy of the inner surface of the tubes and an increase in colombic efficiency of Li/nanotubes rechargeable cells in an aprotic medium. Electrochemical fluoride-ion doping of fullerene C₆₀ thin films (250-450 nm) was carried out in a fluoride-ion conductive solution, MeCN solution of 1 M Et₄NF·4HF. Galvanostatic oxidation yielded C₆₀F_ca.1-3 where fluorine exists as a semi-ionic species in the cavity surrounded by C₆₀ molecules without forming covalent CF bonds     

Quantum-Chemical Study of Yb@C 60 , Yb@B 2 C 58 , and Gd@B 3 C 57 Molecules

Using the DFT PBE0/SDD method, the structural parameters of the Yb@η2-C60, Yb@η6-C60, Yb@η6-B2C58, and Gd@η6-B3C57 molecules, of corresponding anions (1,4-B2C58)2–, (1,3,5-B3C57)3–, and free radicals BkC60–k were calculated. Ytterbium is coordinated by the degraded C=C bond in the Yb@η2-C60 molecule and by the 1,4-diboratacyclohexa-1,3,5-triene fragment, in Yb@η6-B2C58. Symmetric substitution of three atoms of the cyclohexa-1,3,5-triene fragment leads to the formation of cyclopropane fragment, three 1,4-diboratacycloocta-1,3,5,7-tetraene fragments, and three boratacyclobutane fragments. The dipole moment μ(Yb@C60) is directed from the cavity center to Yb; the dipole moment μ(Gd@η6-B3C57) is greater and has the opposite direction (from B3 to Gd). The populations of the 4f-shells of the Yb and Gd atoms are conserved. The binding energy of the endoatom in Ln@BkC60–k is significantly higher than that in Yb@C60.     

Sugar-functionalized water-soluble cyclotriveratrylene derivatives: preparation and interaction with fullerene

Cyclotriveratrylene (CTV) has attracted much attention because of its good chemical stability, small cavity, stable conformation, and facile modification. In this article, two water-soluble CTV derivatives (CTV-G and CTV-L) functionalized by glucose and lactose residues were synthesized, respectively. Unexpectedly, sugar-bearing CTVs exhibit a distinct photoluminescence, which might be ascribed to the enhanced planar conformation of cyclotriveratrylene ring derived from the spatial effect of bulky branch groups. The interaction between the water-soluble CTV derivatives and C(60) was investigated in organic solvent and aqueous solution, which was further characterized by fluorescence spectra, ultraviolet-visible spectra, and Raman spectra. CTV-G can associate with C(60) to form supramolecular complex with 1:1 molar ratio (K(a) = 1.38 × 10(5) M(-1), 298 K). As for CTV-L, a similar complex with a lower association constant (K(a) = 5.09 × 10(4) M(-1), 298 K) can also be formed.